Energetic Status of Alaskan Chinook Salmon: Interpopulation Comparisons and Predictive Modeling Using Bioelectrical Impedance Analysis

Abstract

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.

Assessing Potential Stock Structure of Adult Coho Salmon in a Small Alaska Watershed: Quantifying Run Timing, Spawning Locations, and Holding Areas with Radiotelemetry

“…This allows homeward migrating adults to reach spawning grounds and spawn at a time that optimizes emergence timing of offspring with prey availability (Brannon 1987;Boatright et al 2004;Quinn 2018). For example, populations and species that spawn in locations far inland or at high elevations tend to migrate earlier in the season than populations spawning closer to the coast (Hodgson and Quinn 2002;Brannon et al 2004;Quinn 2018;Courtney et al 2020). Similarly, species and populations spawning at higher latitudes typically spawn earlier than populations in more southern latitudes, consistent with the idea that relatively cool temperatures during embryo incubation require more development time than warm environments (Sandercock 1991).…”

“…In general, Coho Salmon migration timing takes place in the late fall (Sandercock 1991;Quinn 2018). Tag date, used as a proxy for entrance timing, did not distinguish whether a Coho Salmon entering the Buskin River would migrate to the upper tributaries or remain in the main stem, counter to the general assumption that earlier arriving fish travel further (Hodgson and Quinn 2002;Brannon et al 2004;Quinn 2018;Courtney et al 2020). It seems there is little advantage of arriving early to the Buskin River watershed as we observed the entire migration from lower weir to the lake in the upper watershed can be accomplished in a single day by at least some individuals (mean days between entry and Buskin Lake was 17).…”

“…Past studies on river systems larger than the Buskin River have shown a tendency for Pacific salmon that return earlier to natal streams to travel greater distances to spawn (Burger et al 1985;Clark et al 2015;Eiler et al 2015;Courtney et al 2020). In general, Coho Salmon migration timing takes place in the late fall (Sandercock 1991;Quinn 2018).…”

Seasonal variation in the lipid content of Fraser River Chinook Salmon (Oncorhynchus tshawytscha) and its implications for Southern Resident Killer Whale (Orcinus orca) prey quality

“… 11 ). Fortunately, new tools exist—such as microwave energy meters (fat meters)—which can provide rapid and accurate estimates of lipid content/energy density 28 – 31 . Microwave fat meters measure water content and use the inverse relationship between water and lipid content to estimate lipid content 29 , 31 .…”

Energy Condition of Subsistence‐Harvested Fishes in Arctic Coastal Lagoons

“…However, the energy density and percentage of lipid composition of subsistence fishes that occur along the Arctic coast of Alaska are poorly documented, hindering our ability to assess such changes. Many studies (e.g., Trudel et al 2005;Courtney et al 2020) have focused on Pacific salmon Oncorhynchus spp., a universally used food fish throughout the north, but other fishes (e.g., Dolly Varden Salvelinus malma and whitefishes [Coregoninae]) can be harvested in greater amounts in the Arctic because the abundance of spawning salmon populations diminishes in the northerly direction (Nielsen and Ruggerone 2013). Furthermore, salmon are largely harvested during seasonal pulses, whereas other species are more consistently available.…”