Southern Resident killer whale SRKW females and the tragedy of the commons

• Main Author: Balcomb, Kenneth C.
• Format: Text
• Language: English
• Published: Western CEDAR 2018
• Subjects: Southern Resident Killer Whales; Fresh Water Studies; Life Sciences; Marine Biology; Natural Resources and Conservation; Terrestrial and Aquatic Ecology; Pacific; Killer Whale; North Atlantic; Orca; Orcinus orca; Beringia; Killer whale
• Online Access: https://cedar.wwu.edu/ssec/2018ssec/allsessions/83; https://cedar.wwu.edu/cgi/viewcontent.cgi?article=2518&context=ssec

The Endangered population of Southern Resident Killer Whales (Orcinus orca) in the Pacific Northwest is an obligate predator upon fish, with an apparent dependence upon mature Chinook salmon (Onchorhynchus tsawytscha) populations that are also Endangered throughout most of the foraging range of these whales. The whales coevolved with the salmon in a classic predator-prey scenario in which both flourished for the past 15,000 years since the submergence of Beringia allowed the whales to colonize the eastern North Pacific from North Atlantic ancestral populations. The salmon were already in the North Pacific for at least 500,000 years prior, and Chinook salmon had evolved a very successful ecological lifestyle of predation and semelparous anadromy with homing instinct for spawning in the rivers in which they hatched. Along with their multiple populations from many watersheds and optimal run-timing for spawning in habitats from near estuarine to alpine, they were also large and nutritious fish available as killer whale food year-round in coastal and inland sea habitats. The ancestral piscivorous ecotype killer whales that colonized the eastern North Pacific did so in cooperative extended family tribes that tended to breed within the tribe – resulting in the genetically discrete communities of “resident” ecotypes: SRKW, NRKW, etc. Population success in each of these communities was dependent upon female fecundity, and this was ultimately limited by food availability and energetic “catch per unit effort”, CPUE. With no “birth control” the females in these populations could produce a calf as often as every two or three years (18 months gestation, one year lactation) and upwards of perhaps ten calves in a reproductive lifetime (age 11-45 approx). I will present forty years of documented evidence for the SRKW female cohort fecundity related to the tragedy of the commons in Chinook salmon management.