Variation in American Shad Batch Fecundity

—American shad Alosa sapidissima in semelparous and iteroparous populations along its native range are thought to have nearly equivalent lifetime reproductive output due to reciprocal latitudinal trends in fecundity and degree of repeat spawning. Geographic differences in reproductive patterns are believed to be linked to varying environmental conditions, and this fine tuning is considered strong evidence of intraspecific life history evolution in marine fishes. American shad are also multiple or batch spawners, but this reproductive trait has only recently been described. Our objectives were to estimate batch fecundity of American shad in semelparous (St. Johns River, Florida) and iteroparous stocks (York River, Virginia, and Connecticut River, Massachusetts) and to re-evaluate annual and lifetime fecundity in these populations. Hydrated females were collected on the spawning grounds of each river. Hydrated oocytes were counted in subsamples from each ovary, and batch fecundity was estimated gravimetrically. Estimates of hydrated oocytes/g ovary were found to be independent of subsample location in the gonad. Log10-transformed relationships of batch size and total fish weight were highly significant for females in the St. Johns and York rivers and marginally significant for Connecticut River fish. Adjusting for body size, we found no significant differences in batch size among these stocks. We conclude that batch fecundity of American shad does not vary significantly among semelparous (St. Johns River) and iteroparous (York and Connecticut rivers) populations. In all stocks of American shad, spawning frequency and duration are unknown, and seasonal or lifetime egg production cannot be estimated. Thus, hypotheses portraying latitudinal variation in fecundity as an evolutionary response to decreased levels of iteroparity in stocks of American shad are unconfirmed.