40 Fun Facts About Spinner Dolphins

How do resting spinner dolphins manage to keep swimming and surfacing for air while they sleep?

Half the brain stays awake while the other half sleeps, so a resting spinner dolphin can still swim slowly and come up to breathe. A quiet school drifting near shore may well be asleep.

Toxoplasmosis, a disease that has killed Hawaiian spinner dolphins, reaches the sea from which animal's droppings?

Cats shed the parasite's eggs in their droppings, and rain can wash them down to the coast. Fatal infections have been confirmed in spinner dolphins off Hawaii.

Which small shark leaves round crater scars on nearly every adult spinner dolphin off Hawaii?

The cookiecutter shark gouges out round plugs of flesh, as if with a cookie cutter. Its bite marks have turned up on whales, big fish and even submarines.

Wartime sonar crews mistook the dense layer of sea life that spinner dolphins feed on for what?

The seabed seemed to sit far too shallow and to rise after dark, so the layer became known as the false bottom. It is really millions of small animals whose bodies bounce the sound back.

Off Oahu, how do night-hunting spinner dolphins bunch up their prey before pairs dart in to feed?

Circling it together, the school packs its prey into a tight patch, and then a pair at a time swims through the middle to make a catch.

Which hitchhiking fish, gripping with a sucker on its head, can a spinner dolphin's spins shake off?

Remora suckerfish clamp onto a dolphin's skin and add drag, so a hard, spinning splashdown is thought to be one way of knocking them loose.

What filmed 33 swimmers accused of harassing spinner dolphins off Hawaii's Big Island in 2023?

A drone caught the group chasing dolphins that were trying to get away. Swimming within 50 yards of Hawaii's spinner dolphins has been against federal rules since 2021.

While resting in shallow bays, spinner dolphins stop echolocating and rely on which sense instead?

Vision takes over while the sonar is switched off, which is why resting schools keep to clear, calm shallows where they can see what is coming.

Which remote Pacific atoll, scene of a pivotal 1942 naval battle, has spinner dolphins living in its lagoon?

Midway Atoll has a resident pod of about 300 spinner dolphins in its lagoon and nearshore waters, alongside monk seals that raise their pups on the beaches.

Besides shedding hitchhikers, what do experts think a spinner dolphin's noisy, splashy spins are mainly for?

Communication is the leading idea: each splashdown makes a burst of noise that carries through the water to schoolmates that are out of sight.

Which tuna species swims beneath schools of spinner dolphins, a habit that keeps drawing fishing fleets to them?

Yellowfin tuna follow the dolphins in search of food, so crews learned to find the valuable fish by looking for schools of leaping spinners.

Which kind of tuna net, set around whole dolphin schools, killed tens of thousands of spinner dolphins?

Purse seine nets are drawn shut at the bottom like a drawstring bag, trapping whatever is inside. The deaths led to dolphin-safe labels on canned tuna.

Which dolphins often travel in mixed schools with spinner dolphins in the open eastern Pacific?

Spotted dolphins and spinners swim together so often in the eastern Pacific that one long-held idea is that the mixed school helps keep resting spinners safe.

Which small deep-sea fish, named for their glowing light organs, are the spinner dolphin's main prey?

Lanternfish hide in dark, deep water by day and swim up toward the surface after sunset, which is when spinner dolphins dive down to meet them.

Spinner dolphins hunt animals from the ocean's mesopelagic layer, better known by which nickname?

Twilight zone is the popular name for the dim band between roughly 200 and 1,000 metres down, where only a trace of sunlight arrives.

Which spot on Hawaii's Big Island, where Captain Cook was killed in 1779, is a noted spinner dolphin resting place?

Kealakekua Bay on the Kona coast is where the dolphins come in most mornings to rest and to nurse their young in calm, sheltered water.

Which Brazilian archipelago, a UNESCO World Heritage Site, is famed for its resident population of spinner dolphins?

Fernando de Noronha earned its UNESCO listing partly because of its resident spinner dolphins, and one of its best-known bays is simply called Dolphins Bay.

Which 1972 US law makes it illegal to harass, hunt, capture or kill a spinner dolphin?

The Marine Mammal Protection Act covers every whale, dolphin and seal in US waters, endangered or not. Under it, even disturbing a resting school can count as an illegal "take".

Researchers identify individual spinner dolphins by photographing the nicks and notches on which body part?

Dorsal fin shape and damage work like a fingerprint, letting scientists follow the same dolphin for years from photographs alone.

