As delphinid populations become increasingly exposed to human activities we rely on our capacity to produce accurate abundance estimates upon which to base management decisions. This study applied mark–recapture methods following the Robust Design to estimate abundance, demographic parameters, and temporary emigration rates of an Indo-Pacific bottlenose dolphin (Tursiops aduncus) population off Bunbury, Western Australia. Boat-based photo-identification surveys were conducted year-round over three consecutive years along pre-determined transect lines to create a consistent sampling effort throughout the study period and area. The best fitting capture–recapture model showed a population with a seasonal Markovian temporary emigration with time varying survival and capture probabilities. Abundance estimates were seasonally dependent with consistently lower numbers obtained during winter and higher during summer and autumn across the three-year study period. Specifically, abundance estimates for all adults and juveniles (combined) varied from a low of 63 (95% CI 59 to 73) in winter of 2007 to a high of 139 (95% CI 134 to148) in autumn of 2009. Temporary emigration rates (γ') for animals absent in the previous period ranged from 0.34 to 0.97 (mean = 0.54; ±SE 0.11) with a peak during spring. Temporary emigration rates for animals present during the previous period (γ'') were lower, ranging from 0.00 to 0.29, with a mean of 0.16 (± SE 0.04). This model yielded a mean apparent survival estimate for juveniles and adults (combined) of 0.95 (± SE 0.02) and a capture probability from 0.07 to 0.51 with a mean of 0.30 (± SE 0.04). This study demonstrates the importance of incorporating temporary emigration to accurately estimate abundance of coastal delphinids. Temporary emigration rates were high in this study, despite the large area surveyed, indicating the challenges of sampling highly mobile animals which range over large spatial areas.
This study assessed the short‐term responses of humpback whales to whale‐watching vessels during their southward migration along the south coast of New South Wales (NSW), Australia. The behavior of pods was recorded from commercial whale‐watching vessels during tours and compared to pods observed in the absence of vessels from the shore in the same area. While some individuals showed obvious signs of horizontal avoidance, others approached vessels, initiating interactions. Calf pods were more sensitive to the presence of vessels than non‐calf pods. Dive times and the overall percentage of time whales spent submerged were higher in the presence of vessels, but respiration intervals did not differ. Some surface behaviors occurred less often in the presence of vessels. Whales' responses differed according to whether vessels were operating in accordance with regulations or not. Whales were more likely to avoid a vessel moving within the permitted 100 m approach limit than vessels outside the limit. Whales showed some behavioral changes when vessels operated in accordance with whale‐watching regulations, compared with whales in the absence of vessels. Pods that showed no obvious horizontal responses to vessels changed their diving and surface activity when compared with pods in the absence of vessels. Because the long‐term impacts of effects of vessels are unknown, management of the humpback whale‐watching industry should adopt a conservative approach. Improved knowledge of long‐term impacts of multiple exposures to vessels is required to inform management of the effects of whale‐watching.
Stress can increase an organism's susceptibility to disease. Thus, managing stress and its causes are important elements of captive care. Social factors such as changes in group dynamics, competition over resources, and unstable dominance hierarchies are potential stressors for highly social animals such as bottlenose dolphins (Tursiops sp). We present three case studies of mortality and illness in captive bottlenose dolphins and suggest that stress, resulting from social instability and ensuing aggressive interactions, is likely to have played a role in these health consequences. Stress is implicated by blood profiles, loss of appetite, and gastric ulcers, and social problems and instability are evident in the quantitative analysis of individual activity levels and association patterns. This is a unique study on marine mammals in that it demonstrates a correlation between quantitative behavioral indices and physiological measures of stress and health. Recommendations are made for the management of captive dolphins including regular quantitative assessment of behavior and associations and maintenance of appropriate groupings of age and sex classes. Behavioral records can be an important early indicator of health problems and may also serve as a useful tool for recognizing potentially stressful social changes and circumstances. Zoo Biol 21: 5-26, 2002.
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