News: The Deepest Shark

The average depth of the oceans is 4000m and bony fishes (relatives of cod) thrive down to 9000m depth. As man explored into abyssal depths over the past 20 years and new fish species were discovered, scientists became aware that sharks have failed to colonise abyssal depths greater than 3000m. Why sharks have not succeed in the deep is a mystery but has the startling implication that fishermen are already exploiting the last populations left on the planet.

For more information on this topic read the article 'The Absence of Sharks from Abyssal Regions of the World's Oceans' by Prof. Monty Priede, Rainer Froese,David M. Bailey,Odd Aksel Bergstad, Martin A. Collins,Jan Erik Dyb, Camila Henriques, Emma G. Jones & Nicola King which can be found on the Royal Society publications web site.

The deepest shark recorded to date was a Portuguese dogfish, Centroscymnus coelolepis, captured at 3670m by line fishing in the Porcupine Seabight area of the NE Atlantic, SW of Ireland (Forster, 1973). Analysis of captures from the past 150 years rejected records where the sampling gear traversed a wide depth range and therefore depth of capture was uncertain.

The Portuguese dogfish is found in the Pacific and Atlantic Oceans. Dr. Phil Bagley and colleagues at the University of Aberdeen, using a deep-sea lander vehicle with a baited photographic camera and acoustic fish tracking system, first tracked it in 1994 off the South-West of Ireland. The sharks photographed ranged in length from 55-93cm and two individuals were tracked at 1650m with a mean speed of 0.106m/s

Deepwater sharks are caught mainly as by-catch of mixed fisheries for deepwater teleost species and as a targeted species to a lesser extent. Deep demersal sharks are typically slow growing, have a high age at sexual maturity and a low reproductive capacity, all life history characteristics that make them extremely vulnerable to the pressures of overfishing. Recent assessments of deepwater shark stocks have declared the Portuguese dogfish as a species in 'extreme decline'. http://www.ices.dk/marineworld/jaws.asp

Bagley P.M., Smith A. & Priede I.G. (1994) Tracking movements of deep demersal fishes in the Porcupine Seabight, North-East Atlantic Ocean. Journal of the Marine Biological Association of the United Kingdom74: 473-480

Forster, G.R. (1973) Line fishing on the continental slope - the selective effect of different hook patterns. J. Mar. Biol. Ass. U.K. 53,749-751.