Density-dependent predation by brown bears (Ursus arctos) on sockeye salmon (Oncorhynchus nerka)

2003 ◽  
Vol 60 (5) ◽  
pp. 553-562 ◽  
Author(s):  
T P Quinn ◽  
S M Gende ◽  
G T Ruggerone ◽  
D E Rogers
Keyword(s):  
Population Dynamics ◽  
Sockeye Salmon ◽  
Ursus Arctos ◽  
Oncorhynchus Nerka ◽  
Brown Bears ◽  
Density Dependent ◽  
Salmon Population ◽  
Average Proportion ◽  
Stream Size ◽  
Salmon Carcasses

The number of sockeye salmon (Oncorhynchus nerka) killed by brown bears (Ursus arctos) in 13 streams over more than a decade in southwestern Alaska was best explained by an asymptotic increase to about 3000 salmon killed per stream per year as salmon density increased to 10 000 fish·ha–1 of stream. Divergence from this pattern at some streams probably reflected variation in the number of bears using the stream (which we did not determine) and variation in salmon biomass consumed per fish killed. Daily surveys at one creek over 11 years revealed about 100–130 salmon killed per day, ranging from a few to over 600. Higher proportions of the available salmon were killed early and late in the season, when densities were low. Thus the number of salmon killed within and among years increased with salmon abundance but at a declining rate, and the proportion killed generally decreased. Our previous work indicated that the average proportion of salmon killed among streams was controlled mostly by stream size, affecting the ability of bears to catch salmon. These findings are important for understanding the effects of bears on salmon population dynamics and their role in the transport of nutrients from salmon carcasses.

Selective predation by brown bears (Ursus arctos) foraging on spawning sockeye salmon (Oncorhynchus nerka)

2000 ◽  
Vol 78 (6) ◽  
pp. 974-981 ◽  
Author(s):  
Gregory T Ruggerone ◽  
Renn Hanson ◽  
Donald E Rogers
Keyword(s):  
Sockeye Salmon ◽  
Ursus Arctos ◽  
Oncorhynchus Nerka ◽  
The Body ◽  
Upstream Migration ◽  
Selective Predation ◽  
Bristol Bay ◽  
Brown Bears ◽  
Risk Of Predation ◽  
Salmon Population

Selective predation by and predation rates of brown bears (Ursus arctos) foraging on spawning sockeye salmon (Oncorhynchus nerka) in a small shallow creek in the Wood River lake system near Bristol Bay, Alaska, were quantified during 1986 and 1990–1992. Bears killed a high proportion of spawning salmon when few salmon entered the creek (92% of 505 fish) and a much smaller proportion when the spawning population reached a historical high (16% of 15 631 fish). Selective predation on salmon that differed in length, sex, and spawning condition was measured by tagging salmon at the mouth of the creek immediately prior to upstream migration and then recovering dead tagged fish during daily surveys of the entire creek. The relative frequencies of large, medium-sized, and small salmon killed by bears indicated that the risk of predation was more than 150% greater for large than for small salmon. A higher proportion of the male salmon population was killed and a greater proportion of male bodies were consumed than female salmon. Selectivity for male salmon increased as the spawning season progressed, possibly because male salmon weakened earlier and lived longer in a weakened state than female salmon. Male salmon were attacked mostly along the dorsal hump area, whereas female salmon tended to be attacked along the abdomen, where eggs could be exposed. Bears selectively killed female salmon prior to spawning during 1 of the 3 years, but only 6.1–7.8% of the female spawning populations were killed prior to spawning. These data support the hypothesis that selective predation by bears may influence the body morphology of spawning salmon.

Selective predation by brown bears (Ursus arctos) foraging on spawning sockeye salmon (Oncorhynchus nerka)

2000 ◽  
Vol 78 (6) ◽  
pp. 974-981 ◽  
Author(s):  
Gregory T. Ruggerone ◽  
Renn Hanson ◽  
Donald E. Rogers
Keyword(s):  
Sockeye Salmon ◽  
Ursus Arctos ◽  
Oncorhynchus Nerka ◽  
Selective Predation ◽  
Brown Bears

Inferring sockeye salmon (Oncorhynchus nerka) population dynamics and water quality changes in a stained nursery lake over the past ∼500 years

2004 ◽  
Vol 61 (7) ◽  
pp. 1235-1246 ◽  
Author(s):  
Irene Gregory-Eaves ◽  
Bruce P Finney ◽  
Marianne SV Douglas ◽  
John P Smol
Keyword(s):  
Population Dynamics ◽  
Sockeye Salmon ◽  
Environmental Changes ◽  
Oncorhynchus Nerka ◽  
The Past ◽  
The North ◽  
Salmon Population ◽  
High Concentrations ◽  
The North Pacific ◽  
Multiproxy Approach

