Possible causes and consequences of variation in age and size at metamorphosis in flatfishes (pleuronectiformes): An analysis at the individual, population, and species levels

Abstract

Observations on metamorphic ages and sizes in flatfishes are synthesized within a hierarchical framework which ascends from individual to population to species levels. Examples of observations and inferences are given for each level with emphasis on variation among individuals within populations. At the species level, size at metamorphosis ranges from ≈4 to 120 mm and is log-normally distributed. Species-level estimates of ages at metamorphosis from field-collected flatfish are of low resolution if they are derived as the difference between approximate spawning and inferred settling dates. Temperature is the only environmental factor whose effects on metamorphic traits have been evaluated at the population level. Age at metamorphosis increases by more than twofold and metamorphic size is expected to increase slightly as temperature decreases across the viable range. At the individual level, data are available for starry flounder, Platichthys stellatus, and winter flounder, Pseudopleuronectes americanus. Bivariate distributions of metamorphic ages and sizes for these flounders, schematized as metamorphic envelopes, have different locations and orientations, but similar shapes. Metamorphic age has greater within-population variation and is less influenced by parentage than is metamorphic length. Furthermore, maternal contributions to metamorphic traits exceed paternal ones. Effects of metamorphic trait variation on size distributions of young-of-the-year juveniles were evaluated by simulations. In a benign environment lacking mortality bias, the effect of metamorphic age on juvenile size variation was ≈sixfold greater than the effect of metamorphic size. The impact of metamorphic age on juvenile size variation lessened with extension of the spawning interval and with increased duration of juvenile life prior to capture.