Allan W. Stoner, Ph.D., Martha H. Davis, M.S., Catherine J. Booker, M.S.
Produced for: Bahamas Department of Marine Resources
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 2015. 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 m2) (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.
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.