At least 25 species of shark, ray and chimera inhabit the western Mediterranean, according to a study of the diversity and biological abundance of these species which form a group that it is highly vulnerable to the impact of fishing.

The study was carried out by the oceanographic centres of the Balearics, Murcia and Malaga, which are part of the Spanish Institute of Oceanography (IEO), and the University of the Balearic Islands. The data were collected from research in 2013 off the Mediterranean coast of the mainland and off the Balearics.

Research campaigns such as this have been conducted since 1994 by various European countries in the Mediterranean and their general aim is to assess ecosystems and fishing resources that are exploited by trawling and so further assess the impact of this fishing activity.

Of the 25 species, seven were common to the whole area, with nine local to the Balearics, five in the Alboran Sea between southern Spain and Morocco and one off the northeast of the mainland. The most abundant species were medium-sized dogfish sharks, the Galeus catshark, the velvet belly lanternshark and the thornback ray: they constitute 85%.

Two distinct communities were identified at between 40 and 250 metres depth and from 300 to 800 metres, and the highest levels of diversity were in the Balearic continental shelf and the slope of the Alboran.

The IEO points to growing concerns in recent decades about the conservation of chondrichthyes, a class that contains sharks, rays and chimeras (sometimes called ghost sharks) and which plays a vital role in marine ecosystems. They are notable by their biological characteristics, such as having low reproductive rates and slow growth and being highly sensitive to impact from fishing.

With the results, the IEO says that it is fundamental to get to know the spatial patterns of diversity and abundance so that areas with high conservation values can be identified. The results will go towards forming plans of action and management for conservation and protection under the ecosystem approach anticipated for the new Common Fisheries Policy.

"In the western Mediterranean the challenge should be to make compatible the sustainability of trawling with the recuperation and conservation of chimeras, rays and sharks," says the main author of the study, Sergio Ramírez, from the marine ecology department at the university.