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Originally Published in Flyfishing in Saltwaters Magazine, June/July 2009
GETTING IT RIGHT ON DOLPHIN
Tagging fish to get ahead of the curve
For flyrodders, dolphin (frequently called mahi or dorado) may be the single most important offshore species. While we may go out into the deep with dreams of sticking tunas and billfish, we usually end up with mahi. And most of the time that’s just fine, because they are wonderfully aggressive, display extraordinarily beautiful neon colors and offer stunning aerial acrobatics. Because they live their life in the uppermost portion of the water column and possess an innate instinct to associate with Sargasso and other floating objects, they are not only easier to target with fly gear, but they are generally easier to find than other pelagics.
That said, it’s not surprising that dolphin is the number one fish harvested by offshore anglers in the U.S. They are a vitally important to the bluewater recreational fishing industry, yet there is a surprising lack of data on the species.
In 2002, the National Marine Fisheries Service began work on a dolphin fishery management plan. In developing the plan, managers found that they had little concrete information on dolphin movements, occurrence and dispersal patterns. “You have to understand movement patters to property manage a fishery,” says Marine Scientist Don Hammond, “to manage without this info is futile at best.”
So, with strong support from offshore fishermen, the Marine Resources Division of the South Carolina Department of Natural Resources (SCDNR) initiated an angler driven tagging study in 2002. Led by Hammond, it was designed to address the travels of dolphin off US shores so that scientists could begin to define not only movements and migration routes, but the stock's geographic range.
The study was relatively successful in its four years of operation with over 4,900 dolphin tagged and 116 recaptures. While certainly not comprehensive, it did confirm for the first time what many anglers already assumed, that dolphin move from south to north in the spring along the US east coast. But when Mr. Hammond retired from SCDNR in 2005, the program ended.
Don sought federal support to continue the study as a private researcher. Because dolphin are not recognized as an overfished, and overfishing is not occurring, the feds didn’t consider it a priority. Yet since 2005, Don has managed to raise a significant amount of private funds to keep the program going. Since then over 1000 anglers have registered to tag fish and almost 400 boats are involved in the effort. More than 8,500 dolphin have been tagged by volunteers.
The study has revealed some astonishing national and international movements. Dolphin tagged in the Straits of Florida during the early spring were recaptured as far north as Massachusetts in the summer, demonstrating the capability to travel extraordinary long distances at rates of more than 100 miles per day. A recovery off Georgia established the first East Coast link with dolphin found off the south eastern Bahamas. Other recoveries proved that dolphinfish present in Bahamian waters during winter and spring travel northward to and along the U.S. East Coast, and thus evidenced a second entry point for the species moving into the U.S. territorial waters (the first entry point being the Florida Straits.)
The tagging program has also provided the first links between dolphin found off U.S. shores and those found in the eastern Atlantic south of the Azores, off Antigua in the West Indies and off Belize/Mexico in the western Caribbean. Such recovered fish had traveled distances of 1,200 to 2,500 miles.
Still other recoveries show a direct link between dolphin off the U.S. East Coast and those found in the Caribbean Sea and the eastern North Atlantic. “When you look at all of these points, it is not hard to envision a circum-North Atlantic migration route that would span 8,000 miles,” says Hammond, “This is certainly within the dolphin’s ability.”
The wide distribution of recaptures challenges the multi-stock concept currently held for dolphin, which assumes there are separate Western Central North Atlantic, Caribbean Sea and Gulf of Mexico stocks. Recoveries have also shown that some surviving fish do return to the East Coast the following year, indicating a repetitive migration behavior. “So essentially, they can’t be considered our fish anymore” says Don. Such a realization means we need to be concerned about exploitation overseas.
The use of archival, pop-off satellite tags has contributed significantly to the study. These miniature computers record time-specific water temperature and depth at regular intervals along with light intensity, which allows the calculation of the daily geo-location of the fish. Results have shown that dolphin will use waters from 61 to 88 degrees and will dive to depths below 400 feet, which is useful information for determining essential fish habitat. Data have already indicated a possible universal behavior among all fish in which they rise to the surface at first light each morning.
This ongoing program is also looking into other aspects of the dolphin’s life history and the fisheries it sustains. Data sets are being developed to help define the geographic area where anglers capture dolphin thus defining U.S. recreational fishing grounds for the species. Anglers are also helping to collect data on the relationship between the presence of sargassum and dolphin abundance.
Is the fishery changing?
Because of current data deficiencies, any estimate of the health of the dolphin population is purely subjective. Yet, Marine Recreational Fishing Statistics Survey (MRFSS) data has shown a 10 year decline in landings in the Gulf and a 7 year decline on the East Coast. That, by itself does not warrant concern, since it is not clearly correlated with the level of fishing effort during that time period. Don also concedes the unreliability of MRFSS data, saying “it is not the most solid source of information on which to base a claim of a fishery decline.” However, the fact that similar declines occurred in the dolphin fisheries along the Gulf and Atlantic coasts seems more than a coincidence. Don believes that the data should not be taken as a statement of actual decline but rather a reason for closer examination of the health of the stock.
This relatively young research effort has revealed a wealth of information about the dolphins’ movements. Yet if the best available science shows that dolphin are not overfished and overfishing is not occurring, why bother? The answer to that is simple. Don and the team of volunteer anglers hope to get ahead of the curve with dolphin. Historically, fisheries managers don’t look at stocks until they are already in trouble. Thus, they rarely have a good baseline to work from, and because of the politics, many times adopt measures best characterized as “too little too late.”
Don’s revolutionary tagging program hopes to take a different tack with dolphin. In this era of fisheries management and in many cases “mismanagement,” that is terribly refreshing.
To sign up to tag dolphin for this study, anglers should contact Don Hammond by email (firstname.lastname@example.org) or telephone (843) 795-7524. To Report a Tag Recovery, use the convenient forms the web-site: www.dolphintagging.com.