Project Number 08-FEG-12. Erin J. Burge 1, Jim Atack 2, Craig Andrews 3. Report Date: 10 November 2009

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1 Investigating the use of underwater video for the determination of size, stock density, and temporal patterns of habitat usage of grouper on hard-bottom habitats Project Number 08-FEG-12 Erin J. Burge 1, Jim Atack 2, Craig Andrews 3 Report Date: 10 November Corresponding author. Coastal Carolina University, Department of Marine Science, PO Box , Conway, SC 29526, phone: (843) , eburge@coastal.edu 2 In Sea State Inc., 111 SW 20 th St., Oak Island, NC Over & Under Adventures Inc., 4956 Longbeach Rd # Southport, NC 28461

2 ABSTRACT Accurate assessments of economically and ecologically important finfish populations are critical to single- and multi-species fishery management. As such, a diversity of data collection methodologies are advantageous for species of high economic value, both from a scientific desire to ensure the most sound population assessments, and from the perspective of public acceptance of scientific and management recommendations for the use of fishery resources. In this pilot project we investigated the use of a non-traditional and relatively inexpensive, collaborative method for enhancing fishery-independent datasets by collecting underwater video of grouper habitats. To our knowledge, a stationary video supplemental stock assessment for gag grouper (Mycteroperca microlepis) has not previously been attempted. Underwater video techniques were used to document the presence/absence, estimated size, density, behavioral patterns, and temporal habitat usage of gag grouper on shallow water, hard-bottom habitats on the continental shelf of North Carolina. A comparison between video findings and diver visual surveys of groupers at the same locations was also made. Survey dives (n = 57) were conducted from June 2008 January 2009 and resulted in observations of 1813 scamp (M. phenax), 305 gag, 97 yellowmouth grouper (M. interstitialis) and 118 individuals of other serranid species in the total standard definition (SD) video footage analyzed (24.6 h). Comparing equal segments of each video (15 minute) resulted in observations of 760 scamp, 115 gag, 33 yellowmouth, 27 graysby (Cephalopholis cruentatus), 13 red grouper (Epinephelus morio), nine rock hind (E. adscensionis), two goliath grouper (E. itajara), and six unidentified serranids in 8.5 hours of video observation. Comparisons were made at multiple locations, using baited and unbaited camera deployments on ledge and live-bottom habitats. There were no significant differences in the numbers of gag and scamp detected for surveys in which bait was not used, nor were differences detected for scamp between the two habitat types. Gag grouper were more frequently observed on live-bottom habitats. With the necessity of accurate assessments for resource managers becoming more important, non-extractive survey techniques, similar to those employed in this program, should be considered for future applications. These video survey techniques were also valuable for observations of fish community structure and some behavioral traits, suggesting that the addition of similar video observation protocols to MARMAP (or similar) fishery-independent data collections would be very valuable for immediate assessments on critical species, and for longterm monitoring of trends in community structure. 2

3 INTRODUCTION Accurate assessments of economically and ecologically important finfish populations are critical to single- and multi-species fishery management. As such, a diversity of data collection methodologies are advantageous for species of high economic value, both from a scientific desire to ensure the most sound population assessments, and from the perspective of public acceptance of scientific and management recommendations for the use of fishery resources. The latest gag grouper assessment and recommendations (SEDAR10, 2006) utilized data from both fisherydependent and fishery-independent indices of abundance. These fishery-dependent datasets included commercial handline and longline fisheries, recreational headboat landings and MRFSS data from the recreational charter and private boat sectors. Fishery-independent data were developed from the SEAMAP reef fish video survey in the Gulf of Mexico and MARMAP cruises in North and South Carolina. Groupers (Family Serranidae, Subfamily Epinephilinae) play an important global role in hard-bottom ecosystems as high trophic level predators, and also support valuable commercial and recreational fisheries (Parrish, 1987). Groupers primarily live in habitats of complex topography and hard substrates (Chiappone et al., 2000; Smith, 1961) over a range of depths (1 to 300 m), and eat mainly fishes and crustaceans (Parrish, 1987). Certain characteristics of moderate to large species within the group that potentially negatively affect fisheries include slow growth, delayed reproduction, long life span, reduced spawning period, and commonly, protogynous sex reversal (reviewed in Coleman et al., 2000). Along the continental shelf of North Carolina gag and scamp grouper were the most commonly recorded moderate to large serranids from hard-bottom visual diver surveys in the 1970s ( ) and the early 1990s ( ) (Parker Jr. and Dixon, 1998), although they share space with other members of the snapper-grouper complex in this region (Grimes et al., 1982; Parker Jr., 1990; Quattrini and Ross, 2006; Quattrini et al., 2004). Both gag and scamp display reproductive aggregation behavior (Coleman et al., 1996) and appear to have limited home ranges (Heinisch and Fable Jr., 1999; Kiel, 2004). Kiel (2004) reported a tendency of gag to be site specific and to utilize a central core site as a result of numerous relocations of tagged gag on or near specific patch reefs. In this project we investigated the use of non-traditional and relatively inexpensive, collaborative methods for enhancing fishery-independent datasets by collecting underwater video data of gag grouper habitats without fish extraction. Underwater video techniques are useful for quantifying and observing fishes and were used in this study to estimate grouper sizes, densities, behavior, and temporal patterns of habitat usage on hard-bottom habitats near Cape Fear, North Carolina. Numerous previous studies have examined the use and efficacy of underwater video techniques (e. g.: Cappo et al., 2004; Gledhill et al., 1996; Harvey et al., 2007; Harvey et al., 2003; Pfister and Goulet, 1999). Underwater video techniques are practical because the recordings are a less intrusive, non-extractive method of data collection that reduces diver affects and observer bias that can arise with other collection methods (reviewed in Harvey et al., 2004). Video recordings are also valuable because they represent data on a permanent record that allows the opportunity to measure more variables from a given data set (Cappo et al., 2007) and to revisit historical data. The collection of video data also, to a large degree, removes the need for field deployment of scientific specialists, and provides an exciting product for use in communicating science to stakeholders and the general public (see attached video summary).

