Turbot Potting: Regaining Under 35 Fleet Access to the Turbot Fishery While Conserving the Snow Crab Resource

Transcription

1 Turbot Potting: Regaining Under 35 Fleet Access to the Turbot Fishery While Conserving the Snow Crab Resource Prepared by: Scott M. Grant 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 March 2012

2 Executive Summary If a baited pot could be developed to capture commercial quantities of turbot in the large bays on the northeast coast of insular Newfoundland it 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. Four experimental entrance designs were developed at the Marine Institute to determine whether turbot could be captured in a large ( ; 198 cm 198 cm bottom dimension) baited pot currently being used to prosecute cod in shallow coastal waters of Newfoundland and Labrador. Experimental pots were fish at a maximum depth of 250 fathom (460 m) in traditional turbot gillnet fishing grounds adjacent to the community of Triton from November Traditional deepwater (>350 fathom; 640 m) turbot gillnet grounds outside the protection of the headlands were also within steaming distance of the community but were inaccessible due to high winds and sea state (1-2 m) in late November. There were no turbot captured during the current study, apparently due to an autumnal migration to deeper waters of Green Bay outside the protection of the headlands. Although local fishermen reported capturing turbot in the cod gillnet fishery prosecuted at depths of <100 fathoms (183 m) 2-4 weeks prior to the study, there were also no turbot captured in gillnets or pots set at these depths during the study. The current experiments demonstrated that a high percentage of snow crab (mean, 86-91%) could be excluded from the pot catches when both rigid and flexible fish retention devises (FRDs) were used. Catches of snow crab in baited pots with fish FRDs were low averaging 5-11 kg per pot and were released alive and in good condition. This is valuable information that will be used in the design of experiments to be carried out in The following recommendations are proposed from this study: 1) Future turbot potting experiments be conducted in the deepest water accessible within steaming distance (<35 fleet) of the community of Triton and that the experiments be conducted during the summer months when weather conditions are more amenable and the turbot fishery is underway. 2) Gillnet or long-line fishing be conducted in the proposed experimental potting area prior to mobilization of the potting gear and research team to the community of Triton to verify that turbot are present on the fishing grounds. Turbot Potting Experiments Page 2 Centre for Sustainable Aquatic Resources

3 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 2007). In some instances fishermen report catches of over 100 cod at well over 700 lbs per pot in an overnight set (Walsh and Sullivan 2007). 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 all bycatch species (including crab) and undersize cod being released unharmed and produces a top quality product as all cod are alive and in prime condition when brought on board resulting in 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. CSAR (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 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. Within 2-3 minutes nine of the 10 fish entered the baited pot. 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 high 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 rigid one-way triggers, increased the catch rates of Pacific cod but prevented Greenland halibut from entering the pot (Carlile et al. 1997). Turbot is unique among the flatfish species occurring in Newfoundland waters as its body shape approaches that of fusiform round-bodied fish, the right eye has not completely migrated to the left side of the head, and both sides of the body are pigmented. All of these characteristics have led some to suggest that turbot easily adopt a bathypelagic habit spending a considerable amount of time swimming in a vertical position with the dorsal fin upright rather than horizontally as do other flatfishes (de Groot 1970). Thus, rigid triggers may not prohibit the entrance of turbot into pots. Studies that test pots with a large bottom area will help to maximize catch rates and Turbot Potting Experiments Page 3 Centre for Sustainable Aquatic Resources

