Abstract
Marine protected areas (MPAs) are considered viable fisheries management tools due to their potential benefits of adult spillover and recruitment subsidy to nearby fisheries. However, before–after control–impact studies that explore the biological and fishery effects of MPAs to surrounding fisheries are scarce. We present results from a fine-scale spatial gradient study conducted before and after the implementation of a 5 km2 lobster MPA in southern Norway. A significant nonlinear response in lobster abundance, estimated as catch-per-unit-effort (CPUE) from experimental fishing, was detected within 2 years of protection. After 4 years, CPUE values inside the MPA had increased by a magnitude of 2.6 compared to before-protection values. CPUE showed a significant nonlinear decline from the centre of the MPA, with a depression immediately outside the border and a plateau in fished areas. Overall fishing pressure almost doubled over the course of the study. The highest increase in fishing pressure (by a magnitude of 3) was recorded within 1 km of the MPA border, providing a plausible cause for the depression in CPUE. Taken together, these results demonstrate the need to regulate fishing pressure in surrounding areas when MPAs are implemented as fishery management tools.
Highlights
Marine protected areas (MPAs), defined as sea areas where harvesting of target species is partially or fully prohibited, have been established in many regions around the world with the objectives of species conservation and management of fishery resources [1,2]
This empirical study showed that while lobster abundance inside an MPA can rapidly increase with protection, ‘fishing-the-line’ could quickly reduce lobster abundances close to the MPA border to levels below pre-MPA values
While lobster abundance inside an MPA had almost tripled during the first four years of MPA implementation, there was a significant decrease in lobster abundance within 1.5 km outside the MPA borders
Summary
Marine protected areas (MPAs), defined as sea areas where harvesting of target species is partially or fully prohibited, have been established in many regions around the world with the objectives of species conservation and management of fishery resources [1,2]. We show that the implementation of an MPA for lobsters has a simultaneous effect on both target species and the fisheries around it We show this by (1) using before–after time series data to quantify the spatial development of an abundance gradient for lobsters (as indexed by CPUE from experimental fishing) inside and around the MPA, and (2) documenting the changes in fishing patterns that happened in the surrounding unprotected areas. In using CPUE estimates obtained from experimental fishing (hereafter referred to only as CPUE) as an index for lobster abundance for this study, we assumed that lobsters have a similar catchability in baited traps that are deployed within their home range, both inside and outside the protected area. Validation for the optimal model is done by using the Pearson residual and the inspection of residual plots for the zero-inflated models (see electronic supplementary material, S1)
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