Capturing Flatfish in Pots: Can Understanding the Importance of Entrance Type and Visual Stimulus Bring Us Closer to Capturing Turbot?

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1 Capturing Flatfish in Pots: Can Understanding the Importance of Entrance Type and Visual Stimulus Bring Us Closer to Capturing Turbot? Fisheries and Marine institute of Memorial University of Newfoundland Centre for Sustainable Aquatic Resources P.O. Box 4920, St. John s, NL, A1C 5R3 CSAR March 2013

2 Capturing Flatfish in Pots: Can Understanding the Importance of Entrance Type and Visual Stimulus Bring Us Closer to Capturing Turbot? Study Conducted by: Scott M. Grant, Andrew Murphy, and Rennie Sullivan Centre for Sustainable Aquatic Resources & School of Fisheries Fisheries and Marine Institute of Memorial University of Newfoundland Newfoundland and Labrador P.O. Box 4920 St. John s, NL, Canada A1C 5R3 Submitted To: Canadian Centre for Fisheries Innovation P.O. Box 4920 St. John s, NL, Canada A1C 5R3 and Newfoundland and Labrador Department of Fisheries and Aquaculture P.O. Box 8700 St. John's, NL, Canada A1B 4J6 and Everett Roberts PO Box 66 Triton, NL, Canada A0J 1V0 CSAR

3 TABLE OF CONTENTS EXECUTIVE SUMMARY INTRODUCTION MATERIALS AND METHODS Study location, date, and research platform Prototype Pot Pot treatments tested Gillnet survey: verification of the presence of turbot at study site At-Sea Potting Experiments Data Analysis RESULTS AND DISCUSSION Gillnet survey: turbot catches Potting Experiments General observations and importance of artificial light American plaice Experiment Experiment American plaice catch summary and implications Snow crab Experiment Experiment Snow crab summary Atlantic cod Redfish Turbot Spotted wolffish CONCLUSIONS AND RECOMMENDATIONS ACKNOWLEDGEMENTS LITERATURE CITED CSAR

4 EXECUTIVE SUMMARY Development of a pot fishery to capture commercial quantities of turbot in large bays on the northeast coast of insular Newfoundland would provide small vessel (<35 ) fishers an opportunity to re-enter the turbot fishery. As a stewardship measure, the use of gillnets to capture turbot in these deepwater bays was voluntarily banned by the small vessel fishery to protect the snow crab resource. During the current phase of the turbot potting study two exploratory experiments were carried-out at depths of m in the Green Bay Region of Notre Dame Bay from 17 September to 3 October The collapsible Newfoundland cod pot developed at the Marine Institute was the prototype pot used during this study. During the first experiment all pots were baited with squid and herring and four treatment groups were tested: 1) entrance type (conical and trapezoid), 2) diameter of the fish retention device (FRD) triggers (3 mm and 5 mm), 3) spacing between FRD triggers (52 mm, 109 mm, and 166 mm), and 4) artificial light (fishing light present or absent). During the second experiment, a bait treatment was introduced (bait present and absent) to determine whether artificial light alone could lure flatfish into a pot. In the current study, American plaice, a species of flatfish, dominated the finfish catches in pots followed by Atlantic cod, redfish, turbot, and spotted wolffish. Snow crab dominated the crustacean catches followed by toad crab. Artificial light was found to be the most important factor positively influencing the capture of American plaice both in the presence and absence of bait and artificial light also positively influenced the catch rates of Atlantic cod, snow crab, and toad crab in the presence of bait. A gillnet survey prior to and during the current potting study indicated turbot were present and relatively abundant within the study site. Similarly, American plaice were abundant but very few were captured in baited pots until artificial light was added. During this study, a commercially available neutral colour (i.e., green) and relatively high intensity (i.e., 3 lux) electric fishing light was used in an attempt to lure turbot into pots. These properties of this fishing light were demonstrated to be an important factor influencing whether American plaice would enter a pot but had no similar effect on turbot. However, studies show fish behaviour in relation to light stimulus is to some extent species dependent with responses to different colour and intensity of light varying according to their ecology. Thus, disparities in the response of American plaice and turbot to the fishing lights used in this study are attributed to the differing sensitivities these flatfish species have to light. American plaice is a relatively shallow water ( m) flatfish that appears to be well adapted to the high intensity light emitted by the fishing lights and was subsequently lured into the pots. The primary depth distribution of turbot (400-1,000 m) suggests a greater sensitivity to the high intensity artificial light used during this study and is assumed to have discourage turbot from closely approaching and interacting with pots that contained fishing lights. Ultimately, the fishing lights used in the current study exhibited the right-light conditions to lure American plaice into pots and have provided valuable insights on potting behaviours of flatfish that may be expected from turbot once the right-light conditions have been discovered that will lure them to enter a pot. Of the four factors tested in Experiment 1, artificial light and entrance type were found to significantly influence the catch rates of a flatfish. American plaice were captured in 85% of the baited pot sets that contained fishing lights compared to 4% of the pot sets where no fishing light CSAR

5 was used. Further, mean catch rates of American plaice in baited pots that contained fishing lights were significantly higher ( ) in the trapezoid entrance than they were in the conical entrance. Results of Experiment 2 also demonstrate that light alone is sufficient to lure American plaice into a pot with mean catch rates in trapezoid entrance pots that contained only fishing lights exceeding (1.4 higher) the mean catch in pots that contained both bait and fishing lights. Results of this study indicate the physical modifications made to a pot that significantly increased the capture efficiency of flatfish have no effect on mean catch rates of snow crab. Snow crab catch rates were higher when baited pots contained artificial light and this study provides evidence to suggest catches of snow crab could be improved by 50% on average if baited pots also contained relatively high intensity green fishing lights. These light properties were also found to positively influence pot catches of American plaice which increased in the presence of light alone (i.e., bait absent) while catches of snow crab in the presence of artificial light were significantly lower when the olfactory stimulus of the bait was removed. In dim light conditions that occur with increasing depth artificial light can help fish to orient to the entrance of a pot but the visual stimulus of the bait is lost when it is concealed in bait bags. Recent research on wild captive turbot has demonstrated the importance of visual stimulus and movement of the bait to provoke feeding and similarly movement of the bait was required to lure Atlantic halibut into pots in a laboratory setting. The current study has shown that American plaice can be lured into pot by artificial light alone and catches are like to improve in the presence of a visual bait stimulus. It is recommended that future turbot potting studies to determine the artificial light conditions that lure turbot into pots also consider testing artificial baits and development of a pendulum bait mounting apparatus that keeps the bait in motion while a pot is on the seabed. Artificial baits lack the olfactory stimulus that lures crab into a pot and should therefore substantially reduce the bycatch of snow crab. This study has shown that even when they are abundant few turbot and American plaice will enter pots that contain only bait that is visually concealed within a small mesh bait bag. Fishing efficiency of pots is related to fish behaviour to a greater extent than other types of fishing gear and fish are known to approach pots slowly and cautiously. Ultimately, pots and bait must have the right characteristics to lure fish to enter. This study demonstrates that the flat floor configuration of the trapezoid entrance is more suitable for luring flatfish into a pot than the curved floor of a conical entrance. Further, with regard to use of a FRD the stainless steel trigger spacing and diameter used in the current study did not prevent even the smallest flatfish from entering a pot. However, understanding the characteristics of bait and a visual stimulus that lures flatfish to enter a pot is much more complex, particularly in the low light conditions that occur with increasing depth and turbot occur primarily in deepwater habitats (i.e., 400-1,000 m). Given the influence artificial light had as an attractant to the commercial species encountered in this study it is recommended future studies investigate how the colour and intensity of artificial light can be used to not only lure turbot into pots but also help to increase commercial catches in the Atlantic cod and snow crab pot fisheries. Catches of American plaice in pots warrant additional studies on the potential of this fishing gear to capture commercial quantities of American plaice and pot specifications for future studies are outlined in this report. CSAR

6 1.0 INTRODUCTION Historically, there was a vibrant fishery for turbot in deepwater channels in large bays on the northeast coast of insular Newfoundland. This coastal or bay component of the Labradoreastern Newfoundland turbot stock (NAFO Subarea 2J+3KL) has not been fished for over 15 years. In the early years this fishery was prosecuted using longline gear and later shifted largely to the use of gillnets until the decline in groundfish stocks in the early 1990s. The increased importance of snow crab to the Newfoundland and Labrador region in the 1990s and high bycatch of snow crab in gillnets set for turbot resulted in a voluntary closure of the turbot gillnet fishery by the under 35' fleet. However, this is a resource that many hard hit fishermen in the under 35' fleet sector could benefit from if an alternate means of harvesting could be developed that did not damage snow crab. Recently, a large collapsible pot which can be easily fished from 30-35' vessels was developed for capturing Atlantic cod in coastal waters of insular Newfoundland (Walsh and Sullivan 2008). In some instances fishermen report catches of over 100 cod at well over 700 lbs per pot in an overnight set (Walsh and Sullivan 2008). High catch rates are due to the large size of the pot (6.5' 6.5' bottom dimensions) and introduction of a large net bag which provides a region for cod to aggregate and swim freely upon entering the pot. This large bag also facilitates the landing and handling process as it acts like a large codend that can be brought onboard thereby precluding the need to bring the entire pot and its contents onboard. The pot also represents an ecologically sound means of harvesting with bycatch species (including hard-shell crab) and undersize cod being released unharmed. Further, catches in pots result a top quality product as all cod are alive and in prime condition when brought onboard and there is no wastage. Baited pots are used to capture round bodied fish such as Pacific and Atlantic cod (Carlile et al. 1997; Walsh and Sullivan 2007; Thomsen et al. 2010) and preliminary potting experiments conducted by CSAR demonstrated flatfish will enter baited pots. The Centre for Sustainable Aquatic Resources (i.e., Dr. Grant and Mr. Walsh) conducted controlled laboratory potting experiments with Atlantic halibut at the Ocean Sciences Centre in 2004 (unpubl. data). In these experiments halibut were kept in a large tank (8 15 ) behind a blind and under ambient 24 hour light conditions with no direct human contact or visual stimulus for 10 days. The fish were deprived of food for 24 hrs prior to lowering a large baited pot into the tank during the daylight period of the day. The fish were cautious while investigating the pot and did not enter until the bait (chopped herring) was gently moved. The bait was suspended in the centre of the pot by fishing line and the motion of the bait caused nine of the 10 fish to enter the pot within 2-3 minutes. These results indicate how movement of the bait (or prey) can over-ride cautious feeding (or foraging) behaviour in flatfish. The importance of movement of the food (or bait) has also recently been demonstrated in wild turbot held in captivity. Recent discussions over the past 3-4 months with researchers holding wild turbot indicate that even when acclimated to laboratory conditions turbot would not feed on previously frozen capelin until they were attached CSAR

