Population demographics of hickory shad (Alosa mediocris) during a period of population growth

Abstract

Our study goal was to characterize the demographics of the population of Hickory Shad (Alosa mediocris) in the Albemarle Sound-Roanoke River watershed during a period of population in- crease and to assess its susceptibility to harvest. Adults were collected from gillnet surveys and a river recreational fishery from February to May 1996. The male-to-female ratio was similar between the Albemarle Sound (0.73:1) and the spawning grounds in Roanoke River (0.76:1). Ages were 2-7 years, but most sampled fish were age 3 or 4. The von Bertalanffy growth equation was Lt = 460 (1 - e-0.24(t + 1.63)), where Lt was predicted length at time t for sexes combined. Total mortality (Z) was 1.43 for males age 3-5, 1.76 for females age 4-6, and 1.40 for sexes combined. Sexual maturity in both sexes was essentially complete by age 4. Repeat spawning was common: 46.8% of males were virgin, 45.5% had spawned once, and 7.7% had spawned 2 or 3 times. For females, 24.9% were virgin, 45.5% had spawned once, and 29.6% showed evidence of spawning 2, 3, or 4 times. Mesentery fat in both sexes de- creased from the prespawning aggregation (staging) area in the sound to the river spawning grounds, indicating that both sexes feed extensively in ocean waters before the inland portion of the spawning migration. The short lifespan of Hickory Shad, combined with an early age to maturity and an anadromous migration pattern, indicates that mature individuals are very susceptible to recreational and commercial harvest and are removed by exploitation or natural mortality within 1 or 2 seasons.