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The Project

To find where winter flounder prefer to lay eggs within an estuary, we are tagging 70 ( 35 each x 2 years) mature winter flounder with acoustic transmitters, small pingers each with their own coded signal. The fish are tagged on the outside using a saddle for the pinger sewn between the spines of the dorsal fin. The tags can be heard up to a half mile away by hydrophones, or underwater microphones that interpret the ping sound and record its code along with the time it was received. When several hydrophones are close enough to hear the same sound signal, the difference in the arrival time of the same sound between different hydrophones can be use to pinpoint the sound source location, a process called triangulation. The precision depends on all hydrophones having synchronized clock, which they do by getting their time from a global positioning satellite orbiting overhead. While winter flounder might move throughout the bay, spawning behavior can be detected by the convergence of males to a female and circular swimming. The tracks of roaming and spawning fish can be graphed on a chart along with time stamps.

The Place

The Navesink River/Sandy Hook Bay estuarine study area opens to the industrialized New York Harbor/Hudson River estuary. The estuary enters the larger Harbor near its mouth at Sandy Hook, New Jersey. The Navesink River was chosen for this study because it is a known spawning ground for winter flounder and is also an optimal size and shape. The Navesink River is typical of other riverine estuaries in the area in that it has a very narrow mouth, which affects the water flow patterns and bottom type. The Swimming River feeds freshwater into the Navesink and the narrow, elongated shape makes changes in salinity and flow rate easy to measure. Most of the estuary is shallow (less than six feet deep) but a dredged channel of approximately nine feet in depth runs along its length. The river bottom is primarily soft mud with sandy areas near the mouth and along the edges. Temperatures range seasonally from freezing in winter to over 77 F in mid-summer. The estuary is covered with ice in some winters. 


Photo by Townsend Weeks, Associate Professor, Environmental Sciences Department, Brookdale Community College

The Equipment

Tags (acoustic transmitters):

Manufactured by Lotek Wireless, Inc., Ontario, Canada

Model: MAP series



Manufactured by Lotek Wireless, Inc., Ontario, Canada

Model: MAP WHS1400