Marine Reserves, Fisheries and the Spiny Lobster Jasus edwardsii

Abstract

Research in north-eastern New Zealand marine reserves has provided valuable insights into spiny lobster (Jasus edwarsii) behaviour, movement, and reproduction and demonstrated how reserves can allow recovery of lobster populations and contribute to spill-over fisheries. However, over the last 20 years lobster populations in these reserves have undergone considerable declines, raising questions around the effectiveness of reserves in protecting populations from fishing. This thesis examines the effectiveness of two north-eastern New Zealand marine reserves in protecting lobster populations and investigates the drivers and implications of long-term declines in lobster within these reserves. This was assessed using an analytical approach applied to dive and potting survey data, and tag-recapture data, collected within and adjacent to both reserves. The status of fished stocks in the study area was assessed using reserve populations as unfished controls. This analysis estimates spawning stock and biomass in fished areas was 2-3% of unfished levels, which is considerably lower than fishery estimates of stock status. Novel analytical approaches were used to analyse gradients in catch rates across reserve boundaries and found limited evidence of edge effects and spill-over. In addition, seasonal potting caught few lobster on offshore soft-sediment habitats and there were no tag-recaptures on or near offshore boundaries. Seasonal offshore 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 the offshore boundaries and likely reflect comparatively lower population densities. The harvest of lobster undertaking seasonal movements beyond offshore boundaries is believed to have contributed to population declines as populations throughout the reserves were impacted by fishing. In addition, this fishing is believed to have reduced resilience of these populations to an extended period of low recruitment. Overall, these results highlight the poor state of the wider fishery and suggest that while the reserves examined still 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.