7 to fishing line and moved about in the water column (pers. comm., Y. Lambert, Research Scientist, Maurice Lamontagne Institute, Mont-Joli, Quebec). Thus, movement of the bait in the presence of artificial light may prove to be a valuable means of luring turbot into a pot. Movement of bait was considered to be a potential test variable influencing the capture of turbot when this potting study was initially conceived. However, the number of variables tested annually was limited by the number of pots available and vessel at-sea time. The current phase of the turbot potting study focused primarily on the effect pot modifications and artificial light. Flatfish have also been shown to enter baited pots in the wild. For example, in the early stages of development of the Pacific cod pot fishery modifications had to be made to the entrance to reduce the incidental bycatch of Pacific halibut (Carlile et al. 1997). Pacific halibut stocks are depleted and bycatch regulations in the Pacific cod pot fishery led to the research. It was found that the use of fish retention devices (FRDs), in this case large plastic rigid one-way triggers, increased the catch rates of Pacific cod. However, using an appropriate spacing between the triggers prevented Greenland halibut from entering the pot (Carlile et al. 1997). The FRD used in the cod pot developed in Newfoundland uses stainless steel one-way triggers and use of a FRD will be important in turbot pots fished where snow crab also occur as FRDs have been shown to reduce the bycatch of snow crab (Grant 2012). Using stainless steel allows the triggers to move more freely in the FRD housing. Further, stainless steel triggers are available in different diameters and relatively light weight narrow diameter triggers may be easier to push through when fish are entering a pot than thicker heavier triggers. A review of design features of baited pots that influence catch rates over a number of different species found that it is the entrance design and size of the pot that influences catch rates with larger pots exhibiting the highest catches (e.g., Miller 1979). Fishing efficiency of pots is related to fish behaviour to a greater extent than other types of fishing gear. Further, fish are known to approach pots slowly (Furevik 1994) and pots must have the right characteristics to lure fish to enter. It has been known for centuries that fish can be attracted or otherwise affected by artificial light. Fish behaviour in relation to visual stimulus of artificial light is to some extent species dependent with wavelengths of the photons (i.e., colour) and intensity of light eliciting variable responses that can be attributed to foraging ecology and light conditions to which fish have become adapted (Marchesan et al. 2005). For example, Anthony and Hawkins (1983) found that primary sensitivity in Atlantic cod peaks at 490 nm (blue/green light) and a secondary peak occurs at 550 nm (green/yellow). Atlantic cod inhabit a relatively broad depth range from shallow nearshore to offshore waters to depths of m (Rose 1993; de Young and Rose 1993; Rose et al. 2000). Turbot exhibit a peak in abundance over a depth range of 400-1,000 m but can be captured in depths of over 1,500 m (Bowering and Nedreaas 2000). The role of light diminishes with depth to about 1,000 m where the seabed is virtually pitch black and species that typically reside at greater depths may be expected to have greater sensitivities to light than species found at shallower depths. CSAR

8 To reduce costs in the early phase of exploratory research into turbot potting the best approach would be to select a large prototype pot which is proven to capture finfish and test variations of the entrance and FRD triggers to identify characteristics that maximize catch rates of turbot or related flatfish species. Fishing lights come in many forms varying in the colour and intensity of the light emitted. However, in the early phase of exploratory research on the use of artificial light to attract turbot the best approach would be to select readily available fishing lights that emit a neutral colour within the visual spectrum and a light intensity that has been proven to be effective in commercial fisheries. In the current study, modifications were made to the entrance of the collapsible Newfoundland cod pot and FRD trigger diameter and trigger spacing were also varied in an attempt to capture turbot. The effect of a commercially available electric fishing on finfish and snow crab catch rates were also investigated. This study was exploratory in nature with entrance and FRD modifications to pots designed to target turbot, a species of flatfish, and limit the catch rates of snow crab. However, other commercially important flatfish species (e.g., American plaice) also occur in large bays on the northeast coast of insular Newfoundland as well as round bodied fish (e.g., Atlantic cod and redfish). It was unknown how fish and snow crab would react to the pot modifications and specific features of the artificial light (i.e., fishing lights) investigated in this study. The exploratory nature of this study required being prepared to modify the experiments in order to maximize information that would be of benefit to future potting studies for turbot as well as other commercial species. However, modifications to field experiments must be based on sound science. For example, in the current study catches of both turbot and American plaice were low in the absence of an artificial light but American plaice was captured in relatively high numbers when pots contained fishing lights. Subsequently, once adequate information had been obtained to standardize the FRD treatments an additional treatment group (bait present and bait absent) was introduced in an effort to better understand the affects of artificial light on flatfish and snow crab behaviour with regard to pots. Both the colour and intensity of light can affect fish behaviour and the affects are typically species specific and related to their ecology. Thus, turbot, a deepwater flatfish species (400-1,000 m), and American plaice, a relatively shallow water flatfish species ( m; Iglesias et al. 1996), may be expected to exhibit different sensitivities to light and require specific characteristics of light in order to be lured into a pot. Nevertheless, once the right-light conditions (i.e., colour and intensity) have been discovered for one flatfish species (i.e., American plaice) they can provide valuable insights into the behaviours that may be expected from another flatfish species (i.e., turbot) once the right-light conditions have been discovered. The effect of fishing lights of different colour and intensity on catch rates of turbot were beyond the scope of the current study. However, ultimately the use of the right-light (i.e., colour and intensity) as a lure in combination with pot characteristics that are shown to maximize flatfish CSAR

9 capture rates may be the key to catching commercial quantities of turbot while avoiding snow crab. Further, given the recent information on the importance of movement of food provided to captive turbot, certain bait configurations (e.g., pendulum mounted real or artificial bait) may be more effective at luring turbot into pots in the presence of light. But first it is important to determine whether light can be used as a visual stimulus to lure a species of flatfish into the pot before attempting to establish the right-light combination and bait configuration that has similar results for turbot. 2.0 MATERIALS AND METHODS 2.1 Study location, date, and research platform This study was conducted on former turbot gillnet fishing grounds in inshore waters of the Green Bay region of Notre Dame Bay, insular Newfoundland from 17 September to 3 October 2012 (Figure 1). Depth at the study site ranged from approximately m ( fathom). The research platform was a 10.6 m LOA ) (34'11 commercial vessel registered in the community of Triton, NL. 2.2 Prototype Pot Twelve pots based on the collapsible Newfoundland cod pot design (Walsh and Sullivan 2008) were used during this study. Pot frames were made of 12.7 mm )(½ round steel. Pot frame dimensions were 198 cm 198 cm 102 cm (L W H; 6.5' 6.5' 40 ), and covered with green polyethylene 114 mm (4.5 ) stretched mesh throughout The netting extended to a large mesh bag that was floated above the frame with a 20 cm (8 ) trawl float. This large mesh bag provides a region for captured fish to aggregate and also facilitates handling of the catch by providing a codend region. There were two funnel shaped entrances per trap (see Walsh and Sullivan 2008). 2.3 Pot treatments tested Two exploratory potting experiments were carried-out during this study. During the first experiment all pots were baited and four treatment groups were tested: 1) entrance type (conical and trapezoid), 2) diameter of the FRD triggers (3 mm and 5 mm), 3) spacing between FRD triggers (52 mm, 109 mm, and 166 mm), and 4) artificial light (fishing light present or absent). CSAR

