Squid: the biology basics
Squid belong to a group of animals called cephalopods, which includes the octopus, cuttlefish, and nautilus. In Tasmanian waters, we have both the smallest squid in the world, the pygmy squid at a tiny 2cm, and the largest squid - the giant squid, with squid rings as big as truck tyres. From a biological perspective, squid are rather bizarre creatures. They have not one, but three hearts - one at the base of each of two gills to pump deoxygenated blood through the gills, and one main heart to pump oxygenated blood through the rest of the body.
Squids have such high metabolisms that they need to extract oxygen through their skin surface as well as through their gills. To provide fuel for their fast metabolisms and fast growth rates, squid eat huge amounts of food each day. They eat pretty much anything that moves, and tear apart their prey with the jaws of their parrot like beak. A beak to chop their food into tiny little pieces is essential, as their digestive tract actually goes through a narrow channel of cartilage in their brain to get through to the stomach!
You might be surprised to learn that squid are very intelligent creatures with a nervous system as developed as fish, and more advanced than that of any other invertebrate. As they have such a developed nervous system, it's a good idea once you've caught a squid to try and kill them as humanely as possible - either place the squid in an ice slurry which dulls the nervous system before killing them, or remove the head straight away so that it dies very quickly. When squid themselves are "fishing', they actually kill their prey very quickly as well, by biting through the back of the neck of the fish to take out the spinal cord and stop them from struggling. You couldn't exactly call them compassionate creatures though - if they are hungry enough with no sign of dinner in sight, they will quite happily turn around and eat their closest neighbour.Vision is a sense especially highly developed in squid, and this is why their eyes take up such a large proportion of their head.
Squid need highly developed vision as they communicate with each other through changes in body colour patterns and posture. The surface of a squid's skin is covered with pigment filled sacs called "chromatophores" and each sac has independent neural control so that the squid an expand or shrink each chromatophore. By expanding or shrinking all the chromatophores over the body surface, squids can produce many different patterns from ghostly white, to all black, blotchy dark spots, or big thick zebra stripes. Squid can change the patterns on their body in millisecond - more rapidly than a chameleon can!
Squid nuptials Squid display many different colours and postural patterns when they courting, mating, and laying eggs. The squid "nuptial dance" as it has been coined, has been studied in detail in South Australia by Dr Troy Jantzen, and he has been kind enough to allow reproduction of some of his amazing photos. Squid form spawning pairs, with each male actively protecting his female partner and fending off any unwanted 'single" males that try to mate with her. The pairs will mate together several times during a spawning bout, although females may also store sperm, and then lay the eggs on their own. Spawning pairs may aggregate and spawn together in large schools, with several pairs laying eggs on the one egg mop. The eggs appear to be most commonly attached to Amphibolis sea grass, with individual egg capsules containing 4-7 eggs, with 50 to several hundred capsules joined together to form an egg mop. Development of the eggs takes about 3-5 weeks depending on the water temperature, with quicker development in warmer water. Newly hatched calamary are 4-7mm in body length and are hatched as miniature fully competent mini-adults. Reproductive behaviour in southern calamary is elaborate and involves complex courtship postures and colour changes, but mating itself only takes 2 seconds if that! The male has a modified tip at the base of one arm that he uses to grab a packet of sperm from himself and pass to the female. Dr Jantzen has named one of the male colour displays associated with this "the postman', as he said that when he sees that pattern, he knows a package has been successfully delivered!One of the most fascinating things about this unique way that squids communicate with each other is that they can have two conversations at once. A common example of this involves the intense male competition for females on the spawning grounds. If an amorous male is swimming alongside a willing female he can say one thing to her ("Hey baby, how about it?"), and another to any other males hanging around with the other side of his body ("Back off buddy, this babe's mine!"). Female squid can respond with several signals from "I wouldn't mate with you if you were last squid on earth" to 'sure honey'. Sometimes the competition between males escalates into physical fighting, with paired males charging at intruders and literally beating them with their fins. To avoid such aggression, some single males resort to rather dastardly tactics to secure a mate. These males, aptly called 'sneaker males" sometimes show the body patterns of females, so that the paired male thinks the intruder is a female and nothing to worry about. However, such tactics have their downside as 'sneaker males" often attract unwanted attention from other single males!