Brittle stars massing by the hundreds in possible reproduction event at Tagus Cove, Isabela Island, Galapagos Islands, Ecuador, South America

Nurse sharks (Ginglymostoma cirratum), massing in Hol Chan Marine Preserve, inside the Mesoamerican Barrier Reef, Belize

Nurse sharks (Ginglymostoma cirratum), massing in Hol Chan Marine Preserve, inside the Mesoamerican Barrier Reef, Belize

Nurse sharks (Ginglymostoma cirratum), massing in Hol Chan Marine Preserve, inside the Mesoamerican Barrier Reef, Belize

Adult Spinetail Mobula (Mobula japanica) massing in huge schools in the upper Gulf of California (Sea of Cortez), Mexico

Adult Spinetail Mobula (Mobula japanica) massing in huge schools in the upper Gulf of California (Sea of Cortez), Mexico

Blue Sharks (Prionace glauca) massing in deep water around shark diver Bob Cranston. San Clementa Island, California, USA. Pacific Ocean. Model released.