10 During the second experiment, a bait treatment group was introduced (i.e., bait present and absent) and entrance type varied (i.e., conical and trapezoid) while the artificial light treatment and FRD trigger diameter and spacing treatments remained constant (i.e., light present, 5 mm, and 166 mm, respectively) Entrance type The conical entrance consisted of a conical funnel extending to the centre of the pot ( cm). Netting in the entrance was made of 51 mm (2 ) white knotless mesh. The ring at the entrance to the pot was made of 12.7 mm round steel with an inside diameter of 40 cm. The trapezoid entrance consisted of a trapezoid funnel extending to the centre of the trap ( cm). Netting in the entrances was made of 51 mm (2 ) white knotless mesh. The entrance to the trap was a rectangle made of 12.7 mm round steel and exhibited an inside dimension of 60 cm 20 cm (length height) Diameter of FRD triggers Fish retention devices with one-way (a.k.a., non-return) stainless steel triggers were used in the entrance of the pots during this study. Two trigger diameters, 3 mm and 5 mm, were tested. The triggers of the FRD used in the conical entrance were cut to lengths that extended to the outer portion of the metal entrance ring (i.e., 41 cm) while triggers in the trapezoid entrances were cut to extend to the lower portion of the metal frame (i.e., 21 cm). Triggers are commonly extended well beyond the entrance ring when targeting round bodied fish like Atlantic cod that swim vertically in the water column. However, flatfish were assumed to swim horizontally as they entered a pot. In the current study triggers were only extended to the outer frame of the entrance ring and rectangle of the conical and trapezoid entrances in an effort to limit the scraping of the trigger along the eyed side of flatfish as they entered a pot Spacing of FRD triggers Three trigger spacing distances were tested during this study: 1) 52 ± 5 mm, 2) 109 ± 5 mm, and 3) 166 ± 5 mm. Individual trigger fingers were removed from a FRD to obtain the spacing distances Artificial light Relatively inexpensive battery powered electric fishing lights producing a continuous output of light were used during this study (Figure 2). These lights had the following features and specifications: CSAR

11 120 mm 43 mm clear ploy-carbonate resin casing with total weight of 130 g (batteries included), two LED green lamps (523 nm peak wavelength, Linewidth at E c /2 = 26 nm), 3V (LR06 AA size) 2 each alkaline batteries, 400 hour consecutive use battery life, and waterproof to maximum depth of 700 m. Light meter measurements revealed at maximum output these fishing lights produced a relatively high illuminance of 3.0 lux in air at a distance of 30 cm. The manufacturer also produces these electric lights with blue, white, red, amber, and disco LED lamps. The green lamp colouration was selected for the current study for consistency as different light colours can elicit different behavioural responses that are related to the species tested and their ecology (Marchesan et al. 2005). Green is a neutral colour on the visual spectrum (i.e., violet, blue, green, yellow, orange, and red) and may be less disturbing to predators that typically forage under the low light conditions that occur at the depths fished during this study. When artificial light was used in a pot the fishing light was hung from the central region of the pot frame adjacent to and mid-way between the two entrances. Under this configuration the light was approximately 0.75 m above the seabed when a pot was deployed on the ocean floor Bait Throughout this study an approximately equal weight contribution of frozen herring and squid amounting to approximately 3 kg was used. All bait was cut into three pieces and distributed approximately evenly among two small mesh (<1 mm) bait bags. Each bag was hung within a pot by skivers and located approximately 0.5 m in front of an entrance. Old bait was removed and new bait added prior to each pot deployment. Old bait was discarded approximately 1 km from the study site. 2.4 Gillnet survey: verification of the presence of turbot at study site To verify turbot were present at a study site, two gillnets were deployed 12 days prior to the initiation of the potting experiments and again on Day 5 of the experiments. Gillnets used in this study were 91 m (50 fathom) in length and possessed 165 mm (6.5 ) mesh throughout. During each set gillnets were left to soak for two nights. CSAR

12 2.5 At-Sea Potting Experiments As was previously outlined, two exploratory potting experiments were carried-out during this study. Results of Experiment 1 were considered in the design of Experiment 2. During Experiment 1, four treatment groups were simultaneously tested from Day 1-9 (Table 1). During Experiment 1, American plaice was the most prevalent and abundant fish species in the catches in baited pots. However, artificial light had a considerable effect on catches with the great majority (i.e., 99%) of the American plaice captured when pots contained fishing lights (see below). Therefore, Experiment 2 involved a reduction and standardization of the FRD treatments and addition of a fifth treatment group (i.e., bait vs. no bait) to better understand the effects of artificial light on behavior and catch rates of American plaice. Twelve pots were fished during each day of the study with three replicates of each of the four treatment groups incorporated into the experimental design (Table 1). Six of the pots had conical entrances and six pots had trapezoid entrances (Table 1). In Experiment 1, the entrance type treatments and fish retention device (FRD) trigger diameter treatments remained constant while the light and FRD trigger spacing treatments varied from day-to-day (Table 1). In Experiment 2, the entrance type, artificial light, and FRD diameter and spacing treatments remained constant while the bait treatment varied from day-to-day (Table 1). Pots were deployed separately in three groups of four pots with one of the four treatments (i.e., C1, C2, T1, and T2; Table 1) represented in each group. Each group of four pots was deployed at varying depth intervals of approximately m, m, and m (Figure 1). Deployment was random with distance between pots in a group ranging from about m and pots were moved about within each depth interval from day-to-day. On Day 5 of the study all 12 pots were fished for two nights (i.e., approximately 48 hour soak time). For the remainder of the study all 12 pots were fished overnight (approximately 24 hour soak time). The catch was sorted by species for each pot haul. Finfish were counted and total weight (±10 g) was obtained for each species and individual body length (±1 cm) was also measured for each pot haul. Body width measurements (±1 cm) were also carried-out for American plaice with the dorsal and ventral fins lying flat against the body. Catches of snow crab and toad crab were weighed (±10 g) separately for each pot haul. 2.6 Data Analysis Parametric analyses (i.e., independent-samples t-test, one-way ANOVA, two-way ANOVA, and three-way ANOVA) were employed on continuous data. The Bonferroni correction was used to control family-wise error rate in multiple t-test comparisons. ANOVA post-hoc analyses were conducted using the Tukey b test. Catch data were log 10 (n+1) transformed and body length data CSAR

13 were log 10 transformed to improve on normality and homogeneity of variances. Levene s equality of variances was tested for all ANOVA s to validate use of parametric tests. Significance level was set to the more stringent Bonferroni s adjusted alpha level or 0.05 for all statistical analyses which were performed using SPSS (SPSS 2008). 3.0 RESULTS AND DISCUSSION 3.1 Gillnet survey: turbot catches Two gillnets deployed within the study site on September 5 and hauled two days later each captured turbot. One gillnet was deployed at a depth of approximately 366 m (200 fathom) and captured nine turbot ranging in total length from cm (mean, 40.8 cm). The second gillnet was deployed at a depth of approximately 521 m (285 fathom) and captured eight turbot ranging in total length from cm (mean, 44.3 cm). Two gillnets deployed on Day 5 and hauled two days later each captured turbot. One gillnet was deployed at a depth of approximately 366 m (200 fathom) and captured four turbot ranging in total length from cm (mean, 47.2 cm). This gillnet also captured 13 Atlantic cod, 6 redfish, and nine snow crab. The second gillnet was deployed at a depth of approximately 521 m (285 fathom) and captured 10 turbot ranging in total length from cm (mean, 44.8 cm). Two American plaice, one eelpout, and 18 snow crab were also captured in this net set. Dissection and examination of the stomach contents of five turbot that were alive when the gillnets were hauled revealed they had empty stomachs. It is unclear however whether the empty stomachs indicate a lack of feeding prior to capture or digestion and evacuation of the stomach contents while in the gillnet. 3.2 Potting Experiments General observations and importance of artificial light In this study, American plaice dominated the finfish catches in terms of total number captured followed by Atlantic cod, redfish, turbot, and spotted wolffish (Table 2). Miscellaneous finfish included grenadiers, eelpout and sculpins. Snow crab dominated the crustacean catches in terms of total kilograms captured followed by toad crab (Table 2). Light was an important attractant for many of the species captured in terms of both total catch (numbers or kg) and percentage of the pot hauls in which a species was captured (Table 2). Light alone was used as the lure in the bait absent treatment during Experiment 2 and further indicates the importance of light as an attractant to many of the species captured (Table 2). Most CSAR

14 striking were the catches of American plaice during Experiment 1 which were almost all in the presence of both bait and artificial light (i.e., 99%). Further, American plaice were captured in 85% of the pot sets when artificial light was present compared to 4% for pots set where artificial light was absent (Table 2). The importance of artificial light to the catches of American plaice led to the test of the effect of light alone (i.e., bait absent) in Experiment 2. Catches in the bait absent treatment of Experiment 2 not only demonstrate that American plaice can be captured in the presence of light alone but also that artificial light alone can attract and capture more American plaice than when artificial light and bait are used together (Table 2). Baited pots also captured snow crab (Table 2) and capture of partially eaten small American plaice in 31% of the pot hauls where both species occurred together in experiments 1 and 2 suggest that the presence of snow crab may influence the potting behaviour of American plaice. Fewer snow crab were captured when only artificial light was used (i.e., bait absent; Table 2) and may account in part at least for the increased catch rates of American plaice. Light was also an important attractant to Atlantic cod with 65% of the catches in Experiment 1 occurring in the presence of both bait and artificial light while during Experiment 2, 83% of the Atlantic cod were captured in the presence of light alone (Table 2). Similarly, the majority (63%) of the catches of snow crab were in the presence of both light and bait during Experiment 1 and light alone captured 16% of the snow crab in Experiment 2. Light and bait accounted for 82% of the catches of toad crab in Experiment 1 and light alone accounted for 54% of the toad crab catches during Experiment 2. Few turbot and spotted wolffish were captured during this study but both species were captured in the absence of the green relatively high intensity fishing light used in this study. During this study modifications were made to the traditional Newfoundland cod pot in an attempt to capture a flatfish species, specifically turbot. An artificial source of light was also used not only in an attempt to attract and lure turbot into a baited pot but also as a means of luring potential live prey species into the pot. It was assumed that luring potential prey close to the light source within a pot would also increase the probability of turbot entering a pot. Studies show many commercial fish species react to visual stimulation by swimming toward artificial light source and keeping aggregated close by (Ben-Yami 1976; Freón and Misund 1999). Indeed, the specific characteristics of the artificial light used in this study were found to attract American plaice into a pot both in the presence and absence of bait (i.e., squid and herring). Capture of American plaice with light alone was a surprising result and indicates how light alone can be a significant attractant and means of capturing commercial fish species in a pot. Although the data for other species captured in this study is limited, there was also evidence that light alone is sufficient to lure Atlantic cod, redfish, snow crab, and toad crab into a pot. CSAR

