Atlantic puffin Fratercula arctica and common guillemot Uria aalge chick diet and growth as indicators of fish stocks in the Barents Sea

Between 1980 and 2000, Atlantic puffins Fratercula arctica and common guillemots Uria aalge breeding in the southern Barents Sea fed their chicks on varying proportions of 4 main categories of prey: capelin Mallotus villosus, sandeels Ammodytes sp., I-group herring Clupea harengus and 0-group cod Gadus morhua. The varying proportions in both numbers and masses of the capelin, herring and cod in the seabird diet showed clear responses to the independently measured prey stocks. Amounts of capelin, herring and 0-group cod fed to Atlantic puffin chicks were good indicators of fish availability, whereas only amounts of herring fed to common guillemot chicks were correlated with the biomass of I-group herring in the region. The more general response by the Atlantic puffins probably results from their ability to catch only small fishes. Despite large interannual differences in prey consumption plus gradual changes in meal sizes, the growth rates of the chicks of both species remained near their maximum, suggesting physiological restraints in growth during plentiful years and/or compensatory foraging behaviour by the adults.