Energetic Status Of Alaskan Chinook Salmon: Interpopulation Comparisons And Predictive Modeling Using Bioelectrical Impedance Analysis

Adult Pacific salmon Oncorhynchus spp. undertake energetically demanding migrations where they must have adequate energy reserves to survive to reach spawning locations and reproduce. Lethal proximate analysis provides insight into available energy stores (e.g., lipids), but the ability to monitor energetic status nonlethally may be useful for managers. Nonlethal monitoring may be more cost effective, reduce harm to sensitive populations, allow for more fish to be sampled, and assessments can be done relatively quickly. Chinook Salmon Oncorhynchus tshawytscha (N = 129) were sampled for proximate analysis from four populations in Alaska to examine variation in energetic status before and after spawning migration and to create predictive bioelectrical impedance analysis (BIA) models for this species. In addition to proximate analysis we tested the variability between two BIA devices (Q2 and CQR), whether BIA models were generalizable to a congener, Chum Salmon Oncorhynchus keta, and the feasibility of integrating BIA into field studies. The populations that were sampled at prespawning migration had higher %lipid (N = 77; mean = 43%) than those that were collected at postspawning migration (N = 52; mean = 20%). Total %lipid and %water was more accurately predicted based on BIA measurements that were made by using the Q2 device (RMSE = 5.33 and RMSE = 2.43, respectively) than on those that were made by using the CQR device measurements (RMSE = 6.27; RMSE = 2.66). The between-species (Chinook Salmon to Chum Salmon RMSE = 19.47; Chum to Chinook RMSE = 7.69) models were less accurate than species-specific models that were created for Chinook Salmon and Chum Salmon, suggesting that single-species models should be used. We field-tested the BIA model to predict %lipid and %water for Chinook Salmon on a remote Southeast Alaska river. The range of predicted values of %lipid and %water was similar to the results that are obtained via proximate composition from the other populations. Our results indicate that BIA could be a valuable tool for assessing the spatial and temporal patterns of energetic status for Chinook Salmon populations.