MASS MORTALITY OF COMMON DOLPHINS (DELPHINUS-DELPHIS) IN SOUTH-WEST ENGLAND DUE TO INCIDENTAL CAPTURE IN FISHING GEAR

In the first quarter of 1992, 118 dolphin carcases, of which 54 mere p ositively identified as common dolphins (Delphinus delphis), were foun d stranded on the coast of Cornwall and Devon. To determine the cause, detailed post mortem examinations were carried out on 38 of the carca ses, and the results were compared with those from 20 common dolphins that stranded on the coast of Cornwall and Devon in the previous 15 mo nths. There was no evidence that the deaths were due to an infectious or parasitic disease, or acute intoxication by any of the algal toxins , trace metals or chlorinated hydrocarbons measured. However, 30 of th e 38 dolphins showed signs associated with incidental capture in fishi ng gear. Skin lesions characteristic of capture in a small-meshed net and the predominance of recently ingested Atlantic mackerel (Scomber s combrus) and pilchard (Sardina pilchardus) in the stomachs of the dolp hins suggested that they had been caught in the trawl or purse seine n ets used for these fish. There is insufficient information to explain why this high mortality occurred in 1992 and not in other years.