Scavenging by Brown Bears, Ursus arctos, and Glaucous-winged Gulls, Larus glaucescens, on adult Sockeye Salmon, Oncorhynchus nerka

Citation
Tp. Quinn et Gb. Buck, Scavenging by Brown Bears, Ursus arctos, and Glaucous-winged Gulls, Larus glaucescens, on adult Sockeye Salmon, Oncorhynchus nerka, CAN FIELD-N, 114(2), 2000, pp. 217-223
Citations number
27
Categorie Soggetti
Environment/Ecology
Journal title
CANADIAN FIELD-NATURALIST
ISSN journal
00083550 → ACNP
Volume
114
Issue
2
Year of publication
2000
Pages
217 - 223
Database
ISI
SICI code
0008-3550(200004/06)114:2<217:SBBBUA>2.0.ZU;2-U
Abstract
Adult Pacific salmon that have returned to spawn in streams are vulnerable to predation and are also susceptible to scavenging after death by animals such as bears and gulls. The distinction between predation and scavenging i s important in furthering our understanding of the behavior of bears and gu lls as well as the population dynamics of salmon. To understand better the role of these animals, we tagged freshly dead Sockeye Salmon, both spent an d ripe, and recorded instances of scavenging on a small stream in southwest ern Alaska. Both Brown Bears and Glaucous-wing:ed Gulls scavenged about 20 - 30% of the salmon <1 day of tagging (1-2 days after death). With respect to gender, bears exhibited a preference for male salmon, gulls for females. With respect to spawning status, both showed a preference for ripe female salmon, a pattern that gulls also showed for male salmon. The proportion of salmon carcasses scavenged by bears increased to about 70% within 7 days o f tagging, and many carcasses were partly scavenged on more than one occasi on. Because of the high rate of bear scavenging and the tendency for this t o mask scavenging by gulls, it was difficult to quantify gull scavenging ac curately beyond 2-3 days. Bears tended to eat the cranial region of males a nd the bellies of females. The proportion of carcasses scavenged by bears v aried greatly over the course of the spawning run, but was generally high e arly and late in the run when there were fewer live and dead salmon availab le.