Evidence of rebound effect in New Zealand MPAs: Unintended consequences of spatial management measures

Fish size and fish biomass have been shown to increase inside the borders of Marine Protected Areas (MPAs) after the cessation of fishing. However, the effects of marine protection on fishing fleet behaviour and fish catches outside of MPAs are less well understood. Here we investigated changes in total catch and Catch per Unit Effort (CPUE) of bottom trawlers outside the borders of offshore MPAs in New Zealand. We used Regression Discontinuity in Time (before versus after protection) on both aggregate and individual trawl event data for one Marine Reserve, two Benthic Protected Areas, one Closed Seamount Area and one Marine Mammal Sanctuary. Despite the various forms of protection that reduce the total fishable area, total catch tended to increase after MPA implementation. Yet, there was little evidence that this was due to the net-movement of fish from larger populations within MPA boundaries i.e. spillover. Rather, the increases in catch in the post protection period appeared to be a consequence of changes in the behaviours of commercial fishers. This may be an unintended and previously unreported negative consequence of marine protection that could dampen some of the many benefits of MPAs. •Fishing effort was examined at five offshore MPAs in New Zealand.•Fishing effort was analysed before/after protection inside and outside boundaries.•Biomass caught near MPA boundaries increased substantially following protection.•Increased catch was likely driven by fisher behavioural changes rather than increased biomass.•Previously unreported unintended consequences are of interest to spatial planners.