Migration Trends of Sockeye Salmon at the Northern Edge of Their Distribution

Abstract

Climate change is affecting arctic and subarctic ecosystems, and anadromous fish such as Pacific salmon Oncorhynchus spp. are particularly susceptible due to the physiological challenge of spawning migrations. Predicting how migratory timing will change under Arctic warming scenarios requires an understanding of how environmental factors drive salmon migrations. Multiple mechanisms exist by which environmental conditions may influence migrating salmon, including altered migration cues from the ocean and natal river. We explored relationships between interannual variability and annual migration timing (2003–2014) of Sockeye Salmon O. nerka in a subarctic watershed with environmental conditions at broad, intermediate, and local spatial scales. Low numbers of Sockeye Salmon have returned to this high‐latitude watershed in recent years, and run size has been a dominant influence on the migration duration and the midpoint date of the run. The duration of the migration upriver varied by as much as 25 d across years, and shorter run durations were associated with smaller run sizes. The duration of the migration was also extended with warmer sea surface temperatures in the staging area and lower values of the North Pacific Index. The midpoint date of the total run was earlier when the run size was larger, whereas the midpoint date was delayed during years in which river temperatures warmed earlier in the season. Documenting factors related to the migration of Sockeye Salmon near the northern limit of their range provides insights into the determinants of salmon migrations and suggests processes that could be important for determining future changes in arctic and subarctic ecosystems. Received October 24, 2016; accepted March 2, 2017 Published online June 8, 2017

Energy Depletion and Stress Levels in Sockeye Salmon Migrating at the Northern Edge of their Distribution

“…Average, minimum, and maximum water temperatures during the spawning migration (day of year [DOY] 184–243; Carey et al. ) were compared among years at each temperature station along the migration route (Snyder et al. ; Tsang et al.…”

“…Temperature profiles of the lake were also measured in July and August each year of the study (Keith 2016). Average, minimum, and maximum water temperatures during the spawning migration (day of year [DOY] 184-243; Carey et al 2017) were compared among years at each temperature station along the migration route (Snyder et al 2015;Tsang et al 2016). Similarly, average temperatures for the total migration route were compiled across locations from the mouth of the river to the outlet at Salmon Lake.…”

“…The fish weir was operated from ice-out in late June until early September and was monitored 24 h/d and checked regularly. Sockeye Salmon begin passing through the fish weir at the end of June or early July and finish by late August (Carey et al 2017). At the fish weir, we sampled Sockeye Salmon at multiple times in July and early August in 2013 (sampling events = 2), 2014 (sampling events = 4), 2015 (sampling events = 4), and 2016 (sampling events = 3).…”

“…; Carey et al. ). Moreover, exploring the influence of river temperatures in subarctic watersheds will help generalize the impact of in‐river temperature to other Sockeye Salmon populations and help managers anticipate which environmental factors will influence energetic conditions of Sockeye Salmon during spawning migrations.…”

“…There is limited information linking variability in river conditions with energy demands of Sockeye Salmon during spawning migrations in arctic and subarctic ecosystems (Rand et al 2006;Lennox et al 2016). From the few studies in high (>60°N) latitude systems, temperature has been found to influence migration timing, and more research is needed on how temperature affects energy and stress levels during spawning migrations (Mundy and Evenson 2011;Lennox et al 2016;Carey et al 2017). Moreover, exploring the influence of river temperatures in subarctic watersheds will help generalize the impact of inriver temperature to other Sockeye Salmon populations and help managers anticipate which environmental factors will influence energetic conditions of Sockeye Salmon during spawning migrations.…”