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Nature Notes: Ocean Sunfish

Ed Robinson
August 11, 2021

“Is that a shark?!!”

Unless you are a pretty cool customer, those words immediately trigger all kinds of thoughts. When you are on the ocean in a small boat, it means you are suddenly on high alert. Lane is an experienced outdoorsman, not given to hysteria, but I could hear the concern in his voice as I turned to look where he was pointing.

We were on the eastern side of Ram Island, off the southern tip of Orr’s Island, looking for striped bass while checking out the nesting sea birds. Sure enough, there was a large triangular fin sticking out of the water about 40 feet from the boat. The fin was not moving so it didn’t appear we were in danger but the size, shape and position of the fin struck me as unusual. The longer we watched the fin and the shape below in the water, the more it seemed this might not be a shark but something else indeed.

Ocean Sunfish (photo from iStock)

We had encountered one of the heaviest bony fishes in the sea, an ocean sunfish. The scientific name, Mola mola, derives from the Latin word for millstone. As you can see in the photo, this fish is unlike almost any other fish you have ever seen. Mother Nature is a superb designer who rarely puts a foot wrong but she must have had an off day when she cranked out this species. Not only is the creature huge, but it appears to have been assembled from a bunch of mismatched parts. Every creature has its own natural beauty, of course, but this sunfish takes some study to fully appreciate it.

Native to tropical and temperate waters, the ocean sunfish dwarfs the tiny sunfish (i.e., bluegills) I grew up catching in small farm ponds. Looking like a flattened fish head with a huge fan-shaped tail, known as a clavus, these babies have been recorded up to 5,000 pounds in weight. The skin is rough in texture and colored from brown to light gray. When under threat of attack, the sunfish has the ability to change its color within moments. The largest sunfish can measure ten feet from nose to tail or from dorsal fin to anal fin. With tiny fan-shaped pectoral fins, the sunfish is by nature a slow mover, feeding mostly on jellies, squid, fish, larvae and crustaceans. The females hold the record for creating prodigious numbers of eggs, up to 300 million each. Its closest relatives are pufferfish, filefish and porcupinefish that share the round mouth with a prominent beak formed by four large, fused teeth. The mouth remains open all the time.

It will not surprise you to know that the ocean sunfish has few predators, given its massive size. But the slow-moving creatures with few defenses are favored by sharks, orcas, tuna and sea lions. Unfortunately, mankind is primarily responsible for the ocean sunfish being listed as “vulnerable” due to over-harvesting and ocean pollution. Floating plastic bags can resemble drifting jellies, causing serious injury or death if ingested by the sunfish. Sunfish often are caught in large gill nets intended for species like the swordfish. The sunfish are considered a delicacy in Japan, Korea and China but the European Union banned the sale of the fish to offer some protection.

Ocean sunfish often lounge along the surface of the sea, soaking up sunshine, with their long dorsal fin out of the water. Rather than standing erect as a shark or porpoise fin, the sunfish dorsal fin is often seen flopping around or lying flat on the surface, exactly what Lane and I witnessed. This surface activity often brings the sunfish into harms way because they are susceptible to being struck by boats, much like the manatees of south Florida. Imagine running into a beast weighing a ton or more in your small runabout! Sunfish are plagued by a large variety of skin parasites so they are known to hang around in kelp fields where small fish like the cleaner wrasses will dine on the parasites. Seabirds have also been observed plucking parasites from sunfish resting on the surface.

Originally thought to move as a result of ocean currents, studies of tagged sunfish revealed that the fish can swim an average of 16 miles per day. They feed in deeper water at times, recorded to depths of 700 feet or more. As a cold-blooded creature they prefer water above 50 degrees F, explaining their presence off Harpswell’s shores in the summer. Scientists predict that warming ocean temperatures may bring more of the sunfish to our northern waters. Little is known about their life cycle beyond a sunfish in captivity that gained 800 pounds in one year on a rich diet, and another captive sunfish that lived beyond ten years.

Sunfish are docile creatures and pose little threat to humans, even those who skin dive close to the fish for observation and photography. Since the fish can leap out of the water if threatened, there are reports of sunfish landing atop boats. Imagine having one of these giants suddenly appearing from the deep to land on your poop deck!

As with many other creatures that are cloaked in mystery, the ocean sunfish has attracted its own support network, found at www.oceansunfish.org. This group works to support research on the fish and to collect knowledge and data that can be used by scientists worldwide. They invite citizen scientists to report sightings of sunfish, and you can even “adopt” a sunfish for as little as $25. $200 will get you a lovely poster and even a stuffed sunfish toy for cuddling. If you are feeling flush, you could pony up $20,000 which would snag you an invitation to join an expedition to tag sunfish in the sea.

If you like Ed Robinson’s writing, check out his two Nature Notes books! Click here for more information.