Latitudinal variation in ontogenetic behaviour of shortnose sturgeon,Acipenser brevirostrumLesueur, 1818: an artificial stream study

Abstract

Two hypotheses were tested on intraspecific variation in early behaviour of Shortnose Sturgeon, Acipenser brevirostrum: (i) ontogenetic behaviour of Shortnose Sturgeon from a northern and a southern population is different, and (ii) dispersal time by southern Shortnose Sturgeon is longer than that of northern Shortnose sturgeon. The hypotheses were tested by observing habitat preference and dispersal of early life stages = ELS (free embryos, larvae, and juveniles) from a northern river (Connecticut River, MA) and from a southern river (Savannah River, SC) in a common garden experiment. Free embryos (yolk-sac fish) from both rivers were similar, selecting cover and dark habitat, but Savannah River fish used cover less and moved downstream more than Connecticut River fish (a quantitative difference between populations). When fish developed into larvae, fish from both populations preferred an open, bright habitat, left cover, and dispersed downstream mostly at night. Early dispersal of Connecticut River larvae had a 6-day peak, whereas Savannah River larvae had a weak, 4-day peak (another quantitative difference between the populations). After the early peak, dispersal by Connecticut River larvae was multi-peak with low intensity, ending on about day 36 (before larvae developed into juveniles). Savannah River larval dispersal was also multi-peak, but with a greater intensity, and continued to day 60, when observations ended and fish were juveniles (a qualitative difference between the populations for dispersal cessation). The differences in behaviour between the two populations support both of our hypotheses. The results indicate that behavioural-genetic differences exist between northern and southern Shortnose Sturgeon populations, particularly for larval dispersal. Conservation strategies, particularly conservation stocking of Shortnose Sturgeon (and other sturgeons), should consider differences between river populations for local behavioural adaptations of ELS.