rock lobster (crayfish)
Getting to grips with handling and measuring lobsters
Description
New Zealand has two common species of rock lobster: the red or spiny rock lobster Jasus edwardsii and the green or packhorse rock lobster Jasus verreauxi.
The packhorse is the world's largest rock lobster, being found as large as 60 cm and 15 kg. Red rock lobsters are generally smaller but have been measured at 54 cm overall length and weighing over 8 kg.
Life cycle
Mating occurs within a few weeks of the female moult. Females bear up to 550,000 eggs depending on locality and their size. Eggs are carried under the tail, for up to 6 months before hatching. The eggs hatch into spider-like larvae that drift freely as part of the plankton in open waters for at least 9-12 months, where they fall prey to a variety of plankton feeders. The survivors may move considerable distances with ocean currents, returning to inshore areas to settle on the bottom as transparent puerulii, which resemble miniature adults. At this stage they may suffer heavy predation from bottom feeding fish, until they find adequate shelter.
Distribution, habitat and movement
Both Red rock lobsters and Packhorse rock lobsters are widespread throughout New Zealand, particularly in coastal areas where there is plenty of cover.
Rock lobsters usually move by night to search for food and shelter, returning to the safety of crevices during the day. They eat a wide variety of bottom life, with a preference for shellfish, crabs, seaweeds, small fish and sea urchins. There is also a seasonal movement into shallow water for moulting and mating, and another when females move to the edges of reefs to spawn their eggs.
Rock lobsters also migrate in large numbers. Movements of up to 460 km by red rock lobsters, and up to 1070 km by packhorse lobsters have been recorded.
Growth and age
To increase size, a rock lobster needs to shed or moult its shell and grow a new larger one which is initially soft, leaving it very vulnerable to predators. It absorbs water rapidly and expands to its new size. The shell hardens within a few days, taking longer to thicken to full strength. Moulting frequency and times depend on age and sex. Legal size is attained in 5-10 years, depending on the sex of the lobster, area, and growth rates. Rock lobsters may live for over 30 years.
Recreational fishery
Recreational fishing for rock lobsters is largely based on diving, but baited pots are also used. Experienced divers can usually locate and capture the daily limit of 6 legal rock lobsters per taker, and recreational fishing can have a significant impact on stocks in some areas.
The need for different minimum legal sizes
Tail width measurement is used to determine the legal size for spiny rock lobster. Females of similar body sizes have wider tails than males, so different minimum legal sizes are needed for each. This contributes to the effectiveness of the escape gaps that must be used in all rock lobster pots. Escape gaps reduce the damage and possible mortalities on juvenile rock lobsters.
Pot limits
It is an offence to:
Use or possess more than three rock lobster pots per person.
Use or possess more than six rock lobster pots per vessel carring two or more people.
Separate limits for Patersons Inlet - 2 pots per person and Mimiwhagata Peninsula - 1 pot per person per vessel.
Regulation escape gaps to allow undersized lobsters to escape
Round or beehive shaped pots must have at least 3 escape gaps or apertures (other than the mouth). Each aperture must have an inside dimension of not less than 54 mm x 200 mm. Square or rectangular shaped pots must have at least two escape gaps or apertures (other than the mouth) in opposite faces of the pot. Each aperture shall not be less than 80% of the height or length of the face of the pot in which the apertures are contained. Each aperture shall have an inside dimension of not less than 54 mm x 200 mm.
Any rock lobster pot constructed entirely of unaltered spot welded mesh with inside dimensions of 54 mm x 140 mm does not have to have escape gaps/or apertures but must be used without covers or liners or with covers and liners that leave at least 80% of the surface area of each of 2 opposite sides. No escape gap or aperture shall be incorporated in either the top or the bottom of any pot.