There is concern that fishing methods used by the eastern tropical Pacific Ocean (ETP) tuna purse-seine fishery may cause stress to dolphins, and that such stress may be having an adverse impact on reproduction or survival in these mammals. Recent legislation, the 1997 International Dolphin Conservation Program Act, required this review of stress-related research to provide a context for future scientific findings. This review includes background information on the ETP tuna fishery and the dolphins involved. General information regarding stress theory and the physiology of stress is also included. Four general areas of study are reviewed that provide information on physiological and behavioral responses to stress that may be relevant to dolphins involved in the ETP tuna purse-seine fishery. These include laboratory research, research on domestic animals, clinical studies of stress effects in humans, and research on freeranging mammal populations.
Potential stress effects of specific fisheries operations (search, chase, and capture) on the dolphins involved in the ETP fishery are considered. Search operations may cause disruption of habitat utilization, foraging activities, and social activities. Chase and capture operations may cause immediate or short-term physiological responses such as activation of the hypothalamic-pituitary-adrenal axis in response to psychological or social stressors. Psychosocial stressors include separation of mother and young, separation from social groups, social aggression during net confinement, and novelty. Other potential short-term responses of dolphins to chase and capture include severe muscle damage resulting in a condition known as capture myopathy and hyperthermia.
The potential sublethal effects of long-term stress include stress-induced pathologies, compromise to the immune system, as well as impaired reproduction, growth, and metabolism. Based on information from other mammals it is plausible that reproduction for some proportion of female dolphins will be disrupted, either as a result of the hypothalamic-pituitary-adrenal response to stress or through the development of pathologies resulting from chronic stress. Cow-calf separation can occur as the result of chase and capture, and it appears that young animals may be particularly vulnerable to impacts of fisheries operations. Maternal separation and novelty may induce significant hypothalamic-pituitary-adrenal responses in young animals, and this can result in impaired growth.
Although this review of existing literature regarding stress in mammals can not provide a quantitative answer to the question of whether the tuna fishery is causing stress to affected dolphin populations, the available information and evidence point to the likelihood that physiological stress is induced by fisheries activities. It is therefore plausible, that stress resulting from chase and capture in the ETP yellowfin tuna purseseine fishery could have a population level effect on one or more dolphin stocks.
Date of Report: April 23, 2013
Number of Pages: 128
Order Number: G1361
Price: $5.95
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