Little is known about the dispersal of Shortnose Sturgeon Acipenser brevirostrum larvae in the wild. In the Saint John River, New Brunswick, we captured a total of 2,251, 460, 2,100, and 2,083 larvae in 2008–2011, respectively; abundance estimates ranged between 21,000 (2009) and 244,687 larvae (2008). A substantial reduction in larval numbers (49–76%) was recorded over the 4.5‐km distance between the two sampling transects deployed in 2008–2010. We found no consistent pattern of larval distribution across the channel, but we recorded a consistent, significant preference for nighttime (dusk to dawn) over daytime dispersal. Generalized linear models were used to examine the timing and extent of larval migration in the Saint John River during the study period. Logistic models incorporating water temperature and Mactaquac Dam discharge provided good predictions of the timing of larval migration. The probability of larval presence was highest when water temperature reached 15°C. At this temperature, larvae were predicted to disperse when nighttime total dam discharge was 20 106 to 30 106 m3. The extent of larval migration was described using negative binomial models, which indicated that dam discharge and transect location significantly influenced the number of drifting larvae. However, data variability was high, reducing predictive capability. Our findings include the first report of Shortnose Sturgeon larval abundances in the Saint John River. The predictions of timing and extent of drift provide information for future sampling and conservation efforts during this vulnerable period as well as insight into the relationships between environmental variables and larval drift in this protected species.

The densities and overall abundances of overwintering shortnose sturgeon Acipenser brevirostrum were estimated using underwater video at the Kennebecasis River overwintering site in 2009 and 2011. In 2009, underwater cameras coupled with lasers provided image‐based estimates of fish lengths (and therefore ages). The precision and accuracy of laser‐based measurements were estimated by laboratory experiments. In total, 362 and 222 overwintering shortnose sturgeon were counted in the 0.02‐km2 area during 2009 and 2011, respectively. The fork lengths of 83 overwintering shortnose sturgeon measured in 2009 ranged from 54 to 119 cm, corresponding to ages of 11–57 years (20.3 ± 7.9 years [mean ± SD]). Length measurement accuracy was highest (±10% fork length) when fish were positioned at 0 ± 30° or 180 ± 30° to the camera's lens. Three different models of spatial fish density estimated a total of 3,852–5,222 shortnose sturgeon in 2009 and 2011, similar to the 2005 local population estimate of 4,836 shortnose sturgeon. The consistent, high‐density aggregation of subadults and adults at this small site between 2005 and 2011 suggests that the site is important for protection of shortnose sturgeon in the Saint John River system.

Timing of spawning and hatching of shortnose sturgeon, Acipenser brevirostrum , in the Saint John River, New Brunswick, Canada, was estimated using inverse prediction. We examined egg incubation periods at 5, 9, and 13 °C to back-calculate spawning dates. No larvae hatched at 5 °C. At 9 and 13 °C, hatching began after 18 and 8 days post fertilization, respectively. Lengths of yolk-sac larvae reared in the laboratory at 13–21 °C were used to develop a temperature-mediated Gompertz growth model. The inverted Gompertz model, predicting larval age from larval size and water temperature, was applied to 671, 164, and 746 larvae captured in the wild in 2008, 2009, and 2010, respectively. Estimated hatching distributions peaked in late May, and mean spawning events were predicted to occur in late April – early May (9 °C scenario) and middle to late May (13 °C scenario). Larval ages at the two sampling transects, 4.5 km apart, were similar, while catch per unit effort was lower downstream, indicating mortality during dispersal. Inverse prediction of larval ages provides fast and cost-effective estimates of the timing of spawning, hatching, and larval migration in the wild.

We examined the effects of spatial, temporal, and environmental parameters on the feeding habits of the shortnose sturgeon Acipenser brevirostrum. We sampled sturgeon gut contents using colonic flushing, a new, low-impact technique. We found that heavy feeding continued until at least November, when water temperature reached 8 • C. In all seasons, foraging shortnose sturgeon used shallow water (2-8 m); however, in late fall this trend was even stronger, when 50% of the sturgeon were captured in less than 3 m depth. Over 60 families of prey items were identified from 166 colonic samples collected at four points between spring and late fall from seven locations throughout the lower Saint John River, New Brunswick. Samples from freshwater sites contained mainly Gastropoda, Sphaeriidae, Chironomidae, and Gammaridae. Samples from saline and brackish environments contained mostly Gammaridae, Corophiidae, softshell clam Mya arenaria, Cyathura polita, and Chironomidae. We used sensitivity analysis to determine the number of shortnose sturgeon required to obtain a representative sample of the diet. We found that 20-40 gut samples from sturgeons in both brackish and freshwater environments would suffice for a general description of the diet but that complete knowledge of the sturgeon diet and a comparison among several sites would require the sampling of hundreds of fish. The digestibility of prey varied from 77% of the ingested volume in a saline environment to only 6% in freshwater samples. Shortnose sturgeon from freshwater sites had higher ingested volumes and more prey per ingested volume than did those from brackish sites, which indicated further differences in feeding efficiency between the environments. Salinity was a significant parameter in the redundancy analysis of ingested prey items. In freshwater sites the significant factors were season, sturgeon length, ingested volume, number of ingested prey, and number of ingested taxa. In saline sites the significant factors were season, location, ingested volume, and the number of ingested prey. Our findings identified the spatial and temporal gradients in shortnose sturgeon foraging and provided insight into foraging efficiency in this species.Studying a species' foraging ecology is critical to understanding their movements and habitat requirements. Sturgeon diets have been previously studied in several species, e.g.