REMORAS | SEA LIFE WITH A GOOD SUCKER | A DIVE BUDDY THAT STICKS TO YOU
Remora remora is the name for the common remora. They have a highly modified dorsal fin that expands during their development to become an efficient sucker disk on the top of their head. Remoras attach to sharks, mantas, whales, turtles, ships, divers and just about anything to save energy until their next feed. It’s hard to imagine that powerful, open ocean swimmers like mahi-mahi [dolphinfish] and amberjacks are related to remoras. Your opinion about these opportunistic freeloaders might change when you consider what 50 million years of evolution has done by tinkering with the muscles and bone structure of a dorsal fin to produce their quirky edge for survival.
In nature there are relationships like predator-prey and parasitism where one half of the equation benefits at the expense of the other. There is mutualism, a form of symbiosis where both organisms benefit from the relationship to the extreme where one cannot survive without the other. Commensalism describes relationships on a scale between parasitism and mutualism. Where does the relationship between remoras and other sea life belong?
Does the removal of parasites as a service to a host improve survival, longevity or the energy budget of a host like this humpback whale? It must have a hundred or more remoras that increases the effort needed to move through the ocean using precious fat reserves for energy. This mother is feeding its calf on the long journey to summer feeding grounds off Antarctica, so how far south do remoras go before their free ride gets too cool to survive? Do remoras provide a parasite removal service that is worthy of them tagging along or is this an extreme form of commensalism that’s nudging parasitism as a way of life? Remoras are up their with platypus and other anomalies of the natural world that make me wonder what the creator was on while doodling the prototype or was the design brief given to a committee?
Humpback whale, calf and remoras. Tofo, Mozambique. GoPro Screen Shot: Tony Isaacson
A few years ago I jumped off a 30 metre sail training vessel to assist the captain with manoeuvres to get the 60 tonne aluminium hull off two coral bommies. It was quite a jump and when the bubbles cleared, the biggest remora I have ever seen looked confused and it was swimming in tight circles. I can’t publish words that I bubbled out at the time, but I recall the intensity of asking myself, “Where is the shark that giant remora was cruising with?” It wasn’t until the gaff rigged vessel was off the reef that I realised remoras of a metre or more in length been hitching a ride on our sailing ship, leaving large clean patches on the bow section that was otherwise covered by turf algae.
The highly modified dorsal fin functions as a very effective adaptation for attachment to marine megafauna, divers and ships.
There is no doubt about the gripping power of their highly modified dorsal fin. They have been used by hunters to latch onto turtles and other sea life in much the same way as a line is attached to live cormorants to capture much smaller prey. My diving is often with marine megafauna like whales, mantas and sharks, so remoras are frequently part of the experience. Many times they have been dive buddies that have attached or attempted to attach. Of course these are the times when there is no camera for the perfect selfie with sea life? A photo for the caption “Remora remora, a dive buddy that sticks with you.”
Photo: Tony Isaacson
Counter shading, like the sucker could be another adaptation that increases survival for remoras. In many open water species, being dark on top makes sea life difficult to spot against a dark, deep ocean. Being lighter on the belly has a similar effect when viewed from below. Does the black and white design double as a cue to predators to leave remoras alone like cleaner fish that are given a right of entry to remove parasites from the mouth and gills of predators that eat fish of the same size and shape? Black and white patterns do impact on shark behaviour to the extent that wetsuits have been designed to improve the outcome for unexpected human shark encounters. Something is working for remoras as I’ve never seen one attacked nor eaten while observing remoras and sharks on dives like those featured in “Remora Remora”.
With so many similar shapes and counter shading, I look for points of difference to identify individuals in a crowd. The ‘mutant’ remora with a disfigured mouth was my companion for 55 minutes on a baited shark dive at Aliwal Shoal in South Africa. It make gestures to remain friends for ever and I’m sure that it would have had a great story to tell, albeit told with a fishy lisp. Before “Remora remora” was embedded in this blog I posted it on social media to prompt divers to share images of remoras sporting injuries and disfigurements that would have killed most sea life. Nothing came back, so I searched for images with no reward for the time spent. There was a small image on a running blog site showing a remora attached to the back of a “runner” on a fishing boat.
There was a YouTube post of a friendly remora that was doing its best to find a point of attachment to a scuba diver.
A tiger shark swallowed a dead remora bringing into question the idea that remoras are not eaten by sharks.
Having seen remoras at many places around the world, I am now motivated to capture images of individuals that defy the laws of nature by surviving what should have been catastrophic, life terminating injuries.
Bull shark and remoras at The Bistro, Beqa Lagoon, Fiji, Ultimate Shark Experience. GoPro Screen Shot: Tony Isaacson
Like any excuse to justify my diving habit, this quest is a ‘work in progress’ and enduring. I’d like to step up from posts like these. If you can help, please contact me at [email protected]