Implications of a warming eastern Bering Sea for Bristol Bay sockeye salmon

Abstract

Farley, E. V., Starovoytov, A., Naydenko, S., Heintz, R., Trudel, M., Guthrie, C., Eisner, L., Guyon, J. R. 2011. Implications of a warming eastern Bering Sea for Bristol Bay sockeye salmon. – ICES Journal of Marine Science, 68: 1138–1146. Overwinter survival of Pacific salmon (Oncorhynchus sp.) is believed to be a function of size and energetic status they gain during their first summer at sea. We test this notion for Bristol Bay sockeye salmon (O. nerka), utilizing data from large-scale fisheries and oceanographic surveys conducted during mid-August to September 2002–2008 and from February to March 2009. The new data presented in this paper demonstrate size-selective mortality for Bristol Bay sockeye salmon between autumn and their first winter at sea. Differences in the seasonal energetic signatures for lipid and protein suggest that these fish are not starving, but instead the larger fish caught during winter apparently are utilizing energy stores to minimize predation. Energetic status of juvenile sockeye salmon was also strongly related to marine survival indices and years with lower energetic status apparently are a function of density-dependent processes associated with high abundance of juvenile sockeye salmon. Based on new information regarding eastern Bering Sea ecosystem productivity under a climate-warming scenario, we hypothesize that sustained increases in spring and summer sea temperatures may negatively affect energetic status of juvenile sockeye salmon, potentially resulting in increased overwinter mortality.

Marine growth patterns of southern British Columbia chum salmon explained by interactions between density-dependent competition and changing climate

“…Nevertheless, other studies have indicated that salmon that have poor early growth are less likely to survive (Beamish et al 2004b;Farley et al 2011;Jonsson et al 2011). Larger salmonids may be better able to avoid predation (Beamish and Mahnken 2001) and survive better than small salmonids when prey resources are low due to increased lipid stores (Farley et al 2007(Farley et al , 2011.…”

“…Changes in observed total scale size were associated with changes in NPGO, particularly when PDO was negative, reflecting cooler sea surface temperatures (Mantua and Hare 2002) that increased coastal primary productivity (Di Lorenzo et al 2008;Kilduff et al 2015). Metabolic costs decline when water is cooler, resulting in faster growth, especially when coupled with an increase in food availability (Farley et al 2011;Siddon et al 2013). In contrast, warmer sea surface temperature (i.e., positive PDO) increases metabolic costs and, coupled with lower food availability, may decrease body sizes of returning salmon (Hinch et al 1995).…”

“…Density-dependent competition for common prey resources is presumably greatest for the three most abundant species, chum (Oncorhynchus keta), pink (Oncorhynchus gorbuscha), and sockeye salmon (Oncorhynchus nerka), each of which is primarily planktivorous (Davis et al 2004;Kaeriyama et al 2004;Ruggerone et al 2012). Climate variation affects salmon growth (Helle and Hoffman 1998;Jeffrey et al 2017), as the bioenergetics of salmonids can be altered by changes in the amount and composition of salmon prey (Beauchamp 2009) in conjunction with changes in ocean temperature and productivity (Hare and Mantua 2000;Farley et al 2011;Siddon et al 2013). Nevertheless, the relative importance of competition and climate variation and interactions between them remains uncertain for many Pacific salmon populations.…”

“…Weakening of subpolar and subtropical gyres decreases primary productivity (Schwing et al 2002;Behrenfeld et al 2006;Di Lorenzo et al 2008) and has been associated with decreased salmon abundance (Kilduff et al 2015), growth (Wells et al 2006), and body size (Jeffrey et al 2017) due to changes in prey species (Kaeriyama et al 2004). As a result of lower metabolic costs (Farley et al 2011;Siddon et al 2013), cooler temperatures have been shown to increase the growth potential of Pacific salmonids. Large-scale changes in ocean circulation and temperature are represented by climate indices such as Pacific Decadal Oscillation (PDO; related to sea surface temperature anomalies, linked to changes in salmon production; Mantua et al 1997), North Pacific Gyre Oscillation (NPGO; reflects changes in the intensity of circulation in the North Pacific gyre, a strong indicator of changes in the planktonic ecosystem; Di Lorenzo et al 2008), Northern Oscillation Index (NOI; based on sea surface height anomalies, dominated by El Niño and La Niña events; Schwing et al 2002), and Multivariate El Niño -southern oscillation (MEI; based on six oceanic and atmospheric variables, tracks El Niño and La Niña events; Wolter and Timlin 2011).…”

Understanding Smolt Survival Trends in Sockeye Salmon

“…Perhaps growth rates continued to decline after 1991, but slow-growing Sockeye Salmon died at higher rates than did faster-growing Sockeye Salmon (Ruggerone et al 2005;Farley et al 2011) such that measured growth rates in the survivors did not decline. We suggest that Sockeye Salmon survivals began to decline after 1991 for many stocks because an increasing portion of the juveniles were unable to grow to the size (or possess sufficient energy reserves) required to survive some life history stanza, similar to the critical size hypothesis (e.g., Beamish et al 2004a).…”