Abstract

Queen conch can spawn frequently over the reproductive season. However, this requires some minimum density be maintained to promote both copulation in this slow-moving gastropod and sexual facilitation, wherein frequent sexual contact promotes gametogenesis. Field studies by Stoner and colleagues in The Bahamas found no mating activity below 56 adult conch/ha and no spawning below 48 conch/ha, suggesting a strong Allee effect. However, the interpretation of those figures to other areas are entirely dependent on how density is measured, both with respect to technique and spatial/population scale. Past studies estimated density, variously, over a whole shelf, within a portion of the shelf where conch may occur, within the area where spawning was most likely to occur, or within the core of conch aggregations. Measured baseline densities increase, respectively, across this spectrum. Methods giving localized density estimates best relate density to reproductive activity, but they require a large sample size or targeted allocation, whereas long transects more likely will encounter dense aggregations, but this density is diluted as transects span broad areas without conch. Even the threshold values of the Allee effect may be an artifact of methodology. Failure to appreciate how and over what scale density is measured has led to serious errors in the interpretation and application of Stoner and Ray-Culp’s density-reproduction relationship in population ecology, fisheries biology, regional connectivity, population assessment, and management. Lack of understanding of what constitutes a “spawning aggregation” and its relationship to overall conch population distribution prevents the development of a more generalized theory of conch reproduction versus density that could be applied to assessment and management.

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