Humpback whale (melissaf84 / shutterstock.com)

Whales are marine mammals. Instead of vertical caudal fins, they have horizontal flukes. Whales must surface periodically to breathe through their nasal openings (blowholes) located on the tops of their heads. The blue whale is the largest living animal on Earth, reaching 33 meters (110 feet) in length. Baleen whales (Mysticeti) are filter feeders. Their diet is comprised of small organisms, mainly krill. Baleen whales have two blowholes. In contrast, toothed whales (Odontoceti) have only a single blowhole. Larger fish and squid, which are located via echolocation, comprise their main food source.

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