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A Publication Featuring The Information Services Technology of Maine State Government
|Volume VI, Issue 7||July 2003|
By Diane Cowan
Scientists at The Lobster Conservancy (TLC) are using coded wire tags to mark juvenile lobsters at three nursery areas on the Maine coast. The long-term mark/recapture studies are providing information on growth rates, seasonal migrations, and survival from year to year.
There are many challenges involved in unveiling the secrets of the early life of lobsters some practical, others technical. The most significant practical considerations include being able to find, and have access to, very small lobsters in nature. Postlarval lobsters settle to the sea floor at a length of only 0.5-0.75 inches, and are difficult to find and keep track of. To study growth and survival it is imperative to follow them through their first years of life.
|Major technical problems arise due to the impossibility of using external markers (because they are lost when lobsters molt) and the difficulty of placing internal markers in such a way that they (1) are retained when the lobster sheds, (2) will not harm the lobster, and (3) will not harm or be consumed by humans. To solve the problem of finding and keeping track of young lobsters, TLC takes advantage of their use of nearshore habitats exposed at extremely low tides. The lobster nurseries currently censused by community volunteers for TLCs Juvenile Lobster Monitoring Program span from Massachusetts to Down East, Maine (see map).|
To tag individual lobsters, TLC inserts tiny coded wire tags into the muscle at the tip of the second right walking leg using a modified 24-gauge hypodermic needle (see Northwest Marine Technology website; and figure). The tags measure 1 mm length x ¼ mm diameter and are encoded with a numeric code that includes (1) an "agency" code, (2) a "batch" code, and (3) individual identification code that is specific to each lobster. To identify a lobster that has been tagged and recaptured, the tag must be recovered and read using a dissecting microscope. Recaptured animals are then re-tagged. TLC scientists have tagged over 10,000 juvenile lobsters. Although individual lobsters have been captured on up to seven separate occasions, most lobsters are captured only once. About 10% are captured twice. The record length of time for following one individual is four years.
There is no visible indication that a lobster has been tagged. Therefore, each lobster is waved past a field detector (see figure) that recognizes the presence of any metal object and especially the magnetic tag. If the lobster has been tagged the detector emits a high-pitched beep. It is important to make sure that no metal objects such as a watch or snaps on a jacket are worn because they interfere with detection of the tag. It is also a good idea to run each lobster past a powerful magnet to make sure that the tags are fully magnetized. Due to their small size, the metal characteristics alone can go undetected.
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Note from Bob Drury, Maine State Retirement System, to Identifying Lobsters Using Passive Integrated Transponder (PIT) Tags article author Diane Cowan 5/30/2003 (http://www1.maine.gov/newsletter/june2003/Lobsters%20PIT%20tag.htm)
I just read the Transponder Tag article in Junes Maine IS Tech -- very interesting! I find this kind of study fascinating with the use of current technology, however I am curious as to any concern about these tagged lobsters being eaten by humans? If the tags are injected internally, then couldn't that end up on someone's steamed-lobster plate? Perhaps I'm missing something here.
I should have mentioned this in the article. Sorry. There are two major reasons I would not expect the PIT tags to be eaten by humans. Firstly, the lobsters are confined to an enclosure, so they cannot be fished. We do not use the tags in the wild. Secondly, the placement of the tag is such that consumption is unlikely. We've done a few tests with groups of visitors challenging them to find the tag during feeding... Few do.
Thanks for your interest,