Parrotfish size as a useful indicator of fishing effects in a small Caribbean island

There is an urgent need to develop simple indicators of fishing effects for the implementation of ecosystem-based fisheries management in the Caribbean. In this study, we compare the ability of three simple metrics (average individual fish weight, fish density, and fish biomass) derived from the parrotfish assemblage and from an assemblage of highly valued commercial fish species to track changes in fishing pressure at spatial scales relevant to small Caribbean islands. Between June and August 2011, we conducted five consecutive visual fish surveys at six reefs <= 10 km apart along the west coast of Barbados, representing a spatial gradient in fishing pressure. We used these data to identify the fish metrics most strongly correlated with fishing pressure and describe their functional relationship with fishing pressure. Overall, average individual parrotfish weight and biomass and density of commercial fish species were the metrics most strongly correlated with fishing pressure, although for the latter two, such correlations depended on the range of fish body sizes analyzed. Fishing pressure accounted for most of the variability in all correlated fish metrics (R-adj(2) >= 0.75). However, functional relationships with fishing pressure differed qualitatively between metrics. In particular, average individual parrotfish weight was the metric most sensitive to incremental changes in fishing pressure. Overall, our study highlights that assemblage-level average individual parrotfish weight deserves a place in the toolbox of Caribbean reef managers as a simple indicator of both fishing effects on parrotfish assemblages and overall fishing pressure on the reef fish community.