Heraclitus said, “the only thing that is constant is change”. He was a wise man. Every person that has sailed the oceans during the last decades has observed many changes first hand. Some of these changes seem alarming and have direct effects on fishermen’s bank accounts, and yet those changes have always been around. After all, we still call it fishing, not simply catching and it has always been recognized as an inherently risky business enterprise. Other changes are simply curious. Single unexpected observations are usually fascinating and somewhat exciting, and only when they become part of a string of strange sightings are they given more attention.
When I decided to devote an article to squid my first search brought up a series of news articles from 2004, describing that for the first time in anyone’s memory anglers were catching squid in the Sitka harbor. In 2010, large numbers of Humboldt squid, a species typically found in waters off Southern California and Mexico were found near Newport, Oregon and some were even caught in Alaska. Obviously, these squid were changing their distribution and conquering new parts of the ocean. Because of the significant catches (and sales) of squid, the North Pacific Fisheries Management Council quickly decided to separate squid from the species complex managed under “other” and awarded them the status of a separately managed species complex and the attention of a management plan.
There are about 15 species of squid known to live in the Eastern Bering Sea. Less is known about which species inhabit the Gulf of Alaska. The more common ones seem to be of the families of the armhook squid and the loligo family, which are generally smaller squid of temperate regions. All squid are close relatives of octopus, have eight arms plus two tentacles, and unlike octopus posess a single hard structure under the skin of their elongated bodies, which is called the pen.
Squid hold two records in the invertebrate world: They are the fastest swimmers on short distance among the spineless animals, and the largest boneless animal is a squid. The squids mantle is made of strong muscle and their great swimming prowess comes from the ability to use two methods for swimming. They can use their undulating rear side fins like flat fish for slow swimming, but for fast escapes they have jet propulsion. Since I have never had the chance to observe live squid even though I have watched dissections of dead ones, I was curious to see how they used the jet propulsion. There are many videos online, and in all of them the squid swim backwards! The siphon for the expulsion of water from the mantle cavity points towards the squids tentacles, which means that jet propulsion is for fast backoff, not for attack. Yet the larger squid are known to be quick and successful predators. I know that octopus can rotate the direction of the siphon which gives them control over which way to go, but in the movies I looked at the squid used fins for forward motion and jets for backwards. This intrigues me: when they travel past the camera, they are all going backwards.
The explanation for this mode of travel may be found in their ancestry. Extinct members of the cephalopod class, which the squid, octopus, and cuttlefish belong to, had shells. The last remnants of this design are nautilii which still live in the depths of warmer ocean regions. The extinct belemnites had an elongated shell and their fossil remains look like small missiles. During my college years I used to work as a diver on the German Island of Helgoland which, due to a very interesting geology has some areas where the ocean floor is full of fossil ammonites and belemnites. The Island kids collect them and sell them to the numerous tourists that flood the place in the summer. An animal that lives in a bullet shaped shell has no other way to push out water for a quick escape than the opening of the shell.
Thus I reccon that the curious mode of backward travel in squid hails from millions of years of change in the squids body plan leading to the loss of the shell, and the world around it, where a quick escape is still a good skill to posess.