NJ OWL Meeting - E-Z Bass in the Mullica River and Great Bay

NJ Outdoor Women's League Meeting
E-Z Bass in the Mullica River and Great Bay
March 2005

There probably isn’t an angler around that hasn’t wondered where the fish are hiding when they aren’t biting. And if you’re a saltwater angler who is partial to striped bass, a species that migrates, you might ask yourself too, "where do they go, and how long does it take them to get there?"

Researchers at the Rutgers University Marine Field Station (RUMFS) are trying to answer these and other questions by monitoring the movements of striped bass. Clare Ng, a doctoral student in the Department of Ecology, Evolution, and Natural Resources at Rutgers is part of the striped bass research team. She came to NJ OWL’s March meeting to give a fascinating presentation about the project and how acoustic telemetry is being used in the study.

Because striped bass are important to both recreational and commercial anglers, it’s important to define which habitats they prefer, and to understand how they migrate. That way, important areas can be better protected from pollution, over-fishing and other detriments to help make sure there will be fish for future generations.

Clare Ng with a striped bass

Rutgers’ monitoring is being done primarily in the Mullica River and the Great Bay in Atlantic County within the Jacques Cousteau National Estuarine Research Reserve, but striped bass are found in the ocean waters from Canada to Florida, and also in some lakes and rivers. They can grow up to be 6 feet long, weigh as much as 125 pounds, and live over 30 years. Because they are anadromous (leaving saltwater to spawn in freshwater) the research is aimed at determining how far up the estuary they migrate, how long they stay and what types of habitats they prefer while there. The researchers also wanted to find out if the fish returned to the same estuary year after year, or if they went elsewhere.

Clare began by describing the various methods that researchers use to study fish, and the pros and cons of each method. Direct observation is one, but it’s difficult to see underwater unless it’s very clear, and the presence of people influences fish behavior. Another method is to inject a coated microwire tag, which contains a binary code, into the fish. But this isn’t easily detected, and the fish needs to be caught and the tag removed. External tagging involves tagging a fish at the catch site, and if it is subsequently caught, the tag is then removed. But this relies on people to report the tag, and also, a huge number of fish need to be tagged in order for enough data to be collected. Plus, it doesn’t give a clue as to where a tagged fish has been in between the time that it was tagged and caught. Satellite telemetry uses a tag that sends a signal to a satellite to record the animal’s whereabouts. But the animal needs to break the surface of the water periodically in order to send the signal, so it’s only useful on creatures such as whales and dolphins.

Clare said the method that best lends itself to this type of study is acoustic telemetry. Acoustic telemetry tags are surgically implanted into a fish and emit a sound code that is unique for that individual. The sound that the transmitter emits is at an extremely high frequency (ultrasonic) so researchers need special underwater microphones, called hydrophones, in order to hear it.

Clare holding "Sparky", one of the "adopted" bass. Note the yellow spaghetti tag that protrudes from the bottom of the fish identifying it as having an internal acoustic tag.

Fish are caught (one at a time using hook and line methods) and brought aboard the boat; the fish is placed in a receptacle of water to which an FDA-approved anesthetic especially designed for fish has been added. When the fish is unconscious (this usually takes 5 minutes) the transmitter is inserted into an incision in its belly. The transmitter, which is a little larger than a lipstick container, weighs about 1½ ounces and has a battery life of 2 years. Its most important feature, however, is its emission of a pattern of pings, unique to each individual fish, which repeats every five seconds. A smaller external tag identifying the fish as one having the implanted transmitter is also inserted into the fish and each fish receives an antibiotic.

After the fish regains consciousness it is returned to the water. The transmitter’s sounds are picked up by the hydrophones, which are suspended beneath red buoys that are attached to a line anchored to the estuary’s floor. Eleven buoys have been strategically placed in the Mullica River and the Great Bay to pick up the signals of the sixty-eight fish that were part of this research project. Clare likened the hydrophones to E-Z Pass, recording the fish’s presence each time they passed a hydrophone "tollbooth."

In addition to these stationary monitors, the waters between each buoy are checked. To do this, Clare takes a portable buoy/hydrophone with her in a boat and places it into water to pick up signals; she will systemically do this at one-mile intervals. One day a week she spends 11 hours doing distribution tracking. Three days a week she spends gathering information on habitats.

Clare showed us the preliminary results of the study, and it was fascinating to see the records of each individual fish’s movements. Many of the fish in the study have been "adopted" by fishing clubs, class rooms, and individuals, who get to "name" their adopted fish. We reviewed the recorded movements of fish named Blue’s Clues, Desileu, Nicky, and Mr. Noodles. We learned that Sparky took advantage of the tidal movements to go where he wanted to go, and that Bob took 50 days to swim from Maine (which is also conducting a striped bass study and has an array of hydrophones in the Saco River) to New Jersey. So far the data collected has shown that bass prefer the deep water of the river and like to hang out where the river bends. Much time is spent upriver in the spring, and in the bay during the summer, while in the winter most of the tagged fish leave the estuary entirely.

Clare explained that further studies are being done to determine if fish size, water temperature, and schooling habits might be factors in the fish’s preference of habitat and movements.

Clare’s presentation was fascinating, and we greatly appreciate that she took the time to share her knowledge and enthusiasm of this exciting research project with us. You can find more information about this study at the www.stripertracker.org web site. You might even want to adopt a fish, name it, track its movements and at the same time play a part in this very important environmental study.

by Sandy Norman