Blue shark

Blue shark (Shane Anderson / public domain)

The Blue shark (Prionace glauca) have slim bodies with a dark blue back and lighter flanks. Eyes are relatively large. Blue sharks inhabit temperate and tropical regions. They can reach 3.8 meters (12 feet) in length. 13 unprovoked attacks on humans (four fatal) have been reported as of 2022.

Inhabits the Indo-Pacific Ocean.

Inhabits the Atlantic Ocean.

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This supplemental online resource accompanies the book Scuba Diving Hand Signals by Lars Behnke, available on Amazon.