PREDATION RISK DURING THE EARLY-LIFE HISTORY PERIODS OF FISHES - SEPARATING THE EFFECTS OF SIZE AND AGE

We compared predation risk for fish which differed in age at metamorphosis but not in length, and for those which differed in length at metamorphosis but not in age, using laboratory-reared winter flounder Pleuronectes americanus. Pairs of fish were offered to individual predatory shrimp Crangon septemspinosa as prey in a series of laboratory predation trials. In the size experiments, prey length differed on average by 0.5 mm (8%), but age was identical. We could not detect a difference in the number of captures of 'small' and 'large' individuals in 104 trials where only 1 prey was consumed. In the age experiments, prey age differed by 9 d (18% on average), but length was virtually identical. We could not detect a difference in the number of captures of 'young' and 'old' metamorphosing individuals in 56 trials where only 1 prey was consumed. Moreover, time until capture did not vary with increasing age at metamorphosis over a range of 35+ d. These results suggest that any differences in predation risk between fish which exhibit the range of ages and sizes at metamorphosis represented in our experiments are subtle and are potentially ecologically inconsequential. This work, combined with that of others, questions the validity of the inference that, for marine fishes, individuals which are large-at-age have a survival advantage during the early life history periods.