Science & Environment

River of great waiting

Long before the first humans set foot on its banks, the Whanganui River* was snaking its way from the side of Mt Tongariro to the breakers of the  Tasman Sea. Then, 30 years ago — a mere drop in the lifespan of a river — the headwaters of the Whanganui were taken away to drive the hydroelectric stations of central North Island. Now the people of the region are fighting to have the water back.

Magazine

003

ISSUE 003

Jul - Sep 1989

Whanganui river

Tuhua

Oysters

Mt Everest

Waitati

Mosses, Lichens, Liverworts

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Science & Environment

Waitati – Still crazy after all these years?

  Two decades ago Waitati gained a reputation as the hippie centre of the South. Outsiders called its youthful residents freaks and weirdos; residents ignored the labels and carried on living and proclaiming an alternative lifestyle based on creativity and environmental awareness. Kirsten Lawson visited Waitati recently to find out what remained of that era of vitality and idealism

Science & Environment

Bluff gold

Some say they are the finest oysters in the world. Grown slowly in the cold, clean waters of Foveaux Strait; flushed by strong tides bringing a daily intake of plankton and nutrients; plucked from the depths by oystermen and despatched to waiting palates the length of the country — they are the sea's most sensuous fruit, and for more than a hundred years strong men have swooned at the thought of them. On February 28, waking and sleeping tongues involuntarily lick dry lips in anticipation. And in the morning, trumpeted from the media and emblazoned on fishshop windows, the six-month Bluff oyster season begins. Oysters have been taken commer­cially from Foveaux Strait since the 1860s. The fishery began at Oyster Cove, Port Adventure, on Stewart Island, the oysters being gathered from shallow beds without the aid of dredges. Coastal cutters were simply beached on the beds at high tide and the oysters shovelled aboard as the tide dropped. The catch was trans­ported in the shell to the mainland, and right from the outset demand was so high that within a few years the beds were exhausted. New beds discovered off Port William and Halfmoon Bay suffered the same cycle of intense harvesting and depletion until in 1877 a closed season was declared — at the fisher­men's request — and the whole fish­ery was examined. Following the re-opening of the fishery in 1879, new, larger beds were discovered in deeper water, and the centre of activity gradually shifted from Stewart Island to Bluff. So too did the oyster's name, though even today the species is known by at least ten names, including mud oyster, flat oyster, dredge oyster, Foveaux Strait oyster and deep water oyster. The species is actually found throughout New Zealand, but is commonest in the south. Curiously, the Bluff oyster, Ostrea lutaria, is now thought to be the same species as the Chilean oys­ter Tiostrea chilensis, and is starting to be known by that name. The first dredges were operated by hand windlasses and drift-towed with the tide. Catches were meagre: three sacks a day compared with 50 or more today. The installation of oil-powered winches improved the catch rate, but it was not until steam vessels towing two dredges were in­troduced around 1910 that catches approached today's levels. A quota system was introduced in 1963, the 12 oyster boats then en­gaged in the industry being set a limit of 170,000 sacks per season (each sack containing, on average, 800 oysters.) The quota was pro­gressively reduced until in 1970, with 23 boats operating, it was 115,000, or 5000 per boat. (In eating terms, that equates to two dozen oys­ters for every man, woman and child in the country.) Catches have remained fairly con­stant since 1970, with the exception of the excellent 1978/79 seasons, when catches reached 125,000, and the disastrous 1986/87 seasons, when the oyster take was almost halved as a result of an infestation of the parasitic protozoan Bonamia. The effect of Bonamia on oysters is to render them 'watery' and black, and on some beds mortality was as high as 90 per cent. "It was a bit of a scare," says Ben Calder, manager of Johnson's Oysters, one of the Bluff processing factories. The beds are slowly recovering, and although the 1989 quota is still low at 92,000 sacks, Ben says the size and quality of this year's oysters are very good. [Chapter break] Wake up ! you're going oystering!" hisses the hotelier's through the door. There has to be a good reason to wake someone up at 5am on a win­ter's morning in Bluff, but this is cer­tainly one. For the last two days foul weather has kept the oyster