Summer Series 3: Rock lobster with your summer salad

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They don't have a voice – but they do make sounds.

Listen carefully to your red rock lobster (you may call it your crayfish). That disturbing sound is the crayfish grinding its mouthparts. A crustacean version of 'bruxism' (teeth grinding) might be the technical description, although the lobster shouldn't care a jot. It's likely more concerned about its immediate fate.

The neighbouring campers, who you've been getting to know – and like – have dropped in a couple from their early-morning dive. Most generous; will ask them across for drinks this evening. Ah, and the lobsters will be perfect for lunch today with the olds.

Grind....grind.

I've read somewhere about thoroughly chilling them before spiking them. On top of the bag of ice for a couple of hours will have to do.

It's staggering just what travellers these lobsters are. Their most extensive trips are when they are very young. They hatch from under their mother's tail in spring and, as 'phyllosoma' larvae, spend at least 18 months at sea... Really at sea, for they are to be found tens to hundreds of kilometres from land, caught up in eddies and countercurrents. This very curious-looking life form resembles more a transparent, squashed spider than any lobster.

The vast majority of phyllosomas perish at sea – either eaten or starving. The lucky ones that are close enough to shore, and have sufficient energy reserves, metamorphose to the post-larval 'puerulus' stage. Here's someone who really does look like a rock lobster, but transparent and still very much part of the plankton, getting up off the seafloor as night sets in to swim ever closer to shore.

Which is where the puerulus settles, in waters down to about 15m depth. Within a week or so it moults into a fully recognisable miniature lobster, about 25mm long. Your two lobsters are both males (their genital apertures are at the base of their last pair of legs, whereas in females they're at the base of the third pair) and a little over legal size - so they're about 6 years old. This is about the age that red rock lobsters around much of the country mature (the exception being the east coast of central New Zealand, where the lobsters mature at three or four).

In certain parts of New Zealand – particularly in southern areas – some red rock lobsters migrate great distances, against the prevailing west-to-east current, as they approach maturity. Happily, their westward trek against the current perpetuates the species, but what's in it for the individuals – and exactly how they navigate – remains a mystery. It's possible that they have a magnetic sense, as well as using water movements to navigate by, and detecting subtle changes in water chemistry using thousands of chemical-sensory hairs.

So, your lobsters may not only have drifted as larvae hundreds, even thousands, of kilometres, but may also have migrated long distances on the seafloor. The greatest minimum distance recorded for a migrating adult red rock lobster in New Zealand is 460km.

Our red rock lobsters reach more than half a metre in length, and a weight of 8kg. At that size, they are probably 20 or 30 years old – but we can't be more specific because all hard parts are lost at the moult, not leaving any part that can be sectioned for its annual rings as you would a tree trunk. Growth rates fall once the lobsters mature, more of their energy going into reproductive output.

Your two lobsters are now completely limp. They don't react at all to being handled; no more sounds of grinding. Now's the time to spike them. Slide a sharp-pointed knife into the carapace between the two eyes, to sever the brain.

Try serving the tail meat raw – perhaps with soy and wasabi as a dip. Very different taste and texture to what the olds will be used to – and very summery.......

Written by Dr John Booth

John Booth worked as a fisheries scientist, specialising in rock lobsters, at the National Institute of Water and Atmospheric Research (NIWA) and its predecessors, in Wellington, for more than 30 years. His book Spiny lobsters: through the eyes of the giant packhorse was recently published by Victoria University Press. NIWA was for many years the main organisation researching our rock lobsters, looking into all aspects of their lives, from egg to the fishery. NIWA is currently contracted to the Ministry of Fisheries to estimate the levels of puerulus settlement in the main fishery areas. 

An adult red rock lobster, aka ‘crayfish’ or ‘koura’. Credit: John McKoy, NIWA
Red rock lobster ‘puerulus’ or post-larva. Credit: Simon Anderson, Lat.37
Final-stage ‘phyllosoma’ larva of a red rock lobster. Credit: John Booth, NIWA