Petromyzon marinus sea lamprey. Sea lamprey is a large parasite with a complex life cycle (Beamish, 1980). Although sea lamprey spawn and are numerous in the two large systems that bracket the Hudson River, that is, the Connecticut and Delaware Rivers, adults are scarce in the Hudson. Greeley (1937) listed them as rare in the mainstem river. No directed studies of sea lamprey in the Hudson drainage have occurred but there have been reports that suggest some reproduction takes place in a few of the more than sixty tributaries to the tidal river. The system-wide survey by Greeley (1937) caught one larva in Rondout Creek and one adult in Catskill Creek; none were found in the Roeliff Jansen Kill or other tributaries sampled. However, Brussard, Collings-Hall, and Wright (1981) later electroshocked thirty-one ammocoetes from the Roeliff Jansen Kill. More recently, adult sea lamprey were observed near the confluence of Catskill and Kaaterskill creeks (R. Schmidt, Simon's Rock of Bard College, personal observation) and in the Roeliff Jansen Kill (J. Waldman and R. Schmidt, personal observation). Subadult sea lampreys are sometimes seen in the Hudson River attached to American shad (Greeley, 1937; HRA, 1998) and gizzard shad (HRA, 1998).
Why sea lamprey are abundant in the Delaware and Connecticut Rivers but not in the Hudson is not obvious but may be due to habitat limitations. Although sea lamprey have been documented to occur in at least 134 coastal rivers in North America, they do not reproduce in every river available range (Beamish, 1980). Sea lamprey construct nests of rock rubble, in sections of rivers with moderate flows. After hatching, larvae leave the nest and drift downstream to suitable silt beds (e.g., eddies, backwaters, behind obstructions) where the am-mocoetes mature.
The main channel of the Hudson River clearly does not provide suitable spawning habitat for sea lamprey, nor are ammocoetes known to occupy tidal waters. Although some sea lamprey reproduction may occur in a few tributaries to the Hudson River, I believe it is limited by the generally small sizes of these systems, their short lengths below the fall line, and perhaps, their infrequent combinations of good spawning and nursery habitats.
Acipenser oxyrinchus oxyrinchus Atlantic sturgeon. Extant populations of the east coast subspecies occur from the St. Lawrence River to rivers in southern Georgia and, possibly, to the St. John River, Florida (Waldman and Wirgin, 1998). This sturgeon is known to exceed 300 kg in weight and 60 years in age.
Dovel and Berggren (1983) performed the first detailed studies of Atlantic sturgeon in the Hudson River. Sonic transmitters were used to describe movement patterns, which included delineation of spawning as occurring near the salt front (~km 55) in late May and moving upstream as far as Hyde Park later in the season. Growth of younger specimens was found to occur primarily between May and October and to slow after age three. Conventional tagging of immature Atlantic sturgeon showed that some leave the Hudson as early as their fifteenth month, but no later than age six. Specimens were recapturedin coastal waters as far north as Marblehead, Massachusetts, and south to Ocra-coke, North Carolina. Most recaptures occurred in the Delaware River and Chesapeake Bay estuaries, and their pattern implied a northerly migration in spring and southerly movements in autumn. Dovel and Berggren estimated that the 1976 year class of Atlantic sturgeonin the Hudson River totaled about 25,000 in 1978.
Aflourish of studies in the 1990s greatly extended knowledge of the life history of Atlantic sturgeon. Analysis of fin ray sections suggested that Hudson River-stock females reproduce on average every four years (Secor, Stevenson, and Houde, 1997).
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