Watershed‐scale climate influences productivity of Chinook salmon populations across southcentral Alaska

• Published in: Global change biology Vol. 26; no. 9; pp. 4919 - 4936
• Main Authors: Jones, Leslie A., Schoen, Erik R., Shaftel, Rebecca, Cunningham, Curry J., Mauger, Sue, Rinella, Daniel J., St. Saviour, Adam
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-09-2020; John Wiley and Sons Inc
• Subjects: Abundance; Alaska; Animals; Bayes Theorem; Bayesian analysis; Chinook salmon; Climate Change; Closures; Conservation; Density dependence; Ecosystem; Environmental changes; Environmental effects; Environmental indicators; Fish conservation; Fish populations; Fisheries; Fisheries management; Fishery management; Freshwater; Freshwater fishes; Habitats; Incubation period; Individual rearing; Inland water environment; Inlets (waterways); Local communities; Marine fishes; Oncorhynchus tshawytscha; Population decline; Population density; population dynamics; Populations; Precipitation; Primary; Probability theory; Productivity; Rainfall; Rivers; Salmon; Spawning; Stream discharge; Stream flow; Streams; Watersheds; Alaska; United States > US; precipitation; fisheries; Chinook salmon; population dynamics; climate change
• DOI: 10.1111/gcb.15155
• EISSN: 1365-2486
• ISSN: 1354-1013

The ecosystems supporting Pacific salmon (Oncorhynchus spp.) are changing rapidly as a result of climate change and habitat alteration. Understanding how—and how consistently—salmon populations respond to changes at regional and watershed scales has major implications for fisheries management and habitat conservation. Chinook salmon (O. tshawytscha) populations across Alaska have declined over the past decade, resulting in fisheries closures and prolonged impacts to local communities. These declines are associated with large‐scale climate drivers, but uncertainty remains about the role of local conditions (e.g., precipitation, streamflow, and stream temperature) that vary among the watersheds where salmon spawn and rear. We estimated the effects of these and other environmental indicators on the productivity of 15 Chinook salmon populations in the Cook Inlet basin, southcentral Alaska, using a hierarchical Bayesian stock‐recruitment model. Salmon spawning during 2003–2007 produced 57% fewer recruits than the previous long‐term average, leading to declines in adult returns beginning in 2008. These declines were explained in part by density dependence, with reduced population productivity following years of high spawning abundance. Across all populations, productivity declined with increased precipitation during the fall spawning and early incubation period and increased with above‐average precipitation during juvenile rearing. Above‐average stream temperatures during spawning and rearing had variable effects, with negative relationships in many warmer streams and positive relationships in some colder streams. Productivity was also associated with regional indices of streamflow and ocean conditions, with high variability among populations. The cumulative effects of adverse conditions in freshwater, including high spawning abundance, heavy fall rains, and hot, dry summers may have contributed to the recent population declines across the region. Identifying both coherent and differential responses to environmental change underscores the importance of targeted, watershed‐specific monitoring and conservation efforts for maintaining resilient salmon runs in a warming world.
We investigated environmental effects on the productivity of 15 Chinook salmon populations in the Cook Inlet basin, Alaska. Across all populations, productivity declined with increased precipitation during the fall spawning and early incubation period and increased with above‐average precipitation during the juvenile rearing period. Above‐average stream temperatures during spawning and rearing periods had variable effects, including reduced productivity in many warmer streams and increased productivity in some colder streams. Productivity was also associated with regional indices of streamflow and ocean conditions, with high variability among populations.