Researchers tracked a whale shark named Larry for nearly a year after he was tagged in the Gulf of Mexico.
At the time, nobody knew how much information the satellite tag would eventually collect.
The tracking data later showed movements through the Gulf, including waters near Cuba and Honduras, before he returned. The journey provided an unusually detailed record of how one whale shark moved through the region.
Why do these giant fish keep returning to the same waters off Tampa Bay?
Nobody expected Larry to keep traveling this long
The project started because researchers got tips about whale shark sightings from fishermen who said they saw them around here.
Although whale sharks are the largest fish in the ocean, there are not very many of them.
After locating a group offshore, removable clamps and satellite tags were attached to the animals’ dorsal fins. One of the sharks tagged during the expedition was a 26-foot male later named Larry.
Satellite tags like the ones used on Larry can transmit for many months and send location data back to scientists via satellites. The information allows movements to be tracked across areas that are too large to study from a boat or aircraft.
At the time of deployment, the team had no idea just how significant Larry’s upcoming journey would be.
His track would eventually become one of the longest movement records gathered during the project.
The tag was just beginning to tell a much bigger story
Initially, Larry swam down towards the Dry Tortugas before returning to the Tampa Bay area. By September of last year, he had traveled to Cuba and Honduras.
Later, he moved through other parts of the Gulf.
Researchers also observed the whale shark following the edge of the Loop Current, a major warm-water circulation system in the Gulf. The tracking data showed that whale sharks use a much larger area than scientists can easily observe from boats or aircraft.
According to NOAA Fisheries, the year-long track also pointed researchers toward potential feeding regions across the Gulf.
Information like this can help researchers better understand how the species uses different parts of the Gulf throughout the year.
Whale sharks spend 40-60% of their time in the upper ten (10) meters (about 33 feet) of the water column. Spending so much time near the surface can increase the likelihood of interaction with vessels in heavily trafficked marine areas.
A year’s worth of data on Larry has not yet resolved the underlying mystery, though.
Something seems to be causing whale sharks to go back into waters off Tampa Bay.
Researchers finally discovered a new clue
While tagging the whale sharks, researchers noticed something strange. There were so many fish eggs floating around them that it made it hard to see.
Based on earlier observations of whale shark feeding behavior and the timing of fish spawning events, researchers suspected the eggs could be attracting the animals.
In previous years, the species had been observed feeding on little tunny eggs in the Gulf of America.
However, the newly collected samples came from Spanish sardines, a species not previously documented as a food source for whale sharks in the Gulf of America.
How did a mouthful of tiny eggs change the map?
Spanish sardine eggs provided yet another piece of evidence as scientists continue to study distribution and feeding behaviors in the region.
Scientists now know much more about Larry’s travels than they did when he was originally tagged.
Even so, many questions about whale shark movements in the Gulf remain unanswered.
More information may come from tagging additional individuals and collecting more samples in the future.
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