TROUBLED WATERS - Whale and Dolphin Conservation Society

The concept of stressAnimals rely on behavioural and physiological mechanisms, which enable them to maintainhomeostasis in response to external and internal stimuli. These regulatory mechanisms have optimumand maximum tolerance ranges, which depend largely on a species’ evolutionary history, but can bemoderated by individual genetic make-up, as well as short and long-term history. Environmentalstimuli, which fall outside an animal’s adaptive range with regard to duration, intensity or frequency,or because of the nature of the stimulus itself, are associated with pathology and reduced survival.These ‘overtax’ behavioural and physiological control systems and are referred to as ‘stress’ (Broomand Johnston 1993).Stressful conditions, such as confrontation with a predator or rival, disturb homeostasis and result inprofound physiological and behavioural changes, which involve complex interrelated hormonal,metabolic, neural and neuroendocrine responses (e.g., Toates 1995). The main transmitter substancesand hormones involved include glucocorticoids (cortisol, corticosterone), the mineralocorticoidaldosterone, catecholamines (adrenaline and noradrenaline), insulin, thyroid and growth hormone.During stress the body mobilises carbohydrates and fatty acids to provide energy. At the same timeblood pressure, cardiac and respiratory rate increase. This provides the efficient transport of vitalnutrients to the skeletal and cardiac muscles. Less immediately important processes such as digestion,immune defence, reproduction and growth are inhibited to further maximise available energy. Thesechanges are independent of physical activity.Psychological stimuli, including fear, elicit strong adrenal responses and an assessment of how stimuliare perceived is therefore critical. Mason (1971) emphasised the psychological dimensions of allanimal treatments (see also Toates 1995 and von Holst 1998) and considers it virtually impossible toavoid the psychological element of physical stressors.The potential stress effects of whaling and the welfare implications for hunted cetaceans71Physiological indicators of stress and their interpretationStressful situations cause behavioural and physiological changes that can be gauged through a rangeof biological indicators. Measurements of cardiac and respiratory rate, body temperature, as well as anumber of physiological, haematological and biochemical profiles can provide important informationabout whether or not an animal is stressed. Interpreting biological parameters used to assess theimpact of potentially stressful conditions is not always straightforward, and several indicators shouldbe employed to avoid misleading results. The importance of accurate baselines against whichexperimental measurements can be compared is critical. Even without visible signs of stress,biochemical and physiological profiles may be affected, and haematological assessment should,therefore, consider sex, nutritional state, circadian rhythms, seasonal variation, and physiologicalstate. Sampling itself can have effects and lead to persistently overestimated baseline levels. The sameis true for animals that are already stressed when samples are taken. Sampling method, samplepreparation and storage may affect samples.Stress associated with pursuitAcute stress on capture may bring about short and long-term morbidity and mortality in bothdomestic and wild species (Mitchel et al. 1988). Hyperthermia, profuse sweating, hyperventilation,hypotension and degrees of skeletal and cardiac muscle damage are common post-chase and postcaptureconditions.