Seasonal Patterns of Predation on Juvenile Pacific Salmon by Anadromous Cutthroat Trout in Puget Sound

• Published in: Transactions of the American Fisheries Society
• Main Authors: Duffy, Elisabeth J., Beauchamp, David A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2008
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Pink salmon
• Online Access: http://dx.doi.org/10.1577/t07-049.1; https://afspubs.onlinelibrary.wiley.com/doi/pdf/10.1577/T07-049.1

Abstract In the marine environment, Pacific salmon Oncorhynchus spp. suffer the greatest natural losses during early marine residence, and predation is hypothesized to be the key source of mortality during this life history stage. In the face of recent declines in Puget Sound salmon populations, our goal was to determine the extent of predation mortality on salmon during early marine life. In spring and summer of 2001‐2003, we caught juvenile salmon and potential predators at nearshore areas in northern and southern regions of Puget Sound, Washington. We focused on the potential predation impact of coastal cutthroat trout O. clarkii clarkii , which were caught in low but consistent numbers in both regions and were the most abundant large‐bodied potential predators of juvenile salmon in our catches. Cutthroat trout consumed a diverse and dynamic array of diet items and became increasingly piscivorous with increasing fork length above 140 mm. Cutthroat trout consumed a greater biomass of Pacific herring Clupea pallasii than any other prey fish species, but juvenile salmon were particularly important prey between April and June, making up greater than 50% of the fish prey consumed. Cutthroat trout exhibited size‐selective predation, eating salmon that were smaller than the average size of conspecific prey available in the environment. For a hypothetical size‐structured population of 1,000 cutthroat trout, pink salmon O. gorbuscha and chum salmon O. keta contributed the greatest number of salmon to the diet but Chinook salmon O. tshawytscha contributed the greatest salmonid biomass. On an order‐of‐magnitude basis, these predation estimates represented a relatively minor amount of early marine mortality for Chinook salmon and lower rates for the other salmon species. Conversely, juvenile salmon contributed significantly to the spring energy budget for cutthroat trout in Puget Sound.