Few sharks in the deep sea but bony fish still at risk
14 April 2006, CIESM News

An international team of scientists, led by Prof. Priede of the University of Aberdeen, used baited cameras, long-lines with baited hooks and demersal trawling to study deep-sea habitats in the Atlantic, Pacific, Indian Ocean and the Mediterranean (published in the Proceedings of The Royal Society, Biological Series). This, combined with analyses of historical records, revealed that sharks do not colonise the abyssal zone, meaning that the biggest part of the world oceans appears to be mainly shark free. The deepest sharks (the six-gilled shark, Hexanchus grisus and the velvet belly Etmopterus spinax) were found in the Mediterranean Sea at 2,490m. The scientists could not find a simple explanation for the absence of the sharks in the deep-sea. Clearly more research is needed on the physiological adaptations of cartilaginous fishes to pressure. The team concluded that all populations of this group may potentially be more vulnerable to over-exploitation than previously thought, because they are within the reach of fisheries and there is no hidden reserve (see also IUCN Red List).

However, species of bony deep-sea fish are also endangered, as a recent study published in Nature (1) evidences. A research-survey of five species that live on or near the bottom of the continental slope of the North Atlantic Ocean shows that their relative abundance declined over a 17-year period to such an extent that they now meet IUCN criteria for being critically at risk. This traces back to the fact that the shelf fisheries began to collapse in the 1960s and 1970s and harvesting shifted to deep-sea fish species. Many fish populations crashed within only a decade, and their recovery is slow due to their specific life-cycle (i.e. late-maturing, longevity, low fecundity and slow-growth).

Within the Mediterranean realm the General Fisheries Commission for the Mediterranean (GFCM) adopted a measure to ban trawling below 1000 meters as well as driftnets in 2005. CIESM and its well-known Monograph on the Mediterranean Deep Sea (2) contributed actively to raise awareness and concern for the implementation of strict protection measures.

1 J.A. Devine, K.D. Baker, R.L. Haedrich: Deep-sea fishes qualify as endangered. Nature, Vol. 439, 5 January 2006, p. 29.

2 CIESM Monograph 23 entitled “Mare incognitum? – Exploring Mediterranean deep-sea biology” is downloadable.