Underwater encounters – Octopus gardens and shark stacks

“It was winter and the water was a chilly 14 degrees. I inhaled sharply as it soaked through my wetsuit, 7 millimetres of neoprene doesn’t stop you getting goose bumps. Ignoring the cold, we kept swimming out. There was something offshore we’d come to see and it only happened once a year…”

We have another guest post for this series! Marine biologist and keen macro photographer Mitch joined us to chat about his favourite underwater encounters. Let’s dive in!

Meet Mitch (the one on the left)

Huskisson, N.S.W

Today we’re taking you to Huskisson, a small coastal town on the south coast of NSW. Husky, as the locals call it, sits in the Jervis Bay Marine Park. This makes exploring temperate reefs really accessible if you pop on a tank and swim straight out from the beach. Mitch and his buddy had come to dive a site called Dent Rock.

“Dent rock is a small rocky reef sitting 150 metres offshore from Orion beach. It’s marked by a buoy on the surface because the reef can be only 2-5 metres below the surface depending on the tide. This makes it perfect for diving because boats avoid it. We hauled our gear down a steep set of stairs and walked out through the shallow breakers. Picking our way over rocks we began to swim out, the water was only about three metres deep over the weed banks.”

Swimming out over the seaweed Mitch and his buddy kept an eye out for interesting critters to photograph.

“As you move along you find patches in the weed, surrounded by shells. Empty shells from clams, scallops, mussels, pipis, every kind of mollusc that usually buries itself in the sand were piled up in circular clumps. In the centre of the shell piles was a hole that seemed to drop down to nowhere, but if you’re lucky it drops down to an orange, brown and cream speckled octopus.”

Mitch points out one of two octopi/octopuses (whichever you prefer). Can you spot the other one?

Octopus Gardens

These strange homes are called octopus gardens (we know you just started humming the Beatles song). A lot of creatures like the taste of octopus so to avoid being eaten they hide in dens. The octopus camouflages its home by building gardens of shells and rocks around it, some even have a rock ‘door’ they pull over the opening to seal themselves safely inside.

An octopus in its garden of shells

“It’s clear these creatures are full of personality. Some can’t keep their eyes off you, they pop as far out of their hole as they can when you approach. If you float down to the weed bank they float higher to keep an eye on you. Others want absolutely nothing to do with you and sink deep into their holes, pulling shells over their heads for cover.”

Close up of an octopus

“All that and we hadn’t even hit the reef yet! Jervis Bay is a pretty special spot because it serves as a breeding aggregation site for Port Jackson sharks. Breeding aggregation, that doesn’t sound particularly special but you end up with hundreds of sharks piling on top of each other, all with no concept of personal space.”

Port Jackson Sharks

Each year between winter to early spring, Port Jackson sharks migrate to shallow reefs to mate. Here they congregate in small groups, in caves, under overhangs, and in gutters along the rocky bottom.

“So what psychopath is getting in the water with hundreds of sharks? Well that’s the other bonus, Port Jackson’s or PJ’s as we call them, are the puppy dogs of the ocean. These bottom feeders eat sea urchins, crabs and molluscs (invertebrates with shells), anything they can root out of the sandy bottom. They’re really not interested in you unless you give them a hard time.”

“PJ’s for anyone that hasn’t seen one, don’t look like your stereotypical shark. They’re a square headed fish reaching a maximum length of 1.65 metres. Their skin is brown with black lines that make it look like they’re wearing a harness. They have rounded fins with small spines just in front of their dorsal fins. Even their teeth are unusual. They have flattened plates perfect for crushing and grinding up their food, very different to the pointed teeth you normally associate with sharks.”

A Port Jackson shark up close, note its unusual teeth

The divers had finally arrived at Dent Rock. But could they find the sharks?

“It wasn’t hard, they were scattered everywhere over the bottom. Heads and tails were going in every direction, no one was fussed that they were being lain on or were laying on someone else. The great thing is these sharks just don’t care. We spent a lot of the dive just hovering above the sand watching them, face to face. They watch you back. There are honestly few encounters with sharks where you can feel this comfortable.”

Stacks on! Three Port Jackson sharks lay in a gap in the reef

It never ceases to amaze me what you can find by simply swimming off the beach and having a look around. Mitch had researched the timing of the shark aggregation but didn’t expect to see the octopus gardens. He can’t wait to explore more underwater in his own backyard once it’s possible to travel again.

Images are a mix of my own photographs and those provided by Mitch.

2 thoughts on “Underwater encounters – Octopus gardens and shark stacks

  1. I’ve learnt such a lot about Port Jackson sharks – so great to have the amazing photos alongside the text to show their markings and explain how they feed. Also enjoyed the octopus gardens – I’m still humming along!

    Liked by 1 person

  2. I really enjoyed the Port Jackson shark story and images. I’ve always had a great fear of sharks so good to know they aren’t all dangerous!! Would love to hear more about the octopuses garden, so intriguing and loved the images.

    Like

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