title: Maturation trends indicative of rapid evolution preceded the collapse of northern cod.
abstract: Northern cod, comprising populations of Atlantic cod (Gadus morhua) off southern Labrador and eastern Newfoundland, supported major fisheries for hundreds of years. But in the late 1980s and early 1990s, northern cod underwent one of the worst collapses in the history of fisheries. The Canadian government closed the directed fishing for northern cod in July 1992, but even after a decade-long offshore moratorium, population sizes remain historically low. Here we show that, up until the moratorium, the life history of northern cod continually shifted towards maturation at earlier ages and smaller sizes. Because confounding effects of mortality changes and growth-mediated phenotypic plasticity are accounted for in our analyses, this finding strongly suggests fisheries-induced evolution of maturation patterns in the direction predicted by theory. We propose that fisheries managers could use the method described here as a tool to provide warning signals about changes in life history before more overt evidence of population decline becomes manifest.
authors.affiliation: Adaptive Dynamics Network, International Institute for Applied Systems Analysis, A-2361 Laxenburg, Austria. espeom@bio.uio.no
authors.forename: Esben M
authors.initials: EM
authors.lastname: Olsen
authors.forename: Mikko
authors.initials: M
authors.lastname: Heino
authors.forename: George R
authors.initials: GR
authors.lastname: Lilly
authors.forename: M Joanne
authors.initials: MJ
authors.lastname: Morgan
authors.forename: John
authors.initials: J
authors.lastname: Brattey
authors.forename: Bruno
authors.initials: B
authors.lastname: Ernande
authors.forename: Ulf
authors.initials: U
authors.lastname: Dieckmann
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D044822:Biodiversity; D005075:Biological Evolution; D001824:Body Constitution; D005260:Female; D005398:Fisheries; D005399:Fishes / Q000254:growth & development* / Q000502:physiology*; D008297:Male; D011156:Population Density; D018401:Sample Size; D012741:Sexual Maturation / Q000502:physiology; D013997:Time Factors