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By Dave Grant  Several evenings this past summer (1983) swarms of scuds were observed in the surface waters of Sandy Hook Bay. At 6:30 PM, July 8, approximately two hours before sunset, a particularly large concentration was observed near the middle of the bay. We estimated that for a quarter mile, our vessel passed through densities of 250 or more individuals per square meter. Conditions were very calm and the visibility from the surface was excellent (over six feet). Temperatures and salinities were: 24.2°C and 24.0 ppt at the surface; and; 23.3°C and 24.2 ppt in this well-mixed lower part of the Hudson River-Raritan Bay complex. The depth here is 20-feet, close to the bay's average of eighteen. High tide was predicted at 10:12 PM.
Surprisingly, there was no evidence of any fishes or birds taking advantage of the swarm. The majority concentrated 12-18" below the surface and actively avoided our attempts at capture with a dip net. Fortunately two specimens were secured. Like many in the swarm they were coupled and remained so after capture. The male (17 mm) carried the female (12 mm). They were later identified as Gammarus annulatus, an essentially pelagic amphipod of New England, Cape Cod and Long Island Sound. G. annulatus has previously been reported from power plant intake screen along Raritan Bay; and in the literature, ovigerous females are reported from June through September. This lengthy spawning season could explain their behavior at the surface. According to the scientific literature, since the 1940's, benthic amphipods have been greatly reduced in Raritan Bay, presumably as a result of pollution. This appears not to be the case with their pelagic cousins. NOTE: The author is
the director of Brookdale College's Ocean Institute at Sandy
Hook and offers boat trips to students and the public. |