Trophodynamic control on recruitment success in Baltic cod: the influence of cannibalism

Cod is the top piscivore predator in the Baltic Sea ecosystem. Based on sto mach content data from 62427 cod collected during 1977-1994 and food consum ption rates, cannibalism in the Eastern and Western Baltic cod stocks has b een quantified using multispecies virtual population analysis. In the Easte rn Baltic stock, depending on model assumptions, an average of 25-38% of th e 0-group and 11-17% of the 1-group were removed by predation by adults. Th us, between age 0 and age 2 a year class may lose on average about 31% and 44% of the initial number as a result of cannibalism. Cannibalism is lower in the Western Baltic. On average, 19% of the 0-group and 9% of the 1-group are consumed per year, i.e. 24% of the initial cohort is eaten before reac hing age 2. Predation was most intense in 1978-1984, a period with high juv enile abundance and large adult stock sizes in both areas. Subsequently, st ock, recruitment, and cannibalism declined steadily until the early 1990s a nd then increased again. Problems identified in relation to data compilatio n and estimation procedure are discussed with respect to their impact on es timates of cannibalism and stock-recruitment relationships. (C) 2000 Intern ational Council for the Exploration of the Sea.