Influences of Anadromous Spawning Behavior and Optimal Environmental Conditions Upon Striped Bass (Morone saxatilis) Year-Class Success

Abstract

An analysis of the spatial and temporal abundance patterns of developing striped bass (M. saxatilis) ichthyoplankton stages in the Potomac Estuary [USA], including a Markovian description of transport, indicates that annual differences in the distribution of spawning fish are not likely to account wholly for the wide fluctuations in year-class success. Year-class success can be decomposed into the product of 2 factors: one extrinsic, acting upon the eggs and larvae and the other a behavioral property of the adult stock. The effect of extrinsic environmental conditions upon year-class success can be measured relative to the maximum computed survival of eggs to post-finfold larvae among all locations and times during a given year. The behavior of the spawning adult fish is not well matched with the environmental conditions favorable to ichtyoplankton survival, and the actual spawning distribution yields only a fraction (the spawning fitness) of the maximum production possible during that year. Spawning fitnesses were small (< 0.02 of 1.0) and varied by < a factor of 2 over the 3 seasons observed. The year-class success as measured by post-finfold production differed 35-fold over the same 3 yr. The large range in success may be due primarily to the extrinsic, density-independent environmental factors which determine the optimum survivals in combination with spawning behavior. No strong case can be made for behavioral compensation by spawning fish to offset changes in the annual optimum survival conditions for ichthyoplankton.