For over 30 years, mass mortality events along the Atlantic Coast, exclusively of menhaden (Brevoortia tyrannus), have occurred and been attributed to low dissolved oxygen levels. Recently, there has been some debate as to whether a single cause and effect relationship exists between hypoxic events and die-offs of a single pelagic species. In some cases within Long Island Sound, massive mortality events have been associated with 94% prevalence of Lernaeenicus radiatus (ectoparasitic copepod) among dead adult menhaden, in very cold, low saline waters. In a study conducted on menhaden in Delaware Bay from 1999-2001, the highest incidence of parasitism, with L. radiatus, was in September of each year (15.5-38.7%), a season when the highest incidences of hypoxic fish kills often occurs.

The degree to which parasitic copepods affect Atlantic sturgeon under similar conditions is also of interest. Some Atlantic sturgeon have been recently found heavily parasitized with ectoparasitic copepods along the coast of Long Island. Whether these infections are common throughout the year or only for short pulses, is also important in understanding the effects these parasites might have on this threatened fish population.

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It has been hypothesized that injured/parasitized menhaden may seek shallow warm waters when recuperating from injuries. Euryhaline fish returning to freshwater under parasitic infestation is not a novel occurrence and has been recorded for years in UK populations of sea trout infected with Lepeophtheirus salmonis. The presence of these parasites and the physiological costs associated with infection need study to determine if they may be a contributing factor to reduced fitness and the ability of menhaden to escape hypoxic conditions.