Estimating relative energetic costs of human disturbance to killer whales

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Anglet, France

Bioenergetics for management and conservation is a section of the Evolutionary dynamics and management application course at University of Pau and Pays de l’Adour (Anglet, France). In this course, 2nd

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Estimating relative energetic costs of human disturbance to killer whalesby Max Davesne and Quentin Marcon

Published by Charlotte Recapet the November 9, 2018 on 11:22 AM

Some predators are valued by humans, either for their ecological or aesthetic attributes, whereas others are viewed as pests. Increasingly, applied ecologists are asked to consider effects of anthropogenic activities on valued predators (Ormerod 2002). This complexity becomes especially apparent when dealing with conservation and management of cetaceans (whales, dolphins and porpoises), which are long-lived and elusive study animals. Cetaceans are also exposed to a variety of both targeted and incidental human activities in the marine environment. Nowadays, the boat traffic is always increasing as the « whalewatching » and that can cause some trouble as we don’t really knows if that disturb the ecosystem.

Boat approching a killer whale - Mike Baird - CC BY 2.0

This study examined the activities of ‘‘northern resident’’ killer whales (Orcinus orca) in Johnstone Strait, British Columbia, Canada, in July and August, from 1995 to 2002. Disturbance from boat traffic has been identified as a conservation concern for this population. This study aims to test whether or not the boat presence altered whale’s activities and want to estimate the energetic cost of this disturbance for the whales.

The time-activity budgets observed with respect to boat presence were converted to rough estimates of the energetic demand of free-ranging killer whales (Kriete 1995). Only Kriete’s data from Hyak (a 4733 kg adult male) and Yaka (a 2800 kg adult female) were used, rather than values for both adult and sub-adult subjects, because data on the sub-adult female were thought to be unreliable (Kriete 1995).

Behaviour change in the presence of boats and avoidance trend and decrease in the likelihood of rubbing in the presence of boats. From Williams et al. 2006.

There is an increase of 3% in global energetic budget and a decrease of rubbing budget from 17% to 3% and for the feeding from 13% to 10%. These lost feeding opportunities lead to a substantial (18%) estimated decrease in energy intake

This study analyzed the behavioral responses of orcas in the presence of boats. However, the model does not implement the variability between individuals. For example the stress induced by the presence of boats and the physiological differences that this may imply.

Studies demonstrated that many bird species respond to tourism presence by shortening feeding bouts (Burger et al. 1997; Galicia and Baldassarre 1997; Ronconi and St Clair 2002). This has been found also in numerous studies of terrestrial mammals, where feeding activity is easier to observe than in free-ranging cetaceans.

This study only covered one of three killer whale ecotypes. The results of this Northern residents study are difficult to extrapolate to other ecotypes (Southern residents and Migrants).

Cited study: Williams, R., Lusseau, D., and Hammond, P.S. (2006) Estimating relative energetic costs of human disturbance to killer whales (Orcinus orca). Biological conservation 133, 301-311.

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