Lobster and cod benefit from small-scale northern marine protected areas: inference from an empirical before–after control-impact study

Even Moland,Halvor Knutsen,Carl André,Pauline Garrigou,Alf Ring Kleiven,Esben Moland Olsen,Jan Atle Knutsen,Sigurd Heiberg Espeland

doi:10.1098/rspb.2012.2679

Abstract

Marine protected areas (MPAs) are increasingly implemented as tools to conserve and manage fisheries and target species. Because there are opportunity costs to conservation, there is a need for science-based assessment of MPAs. Here, we present one of the northernmost documentations of MPA effects to date, demonstrated by a replicated before–after control-impact (BACI) approach. In 2006, MPAs were implemented along the Norwegian Skagerrak coast offering complete protection to shellfish and partial protection to fish. By 2010, European lobster (Homarus gammarus) catch-per-unit-effort (CPUE) had increased by 245 per cent in MPAs, whereas CPUE in control areas had increased by 87 per cent. Mean size of lobsters increased by 13 per cent in MPAs, whereas increase in control areas was negligible. Furthermore, MPA-responses and population development in control areas varied significantly among regions. This illustrates the importance of a replicated BACI design for reaching robust conclusions and management decisions. Partial protection of Atlantic cod (Gadus morhua) was followed by an increase in population density and body size compared with control areas. By 2010, MPA cod were on average 5 cm longer than in any of the control areas. MPAs can be useful management tools in rebuilding and conserving portions of depleted lobster populations in northern temperate waters, and even for a mobile temperate fish species such as the Atlantic cod.

Highlights

Marine protected areas (MPAs) have received increasing attention as tools in fisheries management and conservation
Partial protection of Atlantic cod (Gadus morhua) was followed by an increase in population density and body size compared with control areas
This study is one of few to use the recommended before–after control-impact (BACI)-approach to assess MPA effects [4], and, to the best of our knowledge, the first to do so for European lobster and Atlantic cod. This approach allowed an unambiguous test of effects of protection on population density and body size of lobster and a relatively robust test of the same for cod

Summary

Introduction

Marine protected areas (MPAs) have received increasing attention as tools in fisheries management and conservation. As far as we are aware, only few studies have previously used this recommended design and none in northern temperate coastal regions We show that both lobster and cod generally responded positively to protection, and that there were clear regional differences in MPA-response and population development in adjacent fished areas. These differences illustrate the value of the BACI study design for science and management. As the CPUE data were skewed towards counts of zero lobsters per trap per day (see the electronic supplementary material, figure S4a), we used a zero-inflated Poisson regression model (function: zeroinfl in R, [37]) to analyse the effects of year, treatment and region on CPUE. In addition to mean size, we estimated the large-size component of the CC as the 90 per cent percentile length (the length that 90% of the fish are smaller than)

Results

Discussion

Findings

20. DFO 2010 Review of the Gilbert Bay Marine