Maturity Schedules of Female American Shad Vary at Small Spatial Scales in Chesapeake Bay

Abstract

Recent assessments of American shad Alosa sapidissima have used stock-specific maturity schedules in biomass-per-recruit models to establish benchmark total mortality rates for management. Because stocks of American shad are managed separately, an appropriate maturity schedule for each stock is required. Additionally, projections of adult biomass require knowledge about year-class strength and the maturation process. Changes in age at maturity can occur when strong year-classes enter the spawning stock; such changes may affect stock assessment models and management decisions. Maturity schedules may also change due to fishing or other external factors. If stock-specific maturity patterns exist, then identical fishery regulations could have different impacts on neighboring stocks. Most American shad matured by age 5 in this study, with year-class-specific estimates of the percentage mature ranging from 46% to 80% in the James River, 58% to 79% in the Rappahannock River, and 49% to 82% in the York River, Virginia. Based on current monitoring, the age of full recruitment to the staked gill-net fishery is age 5, corresponding to the age at which the largest proportion of the population reaches maturity. Harvest of virgin females in the historical fishery was probably a contributing factor to its collapse during the 1980s. Persistent differences in maturity schedules of American shad between the James and York rivers and to a lesser extent between these rivers and the Rappahannock River show that neighboring stocks experiencing similar climate regimes can have stock-specific maturity patterns that persist through time. The delay in maturity observed in the James River stock may result in lower reproductive output and should be considered in management strategies.