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Two tags were attached to this swordfish off the coast of Florida in August 2019. A small antenna on the fin sends data when the fish breaks the surface.
Photo Credit: Steve Doughtery
Scientific Frontline: Extended "At a Glance" Summary: North Atlantic Swordfish Extreme Dives
The Core Concept: Scientists from the Woods Hole Oceanographic Institution discovered that North Atlantic swordfish, which primarily hunt in the ocean twilight zone, occasionally execute extreme vertical dives exceeding 1,000 meters. Researchers hypothesize these rare descents function as an environmental sampling mechanism, allowing the predators to gather navigational cues during long-distance migrations.
Key Distinction/Mechanism: Unlike standard foraging dives constrained to approximately 600 meters, these extreme descents appear unlinked to immediate hunting behavior. The mechanism involves traversing distinct water masses and ocean weather systems, such as eddies and frontal systems, to evaluate the depth and structural characteristics of the surrounding water column.
Major Frameworks/Components:
- Satellite Archival Telemetry: The utilization of pop-up satellite tags deployed for one to six months to track the vertical and horizontal movements of highly migratory fish across thousands of miles.
- Environmental Sampling Hypothesis: The theoretical framework positing that pelagic predators use extreme vertical movements to assess hydrographic changes and navigate oceanographic features.
- Longitudinal Data Aggregation: The methodological requirement of combining long-term tagging datasets across multiple studies to achieve the statistical power necessary to identify rare behavioral patterns.
Branches of Science: Marine Biology, Ichthyology, Oceanography, and Marine Telemetry.
Future Application: Elucidating these deep-water navigational mechanisms will allow researchers to accurately forecast the migratory shifts of highly mobile predators in response to changing oceanographic conditions and regional water masses.
Why It Matters: Swordfish are vital apex predators that stabilize marine food webs and support highly valuable fisheries. Understanding the environmental cues that dictate their long-distance movements is essential for dynamic conservation management and the sustainability of global marine ecosystems.
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| Swordfish are powerful, highly migratory predators that spend much of their time hunting in the ocean twilight zone. Scientists from WHOI are studying why they occasionally dive more than 1,000 meters below the surface and what those rare deep dives may reveal about how swordfish navigate the ocean. Photo Credit: Steve Dougherty |
Swordfish spend much of their time hunting prey around 600 meters below the surface in the mesopelagic zone (the ocean twilight zone), but occasionally, they reach depths of more than 1,000 meters. Now, scientists from the Woods Hole Oceanographic Institution (WHOI) are investigating what may be behind these extreme dives.
The new study, published in Marine Biology, suggests these rare, extreme dives may help swordfish gather information about their surroundings in the open ocean. By moving through different water masses and ocean features, the fish may be sampling changes in ocean conditions for cues that help them navigate during their long-distance movements. The swordfish in the study traveled thousands of miles during their migrations, moving between waters off Canada and the Caribbean.
“If we want to understand how these animals move and navigate to make use of the information in their environment, these rare behaviors can be really valuable,” said Martin Arostegui, a marine biologist at WHOI and an author of the study. “Being able to start to get at that question represents just how much more we know about what happens above the surface of the ocean than what we do under it.”
Researchers analyzed the movements of 34 North Atlantic swordfish using data from pop-up satellite archival transmitting tags deployed for one to six months. During the 3,666 deployment days, the telemetry data revealed 39 extreme dives. These data were collected in partnership with NOAA’s Southeast Fisheries Science Center and the Massachusetts Division of Marine Fisheries.
“It wouldn't have been possible to analyze this from just a single tagging operation, or from a single lab,” said Simon Thorrold, a fish ecologist at WHOI and author of the study. “It was necessary to pull tagging data from different studies and to begin building longer-term datasets to give us enough power to at least begin to sort of ask questions about what those dives might be for.”
“This study demonstrates the value of collaboration and long-term data collection,” said Eric Orbesen, a research fishery biologist at the Southeast Fisheries Science Center and coauthor of the study. “Individual tagging projects provide important snapshots in time and space, but maintaining and combining these datasets over many years allow scientists to identify behaviors and patterns that would otherwise be very difficult to see.”
Understanding how swordfish respond to ocean conditions could also help scientists better predict how these important predators may move as the ocean changes. Swordfish support valuable fisheries and stabilize marine food webs, necessitating a precise understanding of their migratory pathways, environmental drivers, and responses to shifting oceanographic conditions.
“They could be coming into an ocean weather system, like an eddy or a frontal system, where we have a change in water masses. Maybe that change in the ocean system prompts them to check out what’s happening deeper in the water column—to get a sense of where they are, how deep the feature extends, or answer other questions about their world that we don’t even know they’re asking yet,” said Ciara Willis, who led the study as a doctoral student in the MIT-WHOI Joint Program. Willis is now a postdoctoral investigator at the Monterey Bay Aquarium Research Institute.
Researchers still do not know to what extent extreme diving is shared broadly across swordfish or how it varies among populations or life stages. They also want to determine how important these rare dives are to swordfish overall and whether they represent an occasional way of gathering information or a more significant part of how these highly migratory predators
Funding: Open Access funding enabled and organized by CAUL and its Member Institutions. This work was funded in part by Woods Hole Oceanographic Institution’s Grassle Fellowship (to CDB), Ocean Venture Fund (to CDB), and President’s Innovation Fund (to MCA); a Natural Sciences and Engineering Research Council of Canada Postgraduate Scholarship - Doctoral (to CW); two Massachusetts Institute of Technology Martin Family Society of Fellows for Sustainability Fellowships (to CW and CDB); and a NASA Earth and Space Science Fellowship (to CDB), with computation support from AWS. This work was part of the Woods Hole Oceanographic Institution’s Ocean Twilight Zone Project, funded as part of the Audacious Project housed at TED.
Published in journal: Marine Biology
Title: Evaluating the potential role of extreme dives by swordfish (Xiphias gladius)
Authors: Ciara Willis, Camrin D. Braun, Martin C. Arostegui, Gregory Skomal, Eric S. Orbesen, Derke Snodgrass, and Simon R. Thorrold
Source/Credit: Woods Hole Oceanographic Institution
Edited by: Scientific Frontline
Reference Number: mb110926_01