15 Very few turbot were captured during this study and all turbot were captured in baited pots that did not possess an artificial light. However, studies show that when it comes to the use of artificial light as an attractant to commercial fish species both the colour and intensity of the light influences behaviour (Marchesan et al. 2005). It is notable, that very few American plaice were also captured in pots that did not possess an artificial light. Studies show that some fish species are repelled by certain colours within the visual spectrum while others are attracted and some species are also repelled when light intensity is relatively high (Marchesan et al. 2005). The green colouration of the lamps in the fishing lights used in the current study were neutral (523 nm wavelength) within the visible colour spectrum (i.e., nm range in wavelength). However the illuminance was rather high at 3.0 lux. Relatively shallow water fish predators that hunt primarily in low light (i.e., twilight) conditions or deepwater fish predators that spend most of their life in rather low light conditions may be expected to be attracted to neutral colours of relatively low light intensity (Marchesan et al. 2005). Turbot occur primarily in deepwater habitats (400-1,000 m) where light intensity is very low or light is absent and although they may be attracted to artificial light, their behaviour in close proximity to a light source may be influenced both by the colour and intensity of the light. Marchesan et al. (2005) used ecology to classify different visual behaviours exhibited by commercial species at different light intensities and colours. Marchesan et al. (2005) found fish that typically live in low light conditions have a preference for dim light and may be repelled when placed in close proximity to a relatively high intensity light source. When subjected to light of high intensity these fish avoided the brightly lit regions of the experimental arena and settled in relatively dim regions where they exhibited very limited activity. Predatory fish that forage in low light conditions but enter a high intensity artificial light field can go undetected and are likely more at ease when they inhabit relatively dim regions. We suspect that the high light intensity of the artificial light used in the current study negatively influenced the behaviour of turbot while in close proximity to a baited pot. However American plaice, a flatfish species that typically inhabits shallower waters (i.e., m; Iglesias et al. 1996) of higher light intensity, were not only attracted to the visual light stimulus but also entered the pot both in the presence and absence of an olfactory bait stimulus (i.e., squid and herring). Given the influence of artificial light as an attractant to the commercial species encountered in this study and studies conducted elsewhere on other commercial species (Ben-Yami 1976; Anthony and Hawkins 1983; Beltestad and Misund 1988; Freón and Misund 1999; Marchesan et al. 2005) it is recommended that future studies investigate the influence of both the colour and intensity of artificial light on the ability to capture turbot, American plaice, Atlantic cod, and snow crab pots. The importance of movement of the bait in the presence of artificial light and use of artificial baits may also influence catches. It is conceivable, that once the right-light conditions have been discovered that visually stimulate fish to approach and inspect a pot the addition of a pendulum mounted artificial bait may be all that is required to lure them into the CSAR

16 pot. Moreover, use of artificial bait will likely reduce catch rates of snow crab as the olfactory stimulus of real bait lures snow crab into a pot more so than artificial light alone (Table 2) American plaice Experiment 1 As was previously outlined, a great majority of American plaice (i.e., 99%) were captured in baited pots that also contained an artificial light during Experiment 1 indicating the importance of light as a lure for American plaice at the depths fished (i.e., m). Subsequently, analysis of the effect of the remaining treatments on the catch rates and body length of American plaice was only carried-out for treatments in which artificial light was present. A three-way ANOVA indicated entrance type and FRD trigger spacing influenced catch rates of American plaice (Table 3). There was no effect of FRD trigger diameter (i.e., p>0.05; Table 3). Therefore, catches in the FRD trigger diameter treatments were combined to determine the effect of entrance type on American plaice catches within each FRD trigger spacing treatment (Table 4) and the effect of FRD trigger spacing on catches within each entrance type (Table 5). Analysis indicated the catches of American plaice did not differ significantly between entrance types by FRD trigger spacing (Table 4). However, there was a common trend of a lower catch rate in the conical entrance at each trigger spacing (Table 4). Analysis revealed there was no significant effect of FRD trigger spacing on mean catch rates of American plaice within each entrance type (Table 5). Ultimately, these results indicate catches of American plaice can be combined across the FRD trigger diameter and trigger spacing treatments within each entrance type treatment. Subsequently, an independent-samples t-test of the effect of entrance type on mean catch rates of American plaice combined across all FRD trigger treatments indicated the trapezoid entrance captured significantly more American plaice than the conical entrance (t 58 = 3.112, p = 0.003; Figure 3, panel A. During Experiment 1, there were 30 baited pot sets of each entrance type where an artificial light source was used as an additional form of attractant to lure fish into a pot. Overall, the mean catch rate of American plaice in the trapezoid entrance (i.e., 1.26 kg ±0.15 S.E.) was 1.8 higher (Figure 3) than the mean catch rate in the conical entrance (i.e., 0.70 kg ±0.16 S.E.). A three-way ANOVA indicated FRD trigger spacing was the only treatment to have a significant effect on the total body length of American plaice captured in baited pots that contained an artificial light source (Table 6). Post hoc analysis indicated two subsets with overlapping trigger spacing treatments for mean body length: 1) 52 mm and 166 mm and 2) 166 mm and 109 mm. Specifically, when combined across entrance type and FRD trigger diameter treatments, mean body length increased significantly from 27.0 cm to 29.3 cm with an increase in FRD trigger CSAR

17 spacing from 52 mm to 109 mm but mean body length in the 166 mm spacing (i.e., 27.6 cm) did not differ significantly from the means obtained in either the 52 mm or 109 mm spacing treatments. The minimum legal size for American plaice is a total body length 30 cm. Length frequency distributions indicate sublegal size (<30 cm) American plaice dominated the catches for each FRD trigger spacing treatment (Figure 4). Sublegal size American plaice accounted for 73%, 57%, and 65% of the catches in the 52 mm, 109 mm, and 166 mm FRD trigger spacing treatments, respectively. It was not uncommon to observe small American plaice escaping through the meshes of the pots when they were hauled to the surface. The 114 mm mesh used in the pots results in a mm opening which corresponds to the lowest body width measurement obtained for American plaice captured during this study (Figure 5). Thus, as a conservation measure to reduce the bycatch of sublegal size individuals future American plaice potting studies should consider using mm (i.e., ) stretched mesh panels in the net bag (i.e., codend) region of the pot or the entire bag region could be constructed of this larger mesh. American plaice normally occur in waters m deep, however they have been captured at depths >800 m (Iglesias et al. 1996). Further, studies show that juveniles are generally concentrated in the same areas as adults (Powles 1965; Walsh 1982). However, during the early 1980 s a bottom trawl suitable for capturing young flatfish (<30 cm) was introduced to the research vessel surveys conducted on the Grand Bank with surprising results (Walsh and Brodie 1988). Juvenile American plaice were captured in very high numbers (i.e., up to 5,000 per tow) in specific regions of the Grand Bank with most of the large catches located in an area of a large mud deposit (Walsh and Brodie 1988). Small juvenile American plaice are more susceptible to predation than large juveniles and adults and they are more dependent on infaunal invertebrate prey than adults. As such very fine sediments (i.e., mud) may not only provide a refuge from predation by allowing juveniles to easily bury themselves, but also provide an adequate source of food. It is notable that small juvenile flatfish generally prefer finer substrates and a narrower range of sediment sizes than larger juveniles and adults (Moles and Norcross 1995; Aboorike and Norcross 1998). We speculate that the high catches of sublegal size American plaice in baited pots that contained an artificial light are related to the muddy bottom habitat at the deepwater study site. Mud was found to be caked on the bottom of the pots in several of the sets throughout the study area. Although sub-legal size American plaice dominated the catches, legal-size individuals were also well represented and indicate baited pots represent a potential alternative form of fishing for American plaice over that of the gillnet. As was previously outline, use of large mesh panels ( mm) should substantially reduce catch rates of sublegal size American plaice. CSAR

