Reproduction and early life history of a landlocked population of alewife (Alosa pseudoharencus) in Claytor Lake, Virginia

Abstract

Alewives in Claytor Lake matured at age I at 160 mm TL. Fecundity of gravid females increased with age and length, ranging from 17,307 eggs at age I to 37,147 eggs at age III. The majority of alewife spawning was concentrated in littoral areas of a large embayment. Spawning period was protracted (13 weeks), beginning in May and lasting until August. Females apparently did not extrude eggs at one time, but spawned repeatedly.

Growth rates of young-of-the-year alewives were higher in 1978 than in 1979, possibly due to reduced intraspecific competition for food and space following an alewife die-off in winter 1977-1978. Rapid growth of young-of-the-year alewives allowed the earliest spawned cohorts to become morphologically unavailable as prey to age 0 and age I sportfish by mid-July. However, the extended alewife spawning season mitigated availability of alewives by assuring, through subsequently spawned cohorts, that they remain available as prey through the growing season.

Cyclopoid copepods were the principal food item in diets of alewives 6 to 35 mm TL. Bosmina longirostris dominated diets of alewives 36 to 70 mm TL. Size-selective planktivority of larval alewives was equivalent to that of adults at sizes as small as 31 mm TL, and may have significantly contributed to observed changes of zooplankton communities toward smaller forms. Concentrations of young-of-the-year alewives in littoral areas may exert a negative impact on age 0 sportfish which depend on littoral zooplankton populations as a food source.