Mark Quartiano — known as Mark the Shark because he leads shark-fishing expeditions — said he received the video on Monday from the men who recorded it via direct message on Instagram. He said the video appeared to show a blacktip shark being dragged by a rope tied around its tail, presumably after it had already been caught with a rod and reel.

“I couldn’t believe that someone would send me something like this,” he said on Tuesday. “I was horrified.”

Mr. Quartiano, who is based in Miami, shared the video via his own Instagram account the day he received it. That post has gained the video attention on social media — it’s been viewed more than 53,000 times — and from Florida officials.

“It is too early to speculate as to what, if any, violations took place in this incident,” the state’s wildlife commission said in an emailed statement.

It added: “The lack of respect shown in this video for our precious natural resources is disheartening and disturbing, and is not representative of conservation-minded anglers around the world.”