18 Experiment 2 A two-way ANOVA indicated entrance type had a significant effect on the catch rates of American plaice while the bait treatment (presence or absence of bait) had no effect when all pots contained artificial light (Table 7). Subsequently, catches were combined across bait treatments to calculate mean catch rates for 18 pot sets of each entrance type. The results were similar to Experiment 1 with the trapezoid entrance capturing significantly more American plaice than the conical entrance (Figure 3; panel B). Overall, during Experiment 2, the mean catch rate of American plaice in pots with a trapezoid entrance (i.e., 1.58 kg ±0.30 S.E.) were 2.3 higher than the mean catch in pots with a conical entrance (i.e., 0.68 kg ±0.17 S.E.). Although catch rates of American plaice did not differ significantly between bait treatments during Experiment 2 (Table 7), it was found that catch rates in trapezoid entrance pots where bait was absent were 1.4 higher than catches in baited pots (Figure 6). This result is not only surprising and novel but also warrants further investigations to determine whether commercial quantities of American plaice can be captured in pots. Further, it is conceivable that with the right-light combination of colour and intensity commercial quantities of turbot may also be captured with artificial light. A two-way ANOVA indicated that in the presence of artificial light the bait treatments had a significant effect on the total body length of American plaice while entrance type had no effect (Table 8). American plaice captured in pots that did not possess bait exhibited a mean body length of 28.3 cm (±0.7 S.E.) while those captured in baited pots exhibited a mean length of 30.8 cm (±1.0 S.E.). Thus, there was a mean difference in body length of 2.5 cm between the bait treatments. Sublegal size individuals accounted for 43% and 58% of the catches in the presence and absence of bait, respectively (Figure 7). Lower catch rates of snow crab when bait was absent (Table 2) and predation on small American plaice by snow crab in 31% of the pot sets where both species were captured together may account for the increased catch rates of small American plaice when bait was absent (Figure 7) American plaice catch summary and implications This study demonstrated the importance of considering entrance type when targeting American plaice with pots. American plaice is a flatfish species that prefers a trapezoid entrance over a conical entrance. Significantly higher catch rates of American plaice were obtained with a trapezoid entrance in both experiments conducted during this study and resulted in catch rates that were 1.8 to 2.3 higher than those obtained with the conical entrance. Fish retention device trigger spacing and trigger diameter had no effect on catch rates of American plaice. CSAR

19 The stainless steel material used in the construction of the triggers in the FRD used in this study does not appear to limit the movement of flatfish into a pot. These triggers are light weight and swing inward with very little resistance. With suitable spacing between the triggers, a plastic FRD was found to limit the ingress of Pacific halibut into baited pots (Carlile et al. 1997) which may be attributed in part to the thick construction and relatively limited movement of plastic triggers when compared to the stainless steel triggers used in the current study. Use of an artificial light source as a visual lure proved to be an important factor influencing catch rates of American plaice in pots within the depths fished during this study. Very few American plaice were captured in baited pots in the absence of fishing lights and capture of American plaice in pots that possessed light alone indicates the importance of artificial light as an attractant to this species of flatfish. American plaice typically inhabit relatively shallow water ( m; Iglesias et al. 1996) and therefore higher light intensity habitats than those that occurred at the study site which may account for their willingness to enter pots that contained green light of relatively high intensity. Turbot are found in deepwater habitats (400-1,000 m) where low light conditions may cause them to be more cautious when approaching a relatively high intensity light source. Investigations of the effect of colour and intensity of artificial light on catch rates of turbot were beyond the scope of this study. However, given the importance of light as an attractant to American plaice and species specific responses to light of different colour and intensity additional research on the effect of these characteristics of light on catches of turbot in pots is warranted. Given the environmental benefits of pots over gillnets in commercial fisheries and results of the current study it is recommended that future studies investigate the ability of baited pots to capture commercial quantities of American plaice. There is less wastage when fish are captured in pots and bycatch species are released unharmed. Although American plaice can be captured to depths of >800 m (Iglesias et al. 1996) future potting studies should be conducted within the preferred depths and habitats of legal size American plaice. This study has demonstrated that the collapsible Newfoundland cod pot can be used as a prototype pot design for capturing American plaice. Future studies investigating whether commercial quantities of American plaice can be captured in pots should consider incorporating the following features to both maximize catches of legal size and minimize capture of sublegal size individuals: 1) 60 cm 20 cm trapezoid entrances with funnels extending cm into the pot, 2) stainless steel non-return FRDs with trigger diameter and spacing of 5 mm and 166 mm, respectively, 3) contain fishing lights with green lamps, and 4) contain mm escape panels in the net bag or use mm mesh throughout. CSAR

20 3.2.3 Snow crab Experiment 1 In the current study, analysis of the effects of pot modifications on the catch rates of snow crab was examined separately for each artificial light treatment. Levene s test of homogeneity of variances was violated (i.e., p<0.05) for the three-way ANOVAs examining the effect of entrance type, FRD trigger diameter, and FRD trigger spacing on snow crab catch rates within both artificial light treatments (i.e., present and absent). Therefore, the effect of each pot modification treatment was analyzed separately. Analysis of snow crab catches in the absence of an artificial light source indicated FRD trigger diameter had no effect on snow crab catch rates within the trigger spacing treatments for both the conical and trapezoid entrance (Table 9). However, catches in the 3 mm diameter trigger were substantially lower than the 5 mm diameter trigger in all pair-wise comparisons for the conical entrance while pair-wise comparisons in the trapezoid entrance varied without tend (Table 9). Analysis of snow crab catches in the presence of an artificial light source indicated significantly lower mean catch rates of snow crab in the 3 mm diameter trigger at the 166 mm trigger spacing in the conical entrance pots (Table 10). Further, as was observed in the light absent treatment, catches in the 3 mm diameter trigger treatment were substantially lower than the 5 mm trigger treatment in all trigger spacing pair-wise comparisons for the conical entrance (Table 10). As in the light absent treatment, pair-wise comparisons of FRD trigger diameter in the trapezoid entrance varied without tend among the FRD trigger spacing treatments (Table 10). In summary, these results indicate a common trend of a substantial reduction in the catch rates of snow crab in the 3 mm trigger diameter treatment of the conical entrance pot for all FRD trigger spacing pair-wise comparisons both in the presence and absence of an artificial light source. The negative effect of the 3 mm diameter trigger on snow crab catch rates in the conical entrance pot was found to be significant in one of the comparisons. There was no indication of a similar negative effect of FRD trigger diameter on snow crab catch rates in the trapezoid entrance pots. The next step was to test for the effect of FRD trigger spacing on snow crab catch rates. Analysis indicated FRD trigger spacing had no effect on snow crab catch rates within the trigger diameter treatments of either the conical or trapezoid entrance in both the absence (Table 11) or presence (Table 12) of an artificial light source. Overall, results with regard to the effects of FRD trigger diameter and trigger spacing indicate the catches of snow crab can be combined across the trigger spacing treatments to determine the effect of trigger diameter on snow crab catch rates within each entrance type (Table 13) as well as the effect of entrance type within each trigger diameter treatment (Table 14). Analysis CSAR

21 indicated the snow crab catch rates were significantly lower in the 3 mm trigger diameter treatments of the conical entrance pots in both the absence and presence of artificial light (Table 13 and Figure 8). Further, catch rates of snow crab in the 3 mm diameter triggers were significantly lower in conical entrance pots than they were in the trapezoid entrance pots both in the absence and presence of artificial light (Table 14). Fish retention device trigger diameter had no effect on snow crab catch rates in pots with trapezoid entrances (Table 13) and entrance type had no effect on the mean catch rates of snow crab in the 5 mm diameter trigger treatments (Table 14). During this study triggers used in the conical entrance pots were 41 cm in length. At this length, the 3 mm diameter triggers were observed to be more prone to bending along their length than the 5 mm diameter triggers. Further, the narrow diameter of the 3 mm trigger also resulted in greater lateral movement within the plastic FRD non-return housing than the 5 mm trigger. Bending and lateral movement of the 41 cm 3 mm triggers was observed to lead to snagging of the triggers in the netting of the entrance which appears to have limited the ability of snow crab to enter pots with a conical entrance (Table 13; Figure 8). The 41 cm 5 mm diameter triggers were not observed to bend or snag within the netting of the conical entrance. The triggers were shorter in length (21 cm) in the trapezoid entrance and neither the 3 mm nor the 5 mm triggers were observed to bend and become snagged within the netting. Thus, reduced catches of snow crab in the conical entrance pots with 41 cm 3 mm diameter triggers in the FRD appear to result from failure of the materials to maintain their shape and position within the entrance. Snow crab catches in the 5 mm trigger diameter treatment did not differ between entrance types both in the absence and presence of an artificial light source (Table 14). Therefore, catches were combined across entrance type treatments within the 5 mm trigger diameter treatment to test the effect of light on mean catch rates of snow crab (Figure 9). Analysis revealed mean catch rates of snow crab in the presence of an artificial light source (i.e., 20.4 kg ±2.3 S.E.) were 1.5 higher than mean catch rates in the absence of light (i.e., 13.5 kg ±2.6 S.E.) but the means did not differ significantly (t 52 = 1.997, p = 0.051). In this study, mean catch rates of snow crab were comparable to those obtained in the commercial snow crab fishery which is prosecuted with 1.2 m bottom diameter baited pots. Although mean catch rates of snow crab did not differ significantly between light treatments, a 50% increase in mean catch rates when pots contained inexpensive battery powered fishing lights is substantial enough to warrant further investigations. For example, studies may find that use of an artificial light source may reduce the quantities of bait (i.e., squid and herring) required to capture commercial quantities of snow crab. CSAR