fleet bob­bing at the wharf, and writer and photographer have been prowling around on land. This is the message we've been waiting for. Outside there is still a biting west­erly wandering through the empty streets, but the swell is down and the boats are leaving for the Strait. It's a short trip to the new wharf on Bluff's Island Harbour. In the galley of the Lucy Star the crew is tucking into a hearty breakfast of bacon, eggs, saveloys and toast. How sailors can work on a bellyful of fried food is more than I can fathom. Perhaps they do it to spite the rest of us, for whom fat and water definitely do not mix. The hour-plus trip to the beds passes quickly, in pitch darkness only interrupted by the regular sweep of Dog Island light. The east is just lightening when we arrive at skipper John Young's current patch off Ruapuke Island. A quick scan of the radar gives him his bearings and dredging begins. Oysters are not distributed uni­formly throughout Foveaux Strait. Dense and sparse areas occur within short distances of each other. Although the main commercial beds have been mapped, areas of high oys­ter concentration are found largely by trial and error, and once on to a good 'tow' a skipper guards his patch jeal­ously. Indeed, the test of a good oysterman is his ability to work a productive area consistently, before the catch rate falls to an unacceptable level and it is time to move on. The point is made forcibly later in the day. The dredges have just gone down when another oyster boat heaves into view. John says nothing, but Paul Pasco, the engineer, gives me a signal that says, "Watch what hap­pens now!" The intruder — the Argosy ­moves closer. The vessel is clearly towing across our patch — "mollyhawldng", as the practice is known. John changes course to take us directly across the Argosy's tow­path. At the last minute John lifts the dredges and as we pass the two crews flap their arms at each other in bird­like imitation. They both know the rules — and the results. Pull this stunt once too often and it will cost you a mouthful of loose teeth in the pub that night. The Argosy gets the message and steams off . Why the aggro, I ask John. "You can waste a lot of time find­ing a good tow," he explains. "I've been working this tow for the last three and a half weeks and taken 750 sacks. There's probably a thousand here at least. If I let someone else in it'll halve my take and that means I'll have to go looking somewhere else." John has had 13 years oystering. He started as cook when he was 16 and worked as a deckhand and engi­neer before getting his skipper's ticket. During the off-season he fishes for 'wetfish', catching whatever there is a market for. On the Lucy Star the deck is quickly filling up with sacks of oys­ters. The factory has asked for 50 bags today, and at the rate we are going we will be back at the wharf by afternoon tea. The dredges themselves are large, oblong steel frames with steel mesh on both sides. The frame is closed at one end by two rope ties, the other has angled 'bit bars' top and bottom so whichever way the dredge lands on the sea bed it is ready to scoop up oysters from the substrate. Both dredges are towed simultaneously from the port side, on steel hawsers of different lengths. The dredges are usually shot while the oyster boat is stemming the tide. The boat then tows at a slow speed in a half circle downtide; then hauls up the dredges as it steams uptide, com­pleting a large circle. The length of dredge wire is critical. Too much and the dredge will haul up large quan­tities of sand and gravel; too little and it will skim over the sea floor. Today, on the East Bed, we are dredging in 13 fathoms of water. At the surface the dredge is given two or three short, sharp dips to wash off residual sediment, then swung on board, making a mighty "thwack!" as it hits the steel frame­work above the culching platform. Deckhands (two per dredge) untie the ends of the dredge and stand back as a mountain of oysters and oyster shell, along with hermit crabs, brittle stars, whelks and even small octo­puses cascade on to the platform. Culching, the task of sorting out the takeable oysters from the rubbish (culch), has developed almost to an art-form with some deckhands. Ricky Topi uses a rotary technique, both arms revolving like a lawn­mower, chucking good oysters into modified metal buckets and the culch down a chute into the tide. But you have to work quickly. No sooner is one pile of material sorted than the next dredge-load is on its way up. To the rhythmic 'plonk' of shell­fish on metal, John Young talks about the ups and downs of the fishery. He recalls a few years ago when boats were only catching 30 sacks a