Effects of density-dependent and stochastic processes on the regulation of cod populations

Type Article
Date 2001-02
Language English
Author(s) Fromentin Jean-Marc, Myers Ransom, Bjornstad Ottar, Stenseth Nils, Gjosaeter Jakob, Christie Hartvig, Fromentin Jean-Marc, Myers Ransom, Bjornstad Ottar, Stenseth Nils, Gjosaeter Jakob, Christie Hartvig
Affiliation(s) Univ Oslo, Dept Biol, Div Zool, N-0316 Oslo 3, Norway.
Inst Marine Res, Flodevigen Marine Res Stn, N-4817 His, Norway.
Norwegian Inst Nat Res, Sentrum, N-0105 Oslo, Norway.
IFREMER, Dept Resources Halieut, F-34203 Sete, France.
Dalhousie Univ, Dept Biol, Halifax, NS B3H 4J1, Canada.
Natl Ctr Ecol Anal Synth, Santa Barbara, CA 93101 USA.
Source Ecology (0012-9658) (Ecological Society of America), 2001-02 , Vol. 82 , N. 2 , P. 567-579
WOS© Times Cited 84
Keyword(s) Stochastic survival, juvenile, Observation errors, Mortality, direct density dependent, Mortality, delayed density dependent, Gadus morhua, Fjord, Cod population dynamics, Bottom flora coverage
Abstract We analyzed 136 time series (covering from 44 to 73 yr) of juvenile cod to estimate the level of direct and delayed density-dependent mortality (DDM) of 11 populations from the Norwegian Skagerrak coast. The parameters were estimated using a modeling approach that explicitly incorporates observation errors, so that we could quantify the density-independent (stochastic) variation in the survival of juvenile cod. Moderate to strong levels of DDM (direct or delayed) were estimated in eight of the 11 populations. Variability in the 0-group (corrected for observation errors) appeared to be large for most of the populations. Substantial stochastic variability in postsettlement survival was also detected in some areas, indicating that stochastic factors are not only important for egg and larval stages, as stated by the match-mismatch hypothesis, but also for juveniles. We show that the variability in these coastal populations is not only regulated as a function of the strength of DDM processes, but also as an interaction between DDM processes and stochastic factors. We finally postulate that local and regional differences in the strengths of the density-dependent and stochastic processes are related to differences in the quantity and quality of the bottom flora coverage, which govern both food availability and shelter for juveniles.
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Fromentin Jean-Marc, Myers Ransom, Bjornstad Ottar, Stenseth Nils, Gjosaeter Jakob, Christie Hartvig, Fromentin Jean-Marc, Myers Ransom, Bjornstad Ottar, Stenseth Nils, Gjosaeter Jakob, Christie Hartvig (2001). Effects of density-dependent and stochastic processes on the regulation of cod populations. Ecology, 82(2), 567-579. Open Access version : https://archimer.ifremer.fr/doc/00000/712/