The spinner dolphin's species name, longirostris, is Latin for which of its features?

Long beak is the translation, and older books simply call the species the long-snouted dolphin.

Spinner dolphins belong to the genus Stenella, a name built from a Greek word with which meaning?

Narrow is what the Greek stenos means. The name was coined in 1866 by the same London zoologist who had first described the spinner itself decades earlier.

Which Atlantic dolphin arose as a natural hybrid of the spinner dolphin and the striped dolphin?

The Clymene dolphin is the only confirmed case of a hybrid-born species among all the whales, dolphins and seals, and until 1981 it was classed as a kind of spinner.

Spinner dolphins belong to which major group of cetaceans, the one that also includes belugas and narwhals?

Toothed whales have teeth instead of baleen and find their prey by echolocation. Dolphins, the spinner included, are simply smaller members of the group.

Which largest member of the dolphin family is listed among the spinner dolphin's possible predators?

The killer whale, or orca, is itself an outsized dolphin, though sharks are the hunters that spinner dolphins have to watch for most.

Which term describes spinner dolphin society, where huge night-time schools split into small daytime groups?

Fission-fusion means the group keeps breaking up and re-forming: hundreds feed together after dark, then as few as a dozen may rest together by day.

Which spinner dolphin calls, separate from their echolocation clicks, may be used to organise the school?

Whistles carry between animals and may help keep a travelling school in order, while rapid burst-pulse sounds round out the repertoire.

Which camouflage scheme describes the spinner dolphin's dark grey back, lighter sides and pale belly?

Countershading puts the dark colour on top and the pale underneath, a disguise shared with sharks that is thought to blend an animal into its background from above and from below.

Which SeaWorld co-founder, a pioneer of dolphin echolocation research, wrote Dolphin Days about the spinner dolphin?

Kenneth Norris gave the book the subtitle The Life & Times of the Spinner Dolphin, and he taught at UCLA and UC Santa Cruz.

Which Indian Ocean island nation has morning boat trips to watch spinner dolphins in Tamarin Bay?

Mauritius draws visitors to Tamarin Bay, where spinner and bottlenose dolphins are usually seen early in the day before they head back to the open sea.

Resting Hawaiian spinner dolphins favour bays with which kind of bottom, against which predators are easier to see?

White sand makes a pale backdrop that shows up an approaching shark, and the chosen bays also lie close to the deep water where the dolphins feed.

After twisting through the air on a spinning leap, how does a spinner dolphin usually hit the water?

On its side is the usual landing, and a single leap can pack in as many as seven full turns before the splash.

Where does a spinner dolphin build up the rotation that carries it through a spinning leap?

Underwater is where the spin begins: the faster the dolphin is swimming and turning as it leaves the sea, the more rotations it can fit into one jump.

Besides spinning, spinner dolphins perform a leap named after which river-running fish?

Salmon leaps sit in a long repertoire that also includes nose-outs, tail slaps, head slaps, flips and back slaps.

Which US agency's 2021 rule made it illegal to swim within 50 yards of a Hawaiian spinner dolphin?

NOAA Fisheries wrote the rule because crowds of swimmers and tour boats were costing the dolphins the daytime rest they need before a night of hunting.

As their daytime rest ends, spinner dolphin groups swim in which pattern before racing offshore together?

Zig-zags toward open water and back again, first described in 1994, seem to be the signal that gets the whole group ready to leave at once.

The nightly rise of deep-sea animals that spinner dolphins hunt is, by total weight, Earth's largest what?

Migration on this scale happens every single day: countless small animals swim up toward the surface in the evening and sink back down before sunrise.

Tuna crews long called the spinner dolphins swimming above their catch by which technically incorrect name?

Porpoises are a separate family of small cetaceans, but the fleet's name for the dolphins that swam above the tuna stuck.

Along with small fish and shrimp, which soft-bodied molluscs do spinner dolphins dive for after dark?

Squid rise from the depths each evening along with the fish, and the dolphins may dive 200 to 300 metres to reach them.

Kalpitiya, whose coastal waters are home to spinner dolphins, is a peninsula in which South Asian country?

Sri Lanka's Kalpitiya coast also shelters bottlenose and humpback dolphins, sea turtles and the elusive dugong.

The Central American spinner dolphin subspecies is also known by the name of which country?

Costa Rica gives the subspecies its other name. It is the largest of the spinners, with an even longer snout than the ones living farther offshore.