Steller and California sea lion count and diet data in northwest Washington, 2010-2013

In this submission, we share data collected on Steller (Eumetopias jubatus) and California sea lion (Zalophus californianus) in northwest Washington year round from 2010-2013. Our primary objectives were to characterize the diets of Steller and California sea lions and to determine if the sympatric species compete for the same prey resources. We also wanted to determine how much prey each of the sea lions were eating. To determine prey consumption we collected data on the abundance of California and Steller sea lions during surveys. Generally only male California sea lions are present in northwest Washington. For Steller sea lions, all age groups are present and so we also counted by demographic group. We found that Steller and California sea lions have significant dietary niche overlap as the species utilize very similar assemblages of prey. We developed a procedure for estimating prey consumption by the sea lions using published data and our counts and have made our code publically available at https://github.com/jscordino/NW-WA-Sea-Lion-Prey-Consumption. We found that Steller sea lions ate roughly 11,000 metric tons of prey per year from 2010-2013 and that California sea lions ate roughly 9,500 metric tons of prey. A manuscript of our results has been submitted to Fishery Bulletin in April of 2021