Molecular analysis has become a powerful tool in cetacean ecology since it supports efficient conservation policies. Remote biopsy sampling is the most efficient method to obtain epithelial material for analysis purposes; however, as an intrusive technique it presents inherent costs, evidenced by behavioural reactions. Clarifying which factors influence these responses is essential to assess its impact and prevent possible long-term effects. For eleven winters, samples from humpback whales were collected in the Abrolhos Bank, the main breeding ground of this species in the western South Atlantic. We analysed the influence of several characteristics of the shot, vessels, groups and behaviour on the frequency and intensity of the whales' response. The majority of biopsied whales did not show any detectable response. Among those that responded, a low-level category of reaction was most frequent. The use of larger boats resulted in less intense responses. Responses were influenced by group size and behavioural state: large groups, which were involved in aggressive mating behaviour, reacted less frequently than smaller groups. Females with calves showed less intense reactions than non-lactating females. The behaviour of the animals prior to and during the boat approach also affected their response: resting whales responded more intensely than whales involved in social or travel activities. Comparison with previous studies confirmed that reactions vary in intensity according to location: whales biopsied in feeding grounds responded with more intensity than those in breeding grounds, which in turn responded more intensely than whales in migration. This study reinforces existing evidence that biopsy sampling is unlikely to have long-term effects and can thus continue to be used as one of the main tools to access information which is vital for conservation.
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