Fisheries Sustainability Eroded by Lost Catch Proportionality in a Coral Reef Seascape

Abstract

Coral reef and their ecological services of food production and shoreline protection are threatened by unsustainable use. To better understand their status, multiple approaches to estimating fisheries sustainability were compared, namely fisheries-independent stock biomass and recovery rates, fisheries-dependent landed catches, balanced harvest and gear use metrics, and fish length measurements. A community biomass recovery was established over a 45-year no-fishing stock recovery time series from seven fisheries reserves and compared to catch- and length-based estimates of sustainability. The logistic production rates (r = 0.09 ± 0.06 95% confidence interval (CI)) and maximum equilibrium total biomass (~150 ± 30 tons/km2) indicated a broad range of potential maximum sustainable yields, with a likely range of 1.1 to 3.9 (95% CI; mean = 3.8) tons/km2/year. In contrast, the mean annual linear biomass growth rates in reserves were lower but less variable than logistic surplus production estimates, ranging from 2.1 to 3.5 (mean = 2.8 tons/km2/year). Realized catches at landing sites were lower still, ranging from 1.43 to 1.52 (mean = 1.48 ± 0.2 tons/km2/y). Differences between production estimates and capture were largely attributable to changes in taxonomic composition and an imbalance in the estimated proportionality of production potential versus actual capture rates. Lost potential capture was likely due to differences in the vulnerability of taxa to fishing and a lack of compensatory increased production among fishing-resistant taxa. Large proportional losses of catch were measured among snappers, unicorn fish, sweetlips, goatfish, and soldierfish, while smaller proportional gains in the catch samples were found among resident herbivorous rabbitfish, parrotfish, and groupers. Many of these declining taxa have vulnerable schooling life histories that are likely to require special habitat and reserve characteristics. Evaluations of sustainability from length measurements found 17 or 7% of total and 12% of caught species had sample sizes minimally sufficient for evaluation (>30 individuals from 413 catches, 2284 captured individuals composed of 144 species) of length and spawning metrics of sustainability. Seven of these species met length-based and three met spawning potential ratio thresholds for sustainability. Consequently, length-based evaluations had poor species coverage and therefore we were unable to evaluate the sustainability of the larger fish community. Recommendations for future research include a better understanding of the consequences of variability in spillover and proportionality of production potential for sustainability. Management recommendations are to focus management on the recovery of species abundant in unfished locations but not contributing to fisheries yield.