Demographics influence reproductive output in queen conch (Lobatus gigas): implications for fishery management

Abstract

The queen conch (Lobatus gigas) is harvested intensively throughout most of the tropical western Atlantic for its meat, shell, and pearls. If sustainable harvest is to be achieved, fishery managers will have to incorporate into management strategies the species' biology and demography. However, no long-term information exists that links reproductive behavior with age structure in queen conch. As such, we examined queen conch demographics across large spatial and temporal scales in the Florida Keys, where queen conch fishing has been banned since 1986. Our results corroborate earlier reports showing density-dependent reproductive behavior. We never observed mating when aggregation densities fell below 204 adults ha–1; spawning was not observed at aggregation densities less than 90 adults ha–1. Evaluating reproductive behavior by age class, based on lip thickness (i.e., young adult, >10–15 mm; adult, >15–25 mm; very old adult, >25 mm), showed that young adults mated and spawned less often than adults and very old adults. However, the number of eggs in an egg mass showed no significant association with lip thickness. So, while age did not seem to affect the number of eggs in an egg mass, young adults as a group would have lower reproductive output because they do not engage in reproductive activities as often as older queen conch, probably because some of the younger, thinner-lipped conch were not yet sexually mature. Our results indicate that the maintenance of age structure and density is crucial to the stability of queen conch populations and thus sustainable harvest. Therefore, the soundest management approaches are those that maximize reproductive output from aggregations of mature queen conch whose densities exceed minimum thresholds to avoid depensatory effects.