Extinction in multiple species fisheries harvested with the same gear - The Great Lakes ciscoes

Extinction of four deepwater ciscoe species (Coregonus spp.) in the Great L akes occurred during a period of heavy exploitation, but during the same pe riod there were several introduced and invading species and there also was widespread deterioration in the quality of the environment. The cause of th e extinctions is uncertain, but extinction is a threat in multiple species fisheries harvested with a common gear. The possibility that the ciscoe ext inctions resulted from harvesting was investigated using a general form of the surplus production model and computer simulation. In the simulations ex tinctions occurred even with a moderate fishing effort when a large number of different species were caught with the same gear. In the Great Lakes 4 o ut of 8 ciscoe species caught with the same gear apparently went extinct. I n the simulations 4 extinctions out of 8 species was a common event, and th e fishery alone was all that was necessary to cause the extinctions.