Evaluation of Growth, Survival, and Recruitment of Chinook Salmon in Southeast Alaska Rivers

Abstract

Recent reductions in the run sizes of Chinook Salmon Oncorhynchus tshawytscha in Southeast Alaska have resulted in social and economic hardships within the region. For Pacific salmon, including Chinook Salmon, brood year (BY) strength may be determined by size‐selective processes that occur during early marine residence. However, the relative importance of freshwater versus marine growth in determining recruitment success is unknown. We conducted a scale‐based retrospective analysis to examine the relative effects of freshwater and marine growth on survival to the age of reproduction for female Chinook Salmon by BY in the Taku (BYs 1979–1985, 1990–1999, 2002–2004) and Unuk (BYs 1981–1983, 1986–1988, 1994–2003, 2005–2006) rivers located in Southeast Alaska. First‐year marine growth of Chinook Salmon was positively related to total return, productivity (returns per spawner), and marine survival for stocks from both systems. In the Taku River, growth during the third year at sea was positively related to marine survival. Annual growth of Taku River Chinook Salmon was correlated with previous growth through the second year at sea; however, no correlations were detected between adjacent growth zones of Unuk River fish. These findings suggest that current declines in Chinook Salmon abundance in Southeast Alaska is attributed to changes in growth conditions during the first year at sea.

A synthesis of the coast‐wide decline in survival of West Coast Chinook Salmon (Oncorhynchus tshawytscha,Salmonidae)

“…The reasons for poor marine survival of Chinook are likely multiple, with mechanisms proposed in the last decade alone including: growth (Claiborne et al., 2011; Duffy & Beauchamp, 2011; Graham et al., 2019; Howard, Murphy, Wilson, Moss, & Farley, 2016; Lewis et al., 2015; Losee et al., 2014; MacFarlane, 2010; Miller et al., 2014; Ohlberger et al., 2018; Orsi, 2013; Schindler et al., 2013; Tomaro et al., 2012); hatchery practices (Chamberlin et al., 2011; Nelson et al., 2019; Sabal et al., 2016; Tomaro, 2010); predation (Chasco et al., 2017; Friedman et al., 2019; Miller et al., 2013; Nelson et al., 2019; Seitz et al., 2019); competition (Cunningham et al., 2018; Miller et al., 2013); by‐catch mortality in fisheries (Cunningham et al., 2018); and ocean conditions (Dorner et al., 2017; Murphy et al., 2017; Ruff et al., 2017; Sharma et al., 2013).…”

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

“…A growing body of evidence now links the productivity of Alaskan Chinook salmon populations to multiple drivers in both the freshwater and marine environments, including river discharge and temperature this study), precipitation (this study), river ice breakup timing and the NPGO (Cunningham et al, 2018;Ohlberger et al, 2016; this study), winter sea surface temperature and competition with hatchery salmon in the ocean (Cunningham et al, 2018), and growth rates during the first year in the ocean (Graham, Sutton, Adkison, McPhee, & Richards, 2019). No single driver or life stage has been identified that can fully explain these declines, suggesting that multiple drivers are involved, individual populations are responding differently, or both.…”

Community through Culture: From Insects to Whales

“…Nut‐cracking techniques in chimpanzee communities are maintained even when a preferred tool is less effective and may impact foraging success . Resident killer whales off the coast of British Columbia have strong cultural preferences for chinook salmon ( Oncorhynchus tshawytscha ), a prey species whose populations have been in decline in recent years . This, coupled with the avoidance of alternative prey species despite their far greater seasonal abundance, may have resulted in the observed loss of numbers in these resident populations .…”