Abundance and survival rates of juvenile coho salmon (Oncorhynchus kisutch) in Prairie Creek, Redwood National Park

Brakensiek, Kyle

From the Abstract: "Abundance and survival rates of juvenile coho salmon in a northern California headwater stream [Prairie Creek] flowing through old-growth redwoods were estimated using paired summer/fall abundance surveys and a winter mark-recapture study using PIT-tagged fish. Calibrated snorkel/electrofishing abundance surveys were conducted in July and October of 1999 and were used to determine habitat utilization, change in abundance and survival rates by habitat type. Estimated summer survival rates were higher in runs and shallow pools than in riffles. I used Cormack-Jolly-Seber models to estimate period-specific winter survival rates and recapture probabilities based on resightings of PIT-tagged fish from three tag groups released during October and November of 1999, and March of 2000. Parameter estimates from the best supported models provided strong evidence of initial tagging mortality, and also suggested that apparent winter survival rates were affected by fish size. PIT-tagging mortality was suggested by strong differences between estimated period-specific survival rates for fish that had 'just been tagged' as compared to those that had been at large through a previous time period. Estimated apparent winter survival between November and March, for fish originally tagged in October, averaged 45.5 percent for juveniles of "standardized" size. Apparent survival rates were substantially lower for smaller fish and substantially higher for larger fish. Lower apparent survival rates for smaller juveniles may reflect a) size-dependent movement out of the study reach, b) chronic size-dependent mortality due to PIT-tagging, and (or) c) true size-dependent over-winter survival."

Abundance and survival rates of juvenile coho salmon (Oncorhynchus kisutch) in Prairie Creek, Redwood National Park

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