Elasmobranch spatial segregation in the western Mediterranean

Joan Moranta,Adam Gouraguine,Manuel Hidalgo,Aina De Mesa,Francesc Ordines,Carmen Barberá,María Valls,David M. Bailey,Beatriz Guijarro

doi:10.3989/scimar.2011.75n4653

Joan Moranta, Adam Gouraguine + Show 7 more

Open Access

https://doi.org/10.3989/scimar.2011.75n4653

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Journal: Scientia Marina	Publication Date: Jul 15, 2011
Citations: 61	License type: cc-by

Affiliation: University of Oslo, University of Glasgow

Abstract

Basic information on the distribution and habitat preferences of ecologically important species is essential for their management and protection. This study focuses on the depth related trends and the geographic patterns that shape the community of the elasmobranch species in the Balearic Islands (Mediterranean Sea) using data collected from 2001 to 2009. Non-metric Multi-Dimensional Scaling (MDS) ordination was used to detect zonation patterns in the community. Generalized Additive Models (GAMs) were applied to analyse spatial and temporal variation in elasmobranch community descriptors (abundance, biomass, mean fish weight, number of species and diversity), as well as the abundance and mean length of the four individual species (S. canicula, G. melastomus, R. clavata, R. miraletus). Depth was the main factor determining the assemblage composition, and the MDS analysis identified four main groups with 60% of the similarity found to correspond to the continental shelf, shelf break, upper slope and middle slope of the surveyed area. GAM analysis identified spatial patterns that were independent of the bathymetric distribution preference. Although depth was a strong predictor for all the analyses performed, the geographic variation in the elasmobranch abundance was also important. The results also show a reduction in the mean length of the elasmobranch species in the areas with high fishing intensity. Our study evidences a clear spatial segregation of the main species throughout the ontogeny because the geographic and bathymetric effects were highly size dependent, with clear differences between the bathymetric distributions of juveniles and adults but no clear spatial overlapping. This study sheds new light on the spatial distribution of the elasmobranch species off the Balearic Islands, which is essential information for protecting marine organisms along with their habitats and promoting ecosystem based management.

Highlights

The ecological importance of elasmobranchs is becoming increasingly clear (Stevens et al, 2000; Bascompte et al, 2005)
The present study focused on understanding the spatial distribution in relation to biological, environmental and anthropogenic factors in the areas along the continental shelf and slope off the coast of the Balearic Islands
The results of the SIMPER analysis identified the relative importance of several elasmobranch species corresponding to different bathymetric assemblages (Table 2)

Summary

Introduction

The ecological importance of elasmobranchs is becoming increasingly clear (Stevens et al, 2000; Bascompte et al, 2005). There is current concern over the effects of increased fishing intensity on the status of the elasmobranch populations (Stevens et al, 2000) Their low recovery rates are due to sensitive life-history stages (Cailliet et al, 2005), late maturity and low fecundity, which make elasmobranchs highly vulnerable to overexploitation (Stevens et al, 2000). This is of particular concern in the highly exploited Mediterranean, where sharks and rays make up a significant proportion of the by-catch (Carbonell et al, 2003) and are targeted at various bathymetric ranges, which has led to their drastic decline in this area over the last two centuries (Ferretti et al, 2008). Protecting these fish requires detailed information about their distribution and biology; this information is not available for many Mediterranean species and regions

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