Tiny black and white Commerson’s dolphins swim with their belly up when in groups, and marine biologists are just starting to find out why. There are three hypotheses that are currently up for debate, but they could all have some truth to them.
1. By swimming upside down, a Commerson’s dolphin gets a better view of fish it’s hunting.
These dolphins rely on echolocation, where they emit a sound and then listen out for its echo. Researchers think that they can use echolocation more effectively when the dolphin is upside down, especially if teamed up with other dolphins that are swimming the right way up.
2. Swimming on their backs can help find prey buried in the sand
Using echolocation, dolphins can beam sound waves through the sea bed and can tell if there are any animals buried by the returning echo. Swimming upside down might make this easier for Commerson’s dolphins.
3. By displaying their bellies, they can show others their age and sex
Male and female dolphins are very difficult to tell apart, and the only difference is on the lower belly. Male dolphins have one long genital slit where the reproductive organs are kept inside for streamlining purposes, but females have two mammary slits either side of their genital slits. Biologists think that by swimming upside down, Commerson’s dolphins are communicating their gender, age and even dominance rank to others around them.
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