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Chapter 5 -- Anadromous Salmonids and Their Habitats (continued)

Sequence of Habitat Needs for Anadromous Life Cycles (continued)

Pre-Spawner Estuary Holding

Adult salmonids returning from the ocean, referred to as "pre-spawners", often remain in the estuary while waiting for favorable flows for upstream migration. Predation on anadromous salmonid pre-spawners by seals is probably significant. At present, the estuary provides pre-spawners with little cover from predation. In low water years, 25 to 30% of the returning steelhead show bite marks from seals (Waldvogel personal communication 1996). Because steelhead swim faster than chinook and coho, they are more likely to escape from an encounter with a marine mammal predator, which accounts for the greater number of bite marks on steelhead. The implication is that predation is higher on salmon due to their slower swimming speed.

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