4 observed behaviour of flatfish under confined conditions suggest over-crowding may not limit the entry of commercial quantities of turbot into a baited pot. For example, even though there was ample space available in holding tanks, three species of flatfish (i.e., American plaice, Atlantic halibut, and yellowtail flounder) have been observed to crowd together in the corner of holding tanks with fish partially lying upon one another. Further, analysis of stress hormone levels in wild American plaice demonstrated fish were less stressed under similar crowded conditions (Grant et al. 2006). During a review of design features of baited pots that influence catch rates over a number of different species Dr. Grant 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). Ultimately, to reduce costs in the early phase of exploratory research into turbot potting the best approach would be to select a large pot which is proven to capture finfish and test several variations of the entrance to find an entrance design that maximizes catch rates. This is the approach that was taken in this study. Specifically, the entrance of the recently developed Newfoundland cod pot was modified to both increase the likelihood of turbot entering the pot and decrease the likelihood of escapement. Objectives This study had three objectives: 1) peruse the literature on morphology and behavior of flatfish and past potting studies to determine most suitable entrance designs, 2) construct 12 cod pots and incorporate the new entrance designs, and 3) conduct at-sea experiments to test suitability of entrance designs for capturing turbot and minimizing the bycatch of snow crab. Methodology Entrance designs Four types of entrance were designed to increase the probability of turbot entering a pot and prevent escapement from the pot with and without fish retention devices (FRDs). Entrances were based on a funnel design with use of the traditional conical design currently used in the cod pot and a trapezoid design. Thus, the conical funnel entrance ended in a circular ring while a trapezoid funnel entrance ended in a rectangle. Turbot body length to body width ratios obtained during a turbot long-line selectivity study carried out in Nunavut in 2011 were used to determine the minimum opening size of an entrance ring/ rectangle (unpubl. data, S. Grant). It was found that the body width of turbot was on average 40% of the body length. From this result a minimum diameter of 40 cm was chosen to be tested for the entrance ring/ rectangle designs. It was hypothesized that a small entrance diameter would limit the ability of turbot to identify the Turbot Potting Experiments Page 4 Centre for Sustainable Aquatic Resources

5 entrance once it had entered the pot reducing the probability of escapement. Also, a small entrance was presumed to reduce the probability of turbot turning and exiting an entrance funnel. However, to account for unforeseen behavioural limitations two rectangular entrance sizes were constructed one at 40 cm 20 cm (length height) and the second at 60 cm 20 cm (Figure 1). Two conical funnel designs were also constructed both with a circular ring diameter of 40 cm. One conical entrance closely mirrored that of the entrance currently used in the cod pot while the second conical entrance had a flat bottom with a minimum entrance diameter of 30 cm. The ring/rectangle of all entrances was oriented on a 10 angle from vertical to reduce the probability of captured turbot visually identifying the entrance and thereby escaping from the pot. Entrances were also designed to extend to the centre of the trap and were therefore 1 m in length as opposed to the traditional 0.5 m length funnels currently used in the traditional cod pot. Extending the length of the funnel was hypothesized to reduce the probability of escapement once captured and increase the probability of capture by reducing the potential for the fish to turn once they had committed to entering the funnel. Figure 1. Trapezoid funnels with cm (left) and cm (right) rectangular entrances showing rigid fish retention devices. Three replicates of each of the four entrance designs were incorporated into 12 traditional cod pot frames. The resulting four entrance designs were as follows: 1) trapezoid funnel - 40 cm 20 cm rectangular entrance (T1), 2) trapezoid funnel - 60 cm 20 cm rectangular entrance (T2), 3) conical funnel 40 cm diameter circular entrance (C1), and 4) semi-conical funnel 40 cm diameter circular entrance with 30 cm flat base (C2). Two types of fish retention devices (FRD) were tested; one rigid the other flexible. The rigid FRD was the traditional stainless steel trigger used in the cod pot. Flexible FRD was a modification of this trigger by reducing the length of the trigger fingers by 10 cm to allow a piece of flexible heat shrink tubing to be attached. Trigger finger spacing of mm was observed in both the rigid and flexible FRD. Turbot Potting Experiments Page 5 Centre for Sustainable Aquatic Resources

