Consequences of shark declines

25 October 2010

A new review of documented changes in shark populations shows that the fish are vulnerable to even light fishing pressure and that fewer large predatory sharks can entail cascading changes in ecosystems.

Sharks inhabit coastal, demersal and pelagic habitats in all oceans but are concentrated on the continental shelves. Slow growth, late maturity and low fecundity mean that sharks show twice the fishing extinction risk of bony fishes and recover from depletion more slowly. Sharks have been increasingly threatened by the direct and indirect of fishing worldwide, particularly among large oceanic species.

The authors were able to examine more evidence of food-web impacts in coastal ecosystems both because these areas have been intensely fished for a longer period of time and because data are easier to collect.

Citing case studies from around the world, the authors show how the loss of these top predators influences ecosystems in a number of ways. Middle-sized predators can increase, expand their distribution or change their feeding habits when there is less pressure from higher in the food web.

Then the “middle” predators consume greater quantities of smaller fish and shellfish, impacting those populations, ultimately resulting in lower species diversity.

Declining shark populations mean more than just a shift in target species for the fishing industries of the world. They mean a shift in marine populations in ecosystems of the world.

>> Read the paper 

>> A summary is available as part of the Lenfest Research Series