Learn about Spinner Dolphins

Nai’a (Spinner Dolphins) 101

What kinds of dolphins do we normally see off the coast of the Big Island?

Of the 33 to maybe 57 species of dolphins in the world (researchers don’t agree on the number), only 13 species are found off Hawaiian waters, and of those 13, just 4 are commonly seen here — Spinners, Spotted, Rough Tooth, and Bottlenose.

What’s the difference between dolphins, porpoises and whales?

All these animals are members of the order Cetacea, and the sub-order Odontocete, which means all of these animals are toothed whales. The word “dolphin” typically refers to animals who have pronounced beaks, falcate (curved like a boomerang) dorsal fins, and conical shape teeth.  “Porpoises” are animals with a blunt face, spatula shaped teeth (i.e. flat – like your own front teeth)  and triangular dorsal fins. “Whales” are just really big cetaceans. To confuse the subject even more, a lot of local people here refer to the mahi-mahi fish as a dolphin, and to the smaller toothed whales as porpoises. That’s why researchers prefer to use all these animals’ Latin names for identification.

So, what’s the Latin genus and species name for the Spinner Dolphin? And what’s the Hawaiian name?

The Latin name is Stenella longirostris. Stenella comes from a Greek word that means “narrow” and longirostrus means “long snout”. Hawaiians call almost all dolphins “Nai’a” – though the name “Kiko” is used for the Spotted Dolphins (“kiko” means spot or dot).

How did these dolphins get the common name “Spinner”?

Watch these dolphins for a few minutes, and it’s pretty obvious. Spinners are really active on the surface!

Why do they exert so much energy jumping out of the water?

Although it may look like it’s simply a lot of fun, researchers believe that spinning is part of a dolphin’s job.  Spinners spin most often at night, when the pod is more spread out and active. Reentry also creates a huge bubble plume which may make it easier for other dolphins to echolocate. So spinning is a way to keep track of where everyone is in the dark. Another popular theory explaining spinning behavior is that dolphins often have hitchhikers on their bodies (a fish called a remora, and a shark called a “cookie-cutter” shark). Jumping out of the water and landing with a big splash can get rid of those animals pretty quickly!

Do dolphins play with each other?

It sure looks like they do! We’ve seen them pick up debris like leaves or discarded line in the ocean and pass it to each other, balancing it on their pectoral fins.

What are all those sounds that I hear the dolphins making, and why are they so noisy?

Every dolphin has his own distinct whistle and everyone in the pod recognizes whose it is (even calves recognize their Mom’s whistle soon after birth). They make these sounds by moving air around in their nasal sacs, and the chambers behind their melons (their big foreheads). They can use sound to keep track of each other, but they also use it to find prey (biosonar).

Tell me about the life cycle of a Spinner dolphin.

Ok. After about a 10 ½ month gestation period a Spinner is born tail first. We believe his Mom will lift him to the surface for his first breath, but he’s immediately able to swim and suckle. At birth, he’s somewhere around 1 ½ feet to 2 ½ feet long. He’ll nurse on milk from his Mom that’s almost 40% fat (human milk contains about 4% fat). The calf isn’t weaned until he’s somewhere between 12 and 24 months, but he’ll stay in association with his Mom for longer (several years). If the calf is a female, she’ll reach sexual maturity around age 5-7, and if he’s male, he’ll reach sexual maturity around age 10. A fully grown Spinner is pretty small – males average 7 feet long and about 180 pounds and females are slightly smaller. Though a female will calve on average every 2-3 years (and almost always to a single baby – fewer than 1% were observed with twins), we have observed much more frequent mating behaviors. Both males and females mate socially (the female doesn’t have to be in estrus—in heat– for mating to occur) which is unusual in the animal kingdom. Spinners live an average of 20 years.

What’s their family structure like?

Spinners live in “fluid” pods. With the exception of Mom and calf pairs, associations change constantly and there appears to be no real dominance hierarchy (though bigger males mate more frequently). Pod sizes average from a dozen animals to several hundred, and pods are fairly territorial (we know this because we’ve discovered genetic differences between pods that live off of the different Hawaiian Islands).

What do they eat?

Off the shores of the Hawaiian Islands, Spinners typically feed on what’s called “the deep scattering layer”. These are small fish and invertebrates like squid that migrate vertically at night to feed on the plankton nearer the surface. A Spinner consumes about 20% of its body weight daily of these small fish and squid (or around 66,000 calories every day)!

Are Spinner dolphins an endangered species?

Thankfully no, but they are protected by the Marine Mammal Protection Act of 1972, which means we can’t “harass” them or alter their behavior. Though the Spinner population is difficult to count, researchers believe there are somewhere between 3500 and 5000 individuals around the Hawaiian Islands. Spinners are found worldwide from latitudes about 40 degrees north to 40 degrees south, but the world population is unknown.

Tell me some more random Spinner facts.

Spinners are mammals, so they have hair. When Spinners are born, they have hair on their rostrums (beaks), but by the time they’re adults, only the follicles remain.

The main predators for Spinners in Hawaii are Tiger Sharks and Pelagic White Tip Sharks, but Cookie Cutter Sharks frequently take quarter size pieces of flesh from the dolphins.

A Spinner can dive 800 to 1000 feet deep and hold its breath for a couple of minutes!

Spinners and other Odontocetes all have one blow hole. Mysticetes (baleen whales) have two.

Spinners can swim 30-35 mph but use the least amount of energy when they’re cruising at about 5 mph.

Based on the structure of their eyes, Spinners have great vision and can see in color.

Sources:

Norris, K., Wursig, B., Wells, R.S., Wursig, M.  (1994), The Hawaiian spinner dolphin. Univ. of California Press. Berkeley and Los Angeles, California.

Welcome to the Dolphin Place: FAQ: March 2011.

http://thedolphinplace.com/QandA.html#31