Examining the efficacy of a sanctuary to protect sharks in the Galapagos Marine Reserve

In 2016, Ecuador established a no-take marine sanctuary in the northern portion of the Galapagos Marine Reserve (GMR), ostensibly to protect sharks. Arguably because of this, experimental longlining was permitted in the rest of the reserve as part of a compensation package to local fishers. Considering this agreement and very low bycatch rates inside the GMR, we question the efficacy of creating a large no-take area in the existing reserve. To examine the potential efficacy of alternative management strategies to protect sharks, we constructed a stage-structured demographic model for three shark species (scalloped hammerhead [Sphyrna lewini], blacktip [Carcharhinus limbatus], and silky [Carcharhinus falciformis]). We used the model to evaluate the efficacy of mortality reduction based on a spatial management approach and a hypothetical alternative bycatch mitigation scenario. We found that when adult dispersal rates were high, the sanctuary scenario generated lower absolute changes in the population growth rate than the bycatch mitigation scenario. Our results show bycatch reduction strategies likely have a higher conservation impact compared to the establishment of a sanctuary inside a reserve where sharks are already legally protected. With this case study, our work underscores the promising role of demographic models in informing management decisions for marine conservation.