ORIGIN OF THE PRESENT DELAWARE RIVER STRIPED BASS POPULATION AS SHOWNBY ANALYSIS OF MITOCHONDRIAL-DNA

Management options for the Delaware River population of striped bass M orone saxatilis depend on whether or not the population forms a discre te stock. The recent increase in striped bass in the Delaware River fo llows decades of scarcity and concern about the possible extinction of the original population. The increase may have resulted from one or m ore of the following: expansion of a remnant population, repopulation by migrants from the Chesapeake Bay, or repopulation by migrants from the Hudson River. To determine the origin of the present Delaware Rive r striped bass population, we analyzed mitochondrial DNA (mtDNA) from 191 striped bass collected in the Delaware River between 1990 and 1992 . Our results indicate the Delaware River striped bass population is g enetically intermediate between the Chesapeake Bay and Hudson River po pulations; mtDNA major-length genotype frequencies of the Delaware Riv er sample were significantly different (P < 0.05) from those of the Hu dson River stock, whereas mtDNA minor-length genotype frequencies of t he Delaware River sample differed significantly from those of the Ches apeake Bay stock (P < 0.005). This intermediacy, together with informa tion from historical surveys that suggest the original population did not become extinct, favors the hypothesis that the present Delaware Ri ver striped bass stock represents expansion from the original Delaware River stock.