Zusammenfassung: Very simple modells of pelagic marine and freshwater ecosystems have proved very successful and are increasingly widely used. These models are highly aggregated and based in biomass or particle size. Theoretical investigations based primarily on energy flow considerations have provided of the success of these models ans suggest possible ways to extend their applicability.

Zusammenfassung: This paper is concerned with certain computational aspects of estimating the mean fecundity of a single age-class of a population of fish. Four computational methods for estimating mean fecundity are compared by Monte Carlo simulation. One of the four methods is the simple expedient of estimating fecundity at sample mean length, a method known to be downwardly biased. The Monte Carlo study shows that the other three methods reduce bias and provide worthwhile efficiency gains. For small samples, the most efficient of the four methods is a “bias adjustment”, proposed here, that uses easily calculated sample statistics. For large samples, a numerical integration method has the highest efficiency. The fourth method, a “direct summation” procedure which can be done easily in many statistical or spreadsheet programs, performs well for all sample sizes.