Long-term decrease in sex-specific natural mortality of European lobster within a marine protected area

Abstract

Marine protected areas (MPAs) and marine reserves hold promise as tools for nature conservation and fisheries management, but data on long-term demographic effects are still sparse. Here, we use a unique capture-mark-recapture data set from Kåvra, an MPA on the west coast of Sweden where fishing for European lobster Homarus gammarus has been banned since 1989, to directly quantify annual survival probabilities in the absence of harvest mortality. The non-migratory behaviour of this species allowed multiple recaptures and releases of a large number of individuals within the MPA. We found strong evidence for a long-term decrease in sexspecific natural mortality throughout the study period (1994 to 2007). Positive trends were evident in mean body size and in catch-per-unit-effort, the latter indicating an increase in abundance. Together, these findings suggest that after nearly 2 decades of protection, density dependence was still not halting development of the population within the MPA. The present study is the first to quantify long-term (14 yr) changes in natural mortality rates in a protected marine population. Moreover, our study supports the notion that MPAs and marine reserves may act to counter fisheries-induced selection.