day, and it was taking all day to catch them. "We worked from five to five, six days a week. Next year we went back to the same place and got 100 sacks." Bob Street, a marine consultant who has been involved with the Bluff fishery for 20 years, puts the fluctuations down to food supply, and says that the periodic downturns in the oyster fishery coincide with similar reductions in other wildlife such as krill, muttonbirds and salmon. "When the plankton is in good supply the oysters can reach mini­mum takeable size in 18 months," he says. "Under poor conditions it may take three to five years — perhaps longer. Poor feeding means the ani­mals are stressed, and an oppor­tunistic parasite like Bonamia can get in and do a lot of damage." No one is talking about Bonamia this year, though. The oysters are coming in thick and fast and fat, and back at the processing plant the openers are really humming. They stand at a concrete bench with a pile of oysters in front of them and a metal bowl to the side. One hand is gloved; the other wields the knife ­the cut-down, sharpened-up blade of a common household knife embed­ded in a specially shaped wooden handle. The process of opening oysters is intriguing to watch. Most openers develop an almost spastic motion, jerking backwards and forwards as they cut the shell muscle, flip back the top valve and flick the whole oyster into the bowl. An opener earns $6.60 a bowl (that's 240 oysters), and a good opener can account for four bowls an hour. Stab, flip, flick; stab, flip, flick ... And still the sacks of oyster come in from the trucks. Once opened, the oysters are sorted, washed and packed for destinations around the country, but not, surprisingly, overseas. The export of Bluff oysters is prohibited, and it has been right from the early days. The rationale was that this fishery should belong to New Zealanders, and that it shouldn't go the way of other natural resources, where once exports started the local price skyrocketed, and eventually the resource was run into the ground. In the current free market climate, though, this trade restriction has been challenged, and the way is slowly opening for export of Bluff oysters to commence. The customs prohibition is under review, awaiting a recommendation from the Ministry of Agriculture and Fisheries (MAF). At the same time, MAF scientists in Wellington are about to start rearing Bluff oysters under hatchery conditions. The aim is to provide spat (juvenile oysters so named because oystermen thought the adults 'spat' out the young) for reseeding the Foveaux Strait beds and for farming operations. If successful, this research could lead to a situation where there are sufficient oysters to satisfy both the local and export markets. Oystering has always been impor­tant to Bluff. For six months of the year it is a mainstay of the labour force, and many Bluffies have fathers and grandfathers who were in the trade. Oysters are worth at least $10 million a year to Bluff, not counting the spin-offs in tourism. To keep the tourist coffers ticking over, the Bluff Promotions committee ran a month-long Oyster Festival this year — the second time the idea has been tried. Events included an arm wrestling contest, King of the Oyster Beds speedboat race, tug of war, fish­ing contest, bikathon and Polynesian Dancer of the Year contest, as well as oyster opening and oyster eating competitions. Oyster eating competitions are definitely not for those of a delicate constitution. They are, however, a hoot! The contestants (bearing evoc­ative names like 'Enzyme', 'Shark', 'The Beast' and 'The Bite') stand behind a chest-high screen on a makeshift stage in the noisiest bar in town. In front of the screen is a plate of oysters and a couple of toothpicks. The oysters must be skewered with a toothpick and consumed, but the plate must not leave the table. Before eating commences a glass of stout must be downed to "clean the gullet". This proves to be a chal­lenge in itself for some contestants, who need several attempts before they can bring themselves to drain their glasses. With the stout out of the way, the starter gives the signal and the race is on. Oysters slip and slide their way into waiting mouths while the roaring crowd urges each contestant on to superhuman efforts. Like all the competitions, it's more in fun than anything else, and as con­testants stagger from the stage, some heading urgently for the nearest exit, there is a lot of backslapping and all-round good cheer. As schoolteacher and secretary of Bluff Promotions Jean Mullen tells me, "We've got something that's unique here in Bluff, and we're proud of it." Bluff gold, served in the half shell and savoured by the nation.

