Atlantic sturgeon Acipenser oxyrinchus surfacing behaviour

Atlantic sturgeon Acipenser oxyrinchus surfacing behaviour was investigated in Minas Basin (45° 20′ N; 64° 00′ W) and the Bay of Fundy with pop‐up satellite archival tags (MiniPAT) measuring physical variables (pressure, temperature, light ) . Of six tags deployed during June and July, five provided pop‐up locations and two were recovered after c . 4 months. Analysis of recovered archival data revealed that the frequency of surfacing events was highest (78·9%) when A. oxyrinchus were in Minas Basin at depths <10 m. Surfacing frequency decreased substantially when fish migrated into greater depths of the Bay of Fundy (>40 m). The tidal cycle in Minas Basin had a significant relationship to surfacing frequency, with the most surfacing events (49·5%) occurring on the flood tide, from mid‐ to high‐tide. Surfacing events ranged from 0–12 a day and the maximum number occurred between 2300 and 0300 hours. Maximum surfacing ascent speeds ranged from 0·50 to 4·17 m s −1 and maximum descent speeds ranged from 0·17 to 3·17 m s −1 . Buoyancy control, by gulping air to inflate the gas bladder, is proposed as the main reason for surfacing behaviour in A. oxyrinchus .