| TEMPORAL VARIATION IN FISH ABUNDANCE AFFECTS SEABIRD POPULATIONS: COD-GUILLEMOT INTERACTIONS IN THE BARENTS SEA |
| Erikstad, K.E., Norwegian Institute for Nature Research (NINA), FRAM - High North Research Centre for Climate and the Environment, 9296 Tromso, Norway, kjell.e.erikstad@nina.no; Reiertsen, T.K., Barrett, R.T, Dept of Natural Sciences, Tromso University Museum, 9037 Troms, Norway, tone.reiertsen@uit.no, rob.barrett@uit.no; Vikebø, F., Institute of Marine Research, Box 1870, Nordnes, 5817 Bergen, Norway, frovik@imr.no; SANDVIK, H., Centre for Conservation Biology (CCB), Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway, hanno@evol.no |
| Small pelagic fish and young age classes of larger predatory fish constitute the most important prey of seabirds. Fish abundance has long been hypothesized to play a major role in regulating seabird populations. Climatic fluctuations, commercial fisheries and interactions between fish species and the environment may cause pronounced spatial and temporal variation in fish abundance and affect seabird populations in many areas. We have analysed the temporal variation in the population of common guillemots (Uria aalge) in a colony in NE Norway (Hornoya) between 1980 and 2010 in relation to the variation in abundance (acoustic and trawl surveys) of important fish prey species in the Barents Sea. The fish species considered were all age classes of capelin (Mallotus villosus), 0- and I-group herring (Clupea harengus) and 0- and I-group cod (Gadus morhua). The annual variation in guillemot population growth rate could best be explained by the variation in abundance of 0-group cod and the 0-group cod six years earlier (equalling the age of maturation of guillemots). The very strong positive relationship between the youngest age class of cod and the variation in the common guillemot population growth rate undermines the earlier belief that the capelin stock has a major effect on the population dynamics of common guillemots. A numerical ocean model was used to identify mechanisms affecting spatio-temporal prey availability of 0-group cod around the colony during the breeding season. |
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