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Impact du réchauffement climatique sur la distribution spatiale des ressources halieutiques le long du littoral français: observations et scénarios

par Sylvain Lenoir
Université Lille 1 Science - Doctorat 2011

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2. Publication: Modelled spatial distribution of marine fish and projected modifications in the North Atlantic Ocean

Modelled spatial distribution of marine fish and projected modifications in the North Atlantic Ocean

Running head: Niche modelling and fish biogeography

S. Lenoir, G. Beaugrand, É. Lécuyer

Global Change Biology 17(1) 2010

2.1. Abstract

The objectives of this work were to examine the past, current and potential influence of global climate change on the spatial distribution of some commercially exploited fish and to evaluate a recently proposed new Ecological Niche Model (ENM) called Non-Parametric Probabilistic Ecological Niche model (NPPEN). This new technique is based on a modified version of the test called Multiple Response Permutation Procedure (MRPP) using the generalized Mahalanobis distance. The technique was applied in the extratropical regions of the North Atlantic Ocean on 8 commercially exploited fish species using three environmental parameters (sea surface temperature, bathymetry and sea surface salinity). The numerical procedure and the model allowed a better characterisation of the niche (sensu Hutchinson) and an improved modelling of the spatial distribution of the species. Furthermore, the technique appeared to be robust to incomplete or bimodal training sets. Despite some potential limitations related to the choice of the climatic scenario (A2 and B2), the type of physical model (ECHAM 4) and the absence of consideration of biotic interactions, modelled changes in species distribution explained some current observed shifts in dominance that occurred in the North Atlantic sector, and particularly in the North Sea. Although projected changes suggest a poleward movement of species, our results indicate that some species may not be able to track their climatic envelop and that climate change may have a prominent influence on fish distribution during this century. The phenomenon is likely to trigger locally major changes in the dominance of species with likely implications for socio-economical systems. In this way, ENMs might provide a new management tool against which changes in the resource might be better anticipated.

Keywords: ecological niche modelling, climate change, marine fish distribution, ecological niche, projections, biogeography

2.2. Introduction

Fish stocks fluctuate in space and time and the better understanding of these fluctuations have occupied scientists for several decades (Rosenzweig 1995; Barange & Harris 2003; Brander 2007). While it has been difficult to identify causes for some stock fluctuations, changes have often been attributed to stochastic events (Hsieh et al. 2005), hydro-climatic anomalies (Edwards et al. 2002; Lehodey et al. 2006), climate change (Drinkwater 2006; Brander 2007) or both direct and indirect anthropogenic impacts (Hutchings 2000; Jennings et al. 2001; Pauly et al. 2005). Among anthropogenic pressures, overfishing is an important driver of change in marine fish stocks, acting probably in synergy with climate forcing (Hsieh et al. 2006; Brander 2007).

The impact of climate warming on marine ecosystems has become prominent (Root et al. 2003; Intergovernmental Panel on Climate Change 2007b; Rosenzweig et al. 2008). Among these effects, there is a central and growing concern about possible changes in species geographical distribution (Parmesan & Yohe 2003; Deutsch et al. 2008; Thuiller et al. 2008). For example, northward movements in calanoid copepod zooplankton have been observed in the North Atlantic Ocean at a mean rate of up to 23.16 km.y-1 for some species assemblages in a period of 48 years (Beaugrand et al. 2009). These changes in plankton composition were paralleled by a northward migration of both commercial and un-commercial fish species (e.g. Quero et al. 1998; Stebbing et al. 2002; Brander et al. 2003; Beare et al. 2004a; Perry et al. 2005).

Despite the recognition of the importance of ecosystem processes to better manage fish stocks (e.g. Ecosystem Based Fisheries Management; see Cury et al. 2008), current management plans rarely consider that the carrying capacity of the ecosystem may fluctuate and that the natural spatial distribution of the target species may vary. The biosphere is now experiencing a period of rapid and sustained climate change that might even accelerate in the future (Intergovernmental Panel on Climate Change 2007b). A fundamental challenge for future sustainable exploitation and conservation is to dispose of valid estimations of potential changes in future species distributions (Pearson & Dawson 2003; Schwartz et al. 2006; Thuiller 2007). To do so, an increasing number of statistical tools (e.g. bioclimatic envelop models, ecological niche modelling; Guisan & Zimmermann 2000; Thuiller 2003; Austin 2007) have been developed to determine the potential response of species to global warming in both the terrestrial (Harrison et al. 2006; Murphy & Breed 2007; Huntley et al. 2008) and the marine realms (Guinotte et al. 2006; Beaugrand & Helaouët 2008; Cheung et al. 2008a). Based on the Hutchinsonian concept and the relation between species niche and distribution (Hutchinson 1957; Pulliam 2000), these models project the multidimensional distribution of species into an environmental (or Euclidean) space or into a geographical space (Soberón & Peterson 2005; Austin et al. 2006; Hirzel et al. 2006).

The aim of this work is to formulate different scenarios of changes in the spatial distribution of some North Atlantic fish in response to ocean warming. First, the ecological niche (sensu Hutchinson, 1957) of eight exploited fish in the North Atlantic is characterised. Second, the spatial distribution of these species is modelled for the period 1960-1969. Third, an evaluation of the consequences of changes in temperature on spatial distribution of species is carried out during the period 1960-2005. Fourth, scenarios of changes in the spatial distribution of these species are proposed for the middle and the end of this century using two moderate scenarios (A2 and B2). Results are commented in the context of global climate change and associated to the pronounced influence of fishing on exploited resources and marine ecosystems.

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