Parks for sharks: human exclusion areas outperform no-take marine reserves

We collected reef shark population data from a large network of no-take and no-entry reserves (ie human exclusion areas), as well as from fished reefs, in one of the world's most intensively managed marine parks - the Great Barrier Reef of Australia. The sampled reserves have been protected for varying lengths of time, making it possible to use space-for-time chronosequences to infer recovery trajectories of reef shark populations after extractive use is banned, and to compare the effectiveness of shark population recovery in no-take and no-entry reserves. After 20-40 years of protection, density and biomass of sharks in no-entry reserves approached asymptotes (ie plateaus) that were more than double and triple, respectively, those in no-take reserves. These results not only indicate that restoration of near-natural shark populations requires multidecadal time frames, but also clearly demonstrate the superior performance of no-entry reserves in terms of rebuilding shark populations. Ongoing poaching in no-take reserves, which are more difficult for law enforcement to police than no-entry reserves, is the probable cause of the disparity. Given the ubiquitous use of no-take reserves as ecological baselines and the potentially pervasive trophic effects of removing large predators, we argue that current perceptions of the structure and function of natural reef ecosystems may be skewed, which has broad implications for science and management of marine ecosystems.