Low Annual Fidelity and Early Upstream Migration of Anadromous Arctic Char in a Variable Environment

Abstract

The life histories of anadromous Arctic Char Salvelinus alpinus are complex and vary greatly between populations and environments. Here, we detail key aspects of the physical environment and life history of a population of Arctic Char from Nulahugyuk Creek, Nunavut, Canada, to characterize migration traits in a highly variable environment. Over the course of this migration, creek discharge declined precipitously, forcing Arctic Char to migrate through shallow water with large diel temperature fluctuations (>10°C) and high temperature extremes (>21°C). The downstream migration of adults (>55 cm) began in mid‐June and continued into early July, while the downstream migration of smolts (<30 cm) began in late June and continued until late July. The upstream adult migration began in late June and ended in late July, far earlier than most upstream migrations in the region. There was no appreciable upstream migration of juveniles, and Arctic Char 30 to 55 cm in length were absent from the up‐ and downstream migrations. The average age at first migration was 4 years, and the youngest adult Arctic Char migrating upstream were 8 and 9 years old. The missing size‐ and age‐classes, and the fact that most upstream migrants were near reproductive maturity, indicate that Arctic Char in this system typically leave at a length of 19 cm and an age of 4 years and do not return for 4 to 5 years, when they are ready to reproduce. Anadromous Nulahugyuk Creek Arctic Char appear to employ strategies that limit their exposure to restrictive migratory conditions and facilitate their existence in an otherwise uninhabitable system. Understanding such population‐specific migratory strategies is critical to the management of Arctic Char fisheries, which are comprised of populations with highly diverse life histories, and to our understanding of how these life histories may contribute to the adaptability and persistence of the species as climate change progresses. Received November 24, 2015; accepted March 23, 2016 Published online July 28, 2016

Genomics and telemetry suggest a role for migration harshness in determining overwintering habitat choice, but not gene flow, in anadromous Arctic Char

“…For example, the Ekalluk River drains the largest lake on Victoria Island, Ferguson Lake, which could offer more abundant or better overwintering habitats, perhaps resulting in lower overwintering mortality. Nonetheless, other studies of Arctic Char have also found spawning habitat accessibility to be a major constraint to migrations (Gilbert et al., ; Gyselman, ), and the easier migrations afforded by the short Ekalluk River constitute a plausible explanation for the observed patterns of dispersal. This hypothesis, however, assumes the ability of Arctic Char to assess which river provides the most readily accessible overwintering habitat.…”

“…when there are no genetic or evolutionary consequences). Accordingly, there is evidence that Arctic Char (and the closely related Dolly Varden; Salvelinus malma ) home to their natal habitats to spawn, but can use non‐natal habitats to overwinter (Armstrong, ; Gilbert et al., ; Gyselman, ; Moore et al., ). Here, we documented the use of alternative freshwater habitats by the same individuals in consecutive years using acoustic telemetry data.…”

“…Given that optimal spawning habitats likely differ from optimal overwintering habitats, we can predict that individuals might select different habitats in different years depending on their maturity status. Accordingly, there is evidence that Arctic Char home to their natal sites to spawn, but often utilize non‐natal overwintering sites in years when they are not in breeding condition (Gilbert, Donadt, Swanson, & Tierney, ; Gyselman, ; Johnson, ; Moore et al., ). Natal homing to reproduction sites combined with the use of alternative overwintering sites may lead to temporary mixing of different stocks in fresh water, making both population‐specific sampling and fisheries management challenging.…”

“…Migratory harshness can drive local adaptation of life history (Schaffer & Elson, ), morphological (Crossin et al., ) and physiological traits (Eliason et al., ). While studies from Arctic Char have shown the influence of habitat accessibility on freshwater migrations (Gilbert et al., ; Gyselman, ), the extent to which migration harshness drives habitat choice (particularly during overwintering migrations) and local adaptation remains largely unknown.…”

Warm northern river temperatures increase post‐exercise fatigue in an Arctic migratory salmonid but not in a temperate relative

“…>2°C/hr, Clark et al., ; Clark, Sandblom, Cox, Hinch, & Farrell, ; Penney, Nash, & Gamperl, ; Steinhausen, Sandblom, Eliason, Verhille, & Farrell, ) and at prevailing water temperatures in field studies on wild fish (Farrell et al., ; Rodnick et al., ). Variation in natural temperatures more commonly occurs on diurnal (Gamperl et al., ; Gilbert, Donadt, Swanson, & Tierney, ; Rodnick et al., ) to seasonal scales (Farrell, ; Mathes et al., ), or acutely in an irregular manner as fish transition between different thermal environments such as when moving between the ocean, rivers and lakes (Farrell, ), and when diving (Farrell, ; Friedland et al., ; Rikardsen, Elliott, Dempson, Sturlaugsson, & Jensen, ). The ability of poikilotherms such as salmonids to tolerate and acclimate to warming depends on the rate at which the warming occurs (Dowd, King, & Denny, ; Galbreath, Adams, & Martin, ; Mora & Maya, ).…”