Effects of marine reserves on California spiny lobster are robust and modified by fine-scale habitat features and distance from reserve borders

Studies of marine reserves often describe mean differences in organism size or abundance inside versus outside reserves, but recent work indicates that these differences are influenced by habitat and proximity of sites to reserve borders. In this study, we measured mean effects of reserves and the influence of distance from reserve borders on the number and size of legal (≥82.5 mm carapace length [CL]) California spiny lobster Panulirus interruptus trapped at sites across a reserve network at the Santa Barbara Channel Islands, California, USA. Additionally, we controlled for habitat variability across sites (1) by measuring relative abundance of sublegal adult lobsters (i.e. those not removed through fishing) and (2) through visual SCUBA surveys on which we quantified fine-scale habitat features. Traps placed in reserves yielded more (4.81 trap−1) and larger (7.03 mm CL) legal-sized lobsters than traps placed outside. Multiple linear regression revealed that 2.43 more legal lobsters per trap were captured for every 1 km moved from borders towards reserve centers. Additionally, lobsters tagged and released immediately inside reserve borders were recaptured in areas open to fishing at a higher rate than lobsters tagged and released farther inside reserves. These results suggest that abundance gradients inside reserve borders were caused by net emigration of lobsters (spillover). Sublegal lobsters were more abundant inside reserves and nearer to reserve centers, but these increases were much smaller in magnitude than for legal-sized lobsters. Our results indicate that the differences we observed for legalsized lobsters were driven primarily by reserve effects but were partially influenced by habitat heterogeneity.