Evidence that Marine Temperatures Influence Growth and Maturation of Western Alaskan Chinook Salmon

Abstract

Chinook Salmon Oncorhynchus tshawytscha from western Alaska have experienced recent declines in abundance, size, and age at maturity. Declines have led to hardships for the region's subsistence and commercial salmon harvesters, prompting calls to better understand factors affecting the life history of these populations. Western Alaskan Chinook Salmon are thought to spend their entire marine residency in the Bering Sea. The Bering Sea ecosystem demonstrates high interannual variability that is largely driven by the annual extent of sea ice. However, warming is expected to supersede interannual variability in the next several decades as a consequence of climate change. We investigated the influence of sea surface temperatures (SSTs) on the life history of western Alaskan Chinook Salmon by using information from two regional populations subject to long‐term monitoring. We found strong correlations between early marine growth and SSTs. Warmer SSTs appeared to lead to a younger age at maturity, largely through the vector of augmented growth. However, we also present evidence that warmer SSTs may additionally decrease the average age of male recruits through reduced growth thresholds for early male maturation. Our results suggest that the anticipated warming of the Bering Sea will lead to higher early marine growth and a younger average age of maturation for western Alaskan Chinook Salmon.

Interactions between Marine Growth and Life History Diversity of Steelhead from the Situk River, Alaska

“…However, similar to studies of growth and age at maturity in Chinook Salmon (Siegel et al. , ), we were not able to distinguish this “bottom‐up” environmental hypothesis from an alternative hypothesis that variation in mortality rates of older fish could drive temporal patterns in age at maturity of salmonids (e.g., Ohlberger et al. ).…”

Signals of large scale climate drivers, hatchery enhancement, and marine factors in Yukon River Chinook salmon survival revealed with a Bayesian life history model

“…Siegel et al. () provide a potential mechanistic explanation for this relationship, finding a positive correlation between marine temperature and growth of other Chinook salmon populations in this region and suggesting this may result in reduced risk of size‐selective marine mortality (Farley, Murphy, Moss, Feldmann, & Eisner, ; Murphy et al., ). However, our results indicating a positive association between marine survival and temperature for these Chinook salmon populations in the northern portion of Alaska, contrast with findings by Sharma and Liermann () of a net negative association between SST and recruitment of west coast Chinook salmon between Southeast Alaska and Oregon.…”

“…Marine environmental covariates quantified a wide range of oceanographic, atmospheric, climatic, and biotic factors (Table , Supporting Information Figure S1). Oceanographic processes included the timing of ice retreat in the southeastern Bering Sea, given implications for the timing and biomass of the spring plankton bloom and trophic structure of the Bering Sea (Hunt et al., , ), and winter SST at the Pribilof Islands given its observed influence on western Alaska Chinook salmon growth (Mcphee, Leon, Wilson, Siegel, & Agler, ; Siegel, Mcphee, & Adkison, ) and correlation with recruitment of several groundfish species (Mcfarlane, King, & Beamish, ) as potential prey. Covariates related to the marine atmosphere included SLP and wind stress during the first winter at sea given their observed importance for ecosystem productivity, and the duration of May–early June wind vectors in the southern Bering Sea (at the NOAA‐PMEL M2 OA mooring: 56.87°N, −164.06°W) that promote favorable feeding conditions for larval pollock (Megrey & Hinckley, ).…”

“…given implications for the timing and biomass of the spring plankton bloom and trophic structure of the Bering Sea (Hunt et al, 2002(Hunt et al, , 2011, and winter SST at the Pribilof Islands given its observed influence on western Alaska Chinook salmon growth (Mcphee, Leon, Wilson, Siegel, & Agler, 2016;Siegel, Mcphee, & Adkison, 2017) and correlation with recruitment of several groundfish species (Mcfarlane, King, & Beamish, 2000) as potential prey.…”

“…duction have positive survival benefits for juvenile Chinook salmon.The ecological mechanisms and agents of selection underpinning the association between earlier break-up and survival are unknown, but presumably earlier spring break up results in reduced starvation mortality in early spring, enhanced growth opportunity affording increased survival at ocean entry, beneficial shifts in outmigration timing, or a combination of the above. Although data on how migration timing varies among years is limited for this system, there is mounting evidence that variation in the timing of Chinook salmon ocean entry can have large implications for early marine survival(Satterthwaite et al, 2014;Scheuerell, Zabel, & Sandford, 2009).The positive association between Chinook salmon survival during the first winter at sea and SST at the Pribilof Islands(Figure 4) suggests that warmer temperatures foster enhanced productivity of these two Chinook salmon stocks Siegel et al (2017). provide a potential mechanistic explanation for this relationship, finding a positive correlation between marine temperature and growth of other Chinook salmon populations in this region and suggesting this may result in reduced risk of size-selective marine mortality(Farley, Murphy, Moss, Feldmann, & Eisner, 2009;Murphy et al, 2013).…”