Mortality of juvenile sandeel on the Faroe Shelf due to food limitation

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On the Faroe Shelf, sandeel (Ammodytes marinus) spawn around new-year. Since 1974, juvenile sandeel have been sampled during the annual 0-group surveys in late June – early July and the results show large variations, both in the number and the average length of the sandeel sampled. Here, we investigate these variations in recruitment success in relation to food availability. The food of early-life sandeel is dominated by zooplankton, which again depends on the primary production. On the Faroe Shelf, measurements of chlorophyll a and accumulated new primary production during spring and summer have been carried out since 1990 and this shows large inter-annual variations in the spring bloom onset and intensity. In the paper, we compare the time series from sandeel 0-group surveys with data on phytoplankton production and biomass. The results confirm that survival and condition of the early-life stages of sandeel on the Faroe Shelf is dependent on the magnitude of the primary production. Although the sandeel spawns several months before the spring bloom, the timing of the spring bloom start does not seem to have a significant influence on the number or length of juvenile sandeel during the 0-group survey. They seem to be mainly determined by the phytoplankton concentration just before the survey. Sandeel is an important food source for higher trophic levels e.g. seabirds, cod and haddock. The established link between sandeel mortality and primary production may therefore help explain a previously found link between primary production and commercially important fish stocks as well as seabirds on the Faroe Shelf