Dynamics of fish populations with different compensatory processes when subjected to random survival of eggs and larvae

Abstract

It is widely believed that abundance of fish populations is determined during the larval stage, for larval abundance is high, there is high variability in larval survival, and small changes in larval abundance could have large effects on population abundance. In this study, hypothesized population regulation processes were quantified in a mathematical model that was applied to study the importance of compensatory process during the larval stage by replacing them with random survival. The hypothesized population regulation processes were food-limited growth, size-dependent mortality, and age at maturity dependent on size. Variation in population abundance resulting from variation in egg and larval survival depends on the population regulation process. In population where mortality depends on size of individuals, variation in survival of young has little effect on abundance of adults. If age at maturity is flexible, variation in survival of young causes large fluctuations in abundance and the fluctuations follow a pattern of occasional large year classes that are slowly attrited over their lifespans. If age at maturity is not flexible, and if mortality is not size dependent, variation in survival of young causes population abundance to fluctuate widely without a clear pattern. Compensation during the larval life stage was not necessary for regulation of fish population size.