Imagine yourself as a large yellowfin tuna swimming miles out in the blue. You start to feel an itching near your eye. It could be a minor scratch that is healing or a tiny crustacean gnawing at your skin.
What are you going to do? It’s not possible to grab it with your hands. There aren’t any cleaner wrasses around to gently pluck it off your hands like coral reef divers.
We viewed thousands of hours worth of video of open ocean life and discovered that tunas and other fishes can solve this problem. Sharks might be the answer you were looking for.
Sharks are big fish’s favorite mate.
In Research in progressPublié in PLOS OneWe discovered that fishes found in the open ocean such as tunas and sharks used sharks to scratch against them.
Scratching is likely to remove parasites and dead skin. These fishes may be hosts to many parasites but have limited options for their removal.
We found scraping interactions between shark and fish species in the Pacific, Indian, and Atlantic oceans. Fish preferred to scrape on sharks over other fish, as we found. The size of the sharks was also important. Smaller fish were more likely to be eaten than larger sharks.
Dermal denticles, which are small, tooth-like structures that make up shark skin, are made up of tiny structures called dermal. It has a similar feel to sandpaper and was even used in pre-industrial times for that purpose, making it an excellent surface against which it can be scratched.
Our research showed that fishes tend to scratch their heads and sides more often than any other area of their bodies. This is the area where parasite damage can be most severe. It includes the eyes, nostrils, and lateral lines that run down the sides of a fish’s body.
Also, we found that different fish species had different ways of scraping. Tunas were organized and lined up behind sharks, taking turns to touch the tail. Rainbow runners were unruly and formed a group around the shark’s back, darting out in turns to bump into its body.
Use underwater cameras to spy on the ocean wildlife
This behaviour was discovered while analysing thousands upon thousands of hours underwater video that had been taken using baited camera system left to drift at the sea. We reviewed the footage and identified, counted and measured every individual we saw.
We used the data to identify trends in population. However, these videos also revealed some unexpected behaviours.
We first saw a large yellowfin tuna approach a silky shark, then it gently rubbed against its tail before it sailed off. We soon saw a similar interaction between another Yellowfin tuna and another silky Shark.
We eventually observed similar interactions among several shark and fish species from around the world, and recorded the details.
Why scraping is important: Healthy oceans require healthy shark populations
The oceans are the largest habitats on the planet. However, it is difficult to study.
There are few observations of animals’ natural behaviour in open ocean. Interactions among these animals are intriguing not only because they may be unfamiliar to us, but also because we might be able to see their potential implications.
Clear fitness benefits can be derived from the removal of parasites. Fitter animals are more likely reproduce and to pass their genes on to the next generation. These fishes might be benefiting from scraping against sharks.
The question is: What would happen to shark numbers if they become too few for fishes find their scratching spots? Is there a net loss in fitness for these fishes
This is an important question considering the rapid decline of shark populations across the ocean. Some species have been endangered. The decline was as high as 92 percentOff the Queensland coast of Australia
The loss of human relationships, such as the ones we describe, could lead to a further decline in shark populations.
Only scraping was observed in remote areas that have large tunas and sharks. These species are often heavily exploited in other parts of the world. Remote areas offer an insight into how intact ecosystems function and what wild and bizarre things are happening in the ocean.
Marine protected areasIt has been proven that they can conserve behavior in SharksAnd Fishes. These behaviors could be restored and preserved if more of these areas are created.
What’s next?
We will continue to explore remote and offshore areas.
This research may uncover other species that are involved in these interactions, or other interesting behaviours with conservation implications.
Christopher D H ThompsonResearch Fellow, Marine Futures Lab The University of Western AustraliaAnd Jessica Meeuwig, Professor & Director, Marine Futures Lab, The University of Western Australia
This article has been republished from The ConversationUse the Creative Commons license Please read the Original article.
