The Possible Density-Dependence of Larval Mortality and Adult Mortality in Fishes

Abstract

The numbers of fish populations are probably regulated mainly during the larval drift, by a combination of density-dependent growth and density-dependent mortality. During this period, density is maximal; it declines sharply with age. Gulland (1965) distinguished a coarse and a fine control of numbers in a fish population. The coarse control probably occurs during the larval drift and the fine control might occur at a later stage in the life cycle. Cushing (1971) examined the relation between an index of density-dependence and fecundity and found that the index varied with the cube root of the fecundity, that is, with the distance between the larvae in the sea. Harris (in press) examined the critical period during which recruitment was determined by the time taken to grow through it. He looked specifically at the dependence of the critical period on stock and concluded that the stock and recruitment equation of Ricker (1958) could be written:

$$ R\; = \;AP\;\exp \; - \;B{P^{{1/3}}} $$

(1)

where R is recruitment,

• P is stock,

• A is the coefficient of density-independent mortality,

• B is the coefficient of density-dependent mortality.