Taking Stock of Chinook Salmon Energy Densities has Implications for Resident Killer Whales Meeting Their Energy Needs

• Main Author: Lerner, Jacob
• Format: Text
• Language: English
• Published: Western CEDAR 2022
• Subjects: Albion; British Columbia; Canada; Fraser River; Killer Whale; Killer whale
• Online Access: https://cedar.wwu.edu/ssec/2022ssec/allsessions/274; https://cedar.wwu.edu/context/ssec/article/3436/viewcontent/317_0971c5fb7f654eea84447c834b9cfece.pdf

Chinook salmon (Oncorhynchus tshawytscha) rely on large reserves of energy accumulated at sea to complete their journey upstream, mature reproductively, and spawn. In part due to these energy reserves, Chinook are the primary prey species for resident killer whales. However, energy density has been shown to vary significantly among Chinook populations, indicating that data on stock specific energy density are necessary to assess whether available prey can meet resident killer whale energy requirements. In this study, we sought to derive stock specific estimates of Southern British Columbia Chinook energy density. To begin, we evaluated a microwave energy meter as a non-lethal, rapid method for assessing lipid content (a proxy for energy density) in Chinook. Energy meter readings were collected from 60 Chinook which were then fully homogenized and lipid extracted to calibrate the device to measure whole-body lipid content. Our analysis provided a strong linear regression relationship between energy meter measurements and whole-body lipid content (R²=0.88, p < 0.001). Following this analysis we deployed the energy meter at the Albion Fraser River Test Fishery in Maple Ridge, BC Canada in 2020. We collected energy meter readings from 1568 individual Chinook encompassing members of all 5 Fraser management units. We identified three distinct groups of these management units based on average lipid level: Fall-41 (6.7% ± 1.8), Summer-41 (10.8% ± 2.2) and a group containing Spring-42, Spring-52 and Summer-52 (13.0% ± 2.8). Our results show that the Summer-41 group contained 25% more kcal/kg than the Fall-41 group and that the Spring-42, Spring-52 and Summer-52 group contained 40% more kcal/kg than the Fall-41 group. This study indicates how Chinook life history drives energy accumulation and provides values which can be used in conjunction with known Chinook and resident killer whale distribution to more accurately assess whether available prey meet predator energy needs.