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October 26, 2001

Shark Tagging

What are the chances of the same fish being caught again and the tag recovered?

Q: Last summer I tagged and released a 200-pound tiger shark off the Florida Keys. What are the chances of the same fish being caught again and the tag recovered? Are many tiger sharks tagged each year? Where do they migrate? - Bruce Johnson, West Palm Beach, Florida

A: About 20 or so tagged tiger sharks are recaptured in the Atlantic every year, but usually not by recreational anglers - the majority get caught by longliners. However, longliners also release most of the tiger sharks tagged. For example, in 1996, 459 tiger sharks were tagged - the greatest number for any shark species other than blue and sandbar sharks - of which 18 were recaptured, 14 by longliners. Only two of the 18 sharks had been at large more than a year before being recaptured.
Most of the 18 recaptures took place less than 100 miles from the tagging location. Several interesting long-distance exceptions, however, included two tigers tagged off northern Florida in May and June of 1994 that were recaptured off Antigua (1,250 nautical miles) and Brazil (2,421 nautical miles), respectively. Another tiger shark, tagged off North Carolina, was recovered off the Cape Verde Islands after traveling 3,089 nautical miles in only 8 1/2 months.
One of the tiger sharks was injected with the antibiotic oxytetracycline (OTC) as an age-tracking device. The OTC is incorporated into the skeletal age ring currently being formed, much like the age rings on trees, and can be detected under fluorescent light in a cross section of the spine after the shark is recaptured. Unfortunately, there is no difference between the tags used for injected sharks and sharks simply tagged and released, and no cartilage samples were taken from the recaptured OTC-marked fish for age studies.
If you are lucky enough to recapture a tagged shark of any species, the Cooperative Shark Tagging Program in Narragansett, Rhode Island, would like you to keep it. Record the tag number, date, sex, location and method of capture, remove a 6- to 10-inch section of the cartilaginous backbone from the area above the gills and freeze it. Call 401-782-3320 collect, and they'll send you a postage-paid mailer for the sample. For tags, call 401-782-3328.