Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Telemetered adult striped bass <em>Morone saxatilis </em>(<em>n </em>= 170) in two small nonnatal U.S. Atlantic coast estuaries, the Mullica River-Great Bay in New Jersey and the Saco River in Maine, displayed a variety of movements relative to migration and habitat use. Individual presence in both systems ranged from hours to many months from spring through fall but seldom during the winter. Some made upriver runs during the presumed spawning season. An absence of eggs, larvae, or juvenile stage striped bass or suitable spawning grounds suggests that fish utilizing both systems are members of migrant contingents originating elsewhere. In both systems, some seasonal residents occupied individual "home" ranges throughout the salinity gradient, but others were plastic in their behavior and utilized several sites or visited the estuary either briefly or for a whole season in different years. Movement of fish between study sites and recaptures away from them indicated wide dispersal during time away from the study estuaries. The above supports the idea that migratory and seasonal residence behaviors of migrant striped bass are not compulsive or predictive but reactive or learned. Despite long seasonal occurrence in these small estuaries by some individuals, none appeared to become full-time residents. Small estuaries may lack the year-round resources for spawning and feeding to enable this. However, the observed behaviors could promote recolonization of spawning stocks with residents in larger restored rivers and estuaries where they have been previously extirpated. Localized fishery depletion of small estuaries could occur quickly but would be temporary in the absence of stock wide depletion.