Ocean heat maps reveal secrets of migratory fish like tuna

MIAMI, Oct. 21 (UPI) -- By comparing the movements of tagged fish with ocean heat content maps, researchers at the University of Miami were able to uncover unique patterns in migratory fish behavior.

Their analysis proves that large migratory fishes, like yellowfin and bluefin tunas, blue and white marlin, and sailfish, are drawn to ocean fronts and eddies.

Two analytical breakthroughs made the revelation possible. First, researchers realized satellite mapping of ocean heat content, or OHC, a measurement of heat stored in the ocean's upper layers commonly used for hurricane forecasting, could also be used to pinpoint the position of fronts and eddies.

Second, researchers were able to improve the algorithm that analyzes satellite tags from migratory fish. Together, these advances allowed researchers to compare OHC mapping and fish movements.

"Using an advanced optimization algorithm and OHC maps, we developed a method to greatly improve geolocation accuracy and refine fish movement tracks derived from satellite tags," lead researcher Jiangang Luo, a scientist at Miami's Tarpon and Bonefish Research Center, said in a press release.

The data showed that large migratory fish prefer to follow the boundary lines of large water features.

"Using the OHC approach in a new way offers an unprecedented view of how these animals move with currents and eddies in the ocean," Nick Shay, a professor of ocean sciences at Miami's Rosenstiel School of Marine and Atmospheric Science, said in a press release. "Our study provides a more detailed picture of the ocean ecosystem as an entity."

Eddies are circling masses of water that spin off of current fronts. The swirling water pulls nutrients to the surface, making them an ideal place for hungry fish to hang out. Fronts are currents that follow the boundary line between two large water masses, distinguished by a difference in temperatures or salinity.

In the Gulf of Mexico, warm water eddies regularly spin off of fronts formed by masses of Mississippi River water. In the summer and fall, these eddies can energize and intensify a hurricane or tropical storm.

"Our new method shows that hurricanes and highly migratory fish share at least one common oceanographic interest -- warm swirling ocean eddies," said Jerald S. Ault, a professor of marine biology and ecology at Rosenstiel.

The new research was detailed in a paper published this week in the journal PLOS ONE.