Density-dependent Fishing Mortality of American Shad in the Altamaha River, Georgia

Catchability of American shad (Alosa sapidissima) from the Altamaha River, Georgia, was compared with population size of female adult spawners to determine if density-dependent fishing mortality was occurring in that fishery. Mark-recapture techniques and effort and harvest data were utilized to examine this relationship. An inverse power function described the relationship between fishing mortality per unit effort and female population size from 1982 to 1991. The relationship became slightly stronger by holding the flow variable constant. Therefore, shad populations in the Altamaha River are most vulnerable when weak spawning runs are subjected to commercial fishing pressure, and to a lesser extent, when low flows occur.