Study on Sharks and Rays in the Balearic Islands

The ecology and exploitation status of sharks and rays have been studied in the Balearic Islands

Press Release by the Spanish Institute of Oceanography (IEO),
18. January 2012

The conservation level of demersal elasmobranchs in the Islands is better than in other areas of the north-western Mediterranean.

A wide study on elasmobranchs inhabiting marine bottoms off the Balearic Islands and nearby areas has been carried out by researches from the Balearic Oceanographic Centre from the Spanish Institute of Oceanography (IEO). Its results have been published recently as four scientific papers in the journal Scientia Marina.

The study confirms the vulnerability of these species, which show a decrease in their diversity, abundance and mean length in areas off the Balearic Islands subjected to higher fishing pressure, as well as a decrease in their populations as a consequence of the increasing fishing effort during last half century. During last years, this trend seems to be at a standstill or even reverted, as species distributed on the continental shelf show some recovery signs, probably due to a displacement of the fishing effort to deeper areas.

The results also show that the conservation level of demersal elasmobranch populations from the Balearic Islands is better than in other areas of the north-western Mediterranean, probably due to a lower development of the bottom trawl fishery in the Balearic archipelago and to the surrounding type of marine bottoms. However, this situation is far from an optimum, especially for slope bottoms, as it is reflected in a lower abundance and diversity of these species in comparison to those from the Algerian coast with a lower level of development of the deep fishery.

These studies are based on the analysis of two sets of data. First, historical data from bottom trawl landings from the Balearic Islands, between 1965 and 2009. And second, information obtained from oceanographic surveys carried out between 2000 and 2009 off the Balearic Islands and in 2003 and 2004 in the Algerian coast, in the framework of an European program for the assessment of the exploitation status of demersal marine ecosystems.

The demersal elasmobranch community composition and structure have been analysed as well as their bathymetric and geographic distribution. Indicators trends, such as abundance, biomass, mean individual length, specific richness and diversity have been modelled. Finally, trophic ecology from eight elasmobranchs (three sharks and five rays) have been studied by the characterization of their diet and trophic guilds.

These results, obtained by researchers from the ecosystems and demersal resources team from the Balearic Oceanographic Centre (IEO in collaboration with experts from the Glasgow University and the Algerian Ministry of Fisheries, have been published as four scientific papers in the journal Scientia Marina and were presented in the 13th European Elasmobranch Association Conference, celebrated in Palma on 19th-22nd November 2009. The European Elasmobranch Association (EEA) was established in 1996 for coordinating regional and international activities carried out by their 12 organizational members. Its objectives include promoting research, sustainable management, conservation and social awareness of this fish through Europe.

Elasmobranch, a threatened group

Most elasmobranchs, or cartilaginous fish, are in the top of marine trophic webs, which make them good health state indicators of the sea and its ecosystems. Changes in low trophic levels affect, at low or high levels, large predators such as elasmobranchs, which are sited at top levels.

According to the IUCN Red List of Threatened Species, more than 20% of world elasmobranch populations, and more than 30% in Europe, are threatened. Shark fauna in the Mediterranean is highly diverse, with around 86 species (47 sharks and 38 rays), 80% of them are coastal species, most of them benthic (or related to the bottom), and some pelagic species, such as the basking shark. Their main threats are pollution, coastal demographic pressure, illegal trade of shark fins, accidental bycatch in fisheries and, finally, fishing overexploitation.

Bibliographic references:

1. Francesc Ordines, Enric Massutí, Joan Moranta, Antoni Quetglas, Beatriz Guijarro and Khaled Fliti, (2011). Balearic Islands vs Algeria: two nearby western Mediterranean elasmobranch assemblages with different oceanographic scenarios and fishing histories. Scientia Marina, 75(4): 707-717.

2. Adam Gouraguine, Manuel Hidalgo, Joan Moranta, David M. Bailey, Francesc Ordines, Beatriz Guijarro, María Valls, Carmen Barberá and Aina De Mesa, (2011). Elasmobranch spatial segregation in the western Mediterranean. Scientia Marina, 75(4): 653-664.

3. Maria Valls, Antoni Quetglas, Francesc Ordines and Joan Moranta, (2011). Feeding ecology of demersal elasmobranchs from the shelf and slope off the Balearic Sea (western Mediterranean). Scientia Marina, 75(4): 633-639.

4. Beatriz Guijarro, Antoni Quetglas, Joan Moranta, Francesc Ordines, Maria Valls, Natalia González and Enric Massutí. Inter- and intra-annual trends and status indicators of nektobenthic elasmobranchs off the Balearic Islands (northwestern Mediterranean). Scientia Marina. DOI : 10.3989/scimar.03432.22.

The Spanish Institute of Oceanography (IEO), is a public research organization and part of the Spanish Ministry of Science and Innovation, dedicated to research in marine science; especially in relation to scientific knowledge of oceans, sustainability of fisheries resources and marine environment. The IEO represents Spain in most of the international science and technology forums related to the sea and its resources. IEO has nine coastal oceanographic centres, five experimental aquaculture plants, twelve tide gauge stations, one receiving station for satellite images and a fleet of six research vessels.

Source: The Spanish Institute of Oceanography (IEO).



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