Gentle giants
Consider yourself lucky if you set eyes on the elusive ocean sunfish.
Sunfish have been in the news lately when a dead one showed up in the Bras d’Or Lakes. The theory is that it swam in during the summer while chasing its favourite prey, jellyfish, and didn’t get out before the water cooled.
Sunfish are more properly known as ocean sunfish and go by the scientific name of Mola mola, from the Latin mola, which refers to a millstone and is an accurate description of this species which is grey in colour and almost round in shape.
The ocean sunfish has several distinctions associated with it. It is often described as the heaviest bony fish in the world as it may weigh up to 1,000 kilograms. There are larger fish — the whale shark among them — but its skeleton is mostly cartilage. The ocean sunfish also has the distinction of producing the largest number of eggs of any species, up to 300 million at a time.
I have only seen one ocean sunfish and that was on a sharkfishing trip off Halifax a few years ago. We were after blue sharks and were constantly scanning the horizon for the sight of a shark fin on the surface. The appearance of a large fin caused some excitement until our captain identified it as that of a sunfish. Once we knew what we were looking at we could tell the difference as the swimming movements of the sunfish caused the fin to bob up and down in the water compared to the blue sharks, where the movement was steady as the fin remained above the surface.
Ocean sunfish are a seasonal visitor to our waters as they move up every summer from the tropics to feed. While ocean sunfish are the largest bony fish in the world, they attain this bulk by eating one of the least nutritious animals in the sea, jellyfish. This makes them vulnerable, like sea turtles, to eating floating plastic bags. They will also feed on squid, small fish and marine plants such as eel grass.
Ocean fish may be found throughout the water column, from the surface down to 600 metres. These deep dives take place in very cold water and it is thought this results in the sunfish then spending time on the surface lying on their sides to absorb the sun’s heat and warm up. This habit of laying on the surface often results in them being hit by ships. Other than humans, ocean sunfish have few predators other than orcas and sharks which occasionally prey on them.
Ocean sunfish are found in all the world’s oceans and are considered a delicacy in some countries. In Europe and North America, there is some uncertainty whether this species may contain toxins, so it is not consumed as food.
Off our shores, the ocean sunfish will remain a seasonal visitor and, if you get a chance to see one, consider yourself very lucky as they are definitely elusive giants of the sea.