Tuna or Mackerel

Yellowfin tuna (Tom Wang / shutterstock.com)

Tunas and mackerels constitute the family Scombridae. Members of this family have streamlined bodies, 2 dorsal fins, 5 to 12 finlets, and deeply forked caudal fins with at least two keels. The pelvic fins are located below the pectoral fins. Tunas are excellent swimmers, reaching a top speed of about 75 kilometers (47 miles) per hour. Size varies greatly among the different species, ranging from 35 centimeters (14 inches, long-jawed mackerel) to 4.2 meters (13.8 feet, bluefin tuna) in length. Due to commercial fishing pressure, the Atlantic and southern bluefin tuna are classified as endangered on the IUCN Red List.

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