There are two species of crayfish (more correctly crawfish) in New Zealand waters. The commoner is the spiny crayfish (Jasus lalandei) which may be found anywhere along the coastline where conditions are suitable. It lives below tide level in rocky areas, in caverns, in the shelter of seaweed, or at times half buried in sandy gravel. Until recently it was thought that the spiny crayfish was the same as that occurring in Tristan da Cunha, South Africa, South Australia, and Chile, but it is now believed that all these places may have their own distinct species, which differ slightly from each other. The New Zealand variety is spiny (as its name implies) and brightly coloured, variously marked with reddish purple and orange, though these colours change to a uniform red on cooking. The mature males may reach a length of 20 in. and are usually bigger than the mature females.
In the warmer waters of the North Island the females first mature at about 7½ in. in total length and though they may exceed 10 in. in length, these are seldom caught. As one goes south the length of first maturity increases progressively, so that off Southland this is from 10 to 13 in. Egg laying takes place between early April and late May, but there are considerable seasonal and geographical fluctuations. After the eggs are laid in great numbers, they are attached to the silklike hairs of the swimmerettes (pleopods) under the tail by a clear fluid produced from glands situated at the base of these legs. The fluid hardens and binds the small eggs in grapelike bunches to these hairs.
The eggs hatch in some five or six months and, on hatching, the small transparent larvae resemble squashed spiders, about the size of a letter “o” on this page. At first they swim towards light and so keep in the surface water, but later they shun the light and make their way into deeper water, where for about nine months they probably drift in ocean currents. All through their larval growth they are transparent to the unaided eye, and finally they reach a body size of nearly that of a florin. Growth takes place by casting off the outer skin (moulting) and by subsequent swelling up as a result of water intake. The flattened shape of the larva is lost at a single moult, when it is transformed (metamorphosed) into an inch-long transparent crayfish. It now swims inshore, seeks shelter, and takes on the colour of its parents, and there it continues to grow by a series of moults to reach a total length of some 3 in. in about two years from the time of hatching. After the second year growth is slower and averages 1 to 1½ in. each year, but this varies from place to place according to sea conditions and the availability of the food supply.
Much less is known about the smooth-tailed, green, or “packhorse” crayfish (Jasus verreauxi syn. J. hugelii), which is most abundant in the Coromandel and Bay of Plenty areas. This crayfish is much larger than the spiny crayfish and frequently exceeds 24 in. in length. It is easily distinguished from the commoner one, not only by its colour which varies from dark brown to olive green, but also by the smooth upper surface of its tail segments.
by Richard Bevis Pike, B.SC., PH.D.(READING), Senior Lecturer in Zoology, Victoria University of Wellington.