How harbor seals (Phoca vitulina) pursue schooling herring
Only a few reports have described how pinnipeds hunt schooling fish. However, we had the opportunity to systematically observe captive harbor seals hunting a school of herring in a shallow enclosure during daylight. The seals actively pursued the fish, mostly changing from one side of the school to the other, swimming in a supine position close to the water surface. They were often found swimming rapidly down to the fish out of this position. When hunting in the vertical, the seals mostly adopted a dorsal body posture relative to the school. They swam and attacked the school in a supine orientation when approaching from the water surface and swam in a prone orientation when approaching from below. They even maintained this relative body position during turning movements. These phenomena suggest that the seals were constantly keeping the school in their large dorsal visual field, which favors visual hunting during daylight and in clear waters. When interacting with the school, the school mostly split asymmetrically, and the seals were following preferably a smaller number of fish afterwards. Successful prey catch was only observed, when a small group or a single herring had been separated, thus the seals probably avoided the confusion effect of the school. In conclusion, we provide detailed insight in seals pursuing schooling prey, thereby extending previous reports and confirming speculations as well as brief observations.
KeywordsHunting strategy Visual hunting Prey Foraging Pinniped
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- Bjorge, A., Thompson, D., Hammond, P., Fedak, M., Bryant, E., Aarefjord, H., Roen, R., Olsen, M., 1995. Habitat use and diving behaviour of harbour seals in a coastal archipelago in Norway. In: Blix, A.S., Walloe, L., Ulltang, O. (Eds.), Whales, Seals, Fish and Man. Elsevier Science, Amsterdam, pp. 211–223.Google Scholar
- Bonnot, P., 1932. A note on the fishing of the California sea lion. Calif. Fish Game 18, 98–99.Google Scholar
- Hanke, W., Römer, R., Dehnhardt, G., 2006. Visual fields and eye movements in a harbor seal (Phoca vitulina). Vis. Res. 46, 2804–2814.Google Scholar
- Krause, J., Ruxton, G.D., 2002. Living in Groups. Oxford University Press, Oxford. Lavigne, D.M., Bernholz, G.D., Ronald, K., 1977. Functional aspects of pinniped vision. In: Functional Anatomy of Marine Mammals. Academic Press, London, New York, pp. 135–173.Google Scholar
- Marshall, G.J., 1998. Crittercam: an animal-borne imaging and data logging system. Mar. Technol. Soc.J. 32, 11–17.Google Scholar
- Olsen, M., Bjorge, A., 1995. Seasonal and regional variations in the diet of harbour seal in Norwegian waters. In: Blix, A.S., Walloe, L., Ulltang, O. (Eds.), Whales, Seals, Fish and Man. Elsevier Science, Amsterdam, pp. 271–285.Google Scholar
- Weiffen, M., Möller, B., Mauck, B., Dehnhardt, G., 2006. Effect of water turbidity on the visual acuity of harbor seals (Phoca vitulina). Vis. Res. 46, 1777–1783.Google Scholar