Strobe-Light Squids


blog post photo

by William Gilly
Professor of Biology, Hopkins Marine Station

Humboldt squid washing up on Pacific Coast beaches from southern California to British Columbia since early last summer have led to questions. In the U.S. the focus concerned what dangers might exist in human-squid interactions. In Canada the issue was potential ecological impacts exerted by the invading squid on fish, particularly salmon. Whether you are diving with these squid or walking your dog on the beach, your chances of an aggressive attack is undoubtedly much less than having a traffic accident on the way to the encounter. We don’t yet know what interactions with salmon might involve – that jury is still out, but the squid are eating lots of other fish.

Regardless of the havoc that Humboldt squid may or may not be wreaking on humans and ecosystems, one thing is clear. These creatures have an awesome ability to change their skin color, flashing the whole body dark red about 4 times per second in a strobe-like fashion. How are these displays generated and what purpose might they serve?

Color changes in all cephalopods (squid, octopus and cuttlefish) involve minute muscular organs called chromatophores. These are tiny sacs of pigment in the skin that are opened and closed, like pixels on a computer screen, by nervous activity generated in the brain. Humboldt-squid skin has a ‘resolution’ of about 100 dpi, and a full-grown squid the size of human child has about 20 million chromatophores whose activity is almost perfectly synchronized during that eerie flashing.

What the flashing means is a tougher question. Previous examples of flashing have been captured by divers in relatively shallow water or by noisy submarines with bright lights. But this behavior undoubtedly evolved long before any interactions with humans or machines, so we must look for undisturbed, natural behaviors to gain insight to its meaning. But how does one capture this behavior at daytime depths of 1,000 feet or more that are typically inhabited by Humboldt squid?

This challenge led me to sign on with the Brady Barr expedition to the Gulf of California in September to work with Kyler Abernathy of National Geographic’s Remote Imaging unit and deploy a Crittercam on live, free-swimming Humboldt squid. As funny as it may sound, we simply dressed up a squid in a child’s bathing suit (part of one anyway) with an attached camera that filmed for several hours and then detached from the squid and floated to the surface where we picked it up.

And it worked! Deployments during daylight yielded the first natural chromatophore behavior in free-swimming squid. We saw intense flashing displays and arm-spreading when the filming-squid encountered other squid. These displays seemed to make the squid look as big as possible – perhaps a huff-and-puff “I’m really big and you better not mess with me” message related to the infamous cannibalism in this species. We also viewed several examples of likely mating attempts, and mating behavior for this species is essentially unknown. There is much to learn when we continue with this new method. Keep tuned.

Video Preview: “Squid vs. Squid” — As Brady attempts to mount a camera on a helpless giant squid, another squid lurks out of the depths and attacks.

 

Dangerous Encounters
Cannibal Squid premieres July 30 at 9P et/pt.