Histopathological Assessment of Dolphins Necropsied Onboard Vessels in the Eastern Tropical Pacific Tuna Fishery

摘要

During chase and capture operations of the eastern tropical Pacific tuna purse-seine fishery, dolphins encounter multiple stressors that may cause injury. We examined tissue samples from 56 dolphins (26 Stenella longirostris, 28 S. attenuata, two Delphinus spp.) collected during shipboard necropsies on tuna vessels with the objectives of defining a background of naturally occurring disease, defining, if possible, the cause of death, and identifying any residua of disease or injury that might be attributed to stress related to the current or to prior chase and encirclement operations. Three categories of disease were defined for animals dying in the fishery operations: (1) naturally occurring diseases, unrelated to the fishery, (2) acute reactions, related to the immediate circumstances of encirclement, and (3) evidence of past injury, consistent with healing of acute injury related to the fishery or other major stressors. Parasitism was the major natural disease factor in these apparently healthy populations. Essentially all of the animals died of cardiac injury with implied impairment of cardiac conduction, arrhythmia, and widespread evidence of smooth muscle spasm, which we interpret as resulting from massive shock and stress. Acute necrosis of the renal tubules consistent with ischemia, was observed in almost all specimens. It is plausible that that in some cases, these types of injuries will cause delayed mortality, although no such mortality was demonstrated. We caution that lesions found are non-specific to the fishery, and it is possible that residua in these animals could have been produced by non-fisheries related stress in the normal environment.