Commercial fishermen have known for some time that tuna, along with many other species of fish, congregate around objects drifting on the ocean surface. Fishermen often build floating structures called FADs, or fish-aggregating devices, to attract tuna to an area, allowing them to capitalize on this behavior. Using FADs makes the job of finding and encircling the tuna in the purse seine nets much more efficient.
Fishermen also learned that whale sharks are so large that they naturally attract tuna, much like a FAD. This led some fishermen to deploy nets around a whale shark to capture tuna swimming beneath it. In many of the cases, the encircled whale shark was also caught in the net and injured or died.