Age- and Sex-Dependent Migrations of Striped Bass in the Hudson River as Determined by Chemical Microanalysis of Otoliths

Patterns of habitat utilization and migration of Hudson River striped bass, Mm-one saxatilk, were estimated using otolith microchemical analysis to chart ageand sex-dependent movements. Otoliths from 25 males and 25 females were analyzed for seasonal and age-specific patterns in strontium : calcium level. These levels were converted into salinity estimates based upon a relationship derived from experimental studies. Seasonal patterns in saliity habitation indicated annual up-estuary migrations in mature age-classes of males and females, and may represent spawning migrations. Early emigration of young striped bass (<3 yr old) into polyhaline and euhalbre waters was observed for both sexes, but females tended to reside at higher salinities throughout their life span. Otolitb microchemical analysis indicated that 68% of the sampled females and 28% of the sampled males spent significant portions of their lives in euhaline coastal waters. A positive relationship between down-estuary movements and age was observed for both sexes, supporting the hypothesis of size-related dispersion and anadromy in striped bass populations. Individuals collected during the same season or from the same segment of the river had similar lifetime salinities. Thii result suggests that group cohesion (schooling) could persist for substantial periods of an individual’s life span. The most cohesive group was fall-collected males, which may reside permanently in fresh water and estuarine waters. Cohesive migratory groups would have important implications for investigations on effects of contaminants and fishing pressure on Hudson River striped bass. Introduction for the Chesapeake Bay population (Mansueti The Hudson River striped bass, Morone saxatilis, 1961; Kohlenstein et al. 1981), several studies inpopulation has expanded in range and abundance dicate that the Hudson River population may have since 1980 and is thought to contribute substanevolved different migratory behaviors and schedtially to mixed-stocks coastal fisheries (Fabrizio ules. 1987; Waldman et al. 1990; Wirgin et al. 1993). Extensive tagging studies over the past 30 yr The population is facultatively anadromous; follow(1959-1963, Clark 1968; 1976-1977, McLaren et ing spawning runs, adults may remain in riverine al. 1981; 1984-1988, Waldman et al. 1990) have or estuarine habitats or migrate into coastal waters. produced opposing views on migratory behaviors Migrations of Hudson River striped bass among of Hudson River striped bass. Clark (1968) sughabitats is seasonal, but controversy exists over how gested that the Hudson River population was commigrations are related to size, age, sex, and abunprised of several spatially discrete “contingents.” dance (Clark 1968; McLaren et al. 1981; Waldman One contingent resided in the Hudson River and et al. 1990). Whereas ageand sex-dependent Estuary, another contingent migrated and resided coastal migrations have been clearly documented in Long Island Sound during summer and fall months, and a third contingent supported farther * Corresponding author; tele 410/3267229; fax 410/326 ranging migrations. To support his assertion of dis7318; e-mail [email protected]. Crete contingents, Clark presented evidence that