Oregon City, OR, United States
Oregon City, OR, United States

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Wright B.E.,118 NE Vandenberg Avenue | Brown R.F.,118 NE Vandenberg Avenue
Fishery Bulletin | Year: 2011

We described the diet of the eastern stock of Steller sea lions (Eumetopias jubatus) from 1416 scat samples collected from five sites in Oregon and northern California from 1986 through 2007. A total of 47 prey types from 30 families were identified. The most common prey was Pacific hake (Merluccius productus), followed by salmonids (Oncorhynchus spp.), skates (Rajidae), Pacific lamprey (Lampetra tridentata), herrings (Clupeidae), rockfish (Sebastes spp.), and northern anchovy (Engraulis mordax). Steller sea lion diet composition varied seasonally, annually, and spatially. Hake and salmonids were the most commonly identified prey in scats collected during the summer (breeding season), whereas hake and skate were most common in the nonbreeding season. Continued research on Steller sea lion diet and foraging behavior in the southern extent of their range is necessary to address issues such as climate change, interaction with competing California sea lions, and predation impacts on valuable or sensitive fish stocks.

Johnson B.K.,401 Gekeler Lane | Coe P.K.,401 Gekeler Lane | Green R.L.,118 NE Vandenberg Avenue
Journal of Wildlife Management | Year: 2013

Understanding the relative effects of the many factors that may influence recruitment of ungulates is fundamental to managing their populations. Over the last 4 decades, average recruitment in some populations of elk (Cervus elaphus) in Oregon, USA declined from >50 to <20 juveniles per 100 females, and several competing hypotheses address these declines. We developed a priori models and constructed covariates spanning 1977-2005 from hunter-killed elk, elk population estimates, cougar harvest, and weather statistics to evaluate abiotic, bottom-up, and top-down factors that may explain annual variation and long-term trends of pregnancy, juveniles-at-heel in late autumn, and recruitment of juvenile elk in spring. In models of pregnancy status, August precipitation, age, and cougar index had positive effects, whereas previous year (t - 1) winter severity or winter precipitation(t-1) and elk density had negative effects. In models of juvenile-at-heel in late autumn, August precipitation, August precipitation(t-1), cougar index × elk density(t-1), and age had positive effects, whereas cougar index, elk density(t-1), and winter precipitation(t-1) had negative effects. Juvenile recruitment was best explained by positive effects of August precipitation(t-1), lactation rate, and cougar index × elk density(t-1) and negative effects of cougar index and elk density(t-1). Winter severity, precipitation, and temperature were not significant in explaining variation in elk recruitment. Annual variation in pregnancy, juvenile-at-heel, and recruitment was most influenced by August precipitation, whereas long-term trends in recruitment were most influenced by cougar densities with relatively weak effects of elk density. These results provide insight into causes of year-to-year and long-term trends of elk recruitment and provide a basis for more rigorous evaluation of factors affecting recruitment of elk. Copyright © 2012 The Wildlife Society.

Wright B.E.,118 NE Vandenberg Avenue | Tennis M.J.,Pacific States Marine Fisheries Commission | Brown R.F.,118 NE Vandenberg Avenue
Northwest Science | Year: 2010

There is growing concern in the Pacific Northwest over predation by migratory male California sea lions (Zalophus californianus) on threatened and endangered salmonid (Onchorynchus spp.) stocks. We compared movements of 14 male California sea lions known to have previously consumed salmonids at Bonneville Dam on the Columbia River or Willamette Falls on the Willamette River ("river"-types), with 12 animals of unknown foraging history ("unknown"-types). We captured sea lions in the Columbia River and instrumented them with satellite-linked transmitters during 2003-2004, 2004-2005, and 2006-2007. Transmitters operated for an average of 87.9 d (range 23-200 d) resulting in 14,539 location fixes. All 14 river-type animals returned to either Bonneville Dam or Willamette Falls whereas none of the 12 unknown-types exhibited this behavior. Minimum upstream and downstream transit times between the mouth of the Columbia River and Bonneville Dam (210 rkm) were 1.9 d and 1 d. Duration at the dam ranged from 2 d to 43 d. The median start dates of the southbound migration from the Columbia River to the breeding grounds for river-type and unknown-type sea lions were 20 May and 15 June, respectively. The maximum travel speed during migration was approximately 130 km d-1 (5.4 km h-1). Our results clearly show that not all California sea lions in the Columbia River prey on salmonids at Bonneville Dam or Willamette Falls. However, factors influencing recruitment into the upriver salmonid-foraging subpopulation are unknown. © 2010 by the Northwest Scientific Association. All rights reserved.

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