Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9125
Title: Demographic changes in Chinook salmon across the Northeast Pacific Ocean
Author: Jan Ohlberger, E. J. Ward, Bert Lewis, Daniel E. Schindler
Publication Year: 2018
Journal: Fish and Fisheries
Keywords: chinook,salmon,body size,trends,length,age at maturity
Abstract:

The demographic structure of populations is affected by life-history strategies and how these interact with natural and anthropogenic factors such as exploitation, climate change, and biotic interactions. Previous work suggests that the mean size and age of some North American populations of Chinook salmon (Oncorhynchus tshawytscha, Salmonidae) are declining. These trends are of concern because Chinook salmon are highly valued commercially for their exceptional size and because the loss of the largest and oldest individuals may lead to reduced population productivity. Using long-term data from wild and hatchery populations, we quantified changes in the demographic structure of Chinook salmon populations over the past four decades across the Northeast Pacific Ocean, from California through western Alaska. Our results show that wild and hatchery fish are becoming smaller and younger throughout most of the Pacific coast. Proportions of older age-classes have decreased over time in most regions. Simultaneously, the length-at-age of older fish has declined while the length-at-age of younger fish has typically increased. However, negative size trends of older ages were weak or non-existent at the southern end of the range. While it remains to be explored whether these trends are caused by changes in climate, fishing practices, or species interactions such as predation, our qualitative review of the potential causes of demographic change suggests that selective removal of large fish has likely contributed to the apparent widespread declines in average body sizes.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.
Describe the relationships between human activities and species recovery, rebuilding and sustainability.