Rock Lobsters - spiny wanderers

Preview
Think of an expensive seafood meal and rock lobsters (also known as crayfish or koura) will probably come to mind. Rock lobsters fetch high prices, and presently earn New Zealand over $100 million in exports a year. Because of this, most areas around New Zealand are heavily fished by commercial and recreational fishers and - unfortunately - poachers.

	Vital statistics
	Management issues
	Markets

Vital statistics
	Varieties
	Life cycle
	Eggs
	Larvae
	Puerulus larvae
	Distribution and habitat
	Movement

Varieties
New Zealand has two common forms of rock lobster:
	Green or packhorse lobster Jasus verreauxi. The packhorse is the world's largest rock lobster. It has been found as long as 60 cm and weighing 15 kg.	A Spiny Rock Lobster
	Red or spiny rock lobster Jasus edwardsii Red rock lobsters are generally smaller, but some have been measured at 54 cm and weighing over 8 kg. Such large sizes are not often seen now.

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Their hard shell is good protection, but it is a problem when it comes to growing. To increase in size the rock lobster has to shed, or moult, its shell and grow a bigger one. It is very vulnerable while the new shell is hardening. Young rock lobsters moult several times a year, while adults moult annually.

Lifecycle of the Rock Lobster

Eggs
Females can bear hundreds of thousands of eggs (each egg is only about 1 mm wide). Immediately after mating the eggs are attached to fine hairs (setae) under the tail. The female carries them for up to six months before they hatch. She uses the pincers on her hind legs to care for the eggs and later remove the empty egg sacs.

Larvae
The eggs hatch into spider-like larvae which drift freely as part of the plankton in open waters for at least 9-12 months. They must pass through 11 larval stages - growing from 2 to 50 millimetres long. They are eaten by a variety of plankton feeders as they swim and drift through the ocean.

Puerulus larvae
Those larvae that survive may move a long way with ocean currents, returning to inshore areas to settle on the bottom as transparent pueruli. At this stage they are 5 cm long and look like miniature adults, but unlike adults they are able to swim forward. Before they find shelter, many are eaten by bottom feeding fish, such as dogfish and blue cod.

Red rock lobsters are widespread around New Zealand, especially in rocky coastal areas where there are plenty of places to shelter. They are most often found in groups, hiding in crevices and around reefs. They occasionally go onto open ground.

Main Rock Lobster Fisheries

Packhorse rock lobsters are found in areas north of the Mahia Peninsula. They are most common on relatively open ground near Cape Reinga, which is the only known major breeding ground.

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Movement
Rock lobsters feed mainly at night, and eat a wide variety of foods. They like eating shellfish, crabs, small fish and sea urchins. They are not so keen on seaweed, sea sponges and rubbery sea squirts, though they sometimes eat them. They gobble up any scraps lying on the sea floor. Their stomachs have special food-grinding equipment to deal with hard bits of food.Rock lobsters usually move over a small area by night to search for food and shelter. By day they hide in their shelters.

During moulting periods rock lobsters often move to shallow waters. Rock lobsters can migrate in large numbers, often over open sea floor and during the day. Movements of up to 460 km by red rock lobsters and up to 1070 km by packhorse lobsters have been recorded. The reason for these migrations is not known.

One suggestion is that they may be to compensate for the drift of larvae since most of the long distance migrations observed have been in the opposite directions to prevailing currents.

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Management issues
Rock lobsters were brought in to the Quota Management System in 1990 as there was a danger that the fishery might collapse through overfishing. Illegal fishing is a big problem, and poachers are estimated to steal about 450 tonnes of rock lobster each year.

Size limits are set so rock lobsters have a chance to breed before being caught. The size limit used to be based on tail length. This didn't work as some fishers stretched the tail. The size limit is now based on tail width.

The minimum legal tail width for amateur fishers is 54 mm for males and 60 mm for females. (You can easily tell which are female. They have a small extra claw on their rear pair of legs and much larger "swim-merettes" under the tail.).

For commercial fishers, the size limit is the same, except in Gisborne, Otago and the southern South Island.

Recreational fishers probably take between 400-500 tonnes a year. The recreational bag limit is six rock lobsters per person per day. They may not be taken if they are carrying external eggs or if they are in the soft shell stage. It is illegal to remove eggs from rock lobsters.

Commercial fishers have similar rules, although the amount they can take is set by the amount of ACE they hold. The current Total Allowable Commercial Catch was set at around 3500 tonnes for the North and South Islands and around 500 tonnes for the Chatham Islands. A code of practice has been introduced to improve the handling and processing of rock lobsters and reduce the mortality rate among live exports. Most of the commercial catch is from baited pots. There are only a few commercial divers, all operating on the Chatham Islands.

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