Chapter 5: Ocean Ecology of Chinook Salmon
Brian R. Riddell, Richard D. Brodeur, Alexander V. Bugaev, Paul Moran, James M. Murphy, Joseph A. Orsi, Marc Trudel, Laurie A. Weitkamp, Brian K. Wells, and Alex C. Wertheimer
Chinook Salmon Oncorhynchus tshawytscha are likely the most enigmatic of the Pacific salmon. Although least abundant, they are the most diversified in life history expression and show the widest geographic distribution. World famous for their potential body size (exceeding 45 kg), though such fish are rare today, Chinook Salmon are the object of much debate and expense in fishery allocations and restoration efforts, including extensive investments in hatcheries over the past century. Despite those efforts in the Pacific Northwest USA and California, 9 of 17 Evolutionarily Significant Units of Chinook Salmon are listed as endangered or threatened under the U.S. Endangered Species Act (Waples 1991a; Ford et al. 2015a; Williams et al. 2016), and in Canada and Alaska, expert panels have assessed their decline in abundance and productivity (ADFG 2013; Riddell et al. 2013; Schindler et al. 2013). Further, Chinook Salmon are least abundant along the Asian Pacific coasts and their production largely limited to the Kamchatka Peninsula.
Since Healey’s (1991) comprehensive description of Chinook biology and life history throughout the North Pacific region, substantial research efforts have been directed to the marine ecology of Chinook Salmon; particularly their early marine survival, ocean distributions by population of origin, and ocean climate effects. These interests reflect the continued low abundance of many Chinook populations despite significant reductions in fishery exploitation rates and major investments in science reviews and recovery planning; plus increasing variability in Chinook production over time and between populations within a year. Even the past reliance on hatchery produced Chinook Salmon to increase Chinook abundance has come under significant scrutiny (Levin et al. 2001; Brannon et al. 2004a; Naish et al. 2008; Laikre et al. 2010; HSRG 2014; Scheuerell et al. 2015) as large scale hatcheries have clearly failed to restore Chinook abundances.
This chapter will focus on studies of marine ecology of Chinook Salmon largely following from a ‘critical size, critical period’ hypothesis for Pacific salmon stated by Beamish and Mahnken (2001):