Dolphin's 'savage' behaviour in Perth river captured on video: 'Nasty'

Is it a bird? Is it a plane? No — it's a fish flying through the air!

One Perth resident couldn't believe his eyes when he spotted a dolphin repeatedly whacking a fish out of the water during his walk on Monday afternoon.

Despite it being well-known the Swan River is home to a pod of residential dolphins, with the pod recently linked to a fatal shark attack last month, locals don't usually catch one behaving this way. The walker was quick to capture what he called "savage" behaviour on camera before uploading it online.

"It doesn't happen everyday but it's pretty common for dolphins to play with things in the water," Jeff Weir told Yahoo News Australia.

As the Executive Director of the Dolphin Research Institute, Jeff explained there are three plausible reasons why the highly intelligent animal would choose to act this way.

Why would a dolphin 'play' with a fish?

The reasons range from educational to "aggressive", with Mr Weird saying mother dolphins often deploy this "cat and mouse" strategy to teach her young about hunting.

This tactic was also observed in orca mothers, another species of the Cetacea group that includes dolphins. Researchers in New Zealand believe the orca mothers choose to teach their young how to hunt fish as they are considered a low risk of injury compared to other prey.

Despite it being a common educational exercise, Jeff discredited this option as the likely motive for the Swan River dolphin as the aquatic mammals in the video appear to be of similar size.

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Another possibility is the dolphin may have behaved like this in attempt to break up the "big fish" into smaller pieces due to their inability to bite prey into chunks. Without "cutting or chewing" teeth, dolphins are known to throw larger animals out of the water in an attempt to disassemble them before eating the fragmented pieces whole.

"That's a pretty big fish and it might be a bit big for them to swallow, so they could have been doing that," Mr Weir shared. "They often bang squid and jellyfish in the hopes of eating them".

Mr Weir said in this instance he believed the dolphin was playing with the fish simply because it could.

"Just like humans they can be nasty and really aggressive," he shared.

Whether they are hungry and hoping to secure their next meal, or simply wanting to pass the time, dolphins of high intellect have been known to showcase sinister behaviours.

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