22 Experiment 2 Levene s test of homogeneity of variances was violated (i.e., p<0.05) for the two-way ANOVA examining the effect of entrance type and bait (i.e., bait vs. no bait) on snow crab catch rates in the presence of artificial light. Therefore, these treatments were analyzed separately. Analysis indicated mean catch rates of snow crab differed significantly between bait treatments in the conical entrance pots (i.e., t 16 = 6.502, p<0.0001) but did not differ significantly in the trapezoid entrance pots (i.e., t 16 = 1.191, p=0.251) (Figure 10). Mean catch rates of snow crab did not differ significantly between entrance types in either the bait absent treatment (i.e., t 9 = 1.491, p=0.169) or the bait present treatment (i.e., t 16 = 1.943, p<0.070). Therefore, snow crab catch rates were combined across entrance type treatments. Overall, the bait present treatments captured 5 more snow crab than the bait absent treatments, mean catch rates of 13.8 kg versus 2.7 kg, respectively Snow crab summary Snow crab were well represented in the baited pot catches during this study and for the most part were comparable to pot catches in the commercial snow crab fishery. Artificial light, pot entrance type, and FRD trigger spacing did not have a significant effect on snow crab catch rates. Significantly lower snow crab catch rates in the 3 mm diameter trigger treatment of the conical entrance is attributed to increased probability of these narrow triggers snagging in the entrance netting. The 41 cm trigger length required to prevent escapement from the conical entrance proved to be too long for a 3 mm diameter trigger fabricated from stainless steel. Trigger diameter did not affect snow crab catch rates in the trapezoid entrance where trigger length was shorter (i.e., 21 cm). Snow crab catch rates were higher when baited pots contained artificial light and this study provides evidence to suggest catches of snow crab could be improved by 50% on average if baited pots also contained green fishing lights. This study shows that even when pots are not baited with squid and herring snow crab will enter when they contain fishing lights. In conical entrance pots that contained fishing lights, catches of snow crab were significantly lower when bait was absent and although catches were also lower in the absence of bait in trapezoid entrance pots, the difference was not significant. Results of this study indicate that modifications to the entrance of a pot that increase the capture efficiency of flatfish have no effect on catch rates of snow crab. Ultimately, use of trapezoid entrance pots that contain both artificial light and pendulum mounted artificial bait may be the key to capturing flatfish while avoiding the capture of snow crab. Both turbot and American plaice are visual predators and this study has shown that artificial light is required to visually CSAR

23 stimulate large numbers of American plaice to enter pots at the depths fished and that they will even enter pots that contain fishing lights when real bait is absent. Ultimately, finding the rightlight and bait configuration combination that lures turbot into pots may also further reduce catch rates of snow crab Atlantic cod The 32 Atlantic cod captured in pots during this study exhibited a range in body length of cm (mean, 47.0 cm). The majority (n=27; 84%) of the Atlantic cod were capture in pots with conical entrances. The majority (65%) of the Atlantic cod captured in Experiment 1 were taken in pots that contained both bait and artificial light and 83% of the cod captured in Experiment 2 were captured in pots that contained artificial light only. The current results with regard to the effect of artificial light on capture rates of Atlantic cod are preliminary but suggest future studies are warranted on the effects of green coloured fishing lights. It is notable, that recent studies in the Baltic Sea with the same type of fishing lights used in the current study found that catch rates of Atlantic cod in floating pots increased by when baited pots also contained fishing lights (pers. comm., A. Bryhn, Swedish University of Agricultural Sciences) Redfish The nine redfish captured in pots during this study exhibited a range in body length of cm (mean, 41.3 cm). Although redfish were captured in pots that contain artificial light both in the presence and absence of bait too few were captured to inform future studies Turbot A total of five turbot were captured in pots during this study. Four of the turbot were alive and exhibited a range in length of cm (mean, 37.5 cm) while the fifth relatively small turbot (<25 cm) was partially consumed by snow crab. All turbot were captured in baited pots that did not contain an artificial light and the majority (n=4; 80%) were captured in pots with trapezoid entrances. A gillnet survey indicated turbot were present and relatively abundant within the study site and absence of food in the diet of turbot suggests bait fish were not plentiful enough to negatively influence their desire to enter a baited pot. Similarly, American plaice were abundant but very few were captured in baited pots until artificial light was added. Both turbot and American plaice are attracted to baited longlines and baiting of gillnets with herring to increase capture rates of turbot is now a common practice in turbot fisheries in the western North Atlantic. This study has shown that even when they are abundant few turbot and American plaice will enter pots that contain only bait that is visually concealed within a small mesh bait bag. Fishing CSAR

24 efficiency of pots is related to fish behaviour to a greater extent than other types of fishing gear and fish are known to approach pots slowly and cautiously (Furevik 1994). Ultimately, pots and bait must have the right characteristics to lure fish to enter. This study demonstrates that the flat floor configuration of the trapezoid entrance is more suitable for luring flatfish into a pot than the concave or curved floor of a conical entrance. Further, with regard to use of a FRD the stainless steel triggers used in the current study did not prevent even the smallest flatfish from entering a pot. However, understanding the characteristics of bait and a visual artificial light stimulus that lures flatfish to enter a pot is much more complex, particularly in the low light conditions that occur with increasing depth within the habitats occupied by turbot (i.e., 400-1,000 m). For example, in addition to the olfactory stimulus of chopped herring bait, captive Atlantic halibut required a moving visual stimulus to enter a baited pot (pers. comm., P. Walsh, Centre for Sustainable Aquatic Resources), wild turbot also required a moving visual stimulus to feed in captivity (pers. comm., Y. Lambert, Research Scientist, Maurice Lamontagne Institute, Mont- Joli, Quebec), and in the current study a visual artificial light stimulus was required to lure large numbers of American plaice into baited pots. These examples have a common feature of the requirement of a visual stimulus which may be related to visual adaptations of turbot and Atlantic halibut to the relatively deepwater and hence dim light conditions. American plaice typically occur in shallower relatively well illuminated habitats. When American plaice occur in dim light conditions at greater depths they may be attracted to artificial light of relatively high intensity as they may be visually adapted to living in these light conditions. The role of light diminishes with depth to about 1,000 m where the seabed is virtually pitch black and species that typically reside at greater depths may be expected to exhibit greater sensitivities to light and rely more heavily on the detection of movement than species found at shallower depths. Light can help fish to orient to the entrance of a pot when currents carrying a bait plume are perpendicular to the entrance but if artificial light is too bright it may repel fish or only draw them to the periphery of the light field. In water, light intensity or illuminance decreases rapidly with depth or distance from the light source and the area of an artificial light field will depend on illuminance. Turbot is a visual predator adapted to foraging in moderate to low light conditions and occurrence to depths >1,000 m indicates an ability to forage in complete darkness. Depth and hence ambient light distribution of turbot implies high sensitivity to artificial light and the relatively high illuminance (i.e., 3 lux) of the fishing lights used in the current study may have repelled turbot to the relatively dim region at the periphery of the artificial light field which may have extended beyond the pot. It is notable that the illuminance of the full moon on a clear night is lux (Bunning and Moser 1969) which is much lower than the illuminance of the artificial fishing lights used in the current study. Further, older juveniles and adult turbot remain close to the ocean floor throughout a 24-hour cycle while young (age 1-2) juveniles have been shown to migrate into the water column but only at night and particularly around midnight (Jogensen 1997). Overall, these results imply a negative sensitivity to illuminance of >1 lux. CSAR

25 American plaice are concentrated and likely visually adapted to the relatively high illuminance of shallow water habitats and may therefore be considered to be less sensitive to the relatively high illuminance of the fishing lights used in this study. However, their reaction to artificial light provides valuable insights and suggests with the right-light combination of colour and intensity turbot may also be lured into a pot. What was surprising with regard to American plaice was that they were attracted to light and entered pots even in the absence of an olfactory stimulus of squid or herring bait. As was previously outlined, studies of wild turbot in captivity suggest they may require a visual motion stimulus and addition of a pendulum mounted artificial bait in the presence of the right artificial light properties may not only help to lure turbot into a pot but also the lack of an olfactory bait stimulus should reduce catch rates of snow crab which was also an objective of the turbot potting research Spotted wolffish The four spotted wolffish captured in pots during this study exhibited a range in length of cm (mean, 89.8 cm). All four spotted wolffish were released quickly. These wolffish were in good physical condition and observed to swim away when released. Abundance of spotted wolffish within the study site during the potting experiments is unknown. Uncertainty with regard to distribution and abundance and low catches of spotted wolffish in pots during this study indicate it is not possible to determine the effect of artificial light or pot modifications on catch rates. 4.0 CONCLUSIONS AND RECOMMENDATIONS In conclusion, this potting study has demonstrated that American plaice, a species of flatfish, prefers the flat bottom floor of a trapezoid entrance over that of the concave or curved floor of a conical entrance. Fish are known to approach pots slowly and with caution and a flat floor in the funnel section of the entrance would likely be better suited to flatfish behaviour of lying in contact with the seabed or in this case netting as they approach and investigate the entrance of pots. It is notable, that the funnels of both the trapezoid and conical entrances within the pots tested in this study extend approximately cm into the pot while entrance funnels currently in use when this pot is used to target Atlantic cod extend approximately half the distance into the pot (i.e., 50 cm). Given the bottom seeking behaviour of flatfish and their contact with the seabed it was reasoned that a longer entrance funnel would provide a location for flatfish to rest and possibly inspect the entrance prior to entering. Fish retention device trigger diameter and spacing treatments tested during this study had no effect on catch rates of American plaice and are unlikely to influence catch rates of turbot. CSAR

