AGE, SEX CLASS, AND PREY ABUNDANCE INFLUENCE THE FREQUENCY AND TYPE OF PERCUSSIVE BEHAVIOR IN THE SOUTHERN RESIDENT KILLER WHALE (ORCINUS ORCA) POPULATION AT LIME KILN POINT STATE PARK

Abstract

The endangered Southern Resident Killer Whale (Orcinus orca, SRKW) is an iconic species in the Pacific Northwest. Although many ecological aspects of this population have been studied, why SRKW perform above-surface “percussive” behavior such as breaching, cartwheeling, pectoral-fin slapping, tail lobbing, and dorsal-fin slapping remains unclear. In the present study, we observed SRKW in Haro Strait, Washington, to evaluate trends in percussive behavior by age and sex class during the summer of 2016, and used long-term data (1996–2016) to compare the relationship between the seasonal frequency of percussive behaviors and the abundance of Chinook Salmon (Oncorhynchus tshawytscha) the primary food source of SRKW. Over the summer season in 2016, we documented 24 encounters involving percussive behavior. We found a significant difference between ages and sexes in the rate of percussive behaviors performed, with adult females performing the most behaviors among these groups, and tail slaps comprising the most frequent behavior performed. We also found a significant positive relationship between the rate of percussive behaviors and Chinook Salmon abundance in the Salish Sea over the past 2 decades. These findings present a preliminary investigation into the potential for behavioral observations to serve as indicators of population-level health or behavioral trends, which could be important for this population's conservation.