Program charts swordfish migratory patterns
South Florida fishermen are helping fisheries scientists to better understand swordfish as well as uncharted ocean depths through an ambitious, revolutionary satellite tagging program.
The tags will enable University of Washington scientists Peter Gaube and Camrin Braun to learn new information about swordfish, which spend most of their lives in what the researchers call the ocean twilight zone.
Properly known as the mesopelagic zone, Gaube said it is “the layer of the ocean where there is enough light to orient and see, but not enough to drive photosynthesis. We know very little about the mesopelagic zone and by tracking and instrumenting swordfish, we will gain new insight into how this ecosystem functions.”
According to Capt. Tony DiGiulian of Fort Lauderdale, five swordfish ranging from 75 to more than 300 pounds were caught, tagged and released off South Florida earlier this year with the assistance of daytime swordfishing experts RJ Boyle of Deerfield Beach and John Bassett of Boca Raton while photographer Steve Dougherty of Delray Beach documented everything.
“I was very, very proud that we were so successful, and very proud of the guys I hired,” said DiGiulian, who arranged the tagging trips for the scientists and has also set up two swordfish tagging expeditions in the Red Sea for 2020. “We all learned a lot from each other.”
Each swordfish has two types of tags. One stays in the fish and provides GPSlike position data when the fish breaks the surface of the water.
The other is a pop-off tag that records the depth and temperature of the water that the fish traveled in. That will allow Gaube and Braun to get an excellent handle on the fish’s movement. When the pop-off tags detach and float to the surface, they’ll transmit data about each fish’s diving and feeding behavior. Combined with the location tags, the scientists will learn how the fish move in the ocean and what types of water conditions are optimal for them.
Working with the company Wildlife Computers, the scientists also modified a pop-off tag so it could be attached to the fish with a monofilament tether. That way the tag can float to the surface while the swordfish is swimming just below the surface.
An oceanographer at the University of Washington Applied Physics Laboratory, Gaube got his master’s degree in physical oceanography at Nova Southeastern University in 2007 while working at the International Game Fish Association in Dania Beach, which is where he first met DiGiulian.
Gaube said the tags could also provide information on whether swordfish off South Florida tend to remain in the region or are just migrating through, as well as if there are differences in migratory behavior between fish of different sizes.
Information that the tags have already revealed: All five fish survived capture and tagging and were transmitting, and therefore feeding at the surface, within 48 hours of being tagged.
“This speaks volumes to the efforts Tony led to revive and handle the fish in a way to ensure survival,” Gaube said. “This info can be used to make a concrete case for not taking fish out of the water if you want them to survive.”
Another noteworthy finding is that smaller swordfish, in this case weighing about 90 pounds, migrate long distances.
The swordfish that the scientists named Max, which was tagged off Lighthouse Point, has traveled more than 1,600 miles to off the coast of Virginia and Delaware (visit www.ocearch.org /?details=359 for Max’s track). It was not previously known if juvenile swordfish would migrate that far.
“There is another thread that has motivated this project, and that is during their migration, what oceanographic features structure their path?” Gaube said. “We have a treasure trove of satellite observations of the ocean and by having the high resolution tracks we will get from our new tags, we will be able to see the fronts and eddies along which they travel. This information would be invaluable in the proper management of swordfish stocks and fisheries.
“We are also currently working to develop a new generation of tags that will provide measurements of the temperature and salinity of the ocean with quality equivalent to what we get from our large research vessels.
“This is a project that is pending with the Navy and would fundamentally change how we measure the ocean. The project is ambitious and if fully funded, will provide us with over $1 million over four years to develop a prototype and test it on large white sharks.”
Contributions for the project can be made at www.gofundme.com /SwordfishTagging.
Donors or groups of donors that give $10,000 can name a future tagged swordfish and single donors who contribute $20,000 will be invited to join the research team for a day of swordfish tagging.