Sammendrag
When seeking a location for spawning, fish appear to be under the influence of two groups of factors. Firstly, environmental cues such as temperature and salinity. Secondly, interactions with other individuals, like entrainment of recruit spawners or competition for favourable locations. Many stocks have several spawning grounds, each containing several centres of spawning, with variable proportions between these centres. One such stock is North East Arctic cod, which has undergone a history of low stock size and truncated age structure in recent decades, followed by a rapid recovery since the mid 1990’s. Combining time series of egg distribution from the 1980’s, 1990’s and from 2004 to 2012, we attempt to elucidate possible controls for inter-annual variations between centres of spawning in its primary spawning grounds around the Lofoten islands. We describe how the distribution changes from one egg stage to the next and how the proportion observed in the wide fjord between the island chain and the mainland varies on a sub-decadal time scale. In our models we relate egg distribution to population dependent factors (SSB, spawning stock age structure, ratio of recruit and repeat spawners, spatial structuring) and independent factors (local hydrography, Kola-section temperature) and examine possible controls on these temporal variations. We evaluate the contributions of the different factors to the explained variation and discuss possible causal mechanisms for this specific case and in a broader perspective.
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