Every summer in the Cape Cod Canal and throughout other waters of the Cape a large and very strange fish makes an appearance. To some this fish looks like a shark with its large dorsal fin cutting the surface of the water. In fact many people erroneously report a shark sighting when in reality it’s not even related. This is the ocean sunfish (Mola mola) which not only looks unusual, but is quite heavy as well. Some specimens can exceed 2,000 pounds. Most of the fish has a flattened body with extended fins on the dorsal and ventral sides. It has a unique structure called a clavus instead of a caudal fin and uses this to maneuver through the water. It skin is thick without scales and it swims rather slowly.
Though the sunfish is often spotted near the surface, hence the mistaken identity as a shark, it actually spends most of its time underwater as deep as 2,000 feet. The animal usually travels alone and occasionally washes up on the Cape’s beaches in places like Sandy Neck in Barnstable.
The sunfish is a member of the family Molidae and has a couple of other interesting features. For one thing it lacks a swim bladder like other fish. It also has a very high reproductive capacity. A female sunfish can lay up to 100 million eggs. Another amazing fact is that it is quite cosmopolitan being found in tropical and temperate parts of the world’s ocean.
With such a large animal present in the ocean and so easy to find, I wondered about its population status. Ocean sunfish seem to be steady in numbers, maybe because of their high fecundity. But they are vulnerable to environmental problems such as getting trapped in gill nets that are drifting throughout the ocean as death traps.
Another disturbing problem is that the sunfish loves to eat jellyfish. That in itself is not a problem because many jellyfish populations have increased around the world. But a jellyfish can be confused with a floating plastic bag and unfortunately, plastic debris has become a serious marine pollution problem. The sunfish can suffocate when trying to ingest plastic bags like other victims of plastic debris such as sea turtles.
Mola mola is a remarkable animal and always creates excitement and curiosity when seen in the Cape’s waters. With its unique appearance and distinct biology, the ocean sunfish is one of the more interesting visitors to our shores.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.