Dr Benn Hanns1, Associate Profressor Nick Shears1
1University Of Auckland, Auckland, New Zealand
Over the last 20 years populations of lobster, Jasus edwarsii, have undergone considerable declines across North-eastern New Zealand marine reserves, raising questions around their effectiveness at protecting these important reef predators. This study uses an analytical approach applied to dive and potting survey data to examine the effectiveness of two marine reserves in protecting lobster populations and investigates the drivers and implications of long-term declines. Despite reductions in population sizes, estimates of spawning-stock and biomass in fished areas were 2-3% of that in reserves highlighting the poor state of the wider fishery. Gradients in catch rates across reserve boundaries indicated limited evidence of edge-effects and spill-over, and seasonal potting caught few lobster on offshore soft-sediment habitats. Seasonal movements were mostly limited to movements between shallow and deep reef, and young-adult males undertaking nomadic longshore movements were the main demographic caught in adjacent fisheries. These results contrast previous reports which describe spill-over across offshore boundaries and likely reflect lower population densities. The harvest of lobster beyond offshore boundaries is believed to have contributed to population declines as populations throughout the reserves were impacted by fishing. Furthermore, this fishing likely reduced the resilience of these populations to periods of low recruitment. Overall, these results highlight the poor state of this fishery and suggest that while the reserves examined play a role in protecting lobster, they are too small to fully protect lobster populations. The results and methods developed provide important information that can inform both future marine reserve design and fisheries management.
Presentation Slides – Benn Hanns
