Michael A. Banks , Jonathan D. Minch and Allan W. Stoner
Community Conch Report
INTRODUCTION
Identifying genetically distinct populations is a critical link for guiding sustainable management of heavily exploited fishery species. Early genetic studies with queen conch (Strombus gigas) using electrophoretic methods indicated a high degree of gene flow among populations dispersed over the species' geographic distribution, with definitive separation observed only between populations in Bermuda and those in the Caribbean basin (Mitton et al. 1989). Two relatively recent developments indicate that a closer look at population connectivity is warranted. First, we know now that pelagic larvae are often retained within close proximity to the parental stocks by mesoscale and fine-scale ocean circulation in the Caribbean region allowing for localized self-recruitment patterns (Kool et al. 2010). Second, new, more sensitive genetic tools have been developed revealing previously undetected genetic structure within populations of Caribbean species (see Christie et al. 2010) that is relevant to fisheries management. Knowledge of genetic connectivity among stocks is critical in determining the appropriate geographic units for fisheries management including quotas, the design of marine protected areas, and international relations related to sources of recruitment for fishery stocks in a complex geopolitical environment such as the Caribbean Sea. Queen conch are currently harvested in nearly all of the 30 nations and territories occupying the Greater Caribbean region. Declining stocks have resulted in the closure of some of the fisheries, queen conch trade is regulated under the Convention for International Trade in Endangered Species, and the species is currently being considered for Endangered Species status in the United States. This provides important impetus for exploring the molecular genetics of queen conch. This study was conducted to evaluate whether polymorphic DNA microsatellite markers isolated in queen conch by Zamora-Bustillos et al. (2007) can be used to differentiate geographically distant populations of conch in The Bahamas. We concluded that if this preliminary screening revealed genetic distinction in populations separated by 500 kilometers then microsatellite markers can be used for stock identification over the broader Caribbean region and within large nations such as The Bahamas, Cuba, and Venezuela where important fisheries for queen conch are prosecuted.
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.