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, Bahamas National Trust
EXECUTIVE SUMMARY
Field work conducted by Community Conch during 2012 in the Bight of Abaco had two principal goals: 1) to survey the density, abundance and population structure of queen conch stocks in the shallow commercial fishing grounds off Sandy Point and More's Island and 2) to further explore relationships between queen conch shell lip thickness (an index of age) and reproductive maturity and compare it to similar data collected in 2011 near Warderick Wells (WW) in the Exuma Cays Land and Sea Park. The survey was conducted in June, using towed diver surveys at more than 200 locations.
Average 'adult' queen conch densities were the lowest found by Community Conch in four years of surveying commercial conching sites in the Bahamas. In the Sandy Point area densities average 6.4 conch/ha and increased only to 9.8 conch/ha west of More's Island. The minimum density required for reproduction is 56 conch/ha. Subadults or 'rollers' had similar low densities of 10.1 and 7.8 conch/hectare, at Sandy Point and More's Island, respectively. Average shell length ranged from 187 mm in Sandy Point to 198 mm in More's Island. These lengths are comparable to conch measured on the banks in the Berry Islands, off Lee Stocking Island and Warderick Wells and a little larger than those found off the Grassy Cays south of Andros. Average lip thickness ranged from 6 mm in the Sandy Point area to 9 mm west of More's Island indicating very young populations. In 202 tows, only three mating pairs were observed. The estimated total abundance for the surveyed areas was approximately 519,000 adults and 550,500 subadults.
Analysis of the gonad tissues from 57 queen conch collected during the spawning season of 2012 showed that most male conch do not reach sexual maturity until their shell lip thicknesses reach 10mm (more than 3/8'). Most females were not sexually mature until the shell lip thickness was 15mm. The conclusion from the 2011 study that queen conch in The Bahamas with lip thickness 15 mm should not be harvested because they are not yet reproductively mature was borne out by this follow-up study in the Bight of Abaco.
Three observations suggest that queen conch in the Bight of Abaco are severely overfished: (1) densities of flared-lip individuals are extremely low, well below the minimum threshold required for reproduction, (2) the age structure of the populations at both Sandy Point and More's Island is very young, with very few individuals ≥ 15 mm LT, and (3) only three mating pairs were observed among more than a thousand flared lip conch encountered during two weeks of survey work in the middle of the reproductive season. Additionally, it is clear that conch fishers in the Bight of Abaco have become dependent upon compressed air and deep-water populations of queen conch as adult conch are now relatively rare on the traditional shallow-bank grounds. We predict that the Sandy Point and More's Island conch fishing grounds are approaching collapse.
Given the extremely low densities and low total numbers of queen conch in the Bight of Abaco, and almost total absence of reproductive behavior, it is clear that a rebuilding program is needed for both the Sandy Point and More's Island fishing grounds. The following measures could be considered:
a) Partial or total closure of the fishing grounds until densities reach 100 adults/ha.
b) End the use of compressed air for conch fishing or at any depth out of lobster season.
c) Establish a total allowable catch at the fishing grounds and monitor it.
d) Institute a closed season for conch fishing.
Informal interviews with Abaco fishermen suggest that they recognize the declining fishery for queen conch and favor a closed season however the current standing stock of adult conch in the Bight of Abaco is so low that it is doubtful that the increased reproductive output in a closed season would increase local recruitment. The success of any changes in fisheries management will likely depend upon community involvement in management decisions, and fisheries monitoring and enforcement.