Meeting Abstract
Marine reserves provide protection to harvested species within their boundaries, and can reverse the ecosystem-level effects of fishing pressure. This has been well documented in the Cape Rodney-Okakari Point (CROP) marine reserve in northern New Zealand. However, marine reserves may be less effective in protecting mobile species that experience low or highly sporadic recruitment, especially when those reserves are small. In this study, we present recent monitoring data from the CROP marine reserve and two other nearby reserves, showing large-scale declines in populations of the rock lobster Jasus edwardsii. Current lobster biomass within the reserves is less than 20% of historic levels, while biomass outside the reserves is only 1% of historic levels within the reserves. Adult J. edwardsii undertake seasonal migrations beyond the reserve boundaries, and so we hypothesized that the observed declines are likely a result of sustained fishing pressure targeting the reserve boundaries in concert with an extended period of low recruitment. To explore the effects of low recruitment on lobster density within the reserves, we employed an agent-based demographic model. We hindcasted the levels of recruitment at each reserve over the past 10-20 years. Then, we used the model to estimate the recruitment levels that would have been required to sustain lobster densities given current fishing pressure. We found that either consistent, low recruitment, or higher, more sporadic recruitment would be required for sustainability. Together, our results suggest that for mobile species with low or highly variable recruitment, marine reserves must be large enough to encompass the totality of seasonal movements in order to be effective.