26 In the current study, artificial light was found to be the most important factor positively influencing the capture of American plaice in both baited and non-baited pots and artificial light also positively influenced the catch rates of Atlantic cod, snow crab, and toad crab in baited pots. One of the most important findings of this study was that both American plaice and snow crab are attracted to pots that contain an artificial light but that few snow crabs will enter the pot unless it also contains an olfactory bait stimulus, while American plaice will enter a lighted pot even in the absence this bait stimulus. Further, the mean catch rate of American plaice in lighted pots that did not contain bait was 1.4 higher than pots that contained both artificial light and bait. Based on these results, it is conceivable that a suitable colour and intensity of light could be found that both attracts and captures commercial quantities of turbot in pots. The chemical plume produced by the squid and herring bait alone which was visually concealed in a bait bag was not enough of an attractant to lure suitable quantities of either American plaice or turbot into a pot. The colour and intensity of the fishing lights used in this study were a suitable attractant to lure American plaice into the pot. Capture of similar quantities of both turbot and American plaice in the absence of artificial light indicates both flatfish species are attracted to the baited pot but that American plaice required an additional lure (i.e., artificial light) to cause them to enter a pot at the relatively low light levels of the depths fished. During this study, a commercially available neutral colour (i.e., green) and relatively high intensity (i.e., 3 lux) electric fishing light was used in an attempt to lure turbot into pots. The properties of this fishing light were demonstrated to be an important factor influencing whether American plaice would enter a pot but had no similar effect on turbot. At the onset of this study it was unknown how fish and snow crab would react to this specific artificial light source and investigations of the effect of the colour and intensity of artificial light on catch rates were beyond the scope of this phase of the exploratory study. However, given the influence of an artificial light source as an attractant to the commercial species encountered in this study and studies conducted elsewhere on other commercial species (Ben-Yami 1976; Anthony and Hawkins 1983; Beltestad and Misund 1988; Freón and Misund 1999; Marchesan et al. 2005) it is recommended that future studies investigate the influence of both the colour and intensity of artificial light on the ability of pots to not only capture turbot but also commercial quantities of American plaice, Atlantic cod, and snow crab. Longline baits are readily consumed by turbot however fishing efficiency of pots is related to fish behaviour to a greater extent than other types of fishing gear and emphasizes the need for the right characteristics to lure fish to enter. Laboratory studies on captive Atlantic halibut and wild turbot suggest that a visual motion stimulus of food (or bait) is an important feeding motivation and may over-ride cautious hesitation or stress induced feeding restraint. Further, visual motion stimulus of potential prey may promote more aggressive feeding behaviour when in the presence of one or more predators or conspecifics. It is a common practice to place baits in protective mesh bags to prevent scavengers as well as target or non-target species from consuming the bait, CSAR

27 and this study was no exception. However, a cautious and visually motion sensitive predator may require more of an incentive to enter a pot particularly under low light conditions. It is recommended that future turbot potting studies investigate the effects of pendulum mounted baits both real and artificial in the presence and absence of artificial light. In coastal waters American plaice fisheries are prosecuted with gillnets. This study demonstrates that American plaice can be captured in pots yet the commercial potential is unclear because this study was not carried-out within the preferred depth range of American plaice ( m; Iglesias et al. 1996). Based on catches in this study specific recommendations with regard to pot design in future exploratory commercial fisheries for American plaice are provided in Section (i.e., American plaice catch summary and implications) of this report. 5.0 ACKNOWLEDGEMENTS This study was funded by the Canadian Centre for Fisheries Innovation and the Fisheries Technology and New Opportunities Program provided by Newfoundland and Labrador s Department of Fisheries and Aquaculture. In kind contributions were provided by the Marine Institute of Memorial University and Mr. Everett Roberts. 6.0 LITERATURE CITED Anthony, P.D., and Hawkins, A.D Spectral sensitivity of the cod, Gadus morhua L. Mar. Behav. Phys. 10: Aboorike, A.A., and Norcross, B.L Depth and substrate as determinants of distribution of juvenile flathead sole (Hippoglossoides elassodon) and rock sole (Pleuronectes bilineatus) in Kachemak Bay, Alaska. J. Sea. Res. 39: Beltestad, A.K., and Misund, O.A Attraction of Norwegian spring-spawning herring to underwater light. In: proceedings of the World Symposium of Fishing Gear and Fishing Vessel Design, The Marine Institute, St. John s, Newfoundland, pp Ben-Yami, M Fishing with light. In: FAO of the United Nations. Fishing News Books, Oxford. Bowering, W.R Migrations of Greenland halibut, Reinhardtius hippoglossoides, in the Northwest Atlantic from tagging in the Labrador-Newfoundland region. J. Northwest Atl. Fish. Sci. 5: Bowering, W.R., and Nedreaas, K.H A comparison of Greenland halibut (Reinhardtius hippoglossoides (Walbaum)) fisheries and distribution in the Northwest and Northeast Atlantic. Sarsia 85: Bunning, E. and Moser, I Interference of moonlight with the photoperiodic measurement of time by plants, and their adaptive reaction. Proceedings of the National Academy of Sciences of the United States of America 62 (4): CSAR

28 Carlile, D.W., Dinnocenzo, T.A., and Watson, L.J Evaluation of modified crab pots to increase catch of Pacific cod and decrease bycatch of Pacific halibut. N. Am. J. Fish. Manag. 17: de Groot, S.J Some notes on an ambivalent behaviour of the Greenland halibut Reinhardtius hippoglossoides (Walb.) Pisces: Pleuronectiformes. J. Fish. Biol. 2: deyoung, B, and Rose, G.A On recruitment and distribution of Atlantic cod (Gadus morhua) off Newfoundland. Can. J. Fish. Aquat. Sci. 50: Freón, P., and Misund, O.A Dynamics of pelagic fish distribution and behaviour: effects on fisheries and stock assessment. Blackwell Science, Oxford. Furevik, D Behaviour of fish in relation to pots. In: Fernö, A. and Olsen, S. (Eds). Marine Fish Behaviour in Capture and Abundance Estimation. Fishing News Books, Oxford, pp Grant, S.M Turbot Potting: Regaining Under 35 Fleet Access to the Turbot Fishery While Conserving the Snow Crab Resource. Centre for Sustainable Aquatic Resources, Marine Institute of Memorial University of Newfoundland. P-371: 9 p. Iglesias, S., Paz, J., de Cardenas, E Occurrence of American plaice (Hippoglossoides platessoides) at non-habitual depths in the Northwest Atlantic, NAFO Sci. Coun. Stud. 24: Jorgensen, O.A Pelagic occurrence of Greenland halibut, Reinhardtius hippoglossoides (Walbaum), in west Greenland waters. J. Northwest Atl. Fish. Sci. 21: Marchesan, M., Spoto, M., Verginella, L., Ferrero, E. A Behavioural effects of artificial light on fish species of commercial interest. Fish. Res. 73: Miller, R.J Saturation of crab traps: reduced entry and escapement. J. Cons. Int. Explor. Mer. 38: Moles, A., and Norcross, B.L Sediment preference in juvenile Pacific flatfishes. Neth. J. Sea. Res. 34: Powles, P.M Life history and ecology of American plaice (Hippoglossoides platessoides F.) in the Magdalen Shallows. J. Fish. Res. Board Can. 22: Rose, G.A Cod spawning on a migration highway in the Northwest Atlantic. Nature (Lond.) 366: Rose, G.A., deyoung, B., Kulka, D.W., Goddard, S.V., and Fletcher, G.L Distribution shifts and overfishing the northern cod (Gadus morhua): a view from the ocean. Can. J. Fish. Aquat. Sci. 57: Slack-Smith, R.J Fishing with traps and pots. FAO, Rome, 62 p. SPSS SPSS for Windows, Rel Chicago: SPSS Inc. CSAR

29 Thomsen, B., Humborstad, O-B., and Furevik, D.M Fish pots: fish behaviour, capture processes, and conservation issues. In: Behavior of Marine Fishes: Capture Processes and Conservation Challenges. Edited by P. He. Blackwell Publishing. p Walsh, S.J Distribution and abundance of pre-recruit and commercial-size American plaice on the Grand Bank. J. Northwest Atl. Fish. Sci. 3: Walsh, S.J., and Brodie, W.B American plaice distribution on the nose and tail of the Grand Bank. NAFO SCR Doc. 88/ p. Walsh, P., and Sullivan, R Baited cod pots: catching without killing. Centre for Sustainable Aquatic Resources, Marine Institute of Memorial University of Newfoundland, Technical Report, 16 p. + App. CSAR

