Individual growth and size distributions within populations are generally influenced by both biotic and abiotic factors. Positively skewed size distributions may arise as a result of any size-selective process, such as food scarcity or competition. While such patterns have been observed for a variety of terrestrial plant and animal species, size distribution has been less studied for marine fish in the natural environment. This we do in the present paper. In order to investigate the effect of density and environment on juvenile coastal cod (Gadus morhua L.), we assess the length distributions of fish caught at fixed locations along the southern Norwegian Skagerrak coast over the period 1919–1996. We demonstrate that most distributions are skewed to the right, suggesting that competition may influence these systems; such effects seem to be strongest for sheltered stations inside the fjords. Density dependence is inferred as skewness increases with increased density, and the average length decreases with increased density. The skewness, average length, and abundance of juvenile cod caught in the autumn are shown to be influenced by the meteorological conditions in the spring (i.e., during the larval period). Directional wind stress along the shore and toward the shore and high temperatures create favorable conditions for the development of cod larvae. The effects of local abiotic factors may be measured through the North Atlantic Oscillation (NAO) Index, a large-scale climatic proxy.

Biotic component

10.1890/0012-9658(2002)083[1676:ldijcs]2.0.co;2

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Citations (46)

Primary growth rings in Blue Whiting otoliths

12 s. (1979)

Jakob Gjøsæter Inger Marie Beck

Whiting

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Ecological investigations on the spawning grounds of the barents sea capelin

Roald Sætre Jakob Gjøsæter

Capelin

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Citations (49)

Cycles and trends in cod populations

Proceedings of the National Academy of Sciences (1999)

Ottar N. Bjørnstad Jean‐Marc Fromentin Nils Chr. Stenseth Jakob Gjøsæter

Year-to-year fluctuations in fish stocks are usually attributed to variability in recruitment, competition, predation, and changes in catchability. Trends in abundance, in contrast, are usually ascribed to human exploitation and large-scale environmental changes. In this study, we demonstrate, through statistical modeling of survey data (1921–1994) of cod from the Norwegian Skagerrak coast, that both short- and long-term variability may arise from the same set of age-structured interactions. Asymmetric competition and cannibalism between cohorts generate alternating years of high and low abundance. Intercohort interactions also resonate the recruitment variability so that long-term trends are induced. The coupling of age-structure and variable recruitment should, therefore, be considered when explaining both the short- and long-term fluctuations displayed by the coastal cod populations. Resonant effects may occur in many marine populations that exhibit this combination of traits.

Cannibalism

Norwegian

10.1073/pnas.96.9.5066

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Citations (179)

Vekst av juvenile reker (Pandalus borealis Krøyer) ved forskjellig temperatur i laboratoriet

Bjørn Bøhle Jakob Gjøsæter

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