6 Pot construction Twelve cod pots have been constructed based on the traditional cod pot design (i.e., 6.5' 6.5' [198 cm 198 cm] bottom dimensions, 4.5 (11.4 cm) mesh throughout, and a large floating mesh bag). At-sea experiments Final modifications to the pot entrances were completed on 18 November 2011 and pots were transported to Triton and deployed on 21 November Pots were fished for five consecutive overnight sets from 21 to 26 November. Pots were freshly baited daily with an approximately 3 kg 1:1 ratio of herring and squid. All bait was placed in a single large fine mesh bait bag. The bait bag was attached to the centre frame support of a pot between the two entrances by means of two skivers. Pots were deployed in three groupings with one of each of the four different entrance designs (i.e., T1, T2, C1, and C2) represented in each group. Groups of four pots were randomly deployed in waters adjacent to the community of Triton (from White Point to Brandies) and at varying depths ranging from approximately 50 to 250 fathoms (90 to 460 m). Each group of four pots was deployed at similar depths (±20 fathom; ±65 m). Pots were hauled daily and the catch was sorted by species. Soak times ranged from hours. Snow crab catch weights were estimated from the number of tote pans (23 kg/pan) or average weight of randomly selected crab. All other species were counted. There were no turbot captured (see below). A single gillnet was deployed adjacent to the turbot pot sets carried out in relatively shallow water (<100 fathom; 183 m) in an attempt to establish presence/absence of turbot in the study area. Gillnets were not deployed in the deeper waters (i.e., 250 fathom; 460 m) due in part to the high bycatch of snow crab at these depths and proximity of the fishing area to the community of Triton. Discussions with local fishermen revealed that turbot were captured in gillnets set for cod over a time period of approximately 2-4 weeks prior to the potting experiments. These turbot were reported to be approximately cm in length and were captured in relatively shallow waters (<100 fathom). On 23 November, one of the four pot groupings were moved to this depth and a single 50 fathom (91 m) 7 (17.8 cm) mesh gillnet was also deployed. A single gillnet set was also carried-out on 24 November. Duration of the gillnet sets was limited to overnight with soak times of hours. Results and Discussion Unfortunately, there were no turbot captured during the at-sea experiments. This was attributed to the late timing of the study and apparent migration of turbot into deeper water channels of Green Bay in the fall-winter. Communications with DFO confirmed that only very small turbot (<30 cm) were present close to shore at the depths tested during the late autumn potting experiments. Historically, the area fished adjacent to the community of Triton during this study was a good area for capturing turbot during the turbot fishing season (mainly summer) however it appears commercial size turbot migrate out of this area in mid- to late autumn. High winds Turbot Potting Experiments Page 6 Centre for Sustainable Aquatic Resources

7 outside the protection of the bay where the current experiments were conducted combined with high sea state (1-2 m) prevented testing the pots in the deeper water (>350 fathom; 640 m) channels outside the bay. Calmer weather conditions that typify the region in June-July will allow fishing in the deeper water regions in It is notable, that this is when the turbot fishery is open and will thus be a better reflection of the potential for the baited pot to capture commercial quantities of turbot. There were no turbot captured in the gillnet sets. Gillnets captured a single snow crab and Greenland cod and both were released alive. The species targeted during this study was the turbot. Non-targeted species captured in baited pots included snow crab, toad crab, Greenland cod, Atlantic cod, and spotted wolffish. Snow crab was the most prevalent non-targeted species captured both in terms of number and biomass. A single spotted wolffish (approx. 90 cm total length) was captured and released alive. All nontargeted species were quickly returned to the ocean and were in good health when released. Success of a baited pot to prosecute turbot will rely on the ability of the pot to avoid the incidental capture and harm to snow crab. Mean catch rates of snow crab were high (40-61 kg/trap night) in all four entrance types when no fish retention device (FRD) was used (Table 1). Catch rates of crab dropped considerably when both the rigid and flexible FRDs were installed. A two-way ANOVA demonstrated that the catch rates of snow crab did not Table 1. Summary of the mean catch (kg/trap +/- 1SE) of snow crab for each entrance type (see text for definitions) with no fish retention device (FRD), rigid (FRD), and flexible (FRD). Entrance type No. hauls T1 T2 C1 C2 No FRD (6.8) 60.6 (3.8) 51.1 (8.7) 39.8 (3.3) Rigid FRD (3.3) 7.6 (2.0) 7.7 (3.7) 5.6 (0.4) Flexible FRD (1.7) 5.2 (0.3) 6.9 (2.3) 7.6 (1.9) differ significantly between pot entrance types within a FRD treatment (F 35,3 = 2.57; p=0.078) but were significantly less when entrances were fitted with a FRD (F 35,2 = 173.5; p<0.001) and a Tukey-test revealed there was no significant difference (i.e., p>0.05) in the catch rates between the rigid and flexible FRD. Overall, these results are encouraging as they show that the mean catch rates of snow crab can be significantly reduced by as much as 91% (range, 86-91%) for a specific entrance type by installing a FRD and that the rigid and flexible FRDs have similar snow crab excluder properties. Given that some flatfish species may avoid entering baited pots fitted with a rigid FRD (Carlile et al. 1997) and we currently have no information on potting capabilities with regard to turbot it is important to establish that a flexible FRD has the same snow crab excluder properties as a rigid FRD. Conclusions Conclusions with regard to the ability of differing entrance designs in a baited pot to capture turbot cannot be made at this time due to the apparent lack of turbot on the fishing grounds. Shoreward populations of turbot appear to migrate to deeper water in autumn. Although the area fished with the baited pots was traditional turbot fishing grounds prosecuted with gillnets and Turbot Potting Experiments Page 7 Centre for Sustainable Aquatic Resources

