The spectacular scene was captured by photographer Sophia Quach, who was aboard one of Cat Balou's Twofold Bay discovery cruises, at Eden on the NSW South Coast, on Saturday, August 6.

"Seeing that sassy seal throwing the massive octopus around was definitely a highlight and I don't think I'll ever see something like that again," Ms Quach said.

While the tour typically focused on some of the larger and beloved sea creatures, the splashing and thrashing of this particular seal captured the skipper's attention who veered them towards the commotion.

Ms Quach said when they got near she saw the seal tossing something red up and at first averted her gaze thinking it was a bloody scene, until she heard someone say, "I think it's caught an octopus!"

"I gasped and looked up to see it thrashing the octopus around and my first instinct as an avid photographer was to grab the camera," she said.

Within seconds Ms Quach had bolted from the top deck to the bottom and back again, camera in hand in the hopes of capturing the seal's conquest.

Lucky for her the seal launched the octopus in a final and dramatic way, just as she angled the camera towards the scene.

"I wanted to get an angle where you could see the octopus' tentacles and I captured it just before the seal gobbled it up, so I was pretty chuffed with the result," she said.

Skipper and owner of Cat Balou Brad Wills said their cruise photographer and marine biologist, Hannah Cousin, identified the octopus as a Macroctopus, also known as the Maori octopus.

"These are some of the biggest octopuses you can find and although this one wasn't fully grown Hannah estimated it to have had an arm span of 2m and a weight of roughly six to seven kilos," Mr Wills said.

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Mr Wills said while the scene was astonishing to onlookers, seals eating octopuses was actually a common occurrence.

"We often see seals with their catch, but what made this one a little bit more extraordinary was the size of the octopus," he said.

Ms Quach said she'd decided to nickname the attacker Sophie the sassy seal, because it had been committed enough to dive, catch and then "gobble up" an octopus that was big enough to endanger it, if the tables had turned.

"Hannah said to me that octopus could have taken that seal out easily, so it was a pretty lucky and impressive kill," she said.