Policy analysisIdentifying core areas for mobile species in space and time: A case study of the demersal fish community in the North Sea
Introduction
Marine protected areas (MPA) have become an important tool to conserve marine wildlife and manage exploited resources (Edgar et al., 2014; Halpern and Warner, 2003). Locating protected areas for mobile species such as marine fish, however, is a challenging task and it has been debated whether MPAs are the appropriate means to protect such species (Breen et al., 2015; Claudet et al., 2010; Hilborn et al., 2004; Kramer and Chapman, 1999). Intra- and interannual movements of individuals due to foraging, reproduction and environmental changes alter the habitat preferences of individuals throughout their life cycle (Harden Jones, 1968; Pittman and McAlpine, 2003). It is therefore difficult to assign areas large enough to conserve all life stages of a species (Horwood et al., 1998; Rayfield et al., 2008). Temporary conservation areas in combination with permanent protected areas have been proposed as solution (D'Aloia et al., 2019). However, in many situations political and societal circumstances will not allow for a flexible and adaptive designation of conservation sites (Halpern and Warner, 2003; Kaiser, 2005). Hence these sites should be chosen based on locations with consistently high abundances of threatened or overexploited ecosystem components (i.e. threatened species, habitats or exploited invertebrates or fishes) through space and time. Identifying such locations allows for an efficient allocation of limited spatial resources to conservation objectives.
The implementation of MPAs to manage marine resources has gained impetus at the beginning of the 21st century, as the impacts of intensive fishing during previous decades led to the perception of a crisis in quota-based fisheries management (Beddington et al., 2007; Jacquet, 2007; Worm et al., 2006). At this time, many experts advocated alternative approaches to fisheries management such as the establishment of networks of marine protected areas (MPAs) (Gell and Roberts, 2003; Roberts et al., 2005). While MPAs were demonstrated to be efficient management tools to improve the abundance and size composition of fish associated with structured habitats such as rocky habitats and reefs (Claudet et al., 2008; Claudet et al., 2010; Roberts et al., 2001), similar beneficial effects for fish species inhabiting boreal soft-bottom communities are still being discussed (Breen et al., 2015). Many fish species in temperate and boreal systems undergo wide ranging seasonal migrations between spawning areas, nursery habitats and feeding grounds (Harden Jones, 1968), and were therefore considered to be too mobile and too long-lived to benefit from localised spatial protection (Breen et al., 2015; Hilborn et al., 2004; Kaiser, 2005). However, there is increasing evidence that MPAs may also have positive impacts on demersal fish populations in boreal waters (Kincaid and Rose, 2017; Moland et al., 2013).
In Europe an extensive network of MPAs is established through the Birds and Habitat Directives (BD and HD), requiring European Union (EU) member states to designate MPAs in their coastal seas and exclusive economic zones (Agnesi et al., 2017; Fock, 2011; Mazaris et al., 2019). This network of MPAs is referred to as the Natura 2000 network. Borders of the national Natura 2000 MPAs had to be designated by each member state until 2008, resulting in about 23% of the North Sea being covered by the Natura 2000 network (Agnesi et al., 2017). However, while the BD and HD require the establishment of MPAs to protect sensitive benthic habitats (sandbanks and reefs), marine mammals, and sea birds, neither directive is addressing the conservation of marine fish species apart from a small number of diadromous fish species. As a consequence, very few Natura 2000 MPAs were designated with the aim of protecting marine fish species. In addition, there have been considerable delays to this day to agree upon and implement management measures such as fishing restrictions (Álvarez-Fernández et al., 2017; Dureuil et al., 2018). Therefore, identifying areas of consistent fish abundance and diversity remains a prerequisite to evaluate the potential conservation effect of the Natura 2000 MPAs on demersal fish.
This study interpolates and condenses point-abundance data in space and time to identify consistent patterns of demersal fish distribution within the North Sea. We used data from an internationally coordinated bi-seasonal scientific fisheries surveys covering a 21-year period to 1) demonstrate the concept of identifying consistent core areas for mobile organisms in space and time, and 2) analyse the potential of the designated Natura 2000 MPA network to protect demersal fish biodiversity in a heavily fished temperate/boreal region.
Section snippets
Study area and data sources
The Greater North Sea is a semi-enclosed shelf-sea area of the temperate North East Atlantic with a surface area of approximately 570,000 km2 and an average depth of 95 m. The Greater North Sea includes the Kattegat and Skagerrak, connecting the central basin of the North Sea with the Baltic Sea. The North Sea has been affected substantially by anthropogenic impacts (Emeis et al., 2015), but still remains one of the most productive fishing grounds in the world, being the habitat of more than
Patterns of consistent core areas and diversity
Seasonally consistent core areas (CCAW and CCAS) were identified for all 53 species, while species inter-seasonal consistent core areas (CCAWS) were identified for 49 species (Table 2). The only species without overlapping CCAWS were tope Galeorhinus galeus and topknot Zeugopterus punctatus. For five-bearded rockling Ciliata mustela and sea scorpion Taurulus bubalis catch records were too low to identify consistent CCAS. Therefore CCAWS which are important throughout the year could be
Discussion
In this study we provide a generic interpolation and aggregation protocol allowing the identification of important core areas for a large suite of mobile fish species. The method presented herein to identify consistent core areas has several advantages: It is modular by species, seasons and years, it is independent of environmental data, avoids the need for specialist statistical knowledge to apply the appropriate statistical model for highly skewed (zero inflated) distribution while providing
Author statement
We assure that
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The work is all original research carried out by the authors.
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All authors agree with the contents of the manuscript and its submission to the journal.
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No part of the research has been published in any form elsewhere, unless it is fully acknowledged in the manuscript. Authors should disclose how the research featured in the manuscript relates to any other manuscript of a similar nature that they have published, in press, submitted or will soon submit to Biological Conservation or
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study is part of the Thünen-Institute (TI) research initiative on the implementation of the Marine Strategy Framework directive (MSFD) “Definition and validation of indicators and environmental status assessment” (www.thuenen.de) and has been initiated as a result of cooperation between members of the Working Group on Biodiversity (WGBIODIV) of the International Council for the Exploration of the Sea (ICES). SPRG and MM received support for this work under Service Level Agreement ST02G (
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