8 long-line these former fisheries took place largely during summer and the current potting experiments were conducted in late autumn (21-26 November). The maximum depth in the experimental area was approximately 250 fathoms (460 m) and although relatively shallow for turbot, as outlined above, this was a productive area for turbot in past summer fisheries. Inclement weather conditions (high winds) and sea state (1-2 m seas) prevented experiments from being conducted in the deeper waters outside of the protection of the headlands surrounding the community of Triton. Water depths are in excess of 350 fathoms (>640 m) are present outside the protection of the headlands and this area is accessed by the industry partner vessel during the spring-summer snow crab fishery. It is notable, that the initial at-sea research design called for experiments being conducted in this deep water area (>640 m) as early as October. However, resources for entrance design and installation and at-sea studies were limited as experimental potting experiments were also being conducted in 3Ps (i.e., stone crab) which included pot design, fabrication, and at-sea experiments during September-October. Turbot pot entrance design, fabrication, and installation was not completed until late November. It is recommended that future turbot potting experiments be conducted in the deepest water accessible within steaming distance (<35 fleet) of the community of Triton and that the experiments be conducted during the summer months. Fishermen in the Green Bay region voluntarily banned the use of gillnets to prosecute turbot due to the high bycatch, damage, and destruction of snow crab. One of the conditions for the successful adoption of a baited pot to capture turbot will be the ability of the pot to avoid the capture or harm to snow crab. In the current study, pots were tested with and without fish retention devices (FRD) not only to determine whether FRDs increase the catch of turbot but also whether they decrease the bycatch of snow crab. Although conclusions cannot be made with regard to turbot, there was a clear reduction in the catch of snow crab when FRDs were used. Equally important was the finding that both rigid and flexible FRDs exclude snow crab from the catches equally. This is important because it may be found that commercial quantities of turbot can only be captured with pots fitted with a flexible FRD. Reduced catch of Pacific halibut when rigid FRDs were used (Carlile et al. 1997) suggest that this may be the case. However, differing behaviours (levels of aggression) and morphology may result in turbot entering baited pots regardless of the type of FRD used. As this study moves forward, it is recommended that gillnet or long-line fishing be conducted in the proposed experimental potting area prior to mobilization of the potting gear and research team to verify that turbot are present. Recommendations The following recommendations are suggested at this point: 1) Future turbot potting experiments be conducted in the deepest water accessible within steaming distance (<35 fleet) of the community of Triton and that the experiments be conducted during the summer months when weather conditions are more amenable and the turbot fishery is underway. 2) Gillnet or long-line fishing be conducted in the proposed experimental potting area prior to mobilization of the potting gear and research team to the community of Triton to verify that turbot are present on the fishing grounds. Turbot Potting Experiments Page 8 Centre for Sustainable Aquatic Resources

9 References 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: 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: Grant, S.M Mortality of snow crab discarded in Newfoundland and Labrador s trap fishery: at-sea experiments on the effect of drop height and air exposure duration. Canadian Technical Report of Fisheries and Aquatic Sciences 2481: vi + 28 p. Grant, S.M., Hiscock, W., Manning, T., and Hickey, W.M Development of a Live Release Program for American Plaice Captured Incidentally in the Grand Bank Yellowtail Flounder Otter Trawl Fishery: Phase I Factors Affecting At-Sea Estimates of Mortality. Centre for Sustainable Aquatic Resources, Fisheries and Marine Institute of Memorial University of Newfoundland, Canada. P-93: 127p. Miller, R.J Saturation of crab traps: reduced entry and escapement. J. Cons. Int. Explor. Mer. 38: 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, P., and Sullivan, R Baited cod pots: catching without killing. Centre for Sustainable Aquatic Resources, Marine Institute of Memorial University of Newfoundland, Technical Report, 24 p. Turbot Potting Experiments Page 9 Centre for Sustainable Aquatic Resources