Variability in the rates of growth and development in marine fishes and their effect on the timing of early life history transitions

Benoit, Hugues P. (1999) Variability in the rates of growth and development in marine fishes and their effect on the timing of early life history transitions. Masters thesis, Memorial University of Newfoundland.

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Abstract

There is considerable variability in the timing of early life history transitions within and among species of marine fishes. Variability in the ages and sizes at which fish undergo metamorphosis, from larvae to juveniles, may be particularly important in determining survival because metamorphosis represents the culmination of a period of high mortality and corresponds to a stage by which recruitment levels begin to be established. Using a combination of empirical multi-species literature reviews, experiments, and simple analytical modelling, I show that variability in size and age at metamorphosis results from the integration of the variability occurring throughout early development. -- Analysis of several published studies indicates that average metamorphic length is relatively constant within species and mean metamorphic age is the time that it takes to grow to that length. Results from the empirical literature review and from experiments with yellowtail flounder (Pleuronectes ferrugineus) demonstrate that differences in the growth trajectories of individual larvae result in considerable variability in metamorphic age, and to a lesser extent length, within populations. Furthermore results from a growth reconstruction study using otolith growth diameters suggest that the metamorphic age of individuals may be predicted by the size that larvae have achieved two weeks after hatch. Sources of such variance in initial body length were considered in a second experiment, which demonstrated that the hatching length of yellowtail flounder larvae is determined by interactions between rearing temperatures, maternally derived differences in egg diameter and individual differences in development time. These interacting variables result in considerable, environment- dependent scope for variability in initial larval lengths. -- I conclude by making empirical (multi-species) comparisons of individual-level variability in stage duration and length of larvae at hatching and metamorphosis. In doing so I argue that differences among individuals are generated in a fairly consistent manner for developing embryos and larvae. As a consequence, individual developmental trajectories may begin to diverge soon after fertilization, resulting in considerable variability in the timing of metamorphosis. These results are corroborated by a simple analytical model for autocorrelated individual growth. Overall, the results presented in this thesis suggest that small differences in body size or development rate among individuals occurring early during ontogeny can affect events that occur months later, and may determine eventual chances for survival.

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