Review of recent research on Southern Resident Killer Whales to detect evidence of poor body condition in the population

Abstract

This review was commissioned by the SeaDoc Society in light of major concern for the population trajectory of the SRKW population. The review focuses on identifying evidence for poor body condition in the SRKW population from information presented in Seattle, March 6 2017 (see Appendix 1 Agenda). Body condition can be influenced by food availability (quantity and quality), energy balance, disease, toxin exposure, physiological status, genetics and stress from noise and vessel traffic, amongst other factors, although food availability is the most common cause in wild mammalian populations. For SRKW, food availability to individuals is determined by both prey availability and time to find, catch, share and consume prey. Anthropogenic disturbance will reduce food consumption and thus influence body condition. The small population size and complex social structure of SRKW complicate detection of associations between measures of body condition and population dynamics. Stochastic events can skew population-wide trends substantially. Therefore, individual cases must be considered rather than analyses of trends and correlations on limited-sample-sizes. The small sample size problem hinders many analyses of this population's ecology. A recent shift in distribution of Northern Resident Killer Whales (NRKW) into offshore SRKW range complicates choice of a control population. NRKW could compete for space and prey, and may be influenced by environmental variables that influence SRKW. Thus when using a case control approach, and comparing parameters between SRKW and a reference population, care should be taken when using the NRKW, and another population should be used such as the southern Alaskan residents.