title: Evolution of age and length at maturation of Alaskan salmon under size-selective harvest.
abstract: Spatial and temporal trends and variation in life-history traits, including age and length at maturation, can be influenced by environmental and anthropogenic processes, including size-selective exploitation. Spawning adults in many wild Alaskan sockeye salmon populations have become shorter at a given age over the past half-century, but their age composition has not changed. These fish have been exploited by a gillnet fishery since the late 1800s that has tended to remove the larger fish. Using a rare, long-term dataset, we estimated probabilistic maturation reaction norms (PMRNs) for males and females in nine populations in two basins and correlated these changes with fishery size selection and intensity to determine whether such selection contributed to microevolutionary changes in maturation length. PMRN midpoints decreased in six of nine populations for both sexes, consistent with the harvest. These results support the hypothesis that environmental changes in the ocean (likely from competition) combined with adaptive microevolution (decreased PMRNs) have produced the observed life-history patterns. PMRNs did not decrease in all populations, and we documented differences in magnitude and consistency of size selection and exploitation rates among populations. Incorporating evolutionary considerations and tracking further changes in life-history traits can support continued sustainable exploitation and productivity in these and other exploited natural resources.
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington Seattle, WA, USA ; Washington Department of Fish and Wildlife Olympia, WA, USA.
authors.forename: Neala W
authors.initials: NW
authors.lastname: Kendall
authors.affiliation: International Institute of Applied Systems Analysis Laxenburg, Austria.
authors.forename: Ulf
authors.initials: U
authors.lastname: Dieckmann
authors.affiliation: International Institute of Applied Systems Analysis Laxenburg, Austria ; Department of Biology, University of Bergen Bergen, Norway ; Institute of Marine Research Bergen, Norway.
authors.forename: Mikko
authors.initials: M
authors.lastname: Heino
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington Seattle, WA, USA.
authors.forename: André E
authors.initials: AE
authors.lastname: Punt
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington Seattle, WA, USA.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Quinn
keywords: Oncorhynchus nerka; fishery selection; harvest-induced evolution; phenotypic plasticity; probabilistic maturation reaction norms