Partitioning the influence of Chinook salmon productivity and stock-specific abundance on the southern resident killer whale population

The southern resident killer whale ( Orcinus orca , SRKW) population is listed as endangered in both the U.S. and Canada. Reduced prey availability, especially of Chinook salmon, is recognized as an important limiting factor for this population. However, most studies have associated SRKW population dynamics with coastwide Chinook salmon abundance, rather than with differences in Chinook salmon productivity or stock-specific abundance. This study examined how changes in Chinook salmon abundance could impact the SRKW population trajectory in the future (2020─2150) by 1) increasing the overall productivity of Chinook salmon populations and 2) increasing and decreasing the abundance of 4-year-old Chinook salmon individuals from stocks that are positively selected for by SRKW. Model predictions suggested that the SRKW population could decline by 10.6% by 2150 under the current conditions ( Status Quo; i.e., repeating levels observed between 2010 and 2020) and increase (+ 17.6%) if productivity of all Chinook salmon populations included in the model were to double after 2020. The model also predicted that the SRKW population could increase by 107%, if 4-year-old Fraser summer fish were to increase by fivefold in comparison to their highest contemporary (1979-2020) levels. The SRKW population was predicted to grow when increasing the abundance of 4-year-old Fraser spring (+ 45.6%) and Columbia spring (+ 18.1%) Chinook salmon. Our results support the importance of stock specific analyses of prey availability for SRKW, and suggest that future conservation management strategies should prioritize spring and summer Chinook salmon originating from the Fraser River, British Columbia, Canada. • Increasing coastwide Chinook salmon productivity may have limited impact on SRKW • Spring and summer Fraser River Chinook salmon are critical for the recovery of SRKW • Focusing on individual Chinook salmon stocks is key to effective conservation • Fine-resolution conservation measures could promote prey availability for SRKW