30 Table 1. Summary of light and pot alteration treatments tested by fishing day for experiments 1 and 2. Twelve pots were fished per day. Six pots were utilized for each group with three replicates of C1, C2, T1, and T2 fished each day. In Experiment 1, the entrance shape treatment remained constant for Group 1 (conical) and Group 2 (trapezoid). Diameter of the fish retention device (FRD) trigger treatments remained constant for C1 and T1 (5 mm) and C2 and T2 (3 mm), while the light and FRD trigger spacing treatments varied from day-to-day. In Experiment 2, the light treatment and FRD diameter and spacing treatments remained constant for each entrance type while the bait treatment varied from day-to-day. Experiment 1 Group 1 Group 2 Conical Entrance Trapezoid Entrance Day C1 C2 T1 T2 1 No light + 5 mm + 52 mm No light + 3 mm + 52 mm No light + 5 mm + 52 mm No light + 3 mm + 52 mm 2 Light + 5 mm + 52 mm Light + 3 mm + 52 mm Light + 5 mm + 52 mm Light + 3 mm + 52 mm 3 Light + 5 mm mm Light + 3 mm mm Light + 5 mm mm Light + 3 mm mm 4 No light + 5 mm mm No light + 3 mm mm No light + 5 mm mm No light + 3 mm mm 5 No light + 5 mm mm No light + 3 mm mm No light + 5 mm mm No light + 3 mm mm 6 Light + 5 mm mm Light + 3 mm mm Light + 5 mm mm Light + 3 mm mm 7 Light + 5 mm mm Light + 3 mm mm Light + 5 mm mm Light + 3 mm mm 8 No light + 5 mm mm No light + 3 mm mm No light + 5 mm mm No light + 3 mm mm 9 Light + 5 mm mm Light + 3 mm mm Light + 5 mm mm Light + 3 mm mm Experiment 2 Conical Entrance Trapezoid Entrance Day C1 C2 T1 T2 10 Light + 5 mm mm + Bait Light + 5 mm mm + No bait Light + 5 mm mm + Bait Light + 5 mm mm + No bait 11 Light + 5 mm mm + No bait Light + 5 mm mm + Bait Light + 5 mm mm + No bait Light + 5 mm mm + Bait 12 Light + 5 mm mm + Bait Light + 5 mm mm + No bait Light + 5 mm mm + Bait Light + 5 mm mm + No bait CSAR

31 Table 2. Summary of total catches of each species by artificial light treatment during Experiment 1 (E1) and by bait treatment during Experiment 2 (E2). Unit of measure for total catch is kilograms for snow crab and toad crab and number of individuals for all remaining finfish species and the miscellaneous finfish (i.e., grenadier, eelpout, and sculpin combined). Number of pot hauls (n) for each treatment is shown in parentheses and the percentage of the pot hauls a species was captured in for each treatment is also shown. Species Total E1 and E2 Artificial light Absent (n=48) Present (n=60) Absent (n=18) Bait Present (n=18) American plaice (4%) 265 (85%) 98 (89%) 56 (83%) Atlantic cod 32 9 (17%) 17 (17%) 5 (17%) 1 (6%) Redfish 9 4 (8%) 3 (5%) 1 (6%) 1 (6%) Turbot 5 5 (8%) 0 (0%) 0 (0%) 0 (0%) Spotted wolffish 4 4 (8%) 0 (0%) 0 (0%) 0 (0%) Miscellaneous finfish 6 3 (6%) 2 (3%) 1 (6%) 0 (0%) Snow crab 1, (96%) 948 (95%) 49 (67%) 249 (89%) Toad crab (13%) 7.3 (42%) 2.0 (33%) 1.7 (33%) CSAR

32 Table 3. Summary of three-way ANOVA to test the effect of baited pot entrance type (conical and trapezoid), fish retention device (FRD) trigger diameter (3 mm and 5 mm), and FRD trigger spacing (52 mm, 109 mm, and 166 mm) on catch rates of American plaice. All pots also contained an artificial light source (i.e., fishing light). Source df SS MS F-value p-value Entrance * FRD diameter FRD spacing * Entrance FRD diameter Entrance FRD spacing FRD diameter FRD spacing Entrance FRD diameter FRD spacing Error Total *significantly different at p<0.05. CSAR

33 Table 4. Summary of independent-samples t-tests of the effect of entrance type on mean catch rates of American plaice in baited pots by FRD trigger spacing. All pots also contained and artificial light source (i.e., fishing light). FRD trigger spacing Entrance No. of traps Catch (kg) t-test Mean S.E. df t-value p-value 52 mm Conical Trapezoid mm Conical Trapezoid mm Conical Trapezoid *significantly different at Bonferroni s adjusted alpha level (i.e., p<0.0167). CSAR

34 Table 5. Summary of one-way ANOVAs to test the effect of fish retention device (FRD) trigger spacing on mean catch rates of American plaice in baited pots with conical and trapezoid entrances. All pots also contained an artificial light source (i.e., fishing lights). Entrance FRD trigger spacing No. of traps Catch (kg) ANOVA Mean S.E. df F-value p-value Conical 52 mm mm , mm Trapezoid 52 mm mm , mm *significantly different at p<0.05. CSAR

35 Table 6. Summary of three-way ANOVA to test the effect of baited pot entrance type (conical and trapezoid), fish retention device (FRD) trigger diameter (3 mm and 5 mm), and FRD trigger spacing (52 mm, 109 mm, and 166 mm) on total body length of American plaice. All pots also contained an artificial light source (i.e., fishing lights). Source df SS MS F-value p-value Entrance FRD diameter FRD spacing * Entrance FRD diameter Entrance FRD spacing FRD diameter FRD spacing Entrance FRD diameter FRD spacing Error Total *significantly different at P<0.05. CSAR

36 Table 7. Summary of two-way ANOVA to test the effect of pot entrance type (conical and trapezoid) and bait (present and absent) on catch rates of American plaice in pots that contained an artificial light source (i.e., fishing light). Fish retention device trigger diameter and trigger spacing were constant at 5 mm and 166 mm, respectively. Source df SS MS F-value p-value Entrance * Bait Entrance bait Error Total *significantly different at p<0.05. CSAR

37 Table 8. Summary of two-way ANOVA to test the effect of pot entrance type (conical and trapezoid) and bait (present and absent) on total body length of American plaice in pots that contained an artificial light source (i.e., fishing light). Fish retention device trigger diameter and trigger spacing were constant at 5 mm and 166 mm, respectively. Source df SS MS F-value p-value Entrance Bait * Entrance bait Error Total *significantly different at p<0.05. CSAR

38 Table 9. Summary of independent-samples t-tests of the effect of fish retention device (FRD) trigger diameter on the mean catch rates of snow crab in baited pots by entrance type and FRD trigger spacing when an artificial light source was absent. Entrance FRD trigger spacing FRD trigger diameter No. of traps Catch (kg) t-test Mean S.E. df t-value p-value Conical 52 mm 3 mm mm mm 3 mm mm mm 3 mm mm Trapezoid 52 mm 3 mm mm mm 3 mm mm mm 3 mm mm *significantly different at Bonferroni s adjusted alpha level (i.e., p<0.0167). CSAR

39 Table 10. Summary of independent-samples t-tests of the effect of fish retention device (FRD) trigger diameter on the mean catch rates of snow crab in baited pots by entrance type and FRD trigger spacing when an artificial light source was present. Entrance FRD trigger spacing FRD trigger diameter No. of traps Catch (kg) t-test Mean S.E. df t-value p-value Conical 52 mm 3 mm mm mm 3 mm mm mm 3 mm mm Trapezoid 52 mm 3 mm mm mm 3 mm mm mm 3 mm mm <0.001* *significantly different at Bonferroni s adjusted alpha level (i.e., p<0.0167). CSAR

40 Table 11. Summary of one-way ANOVAs to test the effect of fish retention device (FRD) trigger spacing on the mean catch rates of snow crab in baited pots by entrance type and FRD trigger diameter when an artificial light source was absent. Entrance FRD trigger diameter FRD trigger spacing No. of traps Catch (kg) ANOVA Mean S.E. df F-value p-value Conical 3 mm 52 mm mm mm mm 52 mm mm mm Trapezoid 3 mm 52 mm mm mm mm 52 mm mm mm , , , , *significantly different at p<0.05. CSAR

41 Table 12. Summary of one-way ANOVAs to test the effect of fish retention device (FRD) trigger spacing on the mean catch rates of snow crab in baited pots by entrance shape and FRD trigger diameter when an artificial light was present. Entrance FRD trigger diameter FRD trigger spacing No. of traps Catch (kg) ANOVA Mean S.E. df F-value p-value Conical 3 mm 52 mm mm mm mm 52 mm mm mm Trapezoid 3 mm 52 mm mm mm mm 52 mm mm mm , , , , *significantly different at p<0.05. CSAR

42 Table 13. Summary of independent-samples t-tests of the effect of fish retention device (FRD) trigger diameter on the mean catch rates of snow crab in baited pots by presence or absence of an artificial light source and entrance type. Entrance Artificial light FRD trigger diameter No. of traps Catch (kg) t-test Mean S.E. df t-value p-value Conical Absent 3 mm mm Present 3 mm mm Trapezoid Absent 3 mm mm Present 3 mm mm * * *significantly different at Bonferroni s adjusted alpha level (i.e., p<0.025). CSAR

43 Table 14. Summary of independent-samples t-tests of the effect of entrance type on mean catch rates of snow crab in baited pots by presence or absence of an artificial light source and FRD trigger diameter. FRD trigger diameter Artificial light Entrance No. of traps Catch (kg) t-test Mean S.E. df t-value p-value 3 mm Absent Conical Trapezoid Present Conical Trapezoid mm Absent Conical Trapezoid Present Conical Trapezoid <0.001* * *significantly different at Bonferroni s adjusted alpha level (i.e., p<0.025). CSAR

44 Figure 1. Map of study area in Green Bay region of Notre Dame Bay illustrating approximate location of the pot/trap study area and location of one of the gillnet sets. CSAR

45 Figure 2. Photographs of a battery powered electric fishing light. Both photos are of the same fishing light with the photo on the right taken in total darkness. CSAR

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