The potential effects of cannibalism and intraguild predation on anchovy recruitment and clupeoid fluctuations

Abstract

To obtain a first estimate of the potential impact of density-dependent regulation by cannibalism and by inter-specific predation by a guild species (pilchard) on anchovy population growth, a simple model based on a Leslie matrix was constructed. Simulations in which the pilchard biomass was held at 0 and the anchovy biomass increased, demonstrated that the eigenvalue decreased linearly from 1,03 at 1 000 tons to 0,94 at 2 million tons, showing a potential density-dependent mechanism for population regulation. The impact of pilchard on anchovy population growth depended on the assumed clearance rate. At the maximum biomass tested (2 million tons of pilchard) the eigenvalue of the anchovy Leslie matrix varied from 0,91 to 0,36, depending on the anchovy biomass and the pilchard clearance rate used. Field evidence indicates that the fastest clearance rate tested may be the most realistic of the three options. The model assumed uniform distribution of eggs in the spawning area, but the results are sensitive t...