Small marine protected areas cannot sustain spill-over of the seasonally moving spiny lobster Jasus edwardsii

Fishing is often concentrated near marine protected area (MPA) boundaries due to expectations of greater catches associated with the ‘spill-over’ of adult individuals. This is known to reduce populations near MPA boundaries, but our understanding of the long-term sustainability of this harvest remains limited. Over the last 25 yr, the spiny lobster Jasus edwardsii has experienced serious declines within north-eastern New Zealand MPAs. Prior to reductions, commercial fishers concentrated effort on offshore boundaries, targeting lobsters undertaking seasonal offshore movements. While this spill-over highlighted the success of these MPAs, it also indicated they were too small to encapsulate seasonal movements. In recent years fishers rarely target this area, and the extent to which lobsters move offshore is unknown. To address this knowledge gap, potting surveys were conducted in 2018-2019 to examine seasonal shifts in population distribution. Seasonal changes in habitat use were evident but mostly constrained to coastal reef habitat, with ~5% caught offshore of reef and only one individual caught beyond offshore boundaries. Comparison with commercial catch data from reserve boundaries during 1994-1997 revealed reduced abundances and changes in the size and sex of lobsters caught offshore. In contrast to 1994-1997, only large males were caught offshore of reef habitat. At low densities, females and small males may maintain greater association with the protective reef structure. The historic offshore boundary spill-over harvest reflected offshore movements at high population densities but likely contributed to population declines, altering the extent to which lobsters move offshore and eventually closing this spill-over pathway.