MIAMI — It might be one of the longest detailed surveillances ever conducted on a blue marlin, one of the world’s premiere gamefish.
Marine artist-conservationist-scientist Guy Harvey, fishing with friends in the waters off his Grand Cayman Island home in November 2009, implanted a 150-pound blue marlin with a pop-up satellite tag.
The marlin carried the tag for six months, travelling 3,825 miles before it popped off in May 2010. The small cigar-shaped device transmitted reams of data on the marlin’s whereabouts during that time to a satellite.
Mahmood Shivji, director of the Guy Harvey Research Institute at Nova Southeastern University, plotted the fish’s travels on a chart.
After being tagged, the fish wandered north toward Cuba. It milled around between Grand Cayman Island and Cuba until late December 2009, when it travelled to a deep trench south of the Caymans. It milled around in that general area until late January 2010 when it headed northwest, far away from any land mass. In February, it passed fairly close to Cuba, then veered toward Mexico’s Yucatan Peninsula in March. From there, it headed north in the Gulf of Mexico and did loop-de-loops in the eastern Gulf in April. In May, it swam for Cuba again, then north to the Straits of Florida off the Keys, where the tag popped off.
“To us, it’s a big deal that the tag stayed on — one of the very few perspectives in the long term movements of a billfish,” Shivji said.
Scientists with various universities and government agencies have been sticking satellite tags in billfish for more than a decade, but many detach long before they are programmed to release. Others are lost without transmitting any information at all. The Guy Harvey Research Institute, like others, has suffered those kinds of setbacks.
But Harvey himself has been pretty lucky recently — tagging another blue marlin in May off Grand Cayman (while fishing alone) that just released its tag in November. He also tagged six blue marlin off the Pacific coast of Panama this fall that scientists are waiting to receive data from.
It will be up to Eric Prince, veteran billfish scientist at NOAA’s Southeast Fisheries Science Center in Miami, to analyze the tagging data in more detail — specifically how deep the fish dived and where. Prince has been studying how climate change could direct the movements of large ocean predators such as marlin, other billfish and tuna.
In a new scientific paper published in Nature Climate Change, Prince found that expanding dead zones in the central Atlantic and elsewhere shrinks the habitat for those fish, most of which are already overfished throughout their range. These highly migratory species need large amounts of dissolved oxygen to thrive, but as ocean waters warm and become more acidic, oxygen levels drop — compressing their habitat. This habitat “squeeze” forces them to make deep dives or swim close to the surface — wherever they can find areas of high dissolved oxygen concentration.
The more scientists learn about the habits of these top predators, the better they can be managed, Shivji said.
“We need to know where they spend their time to identify critical habitats — which regions are important to them at certain times of year,” he said. “If you can figure out critical habitat, managers can say ‘you need to not fish here because this is a critical time for them.’”
The tracking of marlin movements also is getting an assist from the International Game Fish Association, which launched the “Great Marlin Race” in September at the Club Nautico de San Juan 58th International Billfish Tournament in Puerto Rico.
Six blue marlin were implanted with pop-up satellite tags during the tournament. Four detached prematurely and two more are slated to emerge early next month, according to Randy Kochevar, a marine biologist at Stanford University who is helping with the project.
Organizers are hoping other marlin tournaments get involved, he said. The fishing team whose tagged fish travels the farthest will win a free entry to the same tournament the following year.