Abundances and Feeding Habits of Pinnipeds in the Rogue River, Oregon

This study examines the abundance and feeding habits of three pinniped species found seasonally in the Rogue River, Oregon: the California sea lion (Zalophus californianus); the Steller (or Northern) sea lion (Eumetopias jubatus); and the Pacific harbor seal (Phoca vitulina richardsi). Peak abundance of pinnipeds occurred during the spring, which coincided with the seaward migration of steelhead (Salmo gairdneri) and overlapped the upriver migration of spring chinook (Oncorhyncus tshawytscha). All three pinnipeds fed most heavily on Pacific lamprey (Lampetra tridentatus), as indicated by visual observation of prey species brought to the surface, seal scats collected at river haul-outs, and examination of gastrointestinal tracts. The most preyed upon salmonid was the seaward migrating steelhead. At observed population levels and predation rates, pinnipeds did not constitute a major threat to Rogue River salmonid stocks.