title: The first months at sea: marine migration and habitat use of sea trout Salmo trutta post-smolts.
abstract: The early migration and habitat use of brown trout Salmo trutta post-smolts tagged with acoustic transmitters (n = 50) were investigated in a fjord system in central Norway from 30 April to 26 November 2014. The main aims were to investigate return rate, marine residence time and spatial use of the fjord system. Median seaward migration and return to fresh water dates were 22 May and 4 July, respectively. Of the 40 seaward migrating smolts, 26 returned to fresh water, giving a minimum return rate to fresh water of 65%. Entrance to the fjord from the river occurred mainly at night (80% of the S. trutta), however, no such diurnal pattern was observed during the return migration. Mean marine residence time was 38 days, but with large individual variation (22-99 days). The innermost parts of the study area were more utilized than the outer part of the fjord system during the sea residency, and with more use of the near shore habitat than the open, pelagic areas. Many post-smolts also utilized the outer part of the fjord system, however, and 94% of the post-smolts were recorded at least 14 km from the home river mouth. Marine survival and distribution in the fjord were size dependent with the largest individuals utilizing outer fjord areas and having higher return rates to fresh water. As far as is known, this is the first published study on temporal and spatial behaviour in the marine environment of first-time S. trutta migrants during the full course of their first trip to sea.
authors.affiliation: NTNU University Museum, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.|The Arctic University of Norway, NO-9037, Tromsø, Norway.
authors.forename: A C
authors.initials: AC
authors.lastname: Flaten
authors.affiliation: NTNU University Museum, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
authors.forename: J G
authors.initials: JG
authors.lastname: Davidsen
authors.affiliation: Norwegian Institute for Nature Research, NO-7485, Trondheim, Norway.|The Arctic University of Norway, NO-9037, Tromsø, Norway.
authors.forename: E B
authors.initials: EB
authors.lastname: Thorstad
authors.affiliation: Ocean Tracking Network, Dalhousie University, Halifax, NS, B3H 4J1, Canada.
authors.forename: F
authors.initials: F
authors.lastname: Whoriskey
authors.affiliation: NTNU University Museum, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
authors.forename: L
authors.initials: L
authors.lastname: Rønning
authors.affiliation: NTNU University Museum, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
authors.forename: A D
authors.initials: AD
authors.lastname: Sjursen
authors.affiliation: The Arctic University of Norway, NO-9037, Tromsø, Norway.
authors.forename: A H
authors.initials: AH
authors.lastname: Rikardsen
authors.affiliation: NTNU University Museum, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
authors.forename: J V
authors.initials: JV
authors.lastname: Arnekleiv
mesh_terms: D000162:Acoustics; D025041:Animal Migration; D000818:Animals; D017753:Ecosystem; D063366:Estuaries; D005618:Fresh Water; D009659:North Sea; D009664:Norway; D045483:Rivers; D014337:Trout
keywords: acoustic telemetry; habitat use; marine survival; migratory behaviour