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
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.