Age and Population Size Estimates of Overwintering Shortnose Sturgeon in the Saint John River, New Brunswick, Canada

Abstract

AbstractThe 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.