Abstract

In recent years, Caribbean resource management agencies have increasingly sought to establish protections on economically important aggregating tropical marine fishes such as Nassau grouper. Management actions include seasonal closures during spawning, marine protected areas at aggregation sites, and even complete elimination of harvest. Typically, such active management has been precipitated by steep declines in the abundance of the aggregating species, such that classic methods of abundance estimation (e.g. transects) are ineffective due to low densities. The challenge in assessing the effectiveness of such management thus lies largely in the development of accurate estimates of stock size and rebuilding. We present an in situ visual mark-recapture study design that can be used to estimate the total abundance of spawning fish at an aggregation site. The design takes advantage of the high density and approachability of aggregating Nassau grouper by SCUBA divers. Because recent evidence suggesting aggrega-tions represent the totality of spawning stock for the region served by the aggregation site, this method provides an effective index of spawning stock size, and through time, numerical stock response to management actions.