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Pacific Coast estuaries provide important rearing habitats leading to improved growth and survival for juvenile chinook salmon. However, research has suggested that juvenile salmon have little use for estuarine habitats in the Columbia River. To further understand salmonid recovery needs in estuaries, I compared historical and contemporary life history patterns in the estuary to determine if there has been a change in the importance of the Columbia River estuary to juvenile chinook salmon. Historical data sources provided evidence of diverse estuarine life history strategies for juvenile chinook salmon (retrieved from fish surveys and scale analysis), including differences in time of estuarine entry, growth, and residency. In contrast, contemporary estuarine salmon populations, which are dominated by hatchery-reared juveniles, had highly uniform life-history characteristics; most fish entered the estuary at similar times and sizes and remained for short time periods. The inability to distinguish the origin of unmarked individuals precluded a separate life-history assessment for contemporary wild chinook juveniles. Nonetheless, the results suggest that life-history diversity has declined in response to anthropogenic pressures that directly affect salmonid populations: harvest, hatcheries, habitat loss, and hydropower dams. Because estuarine life histories contribute to the resilience of salmonid populations, recovery efforts should address life history diversity needs in the Columbia River estuary. |
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