Fishing shrinks the size structure of exploited coral reef fishes in Brazil

Coral reef fisheries are important as they support the economy, livelihoods, and food security of millions of people worldwide. However, reef fisheries are widely overfished, impacting the abundance and size structure of highly biodiverse fish assemblages. Here, we assessed the effects of fishing on the size structure of exploited coral reef fishes using size spectra analysis, a method that informs about fishing mortality and ecosystem productivity. We used data from over 500 landing site interviews with hook and line fishers in Northeastern Brazil. The data included 18 fishing grounds (i.e., fringing reefs), fishing effort (fishers/km2) of a widely used gear (hooks and line), and 3690 measurements of exploited fish body size. We fitted linear regressions to body size estimates in the catch of each fishing ground to estimate the slopes of the size spectra and tested for a possible effect of fishing effort on those slopes. We found that fishing effort associated with hook and line negatively affected the slopes of size spectra (p = 0.04; R2 = 0.22). This likely occurred because hook and line generally selects for the largest individuals in the assemblage, so that, as expected, higher levels of fishing effort were associated with smaller size of the exploited fishes. Given body size is usually proportional to trophic level in reef fishes, our finding suggests fishing may be disproportionately affecting predators in the study area. Our study provides the first documentation of fishing impacts on the size structure of coral reef fishes exploited by a predominant gear type in Northeastern Brazil, establishing a baseline for future monitoring of fishing impacts and contributing to the development of sustainable fisheries management strategies.