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Thursday, June 1, 2023

Spinner Dolphins Dance in the Sunset

Far out at sea, off southwestern Costa Rica’s OsaPeninsula, the sunlight falls in shifting, laser-like rays through crystalline blue waters. Through this vast, borderless, pelagic or open-ocean ecosystem swim huge pods of spinner dolphins. They live here, within sight of CorcovadoNational Park and Caño Island Biological Reserve, in unprotected waters. They gather in startling numbers in the same tiny piece of open ocean, day after day, month after month, year after year.

Dear reader, in case you didn’t know, there are no other dolphins like spinner dolphins. Very distinctive is this dolphin’s trademark spin. All day long and probably all night, these dolphins shoot completely out of the water, spinning so fast that they become a blur.

A spinner may spin eight times around before splashdown. For them, spinning may be a kind of fitness training for a very active lifestyle. Spinning also might help remove pesky fish that stick to their smooth sides.

Few other animals spin, and I think I know why. When I try spinning around eight times as fast as possible, I fall down. Even a spinner dolphin can do only so many spins.

This might be why only a small part of the pod is up and spinning at any given time, though even baby spinners spin.

Spinner dolphins are human-sized, unlike their more famous cousins. Bottlenose dolphins are much bigger than the spinners in every way. They have bigger brains, bigger bodies and bigger… well, you get the idea. They are better known because of their exploits as movie and TV stars. Scientists and businessmen have long been big on bottlenoses, because these tough dolphins readily survive in captivity, unlike the more delicate and elegant spinner dolphins.

Costa Rica’s spinner dolphins come way more concentrated than other dolphins, such as bottlenoses. Spinners pack together like people at a rock concert; they might cover an area the size of a hundred stadium shows.

Does that seem big to you? In the open ocean, a stadium could look like a speck, or not even be visible at all.

Thousands of spinner dolphins disappear from the view of observers in smaller boats at about three nautical miles. If the boat has a high enough tower, you might see the white splash of a spinner reentering the water from about five nautical miles away.

Commercial fishing fleets’ helicopters use this white splash to find the spinners from more than 10 nautical miles away. The birds that swoop and hunt over the spinners can sometimes be seen on special tuna fleet radar from at least 24 nautical miles away.

As with icebergs, only the tip of the pod is visible from the surface; the vast bulk is seen only below. Spinners pack together because they are extremely social, constantly chattering and touching. They seem to spend  almost as much time mating and blowing bubbles on each other as they do surfacing to breathe. They are the most gregarious of all Costa Rica’s cetaceans.

Under natural conditions, the Osa’s spinners seem to split into smaller groups only in rough seas. Sadly, here on the Osa, commercial tuna boats split up the groups and kill dolphins almost daily.

But the spinners still keep getting back together in massive groups in the same place, spinning every day, weather and commercial tuna operations permitting. They have been found in this same small, unprotected area for many years, just off the continental slope of the OsaPeninsula, about five to 20 nautical miles off CañoIsland.

They seem to stick to a little piece of the big blue: clear pelagic waters where the bottom drops quickly from about 500 meters to more than 2,000 meters deep. Here, special conditions create an upwelling of deepwater marine life, and that means year-round fish feasts. Thousands of dolphins spinning around and around, night and day, get pretty hungry, and this area gives them plenty to eat.

No matter what spinners are up to, they must come to the surface to breathe and bust off some spins every so often. Probably because of this, they are always on the move, even when they are resting. I have never seen a live spinner stop moving for more than a few seconds. They might swim 10 nautical miles in one day, a little less at night.

The spinner lifestyle is action. They must be in peak shape to swim miles to hunting waters and party areas. There are no fat spinners. Many people look at jumping dolphins and say that they are playing. This is like watching a professional dance group or sports team drill and saying that they are playing. Yes, they are playing, but something much more serious is also going on: You might call it training.

Spinners share their world with a host of other big, strange creatures, most of which the spinners swim circles around.

They frequently make other beasts the butt of their silly sense of humor. They might sneak up on less-aware creatures, mimic their movements or sounds with dramatic and sometimes unnecessary flair, and then cackle and chatter with laughter and high fives, or rather high fins – not that they have done this to me!

One of the most impressive things I have seen any animal do is the spinner sunset dance. When the sun sinks low into a clear sky on a calm sea, the spinner dolphins start to dance. You have to see it to believe it.

As the sun falls into the sea, the dolphins spread out a little, and many dolphins start to jump at once, with less spinning and more hang time. They seem to suspend themselves in the air and bask in the glory of the setting sun. Many more dolphins than normal start to leap at once, flying from the water in synchronized waves. Their reverence for the setting sun is awesome.

The sunset dance of the Osa’s spinner dolphins is not to be missed. Most people around the world will have to settle for watching the Costa Rican stars perform their ritual on the big screen in the upcoming IMAX film “Oceans,” due out next year. But those of us who live here have the chance to see the show on the biggest screen ever: real life.

Long may the spinners dance into the Osa’s sunsets.

Coming up next time: a look at the impact of commercial tuna fishing on Costa Rica’s spinner dolphins and the author’s proposal to create a “pelagic park” offshore of the OsaPeninsula.



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