TROUBLED WATERS - Whale and Dolphin Conservation Society

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The concept of stress Animals rely on behavioural and physiological mechanisms, which enable them to maintain homeostasis in response to external and internal stimuli. These regulatory mechanisms have optimum and maximum tolerance ranges, which depend largely on a species’ evolutionary history, but can be moderated by individual genetic make-up, as well as short and long-term history. Environmental stimuli, 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’ (Broom and Johnston 1993). Stressful conditions, such as confrontation with a predator or rival, disturb homeostasis and result in profound physiological and behavioural changes, which involve complex interrelated hormonal, metabolic, neural and neuroendocrine responses (e.g., Toates 1995). The main transmitter substances and hormones involved include glucocorticoids (cortisol, corticosterone), the mineralocorticoid aldosterone, catecholamines (adrenaline and noradrenaline), insulin, thyroid and growth hormone. During stress the body mobilises carbohydrates and fatty acids to provide energy. At the same time blood pressure, cardiac and respiratory rate increase. This provides the efficient transport of vital nutrients 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. These changes are independent of physical activity. Psychological stimuli, including fear, elicit strong adrenal responses and an assessment of how stimuli are perceived is therefore critical. Mason (1971) emphasised the psychological dimensions of all animal treatments (see also Toates 1995 and von Holst 1998) and considers it virtually impossible to avoid the psychological element of physical stressors. Physiological indicators of stress and their interpretation Stressful situations cause behavioural and physiological changes that can be gauged through a range of biological indicators. Measurements of cardiac and respiratory rate, body temperature, as well as a number of physiological, haematological and biochemical profiles can provide important information about whether or not an animal is stressed. Interpreting biological parameters used to assess the impact of potentially stressful conditions is not always straightforward, and several indicators should be employed to avoid misleading results. The importance of accurate baselines against which experimental 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 physiological state. Sampling itself can have effects and lead to persistently overestimated baseline levels. The same is true for animals that are already stressed when samples are taken. Sampling method, sample preparation and storage may affect samples. Stress associated with pursuit Acute stress on capture may bring about short and long-term morbidity and mortality in both domestic 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 postcapture conditions. The potential stress effects of whaling and the welfare implications for hunted cetaceans 71
72 A REVIEW OF THE WELFARE IMPLICATIONS OF MODERN WHALING ACTIVITIES Both chase and pursuit cause stress in terrestrial mammals; this includes stress-related mortality, a factor which may apply to cetaceans. Pursuit-related stress may manifest as a syndrome called: ‘exertional myopathy’ (EM), ‘capture myopathy’, ‘stress myopathy’, or ‘exertional rhabdomyolysis’. Myopathies are diseases of the muscle fibres. EM, however, is distinguished from other types of myopathy, such as nutritional and toxic myopathies by its cause, as it affects both skeletal and cardiac muscles in response to exertion, fear and stress. Commonly associated with strenuous or prolonged pursuit, capture, restraint or overexertion, EM develops irrespective of capture. Mental stressors, such as fear and anxiety, too, have been recognised as predisposing factors, as have high ambient temperature and impeded thermoregulation. These elements may act singly or together. The acute stress on capture may bring about short and longterm morbidity and mortality. Williams and Thorne (1996) stated “even species that have evolved for efficient running, either for predator avoidance or for predation, may develop EM following intense or prolonged muscular activity associated with extreme stress during air or ground pursuit”. These authors consider pursuit time a major factor in the development of EM. As energy and oxygen reserves are depleted during strenuous exercise, muscles switch to anaerobic glycolysis. This leads to either local or systemic build-up of lactic acid, local heat production, muscle degeneration and death of areas of muscle tissue (necrosis) (Fowler and Boever 1993). Increased cardiac and respiratory rates, elevated body temperature, ataxia, paresis or paralysis and acute muscle disruption are some of the symptoms associated with EM (Harthoon and Young 1974, Bartsch et al. 1977, Chalmers and Barrett 1977, Basson and Hofmeyr 1978; Fowler and Boever 1993). Identifying or interpreting these factors requires knowledge about the animal’s normal undisturbed behaviour. Harthoorn (1973) describes four syndromes associated with the disease, namely hyperacute, acute, subacute and chronic EM, although according to Williams and Thorne (1996) these “represent a continuum of physiologic and pathologic changes that occur over time after the initial exertion insult”. Clinical signs, including death, may occur within minutes or hours, or in the case of muscle necrosis and nephrosis (destruction of functional kidney tissue), more gradually over days, weeks or even months. Affected animals may initially appear normal (Spraker 1993), and even those which recover from acute problems, may die after weeks or months as a result of scar formation in the heart muscle (myocardium) (Jubb et al. 1993). Stress in cetaceans Despite a wealth of evidence from terrestrial species and birds, information on the physical and behavioural effects of stress in cetaceans, and particularly Mysticeti, is limited. However, stress-related changes in adrenal and thyroid hormone levels have been documented in cetaceans (reviews in Dierauf 1990; St. Aubin and Dierauf, 2001and Curry 1999). Chase-capture and restraint of six captive bottlenose dolphins (Tursiops truncatus) led to 100 per cent higher plasma cortisol levels than under calm-capture conditions. However, plasma cortisol measurements increased “even under the calmest conditions of capture”. Unlike most mammals, stressed cetaceans may manifest moderate cortisol elevations, although the physiological consequences of cortisol secretion in the body are maintained. Aldosterone levels on the other hand can increase substantially in cetaceans and may be a better indicator. Aldosterone moderates effective water and sodium resorption and elevated levels result in excessive sodium retention (e.g., Townsend 1999).
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Appendix II Colour plates ©Mark Vo
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Figure 13. Processing minke whales
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TROUBLED WATERS - Whale and Dolphin Conservation Society

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