Size-selective and sex-selective predation by brown bears on sockeye salmon (original) (raw)

Abstract

Breeding activity increases the vulnerability of many animals to predation, and such predation can affect the subset of animals successfully reproducing. To study the ways in which predation might affect the evolution of Pacific salmon, we measured the intensity and selectivity of predation by bears (primarily brown bears, Ursus arctos) on mature sockeye salmon (Oncorhynchus nerka) breeding in a series of small, spring-fed ponds and creeks near Pedro Bay, Alaska, from 1994 to 1998. Bears killed male salmon more often than females; males constituted 60% of the kills but only 35% of the salmon that died of senescence. The bears also killed fish that were larger, on average, than those dying of senescence (males: 462 vs 452 mm; females: 453 vs 443 mm). The level of predation varied greatly, from 4% (females) and 10% (males) in 1994 to 100% of both sexes in 1996 and 1997. The rate of predation also varied among habitats, being lower in larger ponds than in smaller, shallower ponds and the very small interconnecting creeks. Despite the intense and size-selective predation, the salmon in safer habitats (large ponds) were not larger than those in riskier habitats, and salmon densities were only slightly higher in the safer areas. Compared to a nearby population that experiences no bear predation (Woody Island), the male sockeye salmon from the Pedro Pond system had shallower bodies (i.e., less exposure in shallow water) for a given length, consistent with the hypothesis that selective predation can affect the extent of sexual dimorphism among populations. However, the average length at age for both males and females was greater in the Pedro Pond fish, indicating that selective factors besides predation affect length. Overall, the results indicate that bears can be an agent of natural selection within (and perhaps between) sockeye salmon populations, and predation can greatly affect reproductive success among individuals and years for the population as a whole.

Access this article

Log in via an institution

Subscribe and save

Buy Now

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Similar content being viewed by others

Author information

Authors and Affiliations

  1. Fisheries Research Institute, School of Fisheries, University of Washington, Box 357980, Seattle, WA 98195, USA e-mail: tquinn@fish.washington.edu, , , , , , US
    Thomas P. Quinn & Michael T. Kinnison

Authors

  1. Thomas P. Quinn
    You can also search for this author inPubMed Google Scholar
  2. Michael T. Kinnison
    You can also search for this author inPubMed Google Scholar

Additional information

Received: 6 April 1999 / Accepted: 1 June 1999

Rights and permissions

About this article

Cite this article

Quinn, T., Kinnison, M. Size-selective and sex-selective predation by brown bears on sockeye salmon.Oecologia 121, 273–282 (1999). https://doi.org/10.1007/s004420050929

Download citation