Swordfish GPS Tracking Program Underway in South Florida

18 Feb 2020

Fishermen in South Florida are assisting fisheries scientists to learn more about swordfish and uncharted ocean depths through an innovative tagging program.

GPS tracking devices will help scientists Camrin Braun and Peter Gaube from the University of Washington to learn data about swordfish, which researchers claim spend the majority of their lives in the “ocean twilight zone.”

According to Gaube, the ocean layer where there’s enough light to see and orient is called the mesopelagic zone, but there’s not enough light to power photosynthesis. Gaube states they don’t know a lot about this zone and by instrumenting and tracking swordfish, they’ll learn more information about the functions of this ecosystem.

Fort Lauderdale’s Capt. Tony DiGiulian stated earlier this year, there were five swordfish that range between 75 to over 300 pounds that were caught, tagged and then set free off South Florida.

There are two types of GPS tracking tags on each swordfish.

  1. One tag is in the swordfish, providing GPS-like position once the swordfish breaks the water’s surface.
  2. The other tag is a pop-off tag and records the water’s temperature and depth where the fish travel through.

This allows Braun and Gaube to learn a great deal on the movement of the fish. Once the pop-off tags come off the fish and float up to the surface, they start transmitting data about the feeding and diving behavior of each fish. When scientists combine them with the location tags, they’ll the way the swordfish move in the ocean and which water conditions they prefer.

The scientists who work with the company Wildlife Computers, also altered a pop-off tag so they could attach it to the swordfish using a monofilament tether. This way, while the fish are swimming right below the surface, the tag can float to the surface.

The tags could also give them data on whether the fish off South Florida are simply migrating through the region or remaining there, according to Gaube. They can also see if fish of different sizes have migratory behavior differences.

There’s already been data from the tags. Within 48 hours of having a tag attached to them, all five swordfish survived being captured and set free and were feeding at the surface and transmitting data.

Another finding is smaller swordfish (around 90 pounds in this case), migrate long distances. Scientists named one swordfish Max, tagged it off Lighthouse Point and received data it traveled over 1,600 miles off the coast of Delaware and Virginia. It wasn’t known previously if juvenile swordfish were able to migrate long distances.

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