Researchers from the 91±¬ÁÏ are using high-tech tags to record the movements of swordfish — big, deep-water, migratory, open-ocean fish that are poorly studied — and get a window into the ocean depths they inhabit.

The researchers tagged five swordfish in late August off the coast of Miami: , , , and . Their movements can now be viewed in near-real time. And although swordfish are a prized catch, these ones aren’t at higher risk, researchers say, since the website updates only every few hours and these fast-swimming fish spend most of their time far from shore.

“These are animals that migrate into the ocean’s twilight zone that we know next to nothing about,” said , an oceanographer at the 91±¬ÁÏ Applied Physics Laboratory. “Swordfish in different regions have very different behavior. We hope to learn more about these amazing animals and their environment as they migrate between regions.”

This is the first time satellite position tags have successfully been placed on swordfish caught off the coast of the United States.

Earlier tags on swordfish relied on measurements of temperature and light to approximate the animal’s position, which resulted in errors greater than 60 miles (100 km). The new tags act together as a pair: One records detailed temperature, light and depth measurements as the fish is swimming, while the other beams back the precise location when the fish surfaces each day.

By comparing the saved observations with computer reconstructions of ocean conditions, the researchers can re-create an individual fish’s precise travel path in three dimensions, allowing for the first time scientists to understand where these animals feed and providing new insight into deep-sea ecosystems.

Gaube and collaborator , a 91±¬ÁÏ assistant professor of aquatic and fishery sciences, have placed similar satellite tags on other ocean predators, including great white sharks, , and .

“Swordfish are different from the surface-oriented fish that have been tagged, like sharks or whales — these are deep-sea fish,” Braun said. “But because they migrate up and down every day, they break the surface, and the new types of tags allow incredibly fast communication.”

Swordfish often jump at the surface, a behavior that helps make them a popular target for sport fishing.

“That’s why we’re so excited,” Braun said. “Swordfish are a particularly good platform to help us make observations in the deep ocean, while at the same time giving us a better understanding of why and how this predator makes a living.”

Recently, the 91±¬ÁÏ researchers customized satellite tags made by of Redmond, Washington, to work on swordfish. These top predators swim long distances, commonly reach 10 feet (3 meters) in length, and are named for the long, flat bill they use to slash and injure prey.

The fish can swim at 50 miles per hour and typically spend the day at a third of a mile (550 meters) deep. They rise to the surface at night, along with millions of other fish and squid, upon which the swordfish feed.

A by Braun, Gaube and collaborators, published in June in the ICES Journal of Marine Science, analyzed 16 swordfish tagged with simpler tags in the western Atlantic, off Florida and the Grand Banks, and in the Northeast Atlantic, off the coast of Portugal. The results show that juvenile swordfish tagged off Portugal tended to stick to that area, while the mostly adult individuals tagged in the western Atlantic swam long distances between the Grand Banks off Newfoundland and the waters near Cuba.

With the new Florida-based project the team hopes not only to learn more about swordfish but to further explore the mesopelagic, or “twilight zone” of the Atlantic Ocean. These partially lit waters from a tenth to half a mile (200 to 800 meters) in depth are hard to reach and poorly studied, even as fishing is beginning to target these environments.

In January the researchers plan to tag more swordfish in the Red Sea, off the coast of Saudi Arabia.

“This will provide the baseline data we need to understand this ecosystem before it is exploited any further,” Gaube said.

The initial phase of the Florida swordfish-tagging project was funded by the Woods Hole Oceanographic Institution. Researchers are looking for , in the sport fishing community, environmental groups or others, to monitor other swordfish and gather more data.

Next the team is designing new tags that can hold more sensors that could measure properties such as acceleration, depth, water temperature, muscle temperature and stomach temperature. The next-generation tags could also include cameras that could be set to trigger based on various behaviors, such as when the fish dives to a certain depth. They hope to eventually use results from the Florida tagging project to guide shipboard sampling of the marine environment alongside swordfish “oceanographers.�

For more information, contact Gaube at pgaube@uw.edu or Braun at cdbraun@uw.edu.

It’s always good to know where great white sharks are likely to be swimming. That’s true if you’re a nervous beachgoer, a fishing boat trying to avoid illegal bycatch, or a marine biologist hoping to conserve this vulnerable species.

A study from the 91±¬ÁÏ and Woods Hole Oceanographic Institution looked at the movements of adult female white sharks in the Gulf Stream and North Atlantic Ocean. Results showed, surprisingly, that they prefer warm-water eddies — ocean whirlpools that spin clockwise north of the equator — and tend to spend more time deep inside these slowly spinning features.

The open-access was published in May in Nature .

