Introduction

Diadromous fishes are species that, as a routine phase of their life cycle, and for the vast majority of the population, migrate between marine and fresh waters. Of the diadromous fishes, anadromous species spawn in fresh water and catadro-mous forms spawn in salt water. The Hudson River hosts a diadromous ichthyofauna of almost a dozen species (Table 13.1). They range from large, commercially-valuable anadromous fishes such as Atlantic sturgeon and striped bass to small, largely ignored ones such as hickory shad. The only catadromous species in the Hudson is American eel. The Hudson is also home to euryhaline species that typically remain within the estuary (for example, white perch, gizzard shad). Two of these, short-nose sturgeon and Atlantic tomcod, make seasonal movements between fresh and marine waters to the degree that they often are considered to be anadromous. Diagnostic keys, morphological descriptions, and information on the basic biology of the diadromous fishes of the Hudson River are available in Smith (1985).

Populations of anadromous fishes in the Hudson River were established recently - within about 10,000years-astheriverwasrecolonizedfollowing deglaciation (Schmidt, 1986). Other rivers within the Hudson River Estuary complex, such as the Raritan, Passaic, Hackensack, and smaller tributaries supported or still support some diadromous species that run up the Hudson; the extent of reproductive interchange among these subpopulations remains unknown.

Several commercially-fished Hudson River species have experienced fluctuations in abundance in historical times due to anthropogenic effects. Commercial and recreational overhar-vest is primary among them. Entrainment and impingement mortality by electric-generating stations also has decreased the abundance of some diadromous fishes. Information on abundances of a variety of fish species is available from surveys conducted by the Hudson River electric generating companies (for example, Barnthouse et al., 1988).

Table 13.1. Life history mode, importance to humans, and status and trends of the Hudson River's diadromous fishes

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