You may have seen us removing and examining the beaks of the giant and smaller colossal squids yesterday, so we thought we’d give some background on cephalopod beaks and why they’re important. The beaks (one upper and one lower in all squid, octopus and their relatives) are the first stage of the squid’s digestive system – essentially its mouth. They do all the coarse chopping and slicing of food (more on squid prey to follow in another entry) before it is passed down the oesophagus to the stomach and caeca (various digestive compartments). It’s very important to reduce the food to a manageable size, because the oesophagus is quite small (diameter 10-12mm in a mature giant squid), and passes through the middle of the brain! So a bite too large or too sharp could be disastrous.
Inside the beaks, just before the start of the oesophagus, the food also passes through quite a toothy, raspy area comprised of the radula (like a tongue with teeth) and the palatine palps (like cheeks with teeth). The radula moves like a pointy conveyor belt to shunt the food down the oesophagus as it is processed by the beaks.
So the beaks are important to the squid, but they are also important to us, for different reasons. The measurement we take on all of the large squid beaks is called the lower rostral length (LRL) – the length of the straight cutting section of the lower beak. Since the morphology of a cephalopod beak is unique to a species, the length of the LRL corresponds to the size of the animal, and if we get enough specimens together, we can figure out exactly what that relationship is. Ideally an equation can be developed, from which a squid’s size (ML and weight) can be extrapolated using just the LRL, once the beak has been identified to species.
It may seem odd that a beak might need identification without the rest of the squid, or that we would need to figure out the size of the squid from just the beak. But many squid, especially the large ones, are excellent at avoiding capture and collection by humans, so there actually aren’t very many known large specimens in collections. (Hence all the excitement this week!) Their predators, however, which include marine mammals, fish, and birds, are professional squid-catchers, so by studying their gut contents we can learn a lot about the squid that are so good at evading us.
The trouble is, squid tissue dissolves very quickly in the stomach juices of predators, and often the only thing left by the time scientists examine the stomach contents is the hard beak. This is where knowing exactly what the beak looks like for a given species, and what its relationship is to overall squid size, comes in handy. By identifying all the beaks and calculating the size of the squid they came from, we can figure out a predator’s feeding habits (what it eats and how much) and where it’s been. (For example, some squid species only occur in the Antarctic, so if a sperm whale stranded in New Zealand had Antarctic beaks in the stomach, we would know it had recently migrated north from the Antarctic.)
The colossal squid is the largest (heaviest) squid species currently known to science, and we believe sperm whales should be capable of catching even the largest colossal squid. So our best guess about the maximum size of this species comes from the largest colossal beak known from a sperm whale stomach, which had an LRL of 48mm. Yesterday we found that the smaller colossal had an LRL of about 40mm, which is considerably smaller. We haven’t had enough specimens of the colossal yet to work out the equation, so we can’t tell for sure what size squid that 48mm LRL represents, but we do know that the relationship is usually not linear – so a difference of a few millimetres actually represents a substantial difference in overall squid size. Which means, in short, that we still believe colossal squid get MUCH bigger than the smaller specimen we examined yesterday, and examining the beak of the larger specimen today will tell us more about how close we are to the really big ones!
– Kat Bolstad