Signals of large scale climate drivers, hatchery enhancement, and marine factors in Yukon River Chinook salmon survival revealed with a Bayesian life history model

Abstract

Understanding how species might respond to climate change involves disentangling the influence of co-occurring environmental factors on population dynamics, and is especially problematic for migratory species like Pacific salmon that move between ecosystems. To date, debate surrounding the causes of recent declines in Yukon River Chinook salmon (Oncorhynchus tshawytscha) abundance has centered on whether factors in freshwater or marine environments control variation in survival, and how these populations at the northern extremity of the species range will respond to climate change. To estimate the effect of factors in marine and freshwater environments on Chinook salmon survival, we constructed a stage-structured assessment model that incorporates the best available data, estimates incidental marine bycatch mortality in trawl fisheries, and uses Bayesian model selection methods to quantify support for alternative hypotheses. Models fitted to two index populations of Yukon River Chinook salmon indicate that processes in the nearshore and marine environments are the most important determinants of survival. Specifically, survival declines when ice leaves the Yukon River later in the spring, increases with wintertime temperature in the Bering Sea, and declines with the abundance of globally enhanced salmon species consistent with competition at sea. In addition, we found support for density-dependent survival limitations in freshwater but not marine portions of the life cycle, increasing average survival with ocean age, and age-specific selectivity of bycatch mortality in the Bering Sea. This study underscores the utility of flexible estimation models capable of fitting multiple data types and evaluating mortality from both natural and anthropogenic sources in multiple habitats. Overall, these analyses suggest that mortality at sea is the primary driver of population dynamics, yet under warming climate Chinook salmon populations at the northern extent of the species' range may be expected to fare better than southern populations, but are influenced by foreign salmon production.

Hierarchical analysis of wild Atlantic salmon (Salmo salar) fecundity in relation to body size and developmental traits

“…Coupled with declines in abundance of spawners and especially in the abundance of older and larger multi‐sea‐winter females (Chaput, ), the quantitative differences shown in Figure could amount to significant biases in total egg production estimates and erroneous comparisons with conservation limits. The recent development and application of modelling approaches capable of incorporating temporal and geographic variability in a range of life history parameters, including fecundity, will help to provide improved predictions and inferences within management (Cunningham et al ., ; Massiot‐Granier et al ., ).…”

Direction and magnitude of natural selection on body size differ among age‐classes of seaward‐migrating Pacific salmon

“…are ideal species for exploring fitness trade‐offs as a result of selection on traits, such as body size and migratory timing (Quinn, Doctor, Kendall, & Rich, 2009). For anadromous Oncorhynchus spp., high rates of mortality occur during a brief period after juveniles (i.e., “smolts”) enter the ocean (Healey, 1982; Parker, 1971), and correspondingly, population dynamics are largely influenced by this life stage (Cunningham, Westley, & Adkinson, 2018; Rogers & Schindler, 2011). Smolt size and ocean‐entry timing are two correlated traits that influence survival; however, with few exceptions, the ecological agents of selection (sensu MacColl, 2011) are usually unknown.…”

Impacts of co‐occurring environmental changes on Alaskan stream fishes

“…In particular, the rapidly changing winter period is producing some of the greatest impacts on northern species, with potential benefits including improved overwintering survival, leading to increases in biodiversity and productivity (Heino et al, 2009;Reist et al, 2006b;Reynolds, 1997). Additionally, earlier spring break-up and warmer summer temperatures have been linked to increased growth opportunities for Alaskan juvenile salmon, promoting size-dependent overwintering survival and ultimately productivity (Cline, Ohlberger, & Schindler, 2019;Cunningham, Westley, & Adkison, 2018;Ohlberger, Scheuerell, & Schindler, 2016;Schindler, Rogers, Scheuerell, & Abrey, 2005). While many climate change impacts have the potential to produce positive effects on northern fishes in the short-term, continued warming may produce negative effects once species' warming tolerances are surpassed (Comte & Olden, 2017;Crozier & Hutchings, 2014;Heino et al, 2009).…”

“…While many climate change impacts have the potential to produce positive effects on northern fishes in the short-term, continued warming may produce negative effects once species' warming tolerances are surpassed (Comte & Olden, 2017;Crozier & Hutchings, 2014;Heino et al, 2009). Further, changes to summer streamflow may negatively impact stream fishes if feeding or migration activities are compromised, and species are unable to adapt (Cunningham et al, 2018;Heim et al, 2015;Neuswanger, Wipfli, Evenson, Hughes, & Rosenberger, 2015).…”