title: Thermal regime, predation danger and the early marine exit of sockeye salmon Oncorhynchus nerka.
abstract: Marine exit timing of sockeye salmon Oncorhynchus nerka populations on the Haida Gwaii Archipelago, British Columbia, Canada, is described, with specific focus on Copper Creek. Marine exit in Copper Creek occurs > 130 days prior to spawning, one of the longest adult freshwater residence periods recorded for any O. nerka population. Copper Creek presents an easy upstream migration, with mild water temperatures (7 to 14°  C), short distance (13·1 km) and low elevation gain (41 m) to the lake where fish hold prior to spawning. An energetic model estimates that <1% of the initial energy reserve is required for upstream migration, compared with 62% for lake holding and 38% for reproductive development. Historical records suggest that it is unlikely that water temperature in any of the O.nerka streams in Haida Gwaii has ever exceeded the presumed temperature threshold (19° C) for early marine exit. Although it is not impossible that the thermal tolerance of Copper Creek O.nerka is very low, the data presented here appear inconsistent with thermal avoidance as an explanation for the early marine exit timing in Copper Creek and in three other populations on the archipelago with early marine exit.
authors.affiliation: Fisheries and Oceans Canada, Fisheries and Aquaculture Management, P. O. Box 99, Queen Charlotte, BC, V0T 1Y0, Canada.
authors.forename: P J
authors.initials: PJ
authors.lastname: Katinic
authors.forename: D A
authors.initials: DA
authors.lastname: Patterson
authors.forename: R C
authors.initials: RC
authors.lastname: Ydenberg
mesh_terms: D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D001955:British Columbia; D005618:Fresh Water; D015233:Models, Statistical; D010507:Periodicity; D011235:Predatory Behavior; D012474:Salmon / Q000502:physiology*; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013696:Temperature
keywords: Copper Creek; Haida Gwaii; life-history strategy; river entry; timing of migration