Historical and paleolimnological studies have demonstrated that environmental changes in the North Pacific can strongly affect sockeye salmon (Oncorhynchus nerka) abundances. Whether these marine shifts would be influential on sockeye salmon from all lake types, however, has not yet been studied. This study represents the first paleolimnological analysis of past sockeye salmon population dynamics in a stained nursery lake (Packers Lake, Alaska). We adopted a multiproxy approach to determine whether salmon-derived nutrients (inferred from δ15N) would be available for algal uptake (inferred from the diatom species responses) in this stained lake, as high concentrations of humics and iron are known to sequester phosphorus. The strong degree of coherency between δ15N and diatoms, however, suggests that salmon-derived nutrients were bioavailable and enhanced productivity. Overall, our indicators responded to changes in sockeye salmon abundances and volcanic ashfalls over the past ∼500 years. In a section of the core unaffected by tephras (AD ∼1770–1882), our record suggests that the number of sockeye salmon spawners fluctuated widely. Comparison of temporal shifts in inferred sockeye salmon abundances from Packers Lake with other clearwater nursery lakes reveals a broadly consistent pattern, likely influenced by past climatic changes.

Prevalence and patterns of scavenging by brown bears (Ursus arctos) on salmon (Oncorhynchus spp.) carcasses

2020 ◽  
pp. 9-17 ◽  
Author(s):  
A.E. Lincoln ◽  
A.J. Wirsing ◽  
T.P. Quinn
Keyword(s):  
Sockeye Salmon ◽  
Ursus Arctos ◽  
Pacific Salmon ◽  
Oncorhynchus Nerka ◽  
Prey Consumption ◽  
Nutritional Intake ◽  
Total Consumption ◽  
Brown Bears ◽  
Factors Affecting ◽  
Scavenging Rates

Scavenging, an underappreciated mechanism of prey consumption for many predators, can contribute substantially to nutritional intake. Facultative scavengers such as brown bears (Ursus arctos Linnaeus, 1758) may both kill and scavenge Pacific salmon (genus Oncorhynchus Suckley, 1861), though the extent of scavenging and factors affecting this behavior are unclear. We tagged 899 sockeye salmon (Oncorhynchus nerka (Walbaum in Artedi, 1792)) carcasses and placed them on streambanks over 5 years at multiple sites in southwestern Alaska (USA) where brown bears annually prey on spawning sockeye salmon. Examination of carcasses revealed overall scavenging rates of 15% after 1 day and 54% after 3 days. Scavenging rate varied by site and year and increased throughout the salmon run. Contrary to predictions, scavenging was more frequent in senescent or bear-killed carcasses than ripe carcasses. Carcass consumption ranged from minimal to almost complete; body and brain tissues were most frequently consumed after 3 days (68% and 63% of carcasses, respectively). We also documented secondary scavenging (i.e., tissue consumption on two separate events) and delayed scavenging (i.e., scavenging observed after 3 days but not 1 day). Taken together, the results indicated that scavenging in these streams contributes significantly to total consumption of salmon by bears, with ramifications for other components of these salmon-dependent ecosystems.

Complementary use of motion-activated cameras and unbaited wire snares for DNA sampling reveals diel and seasonal activity patterns of brown bears (Ursus arctos) foraging on adult sockeye salmon (Oncorhynchus nerka)

2014 ◽  
Vol 92 (10) ◽  
pp. 893-903 ◽  
Author(s):  
Thomas P. Quinn ◽  
Aaron J. Wirsing ◽  
Brendan Smith ◽  
Curry J. Cunningham ◽  
Jason Ching
Keyword(s):  
Sockeye Salmon ◽  
Ursus Arctos ◽  
Foraging Ecology ◽  
Prey Availability ◽  
Oncorhynchus Nerka ◽  
Activity Patterns ◽  
Diel Activity ◽  
Brown Bears ◽  
Hair Samples ◽  
Hair Snares

The seasonal and diel movements of predators to take advantage of shifts in prey availability are fundamental elements of their foraging ecology, and also have consequences for the prey populations. In this study, we used complementary noninvasive techniques (motion-activated cameras and hair snares) to investigate seasonal and diel activity of brown bears (Ursus arctos L., 1758) along six proximate streams supporting spawning populations of sockeye salmon (Oncorhynchus nerka (Walbaum in Artedi, 1792)) in southwestern Alaska. Camera records over 3 years showed a rapid increase in bear activity around the time salmon arrived in the streams, with differences among streams corresponding to differences in salmon phenology. Bears were active throughout the day and night, but there were clear crepuscular peaks when camera data were pooled. When wire snares (to collect hair samples) were paired with cameras, the data showed similar seasonal patterns, but each technique detected bears missed by the other. Roughly equal numbers of bears left hair but no camera image, and images but no hair, at paired sites. Taken together, the results indicated a close correspondence between bear activity and salmon timing, differences in diel timing among streams, and the complementarity of data obtained by motion-activated cameras and hair snares.