“We’ve decimated some open-ocean shark populations to a fraction of what they were 100 years ago. And yet we don’t know the basics of their biology,” said lead author , a senior oceanographer at the 91±¬ÁÏ’s Applied Physics Laboratory. “If we know where those sharks, or turtles or whales might be in the open ocean, then the fisheries can avoid them, and limit their bycatch.”

Gaube investigates how ocean eddies, or whirlpools, influence the behavior of marine animals. His previous , on loggerhead sea turtles, similarly found that they prefer the anticyclonic, or clockwise-spinning in the Northern Hemisphere, eddies. These features trap large amounts of water at the ocean’s surface and are most often warm, clear and low in nutrients.

The new study analyzes movements of two female great white sharks tagged in September 2012 off Cape Cod and in March 2013 off Jacksonville, Florida. The tricky job of tagging the animals was done by , a nonprofit that focuses on tagging and tracking sharks. One shark just had a position tag, while the other had a second tag that also recorded temperature and depth. The sharks were tracked for nearly 6 years, with one still reporting its position regularly, as they swim north with the Gulf Stream and then out into the open ocean.

The high-tech tags are made by in Redmond, Washington. The early shark-tagging projects could just offer rough ideas of where sharks were swimming, Gaube said. But since precise satellite position networks were made available to the public, and with improvements in computing and batteries, the tags can now collect detailed information as sharks travel throughout the marine environment.

Researchers took the data from the two sharks and compared their position in the ocean with sea-surface height data from satellites showing where the huge, swirling warm- and cold-water eddies were located at that time.

“These eddies are everywhere, they cover 30 percent of the ocean’s surface,” Gaube said. “It’s like what you see if you’re walking along a river, and these eddies form behind rocks, but it happens on a different scale in the ocean: Instead of being a little thing that disappears after a few seconds, they can be the size of the state of Massachusetts, and can persist for months to years. You could be in the middle of an eddy in a ship and you’d probably never know it. The water may be a little warmer, and it could be a little clearer, but otherwise you wouldn’t know.”

Analysis shows that the two sharks spent significantly more time in warm-water eddies than the cold-water eddies that spin the other way. Sharks lounged the longest at about 450 meters (about a quarter of a mile) deep inside the warm-water eddies, especially during the daytime, likely feeding on the abundant fish and squid at these depths. They were more likely to come to the surface at night.

This preference goes against common wisdom, because it’s the cold-water eddies that generally bring nutrient-rich water up from the depths of the ocean, and satellite images show that cold-water eddies are rich in marine plant life. This study is the first to show that sharks gravitate toward eddies, and that they prefer the warmer variety.

“White sharks are effectively warm-blooded,” Gaube said. “They have to keep their body temperature elevated. We believe that these warm eddies allow white sharks to forage longer at depth, where most of the biomass in the open ocean is found. One reason that the sharks might prefer them is by diving in these warm eddies, they can spend more time in the deeper water.”

Second, recent studies suggest that the “twilight zone,” below the depths that satellites can see, contains many more fish than previously believed — and much more than at the surface. Those patterns might be different than the ones we can easily detect from space.

“Could these ‘ocean deserts’ actually be super productive at depth? That’s what we think might be happening,” Gaube said.

Some recent deep-sea net surveys have found larger, toothy fish like pomfret below the surface in anticyclonic eddies, which could provide a motivation for the sharks to dive there.

“These sharks are 2,800 pounds. It’s hard to imagine that they’re just eating krill and small fish all of the time they’re in the open ocean,” Gaube said. “If they can find pomfret and lots of squid in these eddies, then sharks can really get a meal out of that.”

Data collected by sharks could help to protect this “twilight zone” as it’s just beginning to be targeted by major fisheries, Gaube said. And information about where great white sharks like to hang out could help conserve this vulnerable species.

“Maybe if we understand the biology of these animals, how they use these features, we could say, ‘OK, do not fish anticyclonic eddies during this time of year, because you’re more likely to catch white sharks,'” Gaube said. “Instead of cordoning off a particular area, we could say there’s this feature, it moves every day, let’s make a ‘mobile marine protected area’ and not touch it because we know it’s a hot spot for great white sharks.”

Other co-authors are at the 91±¬ÁÏ; , a former graduate student at Woods Hole who is now a postdoctoral researcher at the 91±¬ÁÏ Applied Physics Laboratory; Gareth Lawson, Dennis McGillicuddy and Simon Thorrold at Woods Hole Oceanographic Institution; Gregory Skomal at the Massachusetts Division of Marine Fisheries; and Chris Fischer at OCEARCH. The research was funded by the National Science Foundation, NASA and the Woods Hole Oceanographic Institution’s Ocean Life Institute.

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For more information, contact Gaube at pgaube@apl.washington.edu. More images are available at .