Biotic influences on drift behaviour of larval white sturgeon (Acipenser transmontanus)

Drift by larval white sturgeon (Acipenser transmontanus) results in an ontological habitat shift during early life that may be influenced by changes in the trade-off between mortality risk and growth potential. Despite the importance of early life history to recruitment and conservation, for many species, including white sturgeon, we have a limited understanding of the mechanistic drivers of drift. We tested if two biotic factors, conspecific density and timing of food availability during the yolksac larvae stage, influenced the timing of drift behaviour. We evaluated larval drift timing for yolksac larvae reared in laboratory mesocosms at two densities (10 or 20 larvae) and three feeding initiation times (before exogenous feeding, at the initiation of exogenous feeding, or starvation). We found that drift occurred at 13 days post-hatch (dph) overall, 2 days after the shift from the yolksac stage to the feeding stage (11 dph at 14°C). The timing of food availability in the fed treatments did not affect the timing of larval drift, nor did the density of conspecifics. Starvation delayed drift timing by 2 days, to15 dph. This delay of drift from a habitat with no food availability may disadvantage starving larvae and reduce growth potential.