MEPS 698:191-197 (2022)  -  DOI: https://doi.org/10.3354/meps14155

ABSTRACT: Carbon stable isotope analysis is an important tool in studies of fish ecology. Studies using this tool must account for the effect of lipids present in fish tissue on carbon stable isotope (δ¹³C) values. Simple correction equations have been developed to correct for this effect. For taxa with high fat content, choosing an accurate correction equation can have a significant impact on results. Pacific salmon (Oncorhynchus spp.) are a lipid-rich genus. Their broad marine distribution and ecological, cultural, and commercial importance make them prime candidates for stable isotope analysis. To determine both an accurate lipid correction equation for Pacific salmon δ¹³C values, and the effect of lipid extraction on bulk nitrogen isotope (δ¹⁵N) values, we performed pairwise isotope analysis on lipid-extracted and untreated muscle samples from 68 Chinook salmon O. tshawytscha spanning a size range of 165-750 mm and C:N values of 2.96-14.25. We compared the fit of existing δ¹³C lipid correction equations from 3 previously published models to our data, and optimized the top performing model using a leave-one-out cross validation. The model of Kiljunen et al. (2006; https://doi.org/10.1111/j.1365-2664.2006.01224.x) performed the best (mean squared error: 0.22, r²: 0.91), while the optimized model only slightly improved on it (MSE: 0.20, r²: 0.93). For δ¹⁵N, we determined that Chinook δ¹⁵N values significantly increased by 0.6‰ following lipid extraction. Our results confirm a lipid normalization procedure that is broadly applicable to Pacific salmon, and supports streamlined analysis of δ¹³C and δ¹⁵N from a single untreated muscle tissue sample.

KEY WORDS: Chinook salmon · Oncorhynchus tshawytscha · C:N ratio · Correction equation