Monday, 2 April 2007

Conservation Conversations 8


Big Sharks and Little Sharks


A report (http://environment.guardian.co.uk/conservation/story/0,,2046299,00.html) based on fishery and research vessel records from the 1970s to 2005 claims that the overfishing of the great sharks in all the world's oceans is having some superficially surprising effects on marine food chains. Dramatic reductions in the numbers of large predators (such as Bull, Hammerhead, Tiger, Great White and Mako sharks) appears to be causing an abundance of their prey species namely skates, rays and smaller sharks (such as the Cownose ray, the Little skate and the Atlantic sharpnose shark). The researchers believe that the latter are now decimating the populations of shellfish (e.g. oysters and scallops) on which they feed. If these results are confirmed, it will be yet another illustration of the complex relationships evident between species in ecosystems. 'Taking out' one organism generally has wide repercussions on the food chain.

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