Slow recovery of reef fish populations in an isolated marine reserve

Abstract

Geographic isolation is an important yet underappreciated factor affecting marine reserve performance. Isolation, in combination with other factors, may preclude recruit subsidies, thus slowing recovery when base populations are small and causing a mismatch between performance and stakeholder expectations. Mona Island is a small, oceanic island located within a partial biogeographic barrier - 44 km from the nearest Puerto Rico shelf. We investigated if Mona Island’s no-take zone, the largest in the U.S. Caribbean, was successful in increasing mean size and density of a suite of snapper and grouper species 14 years after designation. The La Parguera Natural Reserve (LPNR) was chosen for evaluation of temporal trends at a fished location. Despite indications of some fishing within the no-take area, a reserve effect at Mona Island was evidenced from increasing mean sizes and densities of some taxa, and mean total density 36% greater relative to 2005. These results should be viewed cautiously, however, as our design lacks seasonal replication within 2005 and 2010. The largest predatory species remained rare at Mona, preventing meaningful analysis of population trends. At LPNR, most commercial species (e.g., lane snapper, schoolmaster, mahogany snapper) did not change significantly in biomass or abundance, but some species (yellowtail snapper, hogfish), increased in abundance owing to strong recent recruitment. This study documents slow recovery in the Mona NTZ that is limited to smaller sized species, highlighting both the need for better compliance and the substantial recovery time required by commercially valuable, coral reef fishes in isolated marine reserves.