Movements of Male California Sea Lions Captured in the Columbia River

Abstract

Abstract 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 ...