Seabird Diet in the Salish Sea and Northern California Current

Seabird diet has been used as an indicator of fish populations, fishery recruitment, climate change and shorter-term climate events, and to understand food web relationships, especially in endangered ecosystems such as the Salish Sea.  To identify information gaps and summarize what is known about seabird diet in the Salish Sea and northern California Current, we created a database of seabird literature that allows users to summarize data available for specific prey and predator taxa, time periods, and/or geographic regions.  The database allows users to identify seabird-species specific diets and also identify the suite of seabird species that eat a given species of fish.  For example, the studies in the database identify 12 seabird species consume Pacific herring (Clupea harengus pallasi).  The distribution of diet studies was not uniform across time, with some seabird species having much more coverage than others.  Several species of alcids, had the longest continuous diet data, with periods of study extending 10 or more years in the late 1990’s and early 2000’s.  An alternative way to assess changes in seabird diet is to compare results from contemporary and historic studies.  Our contemporary research on rhinoceros auklet (Cerorhinca monocerata) diet coupled with work conducted in the 1970s is an example from the database of how seabird diet can be used to assess ecosystem changes over time.  In this study, we sampled auklet diet in the Salish Sea (Protection Island), on the outer coast of Washington (Destruction Island), and at the confluence of both environments (Tatoosh Island).  Over 5729 fish samples (968 bill loads) were collected from auklets during three sampling trips per island per season (2006-2010). In the Salish Sea, Pacific sandlance (Ammodytes hexapterus) and to a lesser degree herring made up the majority of the diet, while the diet on the coast was more diverse.  Despite differences in size of fish among islands, the average weight and energy (KJ/g) per bill load did not differ between the Salish Sea and the coast because birds compensated by returning with more fish per bill load.   When we put our results in an historic context, average bill load weight and diet composition has not changed between the 1970s and today in the Salish Sea. Our work addresses the need for seabird diet data on a particular species in specific regions, while also identifying which regions and species may require more attention in the future.