An Octopus Hunting

By The Marine Detective on April 25, 2021

A female Giant Pacific Octopus hunting . . . photos brought to the surface for you on April 4, 2021.

This individual lives north of Port Hardy, in Browning Pass.

She’s a giant among other giants.

The Giant Plumose Anemones stand tall above her, at up to 1 metre in height.

Her arms feel between the rocks to flush out prey, her mind processing all she detects from her eight limbs, her vision, and the further stimuli upon her skin.

A China Rockfish is hovering nearby, likely often accompanying her when she is hunting to benefit from what prey emerges when touched by her arms.

Her colours change, flashing white at times. Then, again camouflaged among the boulders covered with the pink of coralline algae species, and studded with Orange Cup Corals and the plumes of feeding tentacles of Orange Sea Cucumbers.

Two humans are in awe at chancing upon her and being able to hover, navigating the space between not wanting to disturb and also wanting to amplify the wonder above the surface, hoping it somehow contributes to being better humans.

We’re aware too that we are limited by how much air remains in our tanks; the nitrogen building in our blood; and the cold creeping in through our dry suits (despite the adrenaline surge of watching her).

But she, she is limitless here.

She is perfection.

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Octopus Gender:

I know this was a female because the third arm on the right does not have a “hectocotylus”. Male octopuses have a specialized arm with no suckers at the tip called the “hectocotylus arm” by which they hand off spermatophores to the female. In Giant Pacific Octopuses, the hectocotylus arm is the third on the right. See more in my recent blog “Giant Pacific Octopuses, How Do They Mate?” at this link.

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Octopus Vision:

You can see that the pupil’s shape is very different from ours. Their retina is very different too.

Octopuses and other cephalopods have only one kind of photoreceptor cell while we have rod cells and three types of cone cells allowing us to see in colour. So how can cephalopods discern colour when they have only one kind of light receptor in their eyes? And they must be able to discern differences in colour. Consider how they signal with colour and how they camouflage.

Research from 2016 puts forward that their uniquely shaped pupils act like prisms, scattering light into different wavelengths (chromatic aberration), rather than focussing the light into a beam onto the retina.  The hypothesis, tested with computer modelling, is that cephalopods can then focus the different wavelengths onto their retina separately by changing the distance between the lens and the retina, thereby separating the stimuli and discerning colour. Note that the sharpness of their vision is believed to be different for different wavelengths / colours.

Even with their eyes closed, octopuses can detect light with their skin. This is tied to their ability to camouflage with the photoreceptors in their skin responding to specific wavelengths of light (different wavelengths = different colours).

Note too that octopuses do not have eyelids. They have have a ring-shaped muscular fold of skin around the eye that closes in the way of an eyelid (especially when some annoying human is taking photos).

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More Octopuses Hunting

Here’s the link to another experience where we saw a Giant Pacific Octopus hunting AND interacting with a Wolf-Eel (includes video).

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Sources

Katz, I., Shomrat, T., & Nesher, N. (January 01, 2021). Feel the light: sight-independent negative phototactic response in octopus arms. The Journal of Experimental Biology, 224.

Stubbs, A. L., & Stubbs, C. W. (July 19, 2016). Spectral discrimination in color blind animals via chromatic aberration and pupil shape. Proceedings of the National Academy of Sciences of the United States of America, 113, 29, 8206-8211.