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A Publication Featuring The Information Services Technology of Maine State Government

Volume VI, Issue 6 June 2003


Identifying Lobsters using Passive Integrated Transponder (PIT) Tags

By Diane Cowan

Scientists at The Lobster Conservancy, a non-profit corporation dedicated to sustaining a thriving lobster fishery in the Gulf of Maine[1] (TLC,, have modified three tagging methods to mark individual lobsters. They use Passive Integrated Transponder (PIT) tags to investigate growth in adults; Coded Wire Tags (CWT) to study growth and movements of juveniles; and Sonar Tags to track the movements of egg-bearing females. This, the first in a series of three articles, describes the TLC’s use of PIT tags.

The Lobster Conservancy Logo

The two major challenges encountered when attempting to tag lobsters are molting, and the problem of adhesion of tags in the marine environment. Because lobsters periodically shed their exoskeleton in a process known as molting, any external marker is lost at the time of ecdysis[2]. For long-term studies and investigations of growth rates, this problem is overcome by using internal tags injected into the muscle tissue of the second right walking leg using a modified hypodermic needle.

A PIT tag is a small cylinder about 1/2 the size (but not shape) of a macaroni noodle. TLC uses a 12-gauge hypodermic needle to implant the tag into the lobster’s muscle tissue. The PIT tag has a unique Radio Frequency Identification (RFID) that is programmed to transmit a unique alpha-numeric code when activated by a PIT tag reader. The tag has no battery, so its signal lasts indefinitely. The PIT tag conveys its information via a small antenna. A battery-powered hand-held scanner is used to detect the PIT tag. The receiver/reader generates an electromagnetic signal that temporarily activates the tag so it can be read.

PIT tags are used extensively in all vertebrate phyla[3] including fish, amphibians, reptiles, birds and mammals and at least two invertebrate phyla – the echinoderms and arthropods. Marine invertebrate species being PIT tagged include sea urchin, shrimp, and American lobster. The cost of using PIT tags can be prohibitive.  TLC receives theirs from National Marine Fisheries Service scientists who take them out of dead salmon. The tags cannot be re-coded and re-used in the same group of animals.

Scanning A Lobster

Because there are so many millions (or perhaps billions) of adult lobsters inhabiting the Gulf of Maine, the chances of recapturing PIT tagged lobsters in the wild and having a reader on board are slight. Therefore, the TLC investigates the growth rates and behavior of adult lobsters ranging from 83 – 160 mm CL[4] in a specially modified 6-acre lobster pound enclosure at the Lobster Life Studies Center, in Friendship, Maine.

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Photo taken by Bubba (Arthur) Thompson.  He built the house on the point next to the wharf, and is one of Friendship's Selectmen.

For more information or to purchase PIT tags and readers, visit Biomark, Inc. at

Diane Cowan is the Senior Scientist (, and founder of The Lobster Conservancy.  Contact her with questions or comments by e-mailing

[1]  The TLC accomplishes its vision (building a bridge to join all those sharing the common goal of maintaining a strong and healthy lobster resource) by involving communities in Maine, New Hampshire, and Massachusetts in lobster population monitoring, scientific research, and environmental education.  

[2] the act of molting or shedding an outer cuticular layer 

[3] a direct line of descent within a group

[4] CL is an abbreviation for carapace length. Lobsters are measured (by fishermen and scientists) from the rear of the eye socket to the posterior margin of the carapace (body shield or covering). 83 mm CL (~3 1/4 inch is the minimum legal size for capture and 127 mm CL (5 inch) the maximum. TLC scientists are particularly interested in getting some idea of how frequently "oversized" >127 mm CL lobsters molt, and how much length and weight they gain with each molt. 


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