These Shark Look-Alikes Have Long Confounded Fishers and Scientists on the East Coast. Tracking Where They Migrate Could Help Clear the Confusion

Along the U.S. East Coast, scientists are working to resolve a long-running identification problem involving two sharks that can appear and act remarkably alike. Researchers are attaching tags to spinner sharks in an effort to chart where they travel and when. The work has become more urgent because the distribution of the closely resembling blacktip shark has already been observed changing, raising new questions about which species is being encountered in different coastal waters.

The project is not simply an exercise in labeling animals correctly. When fishers, researchers and coastal observers cannot reliably distinguish between similar sharks, records of sightings and catches can become harder to interpret. A clearer account of spinner shark movements could help separate their presence from that of blacktip sharks, whose physical appearance and behavior can make field identification difficult.

Tracking offers a way to replace isolated observations with a broader picture of movement. Tags can help researchers follow where individual spinner sharks spend time, allowing scientists to compare those patterns with reports from other parts of the coast. If blacktip sharks are appearing in areas differently than before, knowing the ordinary and changing ranges of both species may make future observations more useful.

Beth Bowers, a marine ecologist at the Smithsonian Environmental Research Center, is among the scientists pursuing that information. Her interest in sharks began early. Unlike many young viewers who came away frightened by Jaws, Bowers was captivated by the film’s central animal. Her response was not fear, but fascination with what she saw as an extraordinary predator.

That reaction developed into a career studying sharks in the Atlantic. Bowers now conducts fieldwork that is far removed from the controlled setting of a laboratory. Some research days involve bait, ocean spray and the strong odor that accompanies shark-tagging work, as scientists gather data directly from animals at sea.

During one September outing, Bowers joined a small team near the inlet at Ocean City, Maryland. On a Friday afternoon, the group boarded a fishing vessel with the captain and first mate before heading roughly six miles from shore. Their purpose was a shark-tagging expedition, part of the larger attempt to build a more precise understanding of where these difficult-to-separate species occur.

For scientists, the resemblance between spinner and blacktip sharks presents a practical caveat: a report that identifies one species may need to be considered alongside the possibility of the other. That uncertainty does not mean every observation is wrong, but it can complicate efforts to use field records to describe changing marine patterns. Tagging spinner sharks may provide an independent line of evidence against which those observations can be compared.

The wider significance of the work lies in its potential to show whether apparent changes reflect a true shift in shark distribution, confusion between look-alike animals, or some combination of both. Blacktip sharks have shown a range change, while spinner sharks are now being tracked to establish a stronger baseline for their own movements. The results may also help fishers and researchers better understand what they are seeing offshore.

Much remains to be learned, and tracking data will take time to accumulate across places and seasons. Still, each tagged spinner shark can add to a map that is more informative than a single sighting. As those maps improve, the longstanding uncertainty surrounding two nearly identical East Coast sharks may become easier to untangle.

Source: Smithsonian Magazine