Effects of substrate condition on habitat use and survival by white sturgeon (Acipenser transmontanus) larvae and potential implications for recruitment

To understand links between substrate and recruitment of white sturgeon ( Acipenser transmontanus ), I evaluated the effects of substrate condition on larval drift, hiding, and predation between hatch and 15 days posthatch (dph). Over porous substrates (small gravel = 1.2–1.9 cm; medium gravel = 2.5–5.0 cm; cobble = 10–15 cm), rapid interstitial hiding was observed from 0 to 6 dph at low water velocity (4 cm·s–1), whereas larvae drifted in response to nonporous substrates (sand < 0.2 cm; embedded cobble). Velocities of 20 cm·s–1 led to significantly lower drift only at 1 dph over small gravel. Hiding occurred an average of 2.0–13.3 s after release at 0–6 dph. Predation by sculpins ( Cottus spp.) on larval sturgeon also decreased significantly in response to porous substrates at 1 dph. The strongest expression of increased hiding and decreased predation when small gravel was available suggests that yolksac larvae prefer small interstitial spaces created by that substrate. Considering behavioural responses in preferred natural spawning habitat suggests yolksac larvae predominantly hide in the vicinity of spawning locations. Identification of strong effects of substrate condition on age-specific drift and survival suggests that substrate degradation may contribute to recruitment limitations for sturgeon.