Striped Bass Early Life History in the Macrotidal Shubenacadie River

Abstract

AbstractThis 9‐year study (2008–2016) on the Shubenacadie River estuary in Nova Scotia yielded new insight into the only confirmed nursery habitat for the Bay of Fundy population of Striped Bass Morone saxatilis. In 7 of 9 years, the initial large spawning episode occurred between May 16 and June 1, after the accumulation of 11 to 20 degree‐days above 12°C. Most of the spawning occurred within about 3 weeks in May and June but could run into July. Egg abundance at river kilometer (rkm) 25 (measured from the estuary mouth) exceeded 1,000 eggs/m3 after the largest episodes due to the narrow estuary and high numbers of spawners. The pelagic eggs and prefeeding larvae were passively transported up and down the estuary by the strong tide, their distribution highly dependent on salinity. The salt front defined the upstream boundary of the nursery habitat, with the eggs and larvae normally distributed between 0.15‰ and 15‰ (above rkm 10). The abundance of first‐feeding larvae (5–7 mm TL) in the upper estuary (above rkm 25) was highest (>500/m3) during years when May–June was warm and dry and saltwater intrusion was high (above rkm 32). Heavy rain after spawning was an important lethal factor, limiting saltwater intrusion to rkm 25 and increasing the risk of advection of eggs and larvae into Cobequid Bay. During June, a lack of copepod prey caused larvae to fail to grow, suggesting that starvation is an important lethal factor. Growth from July onwards was limited by temperature but not food: mysids were highly abundant and an important prey for young of the year (>15 mm TL). By late August juvenile mean total length was >9 cm in warm summers but <5 cm in cooler years. Juveniles were widely dispersed in the estuary and Cobequid Bay through September; their apparent abundance each year was poorly related to larvae abundance.