Ultra-high foraging rates of harbor porpoises make them vulnerable to anthropogenic disturbance
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Summary. The question of how individuals acquire and allocate resources to maximize fitness is central in evolutionary ecology. Basic information on prey selection, search effort, and capture rates are critical for understanding a predator’s role in its ecosystem and for predicting its response to natural and anthropogenic disturbance. Yet, for most marine species, foraging interactions cannot be observed directly. The high costs of thermoregulation in water require that small marine mammals have elevated energy intakes compared to similar-sized terrestrial mammals . The combination of high food requirements and their position at the apex of most marine food webs may make small marine mammals particularly vulnerable to changes within the ecosystem [2–4], but the lack of detailed information about their foraging behavior often precludes an informed conservation effort. Here, we use high-resolution movement and prey echo recording tags on five wild harbor porpoises to examine foraging interactions in one of the most metabolically challenged cetacean species. We report that porpoises forage nearly continuously day and night, attempting to capture up to 550 small (3–10 cm) fish prey per hour with a remarkable prey capture success rate of >90%. Porpoises therefore target fish that are smaller than those of commercial interest, but must forage almost continually to meet their metabolic demands with such small prey, leaving little margin for compensation. Thus, for these “aquatic shrews,” even a moderate level of anthropogenic disturbance in the busy shallow waters they share with humans may have severe fitness consequences at individual and population levels.
Wisniewska , D M , Johnson , M , Teilmann , J , Rojano-Doñate , L , Shearer , J , Sveegaard , S , Miller , L A , Siebert , U & Madsen , P T 2016 , ' Ultra-high foraging rates of harbor porpoises make them vulnerable to anthropogenic disturbance ' Current Biology , vol 26 , no. 11 , pp. 1441-1446 . DOI: 10.1016/j.cub.2016.03.069
© 2016, Elsevier Ltd. This work is made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at www.sciencedirect.com / https://dx.doi.org/10.1016/j.cub.2016.03.069
This study was partly funded by the German Federal Agency for Nature Conservation (BfN) under the contract Z1.2-5330/2010/14 and the BfN-Cluster 7 “Effects of underwater noise on marine vertebrates.” D.M.W. and P.T.M. were also supported by the Danish National Research Foundation (FNU) and the Carlsberg Foundation, and M.J. was also supported by the Marine Alliance for Science and Technology Scotland (MASTS) and by a Marie Curie-Sklodowska award.
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