A tentative method to estimate mortality in the egg and early fish larval stages, with special reference to cod (Gadus morhua L.)

Abstract

A tentative method to estimate egg and larval mortality is demonstrated. The material was sampled during the cod egg and larvae surveys in the Lofoten area in the years 1983 and 1984. Correct ageing of eggs and larvae, reliable estimation of the number of individuals in different age groups, and the spawning curve (number of eggs spawned per day) are the principal components in the method. To estimate the mortality, the number of eggs and larvae in different age groups (8-50 days after spawning) are compared with the estimated number of spawned eggs. A mean daily instantaneous mortality rate of 0.12 can explain the reduction in number of spawning products during the period of investigation both in 1983 and 1984. The course of the mortality curve is discussed in relation to starvation and predation.