Coastal Spawning Migration of Shortnose Sturgeon in the Gulf of Maine

Nineteen stage-IV shortnose sturgeon females acoustically-tagged in the Merrimack River were observed departing the river in early spring, moving 130 km to the northeast, then entering the Kennebec River System and eventually occupying three known spawning sites. During four consecutive springs beginning in 2010, migrants departed Merrimack River wintering sites between 15 March–12 April and exited the river mouth between 22 March–20 April. River temperatures during departures ranged between 4.1–11.5°C (mean; 8.1°C), and discharged ranged between 121–1,495 m³/s (mean; 593 m³/s). Migrants entered the Kennebec River between 30 March–4 May, resulting in migration durations of 6.8–22.1 d (mean; 12.1 d). Coastal ocean temperature and salinity levels during pre-spawning movements ranged between 4.6–7.2°C and 28.6–32.2 ppt. After participating in upstream spawning runs within the Kennebec System, 15 migrants returned to the Merrimack River in spring, entering the river mouth between 3–31 May. Two migrants, however, returned later (July and November), and two remained within the Kennebec System. During both pre- and post-spawning migration segments, several fish spent brief periods in the Piscataqua River (four) and the Saco River (six), two smaller drainages positioned between the Merrimack and Kennebec rivers.