Ecosystem Perspective: Temporal Analysis of the Reef Fish Assemblage in Southeast U.S. Atlantic Continental Shelf Waters
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Of the myriad species inhabiting live-bottom reefs off the southeast U.S. Atlantic coast, many are economically valuable finfish species in the snapper-grouper management complex. The majority of these species are managed based on single-species (SS) assessment models, which do not parameterize important variables such as interspecific trophic interactions and environmental impacts (among others). These shortcomings of SS assessments, along with the overexploited status of multiple stocks in the complex and the inherent multi-species nature of the fishery, lend cause for more holistic assessment and management approaches for this fishery. Towards this goal, the current study applied ecosystem indicators to monitor the status of the reef fish assemblage from Cape Lookout, NC to Cape Canaveral, FL (13-60 m depth). Utilizing a 20-year dataset (1990-2009) from a fishery-independent baited trap survey, temporal analysis for all species combined revealed a consistent increase in mean fish size but an overall decrease in the number of fish and total biomass (i.e. there are now fewer, but larger fish in the system). Changes in metrics describing the biomass-size spectrum also indicate temporal shifts in the distribution of fish biomass towards larger size classes. While overall reef fish biomass has decreased, the percentage of community biomass comprised of especially marketable species ("targeted" stocks) has increased. Collective results from size- and production-based indicators are consistent with concomitant fishery-dependent trends, which show a decrease in commercial harvest of reef fishes since 1990 (primarily due to implemented size and catch restrictions). Importantly, temporal decreases in overall biomass highlight the necessity to consider gear selectivity when interpreting time series. Mean community δ¹⁵N (a trophic level proxy), rarefied annual species richness, and annual species heterogeneity (Simpson's index⁻ₑ) showed no overall change from 1990-2009. Future exploratory assessments of reef fishes should emphasize aggregate species approaches, a concept that has already materialized in some management regulations.