Abstract
Marine ecosystems have experienced significant pressure from a range of anthropogenic stressors, in particular fishing, and this has had detrimental effects on ecosystem health and human wellbeing. It is estimated that global fisheries lose $50 billion USD every year and $2 trillion USD accumulatively over the past thirty years due to the degradation of fishery resources and the failure to adequately fund their recovery. Thus, there is a need to transition towards ecosystem-based management in order to incorporate ecosystem considerations into fisheries management to reverse stock declines and promote more sustainable and resilient fisheries. Marine reserves are more frequently being recommended to help rebuild exploited fish stocks by providing a safe refuge from exploitation for a portion of the spawning population, facilitating the build-up of these populations and regeneration of degraded habitats. In New Zealand, the Guardians of Fiordland Fisheries and the Marine Environment (GOFF) successfully implemented a network of marine protected areas (MPAs) in the inner fjords to preserve unique marine habitats and reverse the significant decline in rock lobster and blue cod populations. However, despite this success story, little research has been conducted on the impacts this has had on the commercial rock lobster fishery. Thus, the overall aim of the present study was to investigate patterns in the Fiordland commercial rock lobster fishery (CRA8) before and after the implementation of this network of MPAs while also comparing it to the adjacent Otago commercial rock lobster fishery (CRA7) without such a network. We found the Southern Oscillation Index (SOI) had significant lagged correlations with rock lobster catch per unit effort (kgs/potlift) in both the CRA7 and CRA8 areas consistent with what we know about the effects of ocean circulation and productivity on larval dispersal and growth rates. Our most significant result found that the estimated average treatment effect of implementing a network of MPAs in Fiordland increased the CPUE of CRA8 by 0.822 kgs/potlift compared to CRA7. We also found significant changes in seasonal catches in CRA8 likely due to the stability provided by the network of MPAs, that also allowed fishers to maximise the economic value of their catch over a given season. The study further contributes to our understanding of the effects of oceanographic processes and marine protected areas on the commercial rock lobster fishery in Fiordland and Otago using commercial CPUE data. These findings could have significant implications over how New Zealand manages its rock lobster fisheries given the source-sink dynamics present between separately managed populations.