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VANCOUVER, Canada » High-tech instruments are shedding light on the mysterious movements of marlin caught off Kailua-Kona as anglers participate in the growing field of biologging — tracking animals by satellite or acoustics.
The results of three years of study show the fish travel vast distances, often thousands of miles, in only a few months. One 170-pound blue marlin (named West Marie) tagged last August, for instance, swam from Hawaii to a point near the Marquesas Islands in the South Pacific, a distance of 2,500 miles, in 121 days.
"These fish are wide ocean wanderers and there is a lot of variation in their movement pattern," said researcher George Shillinger after a presentation Friday at the annual meeting of the American Association for the Advancement of Science.
"When we tag more, a lot of these mysteries hopefully will be resolved," said Shillinger, who is affiliated with Stanford University and the Ocean Foundation in Washington, D.C.
Scientists hope biologging will eventually help shape public policy toward marine resource conservation. Similar programs are following leatherback sea turtles and sockeye salmon, and biologging has spread to marlin tournaments in Australia and Puerto Rico.
Hawaii’s Great Marlin Race is run annually in conjunction with the Hawaiian International Billfish Tournament. While the prize in the Kona tournament goes to the biggest fish, many smaller fish are caught and released in the process.
Teams participating in the Great Marlin Race — a contest within a contest — contribute to the $3,500 cost of a tag, which they implant into one side of a marlin’s dorsal fin before letting the fish go. The tag, designed to last for about 120 days, collects information on light, depth and temperature, which can be used to calculate position.
When it pops off, it floats to the surface and uploads the information to an Argos satellite, which transmits it to a Stanford University lab.
The team whose fish swims the longest distance wins free entry in the next year’s billfish tournament, a prize worth $7,500 for a crew of six, said Shillinger.
In 2009, seven fish were tagged and five tags reported in, including three that had traveled near the Marquesas in French Polynesia.
In 2010, 10 fish were tagged with nine reporting in, showing a broader range of migratory paths. The winning fish swam 2,624 miles almost due east.
In 2011, two of 10 marlins tagged swam south of the equator, while six tags surfaced along a swath southeast of the Hawaiian Islands.
That some marlins cross the equator came as a surprise to researchers because the water is hot and low in oxygen, a natural barrier for many species.
The marlin spend a lot of time at the surface, mostly at night, but they also frequent an ocean layer called the thermocline, a depth at which the temperature drops off dramatically, anywhere from about 75 to 150 feet down, Shillinger said.
"That is a pretty consistent pattern, but this data is helping to provide us with a better sense of how billfish across the Pacific use the water column," he said in an interview. "We can couple the horizontal movement with dive data information, and also look at temperatures preferences. And that is all relevant, ultimately and potentially, to how fisheries managers might choose to manage billfish."
One bias in the program, Shillinger conceded, is that the tags go on mostly smaller fish, those under 250 pounds and typically males. The biggest fish, females, are hauled back to the dock.
"In a tournament that involves kill, it is hard to get anglers to let you tag the really big fish, because they want to bring them in and get them weighed," he said. "But many of the tournaments today are using different methods of measuring the fish, doing estimates where killing the fish is not required."
Shillinger was part of a symposium Friday called "Tracking Progress: Success and Failure of Biologging in Protecting the Global Ocean." He described another popular program, the Great Turtle Race, which involves tracking leatherbacks from Costa Rica to the Galapagos Islands. It has drawn support from Stephen Colbert of "The Colbert Report" and rock bands Pearl Jam and R.E.M.
Shillinger, who works with Randy Kochevar at Stanford, said he would like to see the marlin tagging program expand globally, but setting one up takes considerable effort and cooperation from scientists and the fishing community.
The Kona program would never have flown without the support of tournament founder Peter Fithian, the International Game Fish Association, Kochevar and Stanford’s Barbara Block, he emphasized. And the heavy-tackle crews have come to embrace it, he said.
"It gives anglers the opportunity to see that the fish that they interact with at the local level actually are connected to the rest of the world, so that fishing off Puerto Rico or Hawaii or Australia can have an impact somewhere else. It gives them a much closer connection to the resource, and they feel like they are contributing to science. And they are."
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