Hudson River Fishes and their Environment

<em>Abstract.</em>—Hudson River tributaries serve as spawning areas for substantial numbers of anadromous and potamodromous fishes, and are critical habitat for at least alewife <em>Alosa pseudoharengus</em>, sea lamprey <em>Petromyzon marinus</em>, white sucker <em>Catostomus commersonii</em>, and smallmouth bass <em>Micropterus dolomieu</em>. Those species that are resident in tributary mouths are often common, widespread taxa in the Hudson River system but they are rarely present in large numbers. We document high densities of American eel <em>Anguilla rostrata </em>in one tributary mouth (>13,000 eels/ha; 15–30 g/m²) and present observations supporting that this is typical of Hudson River tributaries. We suggest that the biology of American eel substantially determines the structure of the fish community and energy flow within these habitats. The presence of barriers and high density eel populations limit the import of marine and estuarine nutrients into Hudson River tributaries.