Pacific Salmon in Estuaries: Questions, Approaches, and Some Findings

All anadromous salmonids, whether Atlantic (Salmo salar) or Pacific (Oncorhynchus spp.), must pass through estuaries as they move between freshwater and marine environments.  For juvenile Pacific salmon in estuaries, the primary research questions being addressed are the extent and benefits of estuarine use: which habitats are used, for how long, what benefits do fish derive (e.g., growth, survival), and are there species-, stock-, hatchery-wild, or life history differences in this use?  A related question is how contemporary estuaries compare to the historical template, how such alterations influences salmon use, and how to restore functional estuarine habitats.  We use the Columbia River estuary as a case study to document the approaches employed and describe major findings to these questions.  For example, habitat-specific sampling for juvenile salmon indicates a wide diversity of species- and stock-specific habitat use: some species (e.g., steelhead) use deep channel habitats and move rapidly through the estuary, while other species or stocks (e.g., some fall Chinook salmon) have extended residence in shallow estuarine habitats, where growth is rapid.  We also observe differences in estuarine use by hatchery and wild fish.  Although the Columbia River estuary is far from pristine, it supports a wide diversity of inter- and intra-specific habitat use by juvenile salmon.