4 The biology and behavior of fish species of interest are important for determining the underwater video techniques most appropriate for the survey methodology (Willis et al., 2000). This is especially true for baited underwater video techniques which are needed to offset biases introduced by changes in fish behavior (Willis et al., 2000). Baited video observation has been successfully used to document large, mobile species, including members of the snapper-grouper complex (Langlois, 2006; Rand et al., 2006) in the past. In contrast, Posey and Ambrose (1994) found that non-baited cameras may be less intrusive than baited camera systems since the absence of bait ensures that there will be no effective change in fish behavior regarding feeding. There are trade-offs to using non-baited video techniques including greater field time and more expensive equipment to ensure that statistically testable data is collected (Posey and Ambrose, 1994). This pilot project was designed to use underwater video data collection to document the presence/absence, estimated size, density, and temporal habitat usage of gag grouper (Mycteroperca microlepis) on shallow water, hard-bottom habitats on the continental shelf of North Carolina, and to compare the video findings to diver visual surveys of groupers at the same locations. Additional information was collected on other species of observed groupers, including primarily scamp (M. phenax) and yellowmouth grouper (M. interstitialis). Recent stock assessments for the Atlantic gag grouper indicated that the species is experiencing overfishing and noted that there is lack of fishery-independent abundance data for southern North Atlantic gag (SEDAR10 Review Workshop, 2007), indicating a need for additional monitoring of this species for future stock assessments and management recommendations. MATERIALS AND METHODS Study sites Video locations were chosen from a private database of known hard-bottom locations (J. Atack and C. Andrews, personal communication) and also included established MARMAP sampling sites in the depth range of m (Figure 1). Sampling sites included previously visited and unvisited locations by the study authors. Factors used to select sites for each field day included recent local conditions, such as prevailing wind and wave forecasts, recent reports of bottom visibility, satellite imaging (SST composites and chlorophyll a 1 km resolution composites) and elapsed time since the last visit. In general, these sites were km SE of Cape Fear (N 33 50' 38" W 77 57' 43") and included two representative bottom types (Figure 2). Ledge areas consisted of high-relief outcrops of limestone substrate, live-bottom areas of relatively low relief, extensive hard substrate heavily colonized by benthic fauna and flora (Blackwelder et al., 1982; Parker Jr., 1990; Sedberry and Van Dolah, 1984; Wenner et al., 1983). Live bottom areas generally had less than 1 m of sloping vertical relief, while ledge sites generally possessed greater than m of topographic relief, and had numerous undercut ledges and areas of complex bathymetry (see attached video summary). Chosen sites were visited one to four times each during the period June 2008 January At each of the sites a detailed log of dive personnel, water parameters, topographic descriptions, and diver observed fish counts were compiled (Figure 3). 4

5 Video cameras and housings Video cameras used in this study consisted of a pair of Sony HDR-SR11 60GB High Definition (HD) Handycam Camcorders (Sony Electronics, Inc., Kansas City, Missouri) (Table 1) fitted with 0.5 wide angle lenses. Underwater video housings were Light & Motion Stingray HD Underwater Video Housings for Sony cameras (Backscatter Underwater Photo and Video, Monterey, California) (Table 2). Each of the housing and camera units were mounted on a custom made stand constructed of drilled PVC tubing and marine starboard (Figure 4). Dive weights ( kg [4 15 lb) attached under the stand were used to hold the camera in place at the dive locations and elevated the camera housing approximately 25 cm from the surroundings. Camera deployments and diver visual surveys Upon arrival and anchoring at a suitable dive site, a pair of SCUBA divers descended using the anchor line and identified an appropriate location for setting up the camera. Conditions considered acceptable for filming included bottom visibility greater than 25 ft (estimated), appropriate structural habitat (ledge/live-bottom), and a secure anchorage to ensure equipment retrieval. While the camera operator chose a location and deployed the stand the second diver conducted a 2 minute visual census of all groupers visible from the camera location (Colvocoresses and Acosta, 2007). Each fish was assigned an estimated size category (< 12, 12 18, 18 24, 24 30, > 30 ), and these data were recorded on dive slates and transferred to the dive log book (Figure 3) upon completion of the dive. The census diver would then assist in camera positioning and deployment by placing size and distance markers, and, when used, bait or chum. Size marker targets of measured lengths of floating PVC pipe (either 51 or 61 cm [20 or 24 in] length) were placed 6.1 m (20 ft) from the camera in order to give a known size marker for estimating lengths of distant fish (see attached video summary). On a few occasions the size marker was placed at a distance other than 6.1 m, and the diver signaled the distance during setup in the video. In some videos approximately 2-3 L of shrimp heads or lobster parts were used as a forage fish attractant. In some cases the bait was deployed as a frozen block accessible to feeding fish, and in other cases it was contained within a chum pot. After set-up the stationary video camera apparatus was left by the diver team for durations ranging from 18 to 90 min. At the end of the stationary video period a diver team would retrieve the equipment and return to the boat. In some cases a short swimming transect was conducted, however these were of variable length, swimming speed, and area, and were not used for data analysis. Video data collection Video data from each dive were transferred from the Sony Handycam HDR-SR11 and encoded in SD (standard definition) format on 4.7 Gb DVD discs for data collection and archival storage. These discs are compatible with home DVD players and computer DVD drives, and are viewable in standard video player software (e. g. Windows Media Player, Apple Quicktime). In order to generate the most usable information from each dive video the entire video clip was watched and all groupers were noted. Videos were observed separately by three individuals (E. J. Burge, B. M. Binder, L. E. Bohrer; Coastal Carolina University) who then met weekly to compare results within video clips and review the findings. Each grouper observed was recorded in a standardized data sheet constructed in Microsoft Excel 2003 (Figure 5). Data recorded 5

6 included time code (H:MM:SS) (what time in the video the grouper was seen), grouper species, categorical size estimate, size estimate (inches), repeat likelihood code, and a note with information pertaining to behavior, other species of interest, or movements of divers. Categorical size estimates were assigned based on a scale 1 5, while repeat likelihood codes ranged from 0 5 (Table 3). Repeat likelihood codes were designed to account for recounting of the same fish within videos. Fish observations assigned codes 4 or 5 were presumed to represent fish that could be eliminated from the final data analysis. These variables were used as a measure for abundance and estimated size and densities. Habitat notes such as visibility, macroalgal cover, relief, and notable area characteristics were also recorded. After all grouper observations were compiled from all of the available video clips (n = 51; 6 dives did not result in collected video because of technical or field issues), each of the video clips was subjected to a decision tree and determined to meet criteria for inclusion in the study (Figure 6). Video clips meeting all criteria (n = 34) were used in the final analysis. Stated objectives of the project included conducting 48 surveys, with half of those being revisited monthly for the duration of the study. A smaller number of sites were able to be revisited than originally anticipated, and none with the frequency outlined in the original proposal. Effects due to Hurricane Bertha (mid late July 2008), Tropical Strom Cristobal (late July 2008), which formed off of the Carolinas, and Tropical Storm Hanna (late August early September 2008), which made landfall very close to the study locations, affected filming for approximately 12 weeks and disrupted the repetitive sampling originally proposed. Funded projects of longer duration (1 2 years) would be better able to accommodate these types of delays. Due to these unexpected circumstances each survey visit was considered as a unique site for analysis. Final video analysis consisted of collecting data as noted above for a 15 minute interval that began 3 minutes after the presence of divers in the area ceased. This was determined by divers leaving and not reappearing, cessation of audible breathing sounds, and no evidence of diver influence on fish behavior within view. Fish behavior appeared to return to normal within 1 minute of diver departure (personal observation). In the original request for funds a video interval of 10 minutes was suggested for data collection, with 10 minute periods before and after the data collection window (30 minutes video per site). Full viewings of all videos were conducted and this method of data collection was found to not be workable. In many cases the presence of divers lasted longer than 10 minutes at the beginning and video length was also highly variable. During the 15 minute interval, values designated MaxN gag and MaxN scamp were calculated. MaxN refers to the relative density of fishes based on the maximum number of individuals of each species visible at one time on the video, and has been used in other similar studies (Watson et al., 2005; Willis et al., 2000). This MaxN relative density value provides a conservative estimate, and most probably an underestimate, of the number of fish in the area. Data analyses Statistical methods used for data analysis were conducted in R (v ; and SigmaStat v (Systat Software, Inc., Chicago, Illinois). For these analyses the data were not assumed to be normally distributed, and as such, methods used in this report are non-parametric in nature. Alpha values considered significant were α The Wilcoxon rank-sum test was used to test for differences in mean number of observed fish based on categorical variables such as habitat, bait, or sector of occurrence. Chi-Square tests (χ 2 ) for independence were used to test for evidence of a relationship between two categorical variables. 6

7 There are not any distributional assumptions placed on the χ 2 test and hence it was appropriate in this setting. In order to obtain a linear model for the total count of fish based on a quantitative variable (visibility, depth, temperature), it was not possible to use simple linear regression due to the fact that the response variables were not continuous. For count data in this report, Poisson regression and Spearman s r for nonparametric analyses were used for correlations. Spatial mapping of data used ArcMap v. 9.2 (ESRI Inc., Redlands, California) and shoreline data images from RESULTS Inclusion of dives in data collection A total of 57 dives between 8 June 2008 and 3 January 2009 were conducted (Figure 7). Some locations corresponded to previous MARMAP sampling locations, although some visited MARMAP locations did not have the habitat complexity desirable for this study and no data was collected (see Figure 1). This project was originally planned to include monthly repeated visits to four sites (6 months project duration, 24 total surveys) in order to evaluate seasonal changes in grouper species, while the remaining 24 video surveys were planned to occur at unique sites. Repeated visits to representative sites were hampered due to weather and equipment problems, and after the exclusion of videos due to technical issues (Table 4) repetitive site visits were considered as independent surveys. Of the n = 57 dives conducted, deployment of the camera was deemed not worthwhile or technical difficulties precluded video collection for six sites. Of the 51 camera deployments, low visibility resulted in the exclusion of eight video clips from data analysis. Of the remaining 43 video clips, nine were excluded because they were too brief to allow for a data collection window of 15 minutes after the departure of divers. A 15 minute interval for video data collection balanced collecting larger numbers of grouper observations per video with including the largest number of total video clips. Reducing the observation interval window to 10 minutes would have resulted in the inclusion of one additional video clip (filmed 1 November 2008; dive number 20, Figure 7), but inclusion of this dive would have resulted in removal of 5 minutes of footage from all other videos, a loss of 2.8 h of total analyzed video time. General video observations of groupers Observations of the 15 minute intervals from all 34 usable video clips (8.5 h) resulted in inclusive, potentially redundant counts of 760 scamp (Mycteroperca phenax), 115 gag (M. microlepis), 33 yellowmouth (M. interstitialis), 27 graysby (Cephalopholis cruentatus), 13 red grouper (Epinephelus morio), nine rock hind (E. adscensionis), two goliath grouper (E. itajara), and six unidentified serranids. Total counts uncorrected for variable lengths of video clips (24.6 h), and uncorrected for recounting of individuals were 1813 scamp, 305 gag, 97 yellowmouth grouper and 118 individuals of other serranid species. Video count data and inferred minimum population sizes (MaxN) Because sample sizes for species other than scamp and gag were small, MaxN values were only calculated for these two species. These values were used to evaluate the absolute minimum number of fish present at the dive location. Sums of MaxN scamp (= 125) and MaxN gag (= 32) 7

8 represented 18.4 and 27.8 % of all observed individuals of these species during the 15 minute video data collection intervals. For those fish of each species seen simultaneously on the screen of the stationary video at any given time during the 15 minute observation window, the MaxN inferred minimum population sizes by location ranged from 1-4 gag and 1-13 scamp. Observations outside of the 15 minute window indicate that gag grouper could be more abundant than these minimum population estimates, with MaxN gag more than twice as high as that recorded during the window, higher MaxN values were also obtained for videos viewed in high definition (see Discussion). Diver point counts Diver point counts (2 minutes) also likely represent a non-redundant counting method as the diver is able to more accurately track, and not recount, moving fish within the field of view, compared to the stationary video camera. For the two primary species 402 scamp and 390 gag were observed by divers during the 2 minute intervals at all usable video locations (n = 34, 68 minutes total observation), which is slightly higher than the totals using the 15 minute video observations. Population sizes by location estimated from this counting method range between 1 40 scamp and 0 50 gag. No other species of groupers were noted during the diver point counts at the usable video sites, except for red grouper, which were occasionally observed on some dives, and were not expected to be abundant because of their different geographical distribution. Comparisons between the various counting techniques indicate that there is a significant degree of correlation (Spearman s r for nonparametric analysis; Table 5) between the techniques, especially for scamp (Figure 8). Relationships between physical parameters measured and grouper counts Visibility estimates for all usable videos were based on mean values determined by on-site divers and video observers (Figure 9). There was a significant positive correlation (Spearman s rank correlation r = 0.637; p < 0.001) between the different estimated visibilities and as such these values were averaged to provide a reasonable estimation of visibility for each site. Total observed grouper numbers recorded during the 15 minute data collection interval did not differ (Poisson regression model, p = ) due to changes in visibility (Figure 10) once low visibility videos (< 25 ft) were excluded (data not shown). Habitat depth did not significantly affect grouper counts (Poisson regression model, p = ) for gag and scamp groupers over the sampled depth interval of m (Figure 11). Water temperatures varied seasonally over the course of the study and a significant, negative correlation (Poisson regression, p < 0.001) existed between water temperatures ( C) and total numbers of observed gags and scamps (Figure 12). Effect of baiting, geography, habitat type, and date of sampling on grouper counts Bait or chum (shrimp or lobster heads) was used as a forage fish attractant on 18 of 34 video collection dives. The gags and scamps observed in the 15 minute video counts did not differ significantly with the presence of bait (Wilcoxon test, p = ) and the range in numbers of fish for each treatment (baited, n = 18, range, 5 67 fish; unbaited, n = 16, range, 2 69 fish) were highly similar (Figure 13) with the baiting protocol used in this project. Data by location for gag and scamp were compared by segregating dive sites north and east of Frying Pan Tower from those south and west of this location. These sectors roughly correspond to the oceanographic break that occurs at Frying Pan Shoal and separates Long Bay 8

9 from Onslow Bay. Comparison of grouper counts of gags and scamps in aggregate (video counts; Figure 14) were not significantly different between these sectors (Wilcoxon test, p = ). Numbers of fish varied substantially between sites regardless of the counting method used. Total inclusive video counts, which possibly represent an overestimate of fish in the immediate area, may be representative of a larger area than that seen in the video frame since the camera only records a portion of the sphere surrounding it. Fish recounts in the field of view may be offset by groupers in the immediate area that do not enter the field of view. Supporting evidence for this is drawn from the diver visual survey results which utilized 360 views and recorded similar numbers of gag and scamp in aggregate. MaxN values indicated minimum population sizes at each location and tended to be dominated by scamp (Figure 15). Diver point counts suggested that scamp and gag numbers were similar across all sites, although they varied substantially between sites (Figure 16). Counts of video observed groupers were tested to evaluate habitat usage by the most numerous grouper species. Individual dive videos were categorized as ledge (n = 18) or livebottom (n = 16) habitats based on diver notes and video observations. Total observed gags and scamps in aggregate did not differ significantly between the habitat classifications (Wilcoxon test, p = ; Figure 17), however when considered separately by species, gag grouper were significantly more commonly associated with live-bottom habitats (χ 2 test of independence, p < 0.001; Figure 18). This could be due to the fact that the live bottom areas offer less cover and gag would be more visible than in ledge locations that offer overhead cover. There were several instances where classification of the site was determined by the filming direction and the filming structure since the surrounding structure supported both habitat classifications. Total observed numbers of gag and scamp varied substantially from month to month (Figure 19), although there were large differences in the numbers of usable videos for different months. There was a general trend toward increasing numbers of both species into the winter months, with the maximum number of scamps recorded during November and December 2008 dives, and the maximum number of gags observed in early January As noted (Table 4) it was not possible to revisit sites on a consistent basis, and so trends in abundance at the same sites during the study period could not be evaluated. Size distribution of major grouper species Each observed grouper was assigned an estimated size and estimated size category (Table 3) based on three independent video observers. Consensus estimates were reached by agreement between video observers. Size distributions differed significantly for the three most common species (Figure 20), respectively scamp, gag, and yellowmouth grouper (χ 2 test of independence, p = ). Video observation only rarely identified fish < 12 (size category 1; 10 fish counted of 2215 total observations). The dominant estimated size category for scamp were group 3 (18 24 ), group 4 (24 30 ) for gag, and group 4 for yellowmouth grouper. Size categories for all three species were normally distributed (Kolmogorov-Smirnov test for normality; scamp, K-S Dist. = 0.343, p = 0.055; gag, K-S Dist. = 0.228, p > 0.200; yellowmouth, K-S Dist. = 0.191, p > 0.200). Size distributions for scamp and gag recorded by diver visual point counts (n = 34) differed from video observed size classes in that scamp were most commonly identified as group 2 (12 18 ), while gag were most commonly identified as group 3 (18 24 ) (Figure 21). 9

10 TABLES AND FIGURES TABLE 1. Technical specifications of Sony cameras (HDR-SR11 with 60 GB hard drive) used for video collection. Video Weights and Measurements Optics/Lens General Formats Supported HD: MPEG4 AVC/H.264; SD: MPEG2 Video Signal NTSC color, EIA standards Dimensions mm Weight 650 g with Battery Lens Type Carl Zeiss Vario-Sonnar T 35mm Equivalent mm Aperture F Digital Zoom 150x Filter Diameter 37 mm Focal Distance mm Focus Full range auto / Manual Shutter Speed Auto, 1/30-1/250 (Scene Selection Mode) Optical Zoom 12x Wide-angle Lens 0.5x Camera mounted Imaging Device 1/3" ClearVid CMOS sensor (with Exmor technology) Processor BIONZ image processor Recording Media 60 GB Hard Disk Drive, Memory Stick Duo Media Battery Type InfoLITHIUM with AccuPower Meter System (NP-FH60) Power Power Requirements 7.2V (battery pack); 8.4V (AC Adaptor) Power Consumption 4.5W/4.8W/4.9W Audio Audio Format Dolby Digital

11 TABLE 2. Technical specifications of Light & Motion Stingray HD Underwater Video Housing. Construction Marine-grade Aluminum, Anodized, Depth Rated 300 ft Weight 7 lb Dimensions " Multi-Camera Tray Compatible with Sony HD cameras 2.7" Monitor Back: AA battery powered Glass Zoom-Through front Ergonomic Non-Penetrating Electronic Camera Controls Self-Locking Rotating Latches Double O-ring Seals Monitor Back and Lenses Records Photos to Memory Stick Standard Features Ergonomic Grips Easy-Load Self-Locking Camera Tray Moisture/Leak alarm Color Correction filter Integrated Design for Battery Pods/Weight Brackets Quick Disconnect Mounts for Lights Record Indicator Light Power On/Off Record/Standby Zoom/Telephoto Auto-focus On/Off Depth Controls Auto-focus Lock Momentary Auto-focus Video/Photo Mode Manual Focus TABLE 3. Data coding for categorical size estimates and likelihood of recount bins. Size Code Size Category Recount Code Recount Category 0 unknown 1 < 12" 1 not " 2 unlikely " 3 possible " 4 probable 5 > 30" 5 definite 11

12 TABLE 4 Repeated site visits and outcomes of collected video. Site location 2 Outcome Dive # 1 Revisits Latitude Longitude Date of visit Included in study data Reason for exclusion Jun 2008 Yes Jun 2008 Yes Nov 2008 No Low visibility Jun 2008 No Low visibility Nov 2008 Yes Dec 2008 No Low visibility Jan 2009 Yes Jul 2008 No No video Nov 2008 No No video Jan 2009 Yes Aug 2008 Yes Nov 2008 No Low visibility Dec 2008 Yes Aug 2008 No Video length Aug 2008 Yes Nov 2008 No Low visibility Aug 2008 No Video length Oct 2008 No Video length Dec 2008 No Video length 1 See Figure 7; 2 Latitudes and longitudes are reported as DD MM and are rounded to the nearest minute; 3 Low visibility was defined as estimated values less than 25 ft; No video indicates that survey divers did not collect video because of low visibility or camera/housing malfunctions; Video length refers to video surveys less than 18 min in total length; Blanks indicate that a survey was included in the final analysis TABLE 5 Correlation analysis (Spearman s r for non-parametric analysis) of counting techniques. Species Comparison Scamp Gag r p r p Video vs. MaxN < < Diver vs. MaxN Video vs. Diver

13 TABLE 6 Species richness and relative frequency of occurrence for all observed fish and elasmobranch species from all videos. This listing is not limited to videos deemed useful for grouper observation, nor is it limited to the 15 minute interval of analysis used for grouper counts. Frequency of Occurence 1 Common Name Species 2 Family gray triggerfish Balistes capriscus Balistidae amberjack Seriola dumerili Carangidae almaco jack Seriola rivoliana Carangidae tomtate Haemulon aurolineatum Haemulidae white grunt Haemulon plumieri Haemulidae Most frequent hogfish Lachnolaimus maximus Labridae Spanish hogfish Bodianus rufus Labridae vermillion snapper Rhomboplites aurorubens Lutjanidae blue angelfish Holacanthus bermudensis Pomacanthidae gag Mycteroperca microlepis Serranidae scamp Mycteroperca phenax Serranidae knobbed porgy Calamus nodosus Sparidae spottail pinfish Diplodus holbrookii Sparidae scads* Decapterus spp. Carangidae spadefish Chaetodipterus faber Ephippidae spotfin hogfish Bodianus pulchellus Labridae bicolor damselfish Stegastes partitus Pomacentridae Frequent black sea bass Centropristis striata Serranidae graysby Cephalophis cruentatus Serranidae sheepshead Archosargus probatocephalus Sparidae jolthead porgy Calamus bajonado Sparidae saucereye porgy Calamus calamus Sparidae red porgy Pagrus pagrus Sparidae ocean surgeonfish Acanthurus bahianus Acanthuridae doctorfish Acanthurus chirurgus Acanthuridae blue tang Acanthurus coeruleus Acanthuridae trumpetfish Aulostomus maculatus Aulostomidae sand tiger shark Carcharias taurus Carcharhinidae foureye butterflyfish Chaetodon capistratus Chaetodontidae spotfin butterflyfish Chaetodon ocellatus Chaetodontidae reef butterflyfish Chaetodon sedentarius Chaetodontidae banded butterflyfish Chaetodon striatus Chaetodontidae Less frequent squirrelfish Holocentrus adscensionis Holocentridae Bermuda/yellow chub Kyphosus sectatrix/incisor Kyphosidae planehead filefish Stephanolepis hispudus Monacanthidae spotted goatfish Pseudupeneus maculatus Mullidae queen angelfish Holacanthus ciliaris Pomacanthidae red lionfish Pterois volitans Scorpaenidae bank sea bass Centropristis ocyurus Serranidae rock hind Epinephelus adscensionis Serranidae yellow goatfish Mulloidichthys martinicus Mullidae red grouper Epinephelus morio Serranidae yellowmouth grouper Mycteroperca interstitialis Serranidae great barracuda Sphyraena barracuda Sphyraenidae bandtail puffer Sphoeroides spengleri Tetraodontidae queen triggerfish Balistes vetula Balistidae African pompano Alectis ciliaris Carangidae carcharinid sharks* Carcharhinus spp. Carcharhinidae stingrays* Dasyatis spp. Dasyatidae remoras* Echeneis spp. Echeneidae cornetfish Fistularia tabacaria Fistularidae smooth butterfly ray Gymnura micrura Gymnuridae porkfish Anistotremus virginicus Haemulidae blackbar soldierfish Myripristis jacobus Holocentridae bluehead wrasse Thalassoma bifasciatum Labridae tautog Tautoga onitis Labridae red snapper Lutjanus campechanus Lutjanidae gray snapper Lutjanus griseus Lutjanidae orangespotted filefish Cantherhines pullus Monacanthidae Least frequent moray eels* Gymnothorax spp. Muraenidae spotted eagle ray Aetobatus narinari Myliobatidae scrawled cowfish Acanthostracion quadricornis Ostraciidae trunkfish Lactophyrs trigonus Ostraciidae southern flounder Paralichthys lethostigma Paralichthyidae rock beauty Holacanthus tricolor Pomacanthidae gray angelfish Pomacanthus arcuatus Pomacanthidae French angelfish Pomacanthus paru Pomacanthidae cobia Rachycentron canadum Rachycentridae parrotfishes* Scarus spp. Scaridae jackknife fish Equetus lanceolatus Sciaenidae king mackerel Scomberomorus cavalla Scombridae spotted scorpionfish Scorpaena plumieri Scorpaenidae goliath grouper Epinephelus itajara Serranidae greater soapfish Rypticus saponaceus Serranidae red hind Epinephelus guttatus Serranidae speckled hind Epinephelus drummondhayi Serranidae tiger grouper Mycteroperca tigris Serranidae 1 Categories were assigned based on estimates of the frequency of observation of each species among all videos; most frequent: species present %, frequent: species present 25-50%, less frequent: species present 10-25%, least frequent: species present uniquely-10%; 2 Based on classifications presented by fishbase.org; *Identification to species was not possible or ambiguous. 13

14 Figure 1: MARMAP sampling locations (+) and dives completed for this study (open and closed circles). 14

15 (a) (b) Figure 2: Underwater video frame captures of representative hard-bottom habitats. Video stills are not as clear as video footage viewed in real time. (a) Ledge habitat greater than 2 m in relief is visible in the foreground and background. (b) Representative live-bottom habitat with extensive macroalgal and benthic invertebrate cover. 15

16 Figure 3: Example of a survey dive logbook entry. Physical data was accessed from the National Data Buoy Center, Station (33 26'11" N 77 44'35" W) Frying Pan Shoals, NC, for the date and time that most closely matched the actual dive time based on hourly updates ( station_page.php?station=41013). 16

17 Figure 4: Views of the Light & Motion Stingray HD Underwater Video Housing, (a) forward, lateral (b) rear monitor (c) and custom made stand for field deployment. Photos (a) and (b) from 17

18 Figure 5: Example of data entry system for observations. 18

19 Camera deployed at site, n = 57 No Yes Field No video Camera worked, video collected, n = 51 Yes No Est. visibility > 25 ft, n = 43 No Yes No video Lab Video excluded from analysis Video length > 18 min, n = 34 Yes No Video included in final analysis Video excluded from analysis Figure 6: Decision tree applied to all site videos to determine inclusion in final data analysis. The large boxes indicated Field and Lab refer to where the decision on data collection occurred. Of the n = 57 dives conducted, deployment of the camera was deemed not worthwhile for six sites (n = 51). Of the 51 camera deployments low visibility resulted in the exclusion of eight video clips (n = 43). Of the remaining 43 video clips, nine were excluded because they were to brief to allow for a data collection window of 15 minutes after the departure of divers. 19

20 Figure 7: All survey dive locations. See the Appendix data for information on dates corresponding to each dive number. 20

21 (a) (b) Total observed scamp, 15 min Total observed gag, 15 min MaxN scamp (c) MaxN gag (d) 35 Diver point count scamp, 2 min Diver point count gag, 2 min MaxN scamp MaxN gag Figure 8: A comparison of counting methods for the two most abundant grouper species observed, scamp and gag. a) and b) compare total observed individuals with the maximum number of fish of that species visible simultaneously (MaxN) during the 15 minute interval. c) and d) compare the diver point counts to MaxN values. 21

22 22 Visibility estimated from video (m) Visibility estimated by divers (m) Figure 9: Comparison of visibility estimates (feet converted to meters) made by divers on-site (n = 2-4) and from video clips analyzed by others (n = 3). A high correlation (Spearman s rank correlation r = 0.637; p < 0.001) was found between the different observations. Visibility was one parameter which affected whether a video was included for the analysis (see Figure 6), such that only distances greater than 25 ft were considered adequate for video data collection. 22

23 80 Total groupers observed, 15 min Estimated visibility (m) Figure 10: Estimated visibility (m), calculated as the mean of estimates taken from video observers and diver participants, compared to the count of observed groupers during the 15 minute video interval. A Poisson regression model found insufficient evidence of a relationship between visibility and number of visible fish (p = ). 23

24 80 Total groupers observed, 15 min Dive depth (m) Figure 11: Total counts of scamp and gag groupers during the 15 minute video interval compared to the depth at which the video was recorded. Based on Poisson regression methods to predict presence of fish, there is insufficient evidence of a relationship between depth and the number of visible fish (p = ). 24

25 80 Total groupers observed, 15 min Bottom water temperature ( C) Figure 12: Relationship between grouper counts for scamp and gag based on bottom water temperatures. Bottom water temperatures were recorded by the dive computers of diver participants in the study. A significant negative correlation between total counts and temperature was observed (Poisson regression, p < 0.001). 25

26 80 Total groupers observed (15 min) Unbaited Baited Figure 13: Box plots illustrating the effects of the presence of bait or chum (2-3 L of shrimp shells or lobster parts) on counts of total observed groupers. A Wilcoxon test showed insignificant evidence of a difference in the average number of fish between locations with and without bait (p = ). The boundary of the box closest to zero indicates the 25th percentile, a line within the box marks the median, and the boundary of the box farthest from zero indicates the 75th percentile. Whiskers (error bars) above and below the box indicate the 90th and 10th percentiles and filled circles are outliers. 26

27 Figure 14: GIS plot of the spatial distribution of scamp and gag recorded from 15 minute video surveys. Scamp significantly outnumbered observations of gag grouper (Wilcoxon test for scamp vs. gag, p < 0.001). Scale bars are proportional by size to 33 fish. 27

28 Figure 15: GIS plot of the spatial distribution of scamp and gag as MaxN estimates of population abundance (Wilcoxon test for scamp vs. gag, p < 0.001). Scale bars are proportional by size to 6.5 fish. 28

29 Figure 16: GIS plot of the spatial distribution of scamp and gag as diver point count estimates of population abundance (2 min). Scamp and gag numbers are not significantly different (Wilcoxon test for scamp vs. gag, p = ). Scale bars are proportional by size to 26 fish. 29

30 80 Total groupers observed, 15 min Live-bottom (<1 m relief) Habitat type Ledge (>1.5 m relief) Figure 17: Box plots illustrating the distribution of groupers observed in the 15 minute video interval on two qualitative habitat types. Habitat categories are based on descriptions in (Blackwelder et al., 1982; Grimes et al., 1982; Parker Jr. and Dixon, 1998; Sedberry and Van Dolah, 1984). A Wilcoxon rank-sum test for differences between median values indicated that there was no relationship between total observed scamps and gags and habitat type (p = ). The boundary of the box closest to zero indicates the 25th percentile, a line within the box marks the median, and the boundary of the box farthest from zero indicates the 75th percentile. Whiskers (error bars) above and below the box indicate the 90th and 10th percentiles and filled circles are outliers. 30

31 Total fish observed, 15 min (mean ± SD) Ledge Live-bottom 0 Scamp Gag Species Figure 18: In aggregate total observed fish did not differ between habitats (Wilcoxon rank-sum test, p = ), however a χ 2 test of independence provided significant evidence of a relationship between gag and habitat (ledge or live-bottom) (p < 0.001), suggesting that gag groupers were more frequently observed over live-bottom habitats. Habitat categories are based on descriptions from several studies (Blackwelder et al., 1982; Grimes et al., 1982; Parker Jr. and Dixon, 1998; Sedberry and Van Dolah, 1984). 31

32 60 Total observed fish, 15 min (mean ± SD) Scamp Gag 0 Jun Jul Aug Sep Oct Nov Dec Jan n = 2 n = 0 n = 5 n = 0 n = 4 n = 10 n = 8 n = 5 Study Month Figure 19: Distribution of groupers by species and sampling months. Bars represent mean ± SD for each species from all usable dives conducted during that month. Usable dive numbers are indicated as n = x. Attempted trips in July and September did not result in usable video due to poor visibility. 32

