Seems there’s never a shark around when you need one, but have you tried playing the theme from Jaws? If you want to call in a shark, it turns out that cellos are not as effective as Heavy Metal music. An episode of the Discovery Channel's "Shark Week" said that sharks are attracted to heavy metal music, and its low frequencies.

That’s why a film crew looking for a particular shark used an underwater speaker playing heavy metal music to attract great white sharks according to the Huffington Post.
Maybe they should play Great White.

An Australian tour boat captain says sharks are attracted by two AC/DC songs in particular; “You Shook Me All Night Long” and “If You Want Blood.”
The sharks can hear the music and sense low frequency vibrations created by heavy metal that seem to resemble the sound of struggling fish, according to "Bride of Jaws," an episode of the 2015 season of the Discovery Channel's "Shark Week."

The specific shark the crews were looking for, Joan of Shark, was tagged off the coast of Western Australia in April 2014 and is the largest great white shark ever tagged in Australia, according to the Daily Mail.