Mechanisms contributing to variable growth in juvenile southern flounder (Paralichthys lethostigma)

We evaluated mechanisms accounting for skewed and potentially bimodal sizes among juvenile (age-0) southern flounder, Paralichthys lethostigma, in Pamlico Sound, North Carolina. The birth-date distribution of age-0 southern flounder in 1990 was unimodal with a peak in mid-January and birth date and size were unrelated in the juvenile stage. Differential growth, rather than birth date, accounted for the broad dispersion of lengths occurring in the Ist year. By September 1990, females on average reached larger sizes, but they overlapped the whole size range of males; there was evidence for a bimodal juvenile distribution with females dominating the upper size mode. Based on otolith increments, growth rate variation among juveniles through the summer was high, ranging from 0.35 to 1.5 mm per day with an apparent bifurcation in the growth curve beginning at about 75-200 mm total length which corresponded to the onset of piscivory. While variation in the onset of piscivory was the most likely mechanism generating skewed flounder sizes, differential growth may have been magnified because of mismatch of prey size and availability, or environmental factors affecting spatial segregation of small and large individuals from the age-0 cohort.