Travel & Adventure

Operation Thunderbolt

On the afternoon of May 12, 1989, six Polish climbers were on their way down from the summit of Mt Everest when they were struck by a massive avalanche. Four died within hours; a fifth did not survive the night. One injured climber was left stranded on the mountain. New Zealand Geographic-sponsored climbers Gary Ball and Rob Hall were about to leave Kathmandu after their own attempt on the summit when they heard the news and offered to help. What followed was a remarkableand heroic rescue bid.

Geography

The cultured oyster

Oysters have been flourish­ing in New Zealand's coastal waters for millions of years. Fossilised oyster shells are a common feature of the exposed out­crops of mudstone, sandstone and conglomerate found along the north­east coast — some date back 20 mil­lion years. Just a few kilometres from the Mahurangi Estuary (one of New Zealand's prime oyster cultur­ing areas), fossiliferous rocks at Mathesons Bay are packed with oys­ters. Some of these ancient speci­mens would make an oyster glutton drool and even call for a knife and fork, for the shells are the size of bread-and-butter plates. Neither cutlery, nor even humans, were around in those Miocene times, but when humans did eventually arrive on the scene it is clear that they were partial to oysters from their earliest days. In midden material from all around the world ­Denmark, Ireland, east and west coasts of America, Japan and Austra­lia — oysters feature prominently and are often accompanied by the primitive tools needed to open the shellfish. Many of these middens are huge; one in Ireland measured 300m square and 15m high — a vast rub­bish dump containing oysters, cockles, mussels and periwinkles, and showing that shoreline food has long been a staple of humanity. Oysters would have been a most valuable food resource for primitive hunters and gatherers. In addition to the essential proteins in the meat, fat oysters have stores of glycogen; a very good energy food for people living before the days of cereal crops and other cultivated carbohydrate sources. Oysters have been cultured for at least 2000 years, with the earliest re­cords of culturing techniques being those of the Romans. They had an especially high regard for the oyster and sought out naturally bountiful growing areas and different local strains or species as they expanded the Empire. The Romans cultured the shellfish on sticks and ropes suspended from elevated walkways and gantries. Elsewhere around the world cultur­ing methods have been as varied as fashion and local materials have allowed. Generally, culturing has been in quiet waters where wave action is too weak to damage the supporting structures or carry away the develop­ing crop. While protected from storms, these sites invariably have soft bottoms of fine silt which can clog the feeding and breathing appa­ratus of sedentary animals. Creating suitable culturing condi­tions has therefore depended on pro­viding hard surfaces for the oysters to attach to and keeping the shellfish above bottom sediments. Simple methods for cultivating mud oysters involved no more than the spreading of large amounts of cu­lch for the spat to settle on. The culch was usually just empty oyster shell from previous harvests, and there were various penalties and bad omens associated with failure to re­turn this most suitable of all sub­strates to the growing beds. Periodi­cally the beds were raked to lift the developing oysters out of the ever-settling fine sediments. This was a full-time activity for the bed workers in the lowland coastal areas of such countries as England and Belgium where these culturing methods were extensive right up to the last century. In Japan oysters are grown on old shells that have been perforated and strung on ropes suspended from floating rafts or buoyed lines. Else­where they are cultured on recycled roof tiles and slates, custom-made trays, bamboo fences and frames, as well as on sticks set out on racks like those seen in New Zealand today. Oyster farming is still a young in­dustry in New Zealand. It had its beginnings in the late 1960s with the then Marine Department promoting the culture of the New Zealand rock oyster (Saccostrea glomerata). There was considerable appeal in the pros­pect of growing a luxury food for which the affluent might be prepared to pay high prices, just by putting sticks out in the tide. Oyster leases were applied for in harbours and inlets all around north­ern New Zealand, and the now famil­iar geometric arrays of growing racks sprang up as keen culturers rammed tanalised timber and money into the mud. However, the culturing of the New Zealand rock oyster was never a great financial success. The growing time from freshly caught spat to mature oysters of marketable size ­three to four years — was too long for growers to recoup an adequate return on their investment. The long cultur­ing periods also brought other prob­lems, particularly fouling of the oys­ters and competition from other marine organisms. A further problem was erratic and often inadequate set­tlement of spat ('spatfall'). The chance arrival of the Pacific oyster (Crassostrea gigas) in the early 1970s proved to be the saviour of the oyster culturing industry, though at first some growers were reluctant to farm it, and systematically removed young Pacific oysters from their growing sticks. Opposition, however, was futile. The Pacific soon became dominant in the farmers' spat-catching areas and on natural shores. The new species was here to stay. The main problem for farmers in changing over to the Pacific was that optimum growth for these oysters oc­curs about half a metre lower on the shore. Existing rack systems had to be lowered or replaced — a time-consuming and costly process. The benefits, though, were unequivocal: an oyster that settled heavily and consistently, grew three times as fast (reaching marketable size in 10-14 months) and was in good condition over much of the year. New methods to grow and handle the Pacific oyster evolved rapidly, and by the end of the decade the Pacific had replaced the New Zealand rock oyster as the main cultivated species. The change-over to the Pacifc oys­ter caused its share of problems for distributors. Neil Harrington, man­ager of Auckland export packhouse Kia Ora Seafoods, recalls the diffi­culty of having to contend with two rock oysters in a relatively small mar­ket. "We immediately got some con­noisseurs of the native rock oyster who refused point black to eat Pacific oysters, but we also attracted some people who found the mellow flavour of the Pacific more to their taste and possibly for the first time in their lives became oyster eaters." There were plusses and minuses on the export front as well. The Pa­cific oyster had the advantage of a well-established international repu­tation, but the New Zealand rock oys­ter had the advantage of being ex­tremely long-lived out of water (staying fresh for three weeks or more) and of travelling well. Neil Harrington looks nos­talgically on the New Zealand rock oyster as a product which never got the chance it deserved, but for growers like Jon Nicholson of Bio­Marine, a large oyster farm in the Mahurangi Estuary, there is no ques­tion that the arrival of the Pacific was the best thing that could have happened. Pacific oysters are now farmed from Parengarenga in the far north to Ohiwa, near Whakatane, in the Bay of Plenty. Of the current 146 leases the majority are single-lease farms of only a few hectares. There are only half a dozen large ventures (with five or more leases) covering areas of some tens of hectares. Between them they produce an estimated 4000 tonnes per annum (approximately 32 million oysters). In 1988 50% of this harvest was exported, bringing in a revenue of $4.6 million. The main production areas are the Bay of Islands, Whangaroa, Ma­hurangi and Coromandel. In west coast harbours such as the Kaipara growers have the problem of their oysters being heavily overspatted in their second summer. Some growers have overcome this problem by mov­ing oysters to the east coast during the spawning season, while others are using the prolific spatfall to ad­vantage by producing single seed oysters for other growers . The positioning of oyster farms is a compromise between water quality and wave exposure. