Queen Conch Stock Assessment Eastern Sand Bores Tongue of the Ocean, The Bahamas

Transcription

1 Queen Conch Stock Assessment Eastern Sand Bores Tongue of the Ocean, The Bahamas June 2015 Allan W. Stoner, Ph.D. Martha H. Davis, M.S. Catherine J. Booker, M.S. Report produced by Community Conch for: Bahamas Department of Marine Resources Davis_SB Report indd 1

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3 Project Sponsor, Contributors, and Volunteers Project Sponsors This project was sponsored by Community Conch. The mission of Community Conch is to affect sustainable harvest of conch in The Bahamas through research, education and collaboration with local communities, the Bahamian government and other non- governmental organizations. Community Conch is a fiscal sponsorship fund project of Rachel s Network, a 501(c)(3) organization based in Washington, D.C. Community Conch organized the fieldwork and donated the time of the senior scientists collecting and reporting the results. Community Conch Director Martha H. Davis, M.S. Phone: marthadavis@communityconch.org Senior Scientist Allan W. Stoner, Ph.D. Phone: allan.stoner@gmail.com Scientist and Field Representative Catherine J. Booker, M.S. Phone catherinebooker@communityconch.org Project Contributors The geographic scope of this project was established on the basis of discussions with Mr. Lester Gittens, Fisheries Biologist at the Bahamas Department of Marine Resources and several fishers who visit the Sand Bores. The Shedd Aquarium was a critical contributor to the field surveys, providing six days of support for the project on R/V Coral Reef II. Partial funding for the survey was also provided by the Department of Marine Resources. Mr. Marc Vandenrydt helped with outfitting the small boats for instrumentation for the survey. We are grateful to the Shedd Aquarium and Dr. Andrew Kough for inviting Community Conch to conduct their annual survey during in Dr. Kough s cruise focusing on conch larvae dispersal. The Shedd Aquarium provided the boat, fuel, food and crew for the survey. The Coral Reef II captains and crew provided invaluable support in a challenging offshore working environment. Sand Bores Survey 2015 i Community Conch 2015 Davis_SB Report indd 3

4 Project Volunteers We are thankful for the volunteers who assisted in data collection on the Sand Bores. These included Dr. Nathan Truelove from the Smithsonian Marine Station (Fort Pierce, FL), Dr. Andy Kough and Rebecca Gericke from the Shedd Aquarium (Chicago, IL), and Matt Foretich from the University of Miami Rosenstiel School of Marine Science. Volunteers from The Bahamas included Tarran Simms and Gimmel Morley. The GIS maps were generated by Mark Brewer, a geography student at the University of Denver. Sand Bores Survey 2015 ii Community Conch 2015 Davis_SB Report indd 4

5 Table of Contents EXECUTIVE SUMMARY... v INTRODUCTION Focus of study... 1 METHODS Study sites Survey timing Survey vessels Survey protocol Analysis Supplemental sampling and analyses... 4 RESULTS Densities and depth distributions Size and age structures Reproductive behavior Overall stock assessments... 5 DISCUSSION Population characteristics and comparisons Mating behavior comparisons with earlier studies Stock assessment General conclusions.. 8 REFERENCES CITED... 9 Sand Bores Survey 2015 iii Community Conch 2015 Davis_SB Report indd 5

6 List of Tables Table 1. Densities of adult, subadult, and "juvenile" queen conch by depth interval at the Eastern Sand Bores in June Table 2. Densities of subadult queen conch in three blocks of longitude at the Eastern Sand Bores location June Table 3. Comparisons of population parameters for subadult and adult queen conch in Bahamian locations surveyed by Community Conch, 2009 to List of Figures Figure 1. Study area map of the Eastern Sand Bores fishing grounds, at the southern end of the Tongue of the Ocean, where queen conch were surveyed in June Figure 2. Spatial pattern of flared- lip ("adult") queen conch densities at the Eastern Sand Bores fishing ground in June Figure 3. Frequency distribution of shell lip thickness in queen conch at the Eastern Sand Bores fishing ground in June Figure 4. Spatial pattern of "sub adult" queen conch densities at the Eastern Sand Bores fishing ground in June Sand Bores Survey 2015 iv Community Conch 2015 Davis_SB Report indd 6

7 EXECUTIVE SUMMARY Community Conch conducted a field survey for queen conch at the Eastern Sand Bores fishing ground on the Great Bahama Bank, at the southern end of the Tongue of the Ocean (TOTO) in June The goal of this survey was to estimate the density, abundance, population structure and reproductive rates of queen conch stocks in the shallow commercial fishing ground which occurs on the edge of the Great Bahama Bank southeast of Andros Island and west of Great Exuma Island (Fig. 1). Limited time available (6 days), rough weather conditions, and mechanical issues for this field survey did not permit a spatially comprehensive evaluation for the entire planned survey area; however, 157 transect lines were completed, and the survey yielded an excellent characterization of the queen conch population on the Eastern Sand Bores. Average density of flared- lip queen conch ( adults ) in the survey area was 52.1 adults per hectare (one hectare = 10,000 m 2 ) (Table 1). This average density of adults was higher than some other areas surveyed over the previous 6 years in The Bahamas (Table 3), but still slightly below the minimum density required for good levels of reproduction (approximately 56 adult conch/ha). Densities of three year old conch (here called subadults or rollers ) were very low, with an average value of just 3.9 individuals/ha in the area surveyed. Juvenile conch (primarily 2 year olds) were rare, with an average density of less than one individual per hectare (0.37/ha). Average shell length of adult conch was 186 mm on the Eastern Sand Bores. This is slightly smaller than the overall average for flared lip conch in Bahamian fishing grounds but generally comparable to those in nearby populations at the Grassy Cays (South Andros Islands) and the Berry Island to the north (Table 3) where the small phenotype samba conch were abundant. Average shell lip thickness was high (20 mm) and close to the average in the Jumentos Cays. This reflects relatively light fishing pressure and an accumulation of older individuals. Based upon the distribution of shell lip thickness in the Eastern Sand Bores, more than 90% of the flared lip conch were likely to be sexually mature, a positive finding despite the modest density of adults. Reproductive behavior at the Sand Bores was relatively common with 212 mating pairs of queen conch distributed over 38.9% of the tows made. Ninety percent of mating occurred where adult densities were 50 flared- lip conch per hectare or more. This corresponds closely with other areas with moderate to high densities of queen conch in The Bahamas and supports the recommendation of conch experts that fishery management for the species should be designed to achieve minimum densities of 100 adults/ha. Sand Bores Survey 2015 v Community Conch 2015 Davis_SB Report indd 7

8 While the entire fishing ground could not be evaluated during the available vessel time, the estimated total number of conch in the area surveyed was 2.58 million flared lip adults and 194,000 subadults. The very low density and abundance of subadults has two possible explanations. These younger conch were more abundant in the far eastern sector of the survey area, suggesting that the nursery grounds for Sand Bore conch lay east of the survey area. Also, it is possible that the low subadult density could result from a weak 2012 year class or a more generalized loss of recruitment to the area. The fact that subadults were found in low density on the Little Bahama Bank in 2014 surveys might indicate the latter mechanism as reproductive stocks in The Bahamas seem to be more and more depleted except for a few remote locations such as the Jumentos Cays in the southern Bahamas. Surveys have now been conducted at most of the major fishing grounds in The Bahamas. Data collected over the last seven years indicate that most of the grounds have been overfished to densities incapable of reproduction. While reproductive activity was relatively high at the Eastern Sand Bores, only queen conch in the Jumentos Cays appear to be functioning well as a healthy and mature population. Landings of queen conch in The Bahamas appear to remain relatively strong, but this is probably related to two observations: the divers are working deeper and farther from home, and more and more juvenile conch are being harvested as evident in shell middens (Community Conch data under analysis). It is clear that current management and regulations are not adequate to sustain conch resources in the Bahamas. Recommendations for changes in management strategy have been discussed in earlier survey reports. Sand Bores Survey 2015 vi Community Conch 2015 Davis_SB Report indd 8

9 INTRODUCTION 1.1. Focus of study The goal of the 2015 survey was to quantify the density, abundance, population structure, and reproductive potential of queen conch (Strombus gigas) in historically important fishing grounds identified by the Bahamas Department of Marine Resources and fishers familiar with the Sand Bores location at the southern end of the Tongue of the Ocean (TOTO), east and south of Andros Island and west of Great Exuma. The survey was conducted with methods identical to studies made by Community Conch for the Bahamas Department of Marine Resources over the last 6 years allowing for direct comparisons. METHODS 2.1. Study site This survey for queen conch was conducted at an historically important fishing ground at the Sand Bores location at the southern end of the Tongue of the Ocean on the Great Bahama Bank. The survey was concentrated on the outer (northern) edge of the bank working from Fish Rocks on the east at about west longitude to west (Fig. 1). Emphasis was placed on the outermost 6 to 8 nautical miles where conch are typically concentrated. Unlike previous surveys conducted by Community Conch, the Eastern Sand Bores was considered as a single contiguous area. The survey area was stratified by depth zone for both adults and subadults, and three blocks of longitude were examined for subadults because of an apparent east to west pattern in subadult density. The bank environment in the study area is characterized by large sand waves (sand bores) with the deep channels and shallow wave crests running approximately southeast to northwest. The troughs of the bores were vegetated with seagrass (primarily sparse to moderate densities of Thalassia testudinum) and the wave crests can be described primarily as bare coarse sand. Patch reefs and hard bottom ledge habitats were also encountered intermittently. Survey depths ranged from 2.4 to 22.6 m, with a superimposed tidal range of ~1.5 m. Tidal currents, flowing primarily north and south, were particularly strong in the deep channels between sand bores. Water temperatures recorded during the survey ranged from 26.9 to 29.3 C on the surface (n = 57; this represents < 40% of the tows, resulting from the failure of a thermometer on one of the boats). Variation in temperature was probably associated with the state of the tide on the shallow bank, with cooler water entering the bank from the TOTO on flood tide Survey timing This survey was conducted from 20 to 25 June This corresponds with the height of conch reproductive season in The Bahamas (Stoner et al., 1992), and Sand Bores Survey Community Conch 2015 Davis_SB Report indd 9

10 allows for comparison with earlier stock assessments and observations on mating made in recent years at the Berry Islands (Stoner et al., 2009), Andros Island (Stoner & Davis, 2010), the Exuma Cays (Stoner et al., 2011), Bight of Abaco (Stoner et al., 2012a), the Jumentos Cays and Ragged Islands (Stoner et al., 2013), and on the Little Bahama Bank (Stoner et al., 2014) Survey vessels Three small powerboats (17 to 22 feet) were used to tow snorkelers on the Eastern Sand Bores for observations on queen conch density and reproductive behavior (see below). Each boat was fitted with a Garmin Ecomap 54dv GPS and depth sounder. The position of grid corners for the conch grounds were uploaded into the GPS units for easy location in the field. Coordinates for the beginning and end point of each survey tow, along with depth and temperature data, were downloaded at the end of each day of sampling Survey protocol Queen conch stock assessment on the Eastern Sand Bores followed the methods developed by Community Conch for earlier surveys in the Berry Islands (see Stoner et al., 2009) and other shallow bank areas in The Bahamas. The use of similar protocols allows for direct comparison of data on conch density and reproductive behavior from earlier surveys. Maps of the study site were overlaid with a grid of one minute latitude and longitude, yielding blocks approximately one nautical mile on a side (1855 m in the north- south dimension, 1702 m in the east- west dimension) and 316 hectares (ha) in surface area. Each block, identified by the latitude/longitude coordinate of the southeast corner, was surveyed by towing a snorkeler on the surface over a standard distance of 1,000 m (determined with GPS). In some of the locations where mapping was inaccurate, depths were too great to be surveyed by divers towed on the water surface (see below) and some of the survey blocks needed to be abandoned. The general approach was to tow the diver from the southeast corner of the block (or the nearest possible point) toward the center of the block in either northwest or southeast direction such that the center of the block was always surveyed. A transect 6 m wide was observed for conch, yielding a sample unit of approximately 6,000 m 2. In some cases total distance covered was slightly longer or shorter than the design 1,000 m (e.g., because of shoals or land masses, or slight over- runs), and surface area was calculated independently for each block, eliminating land area, intertidal bank areas, and other habitats unlikely to support adult and subadult conch. Average tow length was 1048 m (SD = 125). Sand Bores Survey Community Conch 2015 Davis_SB Report indd 10

11 Each transect line was surveyed for: a) Number of adult queen conch. These are identified by a flared shell lip and are at least 3.5 years old. (See below for elaboration on this definition.) b) Number of subadults ( rollers ). These are large juvenile conch (greater than ~10 cm shell length) without a flared shell lip, and are typically between 2.5 and 3.5 years old. c) Number of juveniles. These are small juveniles (less than ~10 cm), and are generally 1-2 years old. d) Number of mating pairs. Where two individuals are in copulation orientation, with shells in direct contact. In past surveys, numbers of egg- laying females have also been recorded. However, this survey included a large number of tows that were in depth > 5 m and egg- laying could not be reliably assessed. Egg laying is not reported here. In The Bahamas, a well flared shell lip provides the traditional definition of an adult and this is currently the only form legal for harvest. However, we know from histological studies in the Exuma Cays (Stoner et al. 2012b) and the Bight of Abaco that sexual maturity does not occur in the majority of queen conch until a lip thickness of mm is achieved. Therefore, where adult conch were abundant, opportunistic collections were made to measure for the following: a) shell length (SL) (± 1 mm) with large Vernier calipers, and b) shell lip thickness (LT) (± 1 mm) using small Vernier caliper, to provide an index of age. For analytical purposes, queen conch with shell lip thickness 15 mm were considered to be mature, while those with lip thickness < 15 mm were classified as immature Analysis Densities of adult, subadult, and juvenile queen conch were evaluated for patterns related to water depth and location on the Eastern Sand Bores. Count data were standardized to number of conch per hectare (10,000 m 2 ) for each age group in each depth zone. Total numbers of conch in a block were extrapolated from the density estimate for that block and its surface area. These numbers were then summed to yield an estimate for the total number of conch (abundance) for the area surveyed. Depth zones considered for analysis were: B: m C: m D: m E: m Sand Bores Survey Community Conch 2015 Davis_SB Report indd 11

12 Past surveys included a depth zone A (0 2.5 m), but depths in this range on the Sand Bores were rarely encountered Supplemental sampling and analyses Video cameras were carried on a tow board for some of the survey lines on the Eastern Sand Bores. The goal was to quantify precisely the microhabitat associations of queen conch, and to provide a permanent record to the habitat. Preliminary results indicate that photographic mosaics of the transect lines could be useful in achieving the analytical goals. Dr. Andrew Kough will report on those results in the future. Forty six genetic samples for queen conch were collected on the Eastern Sand Bores by Dr. Nathan Truelove. This is part of a larger project designed to evaluate population connectivity among the conch fishing grounds in The Bahamas and the wider Caribbean. An attempt is also being made to determine whether samba conch can be distinguished genetically from the more typical large adult conch. Results of DNA analysis will be reported in a separate report from Dr. Truelove. RESULTS 3.1. Densities and depth distributions Substantial numbers of adult queen conch (5,084 individuals) were observed by the divers in the survey of the Eastern Sand Bores survey, but subadult conch (375) were uncommon, and younger juveniles were rare (37 individuals 2 years old). Conch with flared shell lips were observed in 89.8% of the 157 tows. The average density was 52.1 adults /ha (SD = 55.6). Highest observed density was 351 adults /ha. Age- 3 subadults were much less common, observed in 37.6% of tows, and the average density was just 3.9/ha (SD = 9.7). Juveniles were observed in just 17 tows (10.8%), and the average density was 0.37/ha (SD = 1.36). Densities of adult queen conch were highest in the 5m to 10 m depth stratum (58.3/ha), and slightly lower in the deeper depth zones surveyed (42.5 to 43.4/ha) (Table 1). Densities of subadult queen conch generally decreased with increasing depth, with highest average density (7.0/ha) in the shallowest depth stratum (2.5 to 5 m depth). These 3 year old conch were relatively uncommon at greater depths (Table 1). While adult conch showed no apparent geographical pattern of density over the study site (Figure 2), subadults were more commonly observed in the eastern part of the survey area, with relatively higher density east of west longitude and very low density west of west longitude (Table 2). Average depth in the eastern sector was slightly deeper than the western sector (Table 2), so the east- west pattern of subadult density was independent from the depth pattern shown in Table 1. Sand Bores Survey Community Conch 2015 Davis_SB Report indd 12

13 Densities of juvenile conch (mostly 2 year old individuals) also decreased with increasing depth (Table 1), and none were observed at depths greater than 15 m. Movement of conch to deeper water with age is common in The Bahamas and other Caribbean locations Size and age structures One hundred sixty- one (161) queen conch with flared shell lips were measured for shell length and lip thickness. Flared- lip individuals at the Eastern Sand Bores location were highly variable in shell length ( mm), with small but thick- lipped samba conch mixed with larger conch throughout the eight locations where conch were measured. The overall average shell length was just 186 mm (SD = 15 mm). Shell lip thickness values ranged from 9 to 31 mm, with an average of 20 mm (SD = 4 mm) over the study area. The distribution of lip thickness measures was relatively narrow (Figure 3); more than 82% of the conch had lip thickness between 15 and 24 mm, and < 1% had shell lips less than 10 mm. Queen conch with lip thickness 15 mm are likely to be sexually mature (Stoner et al. 2012b), and these mature conch made up 90.2% of the overall sample of conch with flared shell lips at the Eastern Sand Bores location Reproductive behavior A total of 212 mating pairs were observed on 61 of the 157 survey tows (38.9%) made in the Eastern Sand Bores survey. This ranged from just one mating pair observed on a survey tow to 14 pairs observed on one tow in an area with 7 m depth. Only 4 mating pairs (1.9% of 212 pairs) were found in depths < 5 m. Mating occurred generally at locations with highest densities of flared- lip conch. More than 90% of all mating pairs were observed where densities were higher than 50 flared lip individuals per hectare, as would be expected. However, two mating pairs were observed where density was just 6.3 flared- lip conch/ha Overall stock assessment The Eastern Sand Bores fishing ground was not surveyed in its entirety. This is evident from the relatively high adult densities in survey cells at or near the periphery of the survey area show in Figure 2. Given the partial survey, a spatially comprehensive stock assessment for the whole ground is not possible. However, because adult conch were observed in almost 90% of the tows, we believe that the survey was conducted in a representative section of the fishing ground. The survey area covered 49,612 hectares (49.6 km 2 ), and the stock assessment is confined to that specific area. Extrapolating densities over the geographic blocks surveyed, the estimate for total numbers of flared lip queen conch in the Eastern Sand Bores area investigated in June 2015 was approximately 2,584,000. Based upon shell measures and considering conch with shell lip thicknesses 15 mm (90.2%) (see above), approximately 2,330,000 of these conch are likely to be sexually mature. Subadults Sand Bores Survey Community Conch 2015 Davis_SB Report indd 13

14 were much less common than individuals with flared shell lips, and the total estimate for subadults in the survey area is approximately 194,000. The Eastern Sand Bores survey was not intended for counting juvenile conch (1-2 years old, and a stock assessment value is not reported here. However, it is clear that these small conch are rare in the Sand Bores location. DISCUSSION 4.1. Population characteristics and comparisons Average density of queen conch with a flared shell lip ( adults ) on the Eastern Sand Bores was higher than many other fishing grounds surveyed in The Bahamas over the last seven years but less than half the values observed in the Grassy Cays southeast of Andros (where small phenotype samba conch made up a large proportion of the adult conch) and in the Jumentos Cays and Ragged Islands (Table 3). These three grounds with high densities are distant from the primary markets, in open bank environment making fishing there hazardous, and each appears to be relatively lightly fished. Despite a relatively high density of flared lip conch at the Eastern Sand Bores the average is just below the minimum threshold (i.e., 56/ha) identified by Stoner & Ray- Culp (2000) for reproduction and well under the density recommended by the Queen Conch Expert Panel (CFMC, 2012) (100 adults/ha) for a sustainable fishery (see below). Average shell lip thickness on the Sand Bores was very similar to values reported earlier for the Exuma Cays Land and Sea Park and for the Jumentos Cays and Ragged Islands (19-21 mm). Shell lip thickness distribution provides a good indication of the age structure for a conch population and the exploitation rate. The east coast of Andros Island, the Lee Stocking Island area in the Exuma Cays, the Bight of Abaco, and the as yet unprotected waters of the Berry Islands Marine Fishery Reserve are all heavily fished as characterized by conch with lip thicknesses averaging < 10 mm (Table 3). This means that the conch in all of these areas are very young, and many of the flared- lip individuals have not reached reproductive maturity (see earlier reports Stoner et al., 2011, 2012a). Measurements made during the Eastern Sand Bores survey indicate that over 90% of the flared- lip queen conch were sexually mature, and reproductive frequencies were relatively high, even where conch densities were low. This is an encouraging observation. The relatively mature structure of the queen conch population at the Eastern Sand Bores corresponded with a low density of subadults (just 3.9/ha) (Table 3). This fishing ground had the lowest ratio of subadults to adults ever observed in Community Conch surveys. Possible reasons for low numbers of subadults are discussed below. Depth distributions of both adult and subadult queen conch at the Eastern Sand Bores were similar to the patterns observed in other Bahamian locations. Highest densities of adults were found between 5 and 10 m depth, while highest Sand Bores Survey Community Conch 2015 Davis_SB Report indd 14

15 densities of subadults occurred in shallower water (2.5 5 m depth). This is related to a general pattern of larval settlement on shallow sandy banks and seagrass meadows followed by migration with age to deeper water (Stoner, 2003). While the density of subadult conch was low throughout the survey area (just 3.9/ha on average), highest densities occurred in the eastern sector of the survey area, and densities declined rapidly with distance to the west. This suggests that larval recruitment and nursery grounds probably lay to the east of the Sand Bores fishing ground on shallower parts of the Great Bahama Bank. This distribution pattern warrants further investigation. The fact that maximum density of adult queen conch in depths ranging from 5 to 10 m means that the vast majority of conch can be exploited by free- diving or with hookah gear, and that the deep- water reserve is relatively small. The Eastern Sand Bores population, despite being protected to some extent from severe overfishing by distance from landing sites, is otherwise vulnerable to fishing pressure Mating behavior comparisons with earlier studies The importance of high adult density for mating and reproduction in queen conch is now clearly established (Stoner & Ray- Culp, 2000; Stoner et al., 2012c). These earlier studies have shown that the absolute minimum adult density for reproduction is 56 per hectare. On the basis of those studies, the Caribbean Fisheries Management Council recommended that densities of queen conch should be managed to yield a minimum density of 100 adults/ha on the fishing grounds. The goal is to insure adequate mating (CFMC, 2012). Our observations from the Eastern Sand Bores on mating closely follow patterns found in earlier surveys in other locations in The Bahamas. In the case of the Sand Bores, ninety percent of all mating pairs (212 pairs) were observed in survey tows where densities of conch with flared shell lips were more than 50 per hectare. While most mating behavior at the Eastern Sand Bores occurred in association with relatively high adult densities, some mating was observed in tows with adult densities less than 56 per hectare (down to only 6.3 adults/ha). Mating at such low densities has been very unusual in Community Conch surveys conducted over the last seven years. The most likely explanation for this observation is that a very high percentage of flared- lip conch at the Sand Bores were identified as mature adults. That is, over 90% of the flared- lip conch measured had lip thicknesses > 15 mm. In other locations surveyed since 2009, the percentage of mature individuals has varied substantially, but in heavily fished areas the percentages were generally low (Community Conch data under analysis). For example, overall maturity on the Little Bahama Bank in 2014 was just 16%, and in the Bight of Abaco in 2012 the maturity was only 7.2%. In such cases, most of the adult conch observed in surveys are not capable of mating or egg- laying. Our conclusion is that heavy fishing results in very young populations with low reproductive potential. Also, it is now clear that reproductive potential of a conch population is dependent upon both density and the age structure of conch with flared shell lips. It should be reiterated that a flared shell lip does not mean that a queen conch is sexually mature. Maturity of conch in The Bahamas occurs when shell lip thickness reaches about 15 mm (Stoner et al., 2012b). Sand Bores Survey Community Conch 2015 Davis_SB Report indd 15

16 4.3. Stock assessment More than 2.5 million flared- lip queen conch were estimated to be present in the Eastern Sand Bores area surveyed in June In some locations densities of these adult conch were relatively high on the periphery of the survey area. For that reason, it is clear that we did not cover the entire eastern part of the fishing ground with diver tows, and it is likely that the total number of flared- lip conch is substantially greater than the number reported here. Nevertheless, the survey, covering almost 50 square kilometers (about half of the fishing ground that was intended for survey), allowed observations on a wide cross section of habitat and depth range on the shallow bank in the southern Tongue of the Ocean. We believe that this represents a characteristic and significant portion of the fishing ground. The low average density of age- 3 subadult conch (3.9/ha) resulted in low abundance values, just 194,000 individuals. This is the lowest density of subadults observed over the last seven years in queen conch fishing grounds in The Bahamas. There are at least two possible explanations for this low density on the Sand Bores: First, because the entire fishing ground was not surveyed, it is possible that the primary habitat of subadults was not included in the 2015 survey. The rarity of juveniles in the survey suggests that nursery grounds may be farther away, perhaps to the east, as discussed above. The advanced age of conch in the survey area may be related to the time it takes for conch to reach this location from the most important nurseries, perhaps two or three years. Second, low density of subadults could represent weak larval recruitment to the fishing grounds in 2012, or a more generalized loss of recruitment in the northern Bahamas. The fact that subadults were relatively uncommon on the Little Bahama Bank in 2014 surveys might indicate that a general decline in recruitment has begun General Conclusions The results of surveys made in The Bahamas by Community Conch over the last seven years show that the vast majority of fishing grounds have been overfished. Only the Jumentos Cays still have densities of adults and age structure indicating a healthy and mature population. This is no doubt related to the remoteness of the location and distance from primary markets. It is clear that the current management strategy for queen conch in The Bahamas is not working well enough for a sustainable fishery, and changes are needed. Recommendations have been made in earlier survey reports. Sand Bores Survey Community Conch 2015 Davis_SB Report indd 16

17 REFERENCES CITED Caribbean Fisheries Management Council (CFMC) Recommendations of the Queen Conch Expert Workshop, Miami, United States of America, May p. Stoner, A.W What constitutes essential nursery habitat for a marine species? A case study of habitat form and function for queen conch. Marine Ecology Progress Series 257: Stoner, A. and M. Davis Queen Conch Stock Assessment: Historical Fishing Grounds, Andros Island, Bahamas, June, Technical report to The Nature Conservancy, Northern Caribbean Office, Nassau, The Bahamas. 15 p., plus electronic appendices. Stoner, A.W. and M. Ray- Culp Evidence for Allee effects in an over- harvested marine gastropod: density- dependent mating and egg production. Marine Ecology Progress Series 202: Stoner, A.W. and V.J. Sandt Population structure, seasonal movements and feeding of queen conch, Strombus gigas, in deep- water habitats of the Bahamas. Bulletin of Marine Science 51: Stoner, A.W., V.J. Sandt and I.F. Boidron- Metairon Seasonality of reproductive activity and abundance of veligers in queen conch, Strombus gigas. Fishery Bulletin, U.S. 90: Stoner, A., M. Davis and C. Booker Queen conch stock assessment: proposed MPA and fishing grounds, Berry Islands, Bahamas. Technical report to the Department of Marine Resources, Nassau, The Bahamas. 49 p. Available online at: Stoner, A., M. Davis and C. Booker Surveys of queen conch populations and reproductive biology at Lee Stocking Island and the Exuma Cays Land and Sea Park, The Bahamas, June/July Technical report to the Department of Marine Resources, Nassau, The Bahamas. 27 p. Available online at: Stoner, A., M. Davis and C. Booker. 2012a. Surveys of queen conch populations and reproductive biology at Sandy Point and More s Island, Bight of Abaco, The Bahamas, June Technical report to the Department of Marine Resources, Nassau, The Bahamas. 22 p. Available online at: Sand Bores Survey Community Conch 2015 Davis_SB Report indd 17

18 Stoner, A.W., K.M. Mueller, N.J. Brown- Peterson, M.H. Davis, C.J. Booker. 2012b. Maturation and age in queen conch (Strombus gigas): urgent need for changes in harvest criteria. Fisheries Research 131: Stoner, A.W., M.H. Davis, C. Booker. 2012c. Negative consequences of Allee effect are compounded by fishing pressure: comparison of queen conch reproduction in fishing grounds and a marine protected area. Bulletin of Marine Science 88: Stoner, A.W., M.H. Davis, C.J. Booker. 2012d. Abundance and population structure of queen conch inside and outside a marine protected area: repeat surveys show significant declines. Marine Ecology Progress Series 460: Stoner, A.W., M.H. Davis, C.J. Booker Queen conch stock assessment Jumentos Cays and Ragged Islands, The Bahamas, June Technical report to the Department of Marine Resources, Nassau, The Bahamas. 43 p. Available online at: Stoner, A.W., M.H. Davis, C.J. Booker Surveys of queen conch populations and reproductive biology on the Little Bahama Bank, The Bahamas., June Technical report to the Department of Marine Resources, Nassau, The Bahamas. 27 p. Available online at: Sand Bores Survey Community Conch 2015 Davis_SB Report indd 18

19 Table 1. Densities of juvenile, subadult, and adult queen conch by depth interval at the Eastern Sand Bores location in June Values for each depth interval are reported as mean and standard deviation for the numbers of individuals per hectare (no./10,000 m 2 ). No tow averaged less than 2.5 m in depth (zone A in earlier surveys). One tow with undetermined depth is included under the combined data Depth interval No. of tows Juvenile density Subadult density Adult density B: 2.5 to 5.0 m ± ± ± 21.5 C: 5.0 to 10 m ± ± ± 59.3 D: 10 to 15 m ± ± ± 48.3 E: 15 to 20 m 3 0 ± ± ± 34.0 Combined data ± 1/ ± ± 55.6 Table 2. Densities of subadult queen conch with respect to three blocks of longitude in the study site. Values are mean ± standard deviation. Longitude interval No. of tows Average Depth (m) Subadult density W to W ± W to W ± W to W ± 1.21 Sand Bores Survey Community Conch 2015 Davis_SB Report indd 19

20 Table 3. Comparisons of population parameters for subadult and adult queen conch in Bahamian locations surveyed by Community Conch, 2009 to In 2009, the conch population in the Berry Islands Marine Fishery Reserve was not yet protected from fishing. Values reported for density, shell length and lip thickness are mean ± standard deviation. Data reported are for bank areas < 15 m deep where fishing can occur by free- diving and hookah. Data from surveys conducted at greater depths, primarily in the Berry Islands and Exuma Cays, are not incorporated here. nd = no data. Sources of comparative data include: Stoner et al. 2009, 2011, 2012a, 2013, 2014; Stoner & Davis 2010). Location surveyed Year of survey Number of survey lines Density of subadults (no./ha) Density of adults (no./ha) Shell length (mm) Lip thickness (mm) Berry Islands SW fishing ground Berry Islands West bank Berry Islands Marine Fishery Reserve East coast of Andros Island Grassy Cays, Andros Island Lee Stocking Island, Exuma Cays (banks only) Exuma Cays Land and Sea Park (banks only) Sandy Point, Bight of Abaco Mores Island, Bight Of Abaco Jumentos Cays & Ragged Islands ± ± ± ± ± ± 1.8 nd nd ± ± ±30 3 ± ± ± ±42 8 ± ± ± ±27 15 ± ± ± ± 21 9 ± ± ± ± ± ± ± ± 19 6 ± ± ± ± 24 9 ± ± ± ± ± 7 Little Bahama Bank ± ± ± ± 7 Eastern Sand Bores ± ± ± ± 4 Sand Bores Survey Community Conch 2015 Davis_SB Report indd 20

21 Community Conch 2015 Figure 1. Study area map of the Eastern Sand Bores conch survey where queen conch were surveyed in June, Sand Bores Survey 2015 Figure 1. Study area map of the Eastern Sand Bores conch survey where queen conch were surveyed in Sand Bores Survey 2015 Davis_SB Report indd Community Conch 2015

22 Community Conch 2015 Figure 2. Spatial pattern of "adult" queen conch densities at the Eastern Sand Bores fishing ground in June, Sand Bores Survey 2015 Figure 2. Spatial pattern of "adult" queen conch densities at the Eastern Sand Bores fishing ground in Ju Sand Bores Survey 2015 Davis_SB Report indd Community Conch 2015

23 Figure 3. Distribution of shell lip thickness for flared lip queen conch measured on the Eastern Sand Bores fishing ground, June The distribution is relatively narrow compared with earlier surveys. Using a minimum threshold for maturity set at 15 mm shell lip thickness, more than 90% of the conch were likely to be sexually mature. 60 Percent of population Shell lip thickness (mm) Sand Bores Survey Community Conch 2015 Davis_SB Report indd 23

24 Figure 4. Spatial pattern of "sub adult" queen conch densities at the Eastern Sand Bores location in June, Sand Bores Survey 2015 Davis_SB Report indd 24 Community Conch Sand Bores Survey 2015 Figure 4. Spatial pattern of "sub adult" queen conch densities at the Eastern Sand Bores location in June 16 Community Conch 2015