33 log10 (Total observed fish, 15 min) Gag Scamp Yellowmouth 0.0 <12" 12"-<18" 18"-<24" 24"-<30" >30" Size Category (in) Figure 20: Individual observed grouper were speciated and assigned to an estimated size category (Table 3) based on video observation. The three most numerous species observed were scamp (n = 1813), gag (n = 305), and yellowmouth (n = 97) groupers. A χ 2 test of independence provided significant evidence of a relationship between size of the individual and species of grouper (p = ). 33

34 Scamp Gag Diver point counts, 2 min < 12" 12-18" 18-24" 24-30" > 30" Size category (in) Figure 21: Size category distribution of scamp and gag recorded from diver visual point counts of 2 minute during each dive (n = 34). 34

35 (a) (b) Figure 22: Video frame captures illustrating difficulties associated with grouper species identification and recount frequency. Video stills are not as clear as video footage viewed in real time. Frames were taken six minutes apart from a dive conducted 23 November 2008 and show co-occurring scamp and yellowmouth grouper. A 24 length estimation marker (vertical bar in the center of frame) is visible. (a) Two scamp grouper are visible on the far right (top, light fish) and (bottom, dark fish) and an adult yellowmouth grouper is visible on the bottom center. (b) Scamp and yellowmouth are visible in the left top of the frame. Comparing (a) and (b) it is not clear whether the yellowmouth groupers, seen minutes apart on the same video, are the same fish. 35

36 (a) (b) Figure 23a: Near simultaneous (< 1 s due to differences in viewer software) video screen captures illustrating (a) standard definition (SD;.mpg encoding) and (b) high definition (HD;.m2ts encoding) resolution differences. Video stills are not as clear as video footage viewed in real time. Relative image width is also different between SD and HD video players. Data collection utilized SD DVDs and resulted in some fish, especially distant ones, being unidentified. HD video collection results in higher fish counts, especially at the edge of visibility due to crisper silhouettes of fish. This figure is best viewed at higher magnification (200% or higher). 36

37 (c) (d) Figure 23b: Near simultaneous (< 1 s due to differences in viewer software) video screen captures illustrating (c) standard definition (SD;.mpg encoding) and (d) high definition (HD;.m2ts encoding) resolution differences. Video stills are not as clear as video footage viewed in real time. Relative image width is also different between SD and HD video players. Data collection utilized SD DVDs and resulted in some fish, especially distant ones, being unidentified. Arrows in (c) indicate gag grouper counted from SD video. Arrows in (d) indicate total gag present. HD video collection results in higher fish counts, especially at the edge of visibility due to crisper silhouettes of fish. This figure is best viewed at higher magnification (200% or higher). 37

38 DISCUSSION Primary objectives of this pilot project included using underwater stationary video surveys to document the presence/absence, estimated size, density, and temporal habitat usage of gag grouper (Mycteroperca microlepis) on shallow water, hard-bottom habitats on the continental shelf of North Carolina. Other important objectives included comparing video findings to diver visual surveys of groupers to investigate the use of underwater videos to augment fisheryindependent surveys. As a pilot project, this study demonstrated that underwater stationary video techniques can record large numbers of groupers in a non-extractive way. The addition of this technique to MARMAP (or similar) fishery-independent surveys has the potential to be very valuable. For example, video numbers could be compared to extractive methods for grouper species at appropriate sampling locations and/or intervals (see discussion in Sedberry and Van Dolah, 1984). Video observation of fishes for this project had both unique advantages and disadvantages when compared to a more traditional population assessment for large, mobile bottom fish, such as gag and scamp groupers. Extractive methods like angling, trawling and trapping provide accurate size, weight, and age measurements, and can have reduced post-survey laboratory analyses (Willis et al., 2000). Video surveys involve substantial field time, along with a large amount of post-survey laboratory time to analyze videos (depending on fish density), but generally need less personnel than other methods. More often than not, the greatest limitations with video surveys include low water visibility (Cappo et al., 2007). Nevertheless, video surveys can simplify data collection, and require fewer personnel and fewer hours in the field. For example data collection in the form of video camera deployment and retrieval can be accomplished quite easily with a minimum of training for qualified SCUBA divers, and decreases the need for scientific specialists on hand. The use of non-specialists however does increase the likelihood that sampling protocols may not be closely adhered to and that data collection methods could change unexpectedly. These problems can be minimized by additional training in quality data collection. Data analysis of collected videos requires a significant time investment post-collection. On average, video observation and data recording in this study took three times the length of the collected video and it was desirable to have multiple observers for each video segment that would meet to compare findings. Experience in fish identification and size estimation was also very important. Both underwater and on video, it was sometimes difficult to differentiate individuals of different grouper species from each other. This was especially true for small, demersal groupers, including graysby, rock hind, red hind, speckled hind, juvenile goliath grouper and juvenile red grouper, because they utilized cover more frequently than larger fish. Identifications were also sometimes problematic for large scamp and yellowmouth groupers, which have similar body shapes and habits, and they utilize social and behavioral color changes (Gilmore and Jones, 1992). Similar difficulties in species identification between gag and black groupers (M. bonaci) have been reported previously (Chih, 2006). Yellowmouth groupers made up 4.3 % (33 yellowmouth/760 scamp) of the total number of scamp seen on video, and they always co-occurred in videos (Figure 22), but no yellowmouth groupers were recorded by the diver point count methods, likely because divers were not instructed to identify yellowmouth as a separate species. The highest MaxN yellowmouth recorded was two (data not shown). A minimum visibility of 6.1 m (25 ft) was necessary for video data collection to be feasible. It is unlikely that this variable is a consideration when using extractive fishing methods such as 38