Interactions between life history and the environment on changing growth rates of Chinook salmon

Abstract

Fish in all the world’s oceans exhibit variable body size and growth over time, with some species or populations exhibiting long-term declines in size. These patterns can be caused by a range of biotic, abiotic, and anthropogenic factors and impact the productivity of harvested populations. Within a given species, individuals often exhibit a range of life-history strategies that may cause some groups to be buffered against change. One of the most studied declines in size at age has been in populations of salmon; Chinook salmon in the Northeast Pacific Ocean are the largest bodied salmon species and have experienced long-term declines in size. Using long-term monitoring data, we develop novel size and growth models to link observed changes in Chinook size to life history traits and environmental variability. Our results identify three distinct trends in size across the 48 stocks in our study. Differences among populations were correlated with ocean distribution, migration timing, and freshwater residence. We provide evidence that trends are driven by interannual variation in certain oceanographic processes and competition with pink salmon.

Identifying drivers of demographic rates in an at‐risk population of marine mammals using integrated population models

“…Future analyses using our model could account for such variation by incorporating interactions between SRKW pod and salmon abundance in the survival and fecundity regressions. An alternative explanation, not explored here, is that the relationship between salmon abundance and SRKW vital rates is changing over time because the whales' physiology and demography may be responding to changes in Chinook salmon growth, which have decreased in size and energy density over time (Buckner et al 2022; Lerner & Hunt 2023; Malick et al 2023; Ohlberger et al 2019; O'Neill et al 2014). Similarly, it is possible that these relationships could change because of bias in fishery indices resulting from redistribution of Chinook populations in the eastern‐Pacific (Shelton et al 2021).…”

Trends in Chinook salmon spawner abundance and total run size highlight linkages between life history, geography and decline

“…Chinook salmon are also getting smaller over time, with potentially serious implications for their demographic productivity and ability to support fisheries in the future (Ohlberger et al, 2018; Oken et al, 2021; Xu et al, 2020). These changes in size are likely driven by a multitude of factors including shifting climate and marine food webs, competition with pink salmon, and harvest; and much like survival trends these changes in size are shaped by life history, watershed of origin and marine distribution (Buckner et al, 2022). Many Chinook populations we evaluated have also experienced higher‐than‐average en route and pre‐spawn mortality in recent years (Bowerman et al, 2021; Doutaz et al, 2021; Teffer et al, 2018; Thompson et al, 2012).…”

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“…3. Numerous studies document biennial fluctuations in various aspects of salmon productivity (Kaeriyama et al 2000;Ishida et al 2002;Ruggerone and Irvine 2018;Ruggerone and Nielsen 2004;Cline et al 2019), including studies that focused on chum (Azumaya and Ishida 2000;Kaga et al 2013;Litz et al 2021), sockeye (Bugaev et al 2001;Ruggerone et al 2003Ruggerone et al , 2005Ruggerone et al , 2007Ruggerone et al , 2016Ruggerone et al , 2019McKinnell & Reichardt 2012;Connors et al 2020), Chinook salmon (Ruggerone and Goetz 2004;Kendall et al 2020;Anderson et al 2021;Claiborne et al 2021;Buckner et al 2023) and steelhead (Myers 2018).…”