Night Shift

spinner dolphinsSpinner Dolphins
Kingdom: Animalia , Phylum: Chordata, Class: Mammalia, Subclass: Eutheria, Order: Cetacea, Suborder: Odontoceti, Family: Delphinidae, Genus: Stenella Species: longirostris
Scientific name: Stenella longirostris
Common name: Spinner Dolphin
Hawaiian name: Nai'`a

Spinner Dolphins are distributed across all tropical oceans between the latitudes of 40 degrees North & South. They are divided into four subspecies. While most records of Spinners worldwide are associated with islands, banks and reefs, they are primarily a pelagic, deepwater species. In island groups such as Hawaii they frequent inshore waters during the day. They have long, narrow beaks. Both upper and lower jaws are equipped with between 45-65 sharply pointed teeth. Adults range in size to 8 feet in length and weigh up to 170 lbs.

These dolphins are highly social and their schools vary from just a few animals up to thousands. In Hawaii they rest during the day where they swim gently back and forth in sheltered waters close to shore and adjacent to deep water. At night they head out into the open ocean to hunt primarily for fish, squid and crustaceans using echolocation to find their prey, an adaptation particularly favorable to hunting at night. Their primary food source, small mid-water fishes such as lantern fish (Myctophidae), shrimps and many others, obligingly migrate toward the surface at night to feed. Here they become easily accessible to dolphins and many other nocturnal reef species that hunt them.

Dolphins vocalize to communicate with other members of their pod or school using a complex array of clicks and whistles. Spinner dolphins also communicate through other means such as tail-slapping and spinning. They can leap high out of the water and spin laterally many times before crashing back into the waves and, very occasionally, flip end over end – hence their common name.
Spinner dolphins are gregarious and frequently are found in association with whales and spotted dolphins. Their association with schools of Yellowfin tuna has likely been pivotal to their population collapse. In the eastern Pacific it is believed that their population has been reduced by 65% and while their population has stabilized it is not recovering. Anecdotally, for example, the huge schools that commonly frequented the Galapagos Islands in the past are rarely encountered today.

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