Reconstructing a century of coastal productivity and predator trophic position in the Salish Sea using archival harbor seal bone.

• Main Author: Feddern, Megan
• Format: Text
• Language: English
• Published: Western CEDAR 2020
• Subjects: Fresh Water Studies; Life Sciences; Marine Biology; Natural Resources and Conservation; Terrestrial and Aquatic Ecology; Pacific; harbor seal
• Online Access: https://cedar.wwu.edu/ssec/2020ssec/allsessions/70; https://cedar.wwu.edu/cgi/viewcontent.cgi?article=3128&context=ssec

Following the passage of the Marine Mammal Protection Act of 1972, pinniped populations along the west coast of North America experienced exponential population increases following historic lows in the 1970's. In the Salish Sea, this increase in pinniped abundance also corresponded to large scale changes environmental condition (ie. Pacific Decadal Oscillation; PDO) and declines of prey species (forage fish, salmon), creating new challenges and tradeoffs for fisheries management in the region. The objective of this research is to understand how an abundant top predator, harbor seals, respond to bottom up forces in the system such as shifts in primary productivity and prey availability. 140 archival bones were sampled from specimens curated at institutions in the US and British Columbia, representing individuals from 1928 to 2014. Samples were analyzed for the 15N/14N of 11 individual amino acids (AAs), including both trophically fractionated (trophic) and trophically conserved (source) amino acids. Source amino acids are reflective of the 15N/14N of the base of the food web and can be used as an indicator of overall system productivity. When combined with the 15N/14N of trophic amino acids, the 15N/14N of source amino acids can also be used to calculate trophic position from historic samples. By comparing source and trophic position stable isotope data with environmental and ecological (prey abundance) time series we have identified bottom up forces, specifically environmental condition, are important drivers in harbor seal trophic position and productivity in the Salish Sea over the last 100 years.