Inversely density-dependent natal dispersal in brown bears Ursus arctos

Oecologia ◽  
2006 ◽  
Vol 148 (2) ◽  
pp. 356-364 ◽  
Author(s):  
Ole-Gunnar Støen ◽  
Andreas Zedrosser ◽  
Solve Sæbø ◽  
Jon E. Swenson
Keyword(s):  
Ursus Arctos ◽  
Natal Dispersal ◽  
Brown Bears ◽  
Density Dependent

scholarly journals Stable isotopes reveal variation in consumption of Pacific salmon by brown bears, despite ready access in small streams

2020 ◽  
Author(s):  
HyeJoo Ro ◽  
Jennifer H. Stern ◽  
Aaron J. Wirsing ◽  
Thomas P. Quinn
Keyword(s):  
Stable Isotope ◽  
Sockeye Salmon ◽  
Ursus Arctos ◽  
Pacific Salmon ◽  
Brown Bears ◽  
Small Streams ◽  
Hair Samples ◽  
Wide Range ◽  
Stable Isotope Signatures ◽  
Ready Access

Brown bears Ursus arctos consume a wide range of organisms, including ungulates and plants, but Pacific salmon Oncorhynchus spp. are especially important to their diet where their ranges overlap. Although some bears minimize antagonistic encounters with other bears or infanticide by avoiding streams where salmon spawn, studies generally assume that bears with ready access to salmon feed heavily on them. To test this assumption, and the hypothesis that male bears would feed more heavily on salmon than females (owing to their sexual size dimorphism), we collected hair samples from brown bears using barbed wire on six small tributaries of Lake Aleknagik, Alaska where adult sockeye salmon O. nerka are readily accessible and frequently consumed by bears. Analysis of DNA distinguished among the different bears leaving the hair samples, some of which were sampled multiple times within and among years. We assessed the contribution of salmon to the diet of individual bears using carbon and nitrogen stable isotope signatures. The 77 samples analyzed, from 31 different bears over four years, showed isotopic ratios consistent with reliance on salmon, but the wide range of isotopic signatures included values suggesting variable, and in one case considerable, use of terrestrial resources. Stable isotope signatures did not differ between male and female bears, nor did they differ between two sides of the lake, despite marked differences in sockeye salmon density. The hair samples were collected when salmon were present, so there was some uncertainty regarding whether they reflected feeding during the current or previous season. Notwithstanding this caveat, the results are consistent with the hypothesis that salmon were sufficiently available to provide food for the bears, and that the considerable isotopic variation among bears with access to salmon reflected their age, status, and behavior.

scholarly journals Sockeye salmon population dynamics over the past 4000 years in Upper Russian Lake, south-central Alaska

2018 ◽  
Vol 60 (1) ◽  
pp. 67-75
Author(s):  
Molly D. McCarthy ◽  
Daniel J. Rinella ◽  
Bruce P. Finney
Keyword(s):  
Population Dynamics ◽  
Sockeye Salmon ◽  
The Past ◽  
South Central ◽  
Salmon Population

Density-Dependent, Trophic Level Responses to an Introduced Run of Sockeye Salmon (Oncorhynchus nerka) at Frazer Lake, Kodiak Island, Alaska

1988 ◽  
Vol 45 (5) ◽  
pp. 856-867 ◽  
Author(s):  
G. B. Kyle ◽  
J. P. Koenings ◽  
B. M. Barrett
Keyword(s):  
Trophic Level ◽  
Sockeye Salmon ◽  
Inverse Relationship ◽  
Oncorhynchus Nerka ◽  
Density Dependent ◽  
Kodiak Island ◽  
Egg Plant ◽  
Threshold Length ◽  
Average Body Length ◽  
Average Body

Sockeye salmon (Oncorhynchus nerka) have developed into a major run at Frazer Lake, Kodiak Island, Alaska, reaching over 600 000 adults 34 yr after the first egg-plant in 1951. In the last nine years (1978–86), escapements have averaged over 250 000 with a record high of 486 000 adults in 1985. The increase in escapements were inversely related to seasonal macrozooplankton densities (p < 0.05; r2 = 0.42) but directly correlated with increases in the cladoceran to copepod ratio (p < 0.001). In addition, the average body length of the smallest macrozooplanker (Bosmina) has shifted below the observed threshold length of 0.40 mm for juvenile sockeye prey. We also found an inverse relationship between greater parental escapements and age 1. smolt length (p < 0.01; r2 = 0.75). Small-sized smolts produced from a density-dependent rearing environment indicate that spawning capacity equals or exceeds rearing capacity. Juvenile recruits from larger escapements (~400 000) exerted a controlling, density-dependent influence on the secondary trophic level which drastically reduced subsequent adult returns. Moreover, adverse trophic level changes, particularly after the largest escapements, also appeared to reduce the rearing efficiency for lower densities of juveniles, as subsequent smolt sizes from smaller escapements were less than expected. Thus, these findings not only provide a rationale for suggesting that fewer spawners would provide recruits more closely matching the rearing capacity of this lake, but also provide empirical evidence for the potential adverse density-dependent effects of large escapements.

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