Arrow squid – Ngu – Notodarus sloanii
The Arrow Squid's Story: There are two species of arrow squid in New Zealand waters. Nototodarus gouldi, found around the North Island and Notodarus sloanii, found around the South Island. Their fishery is managed as one species, except for around Auckland and Campbell Islands (MPI, 2009). Between 1986 to present, the whole New Zealand arrow squid fishery caught between about 20 000 to 114 000 tonnes, out of that between about 1 000 to 35 000 tonnes were from the Southern Islands alone (MPI, 2014). Some of the fishery uses jigging (long lines of lures that catch only squid), but the Southern Island fishery uses bottom trawling, which catches anything in the path of the net including seabirds and marine mammals. The total allowable catch for arrow squid from the Southern Islands is based on the number of endangered New Zealand sea lions (between 32 and 150 sea lions) that are accidentally killed by these trawl nets each year. The total allowable catch for all arrow squid is based on a total biomass estimate, but this is not ideal because squid populations have booms and crashes and are very difficult to estimate (Mattlin & Coleman, 1988).
Both species of arrow squid are known as 'flying squids' for their ability to leap out of the water and glide along the surface (something that many squids in their family can also do) (Roper et al., 1984). Most often, however, they swim forward by waving their fins, or by shooting water through their funnel, which acts like jet-propulsion, pushing thembackward. They have a pen that holds the body shape as the muscles contract, which is made out of chitin - the same material as the beak and sucker rings. As they bring water into their bodies, it washes over their gills and they have three hearts to move the blood in their body. One heart pumps oxygenated blood through the body, and the two other hearts (one for each gill) bring deoxygenated blood through the gills. Squid blood has haemocyanin (made with copper) instead of haemoglobin (made with iron), and the copper makes their blood clear and bluish instead of the bright red colour of human blood. Copper does not hold onto oxygen as well as iron, so if their tissues need more oxygen, they need to circulate more water over their gills. In order to figure out their orientation in the water, they have two statocysts (fluid-filled pockets in their head) full of sensory hairs and a statolith (similar to the inner ear bones in humans).
Like most squid, they have ten appendages: two tentacles and eight arms. The tentacles are smooth until the very end where they have a club covered in sucker rings which they shoot out to catch prey. They bring the prey towards their mouth, grabbing hold with their arms, which are covered with suckers with sharp sucker rings covered in teeth (Smith et al., 1987).
One of the arms covered with suckers with sharp sucker rings covered in teeth. Photo: Bernard Potter.
When they reproduce, the male squid uses a modified pair of arms to pass packets of sperm (spermatophores) to the female that implant in the tissue around her beak. It is not known how sperm and eggs meet in arrow squid, but it is suspected that the female will mix eggs, sperm, and jelly together as she forms a large jelly-like ball (about 1.5 meters in diameter) that will float in the ocean until the baby squid hatch and swim away (O'Shea et al., 2004). Like most squid, they only live about one year (Jackson et al., 2005).