Effect of Experimental Manipulation of Feeding Conditions on the Population Stucture of Larval Cod (Gadus morhua) and Herring (Clupea harengus).

Abstract

Cod and herring larvae were fed either rotifers or mixtures of rotifers, Artemia, and wild plankton to test the effects of feeding conditions on the development of population size structure. The population size structure at each sample date was characterized by the skewness, the standard deviation of mean length, the coefficient of variation of mean length and the Gini coefficient. The development of size structure through time was characterized by the spreading rate, which is the rate of change in the standard deviation of mean length over time. Larvae fed on a single, small-sized prey item (rotifers) grew slowly, and size variation increased slowly. Larvae fed on mixed prey species showed better growth; the population structure changed more rapidly, and often led to a skewed size distribution dominated by larger individuals. The presence of larger prey items resulted in disproportionate growth rates in the mixed-diet groups. The presence of these faster-growing individuals was the most important factor in determining the shape of the final size distributions and the development of the population size structure.