title: Effect of a fish stock's demographic structure on offspring survival and sensitivity to climate.
abstract: Commercial fishing generally removes large and old individuals from fish stocks, reducing mean age and age diversity among spawners. It is feared that these demographic changes lead to lower and more variable recruitment to the stocks. A key proposed pathway is that juvenation and reduced size distribution causes reduced ranges in spawning period, spawning location, and egg buoyancy; this is proposed to lead to reduced spatial distribution of fish eggs and larvae, more homogeneous ambient environmental conditions within each year-class, and reduced buffering against negative environmental influences. However, few, if any, studies have confirmed a causal link from spawning stock demographic structure through egg and larval distribution to year class strength at recruitment. We here show that high mean age and size in the spawning stock of Barents Sea cod (Gadus morhua) is positively associated with high abundance and wide spatiotemporal distribution of cod eggs. We find, however, no support for the hypothesis that a wide egg distribution leads to higher recruitment or a weaker recruitment-temperature correlation. These results are based on statistical analyses of a spatially resolved data set on cod eggs covering a period (1959-1993) with large changes in biomass and demographic structure of spawners. The analyses also account for significant effects of spawning stock biomass and a liver condition index on egg abundance and distribution. Our results suggest that the buffering effect of a geographically wide distribution of eggs and larvae on fish recruitment may be insignificant compared with other impacts.
authors.affiliation: Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, N-0316 Oslo, Norway; n.c.stenseth@ibv.uio.no l.c.stige@ibv.uio.no.
authors.forename: Leif Christian
authors.initials: LC
authors.lastname: Stige
authors.affiliation: Demersal Fish Laboratory, Knipovich Polar Research Institute of Marine Fisheries and Oceanography, Murmansk 183038, Russia.
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Yaragina
authors.affiliation: Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, N-0316 Oslo, Norway.
authors.forename: Øystein
authors.initials: Ø
authors.lastname: Langangen
authors.affiliation: Demersal Fish Research Group, Institute of Marine Research, N-5817 Bergen, Norway.
authors.forename: Bjarte
authors.initials: B
authors.lastname: Bogstad
authors.affiliation: Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, N-0316 Oslo, Norway; n.c.stenseth@ibv.uio.no l.c.stige@ibv.uio.no.|Flødevigen Marine Research Station, Institute of Marine Research, N-4817 His, Norway.|The Centre for Coastal Research, University of Agder, NO-4604 Kristiansand, Norway.
authors.forename: Nils Chr
authors.initials: NC
authors.lastname: Stenseth
authors.affiliation: Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, N-0316 Oslo, Norway.|Research Group of Oceanography and Climate, Institute of Marine Research and Hjort Centre for Marine Ecosystem Dynamics, N-5817 Bergen, Norway.
authors.forename: Geir
authors.initials: G
authors.lastname: Ottersen
mesh_terms: D000818:Animals; D002980:Climate; D003247:Conservation of Natural Resources / Q000379:methods*; D005260:Female; D005398:Fisheries; D048389:Gadus morhua / Q000502:physiology*; D005843:Geography; D007814:Larva / Q000502:physiology; D008297:Male; D009664:Norway; D009792:Oceans and Seas; D010063:Ovum / Q000502:physiology; D011157:Population Dynamics; D011158:Population Growth; D012426:Russia
keywords: Gadus morhua; age and size truncation; climate effects; fisheries; population dynamics