Ontogeny and life history of shortnose sturgeon (Acipenser brevirostrum Lesueur 1818): Effects of latitudinal variation and water temperature

Ontogenetic niche shifts usually occur concurrently with a change in developmental stage and likely evolved as a strategy to reduce mortality and optimize growth at each developmental stage. The optimal shift point may be flexible, however, and may be influenced by environmental cues. In this dissertation I address the following three objectives: (1) Compare habitat preferences and dispersal duration and timing of early life stages of shortnose sturgeon from a northern (Connecticut River, MA, USA) and a southern (Savannah River, SC, USA) river, (2) Determine the effect of three temperature regimes on the timing and pattern of downstream dispersal of shortnose sturgeon larvae, and (3) Link changes in morphological development with ontogeny of behavior in shortnose sturgeon.; During the period of yolk-sac absorption, fish from the Connecticut and Savannah Rivers which were reared at the same temperature selected cover and dark habitat, sheltering under rocks and preferring darkness and black substrate. Once fish began feeding exogenously, they switched rapidly to a preference for open, bright habitat, emerging from rocks and selecting illuminated areas and white substrate. Connecticut River fish moved downstream for 6 days (days 7--12 after hatching) beginning immediately after feeding began. However, Savannah River fish had a longer dispersal with multiple, prolonged peaks and fish continued a low level of downstream movement for the whole larval period and as early juveniles (at least until day 62). The differences in dispersal between Connecticut and Savannah River fish, however, were expressed under the same laboratory conditions, including temperature. Thus, genetic differences between the populations do exist and conservation strategies should consider this. In tests with Connecticut River fish to determine temperature effects on dispersal pattern, rearing fish at 10°C delayed the onset of dispersal, but increasing the temperature (15 and 20°C) produced a dispersal with multiple peaks, rather than simply shifting the peak to a younger fish age. Fish were morphologically similar when they began dispersing, regardless of river or temperature. Colder temperature caused development to slow and fish to delay beginning dispersal. These results show dispersal of shortnose sturgeon early life stages is influenced by river temperature.