Global baselines and benchmarks for fish biomass: Comparing remote reefs and fisheries closures

Abstract

Baselines and benchmarks (B&Bs) are needed to evaluate the ecological status and fisheries potential of coral reefs. B&Bs may depend on habitat features and energetic limitations that constrain biomass within the natural variability of the environment and fish behaviors. To evaluate if broad B&Bs exist, we compiled data on the biomass of fishes in ~1000 reefs with no recent history of fishing in 19 ecoregions. These reefs spanned the full longitude and latitude of Indian and Pacific Ocean reefs and included older high-compliance fisheries closures (>15 yr closure) and remote reef areas (>9 h travel time from fisheries markets). There was no significant change in biomass over the 15 to 48 yr closure period but closures had only ~40% of the biomass (740 kg ha −1 , lower confidence interval [LCI] = 660 kg ha −1 , upper confidence interval [UCI] = 810 kg ha −1 , n = 157) of remote tropical reefs (1870 [1730, 2000] kg ha −1 , n = 503). Remote subtropical reefs had lower biomass (950 [860, 1040] kg ha −1 , n = 329) than tropical reefs. Closures and remote reef fish biomass responded differently to environmental variables of coral cover, net primary productivity, and light, indicating that remote reefs are more limited by productivity and habitat than closures. Closures in fished seascapes are unlikely to achieve the biomass and community composition of remote reefs, which suggests fisheries benchmarks will differ substantially from wilderness baselines. A fishery benchmark (B 0 ) of ~1000 kg ha −1 adjusted for geography is suggested for fisheries purposes. For ecological purposes, a wilderness baseline of ~1900 kg ha −1 is appropriate for including large and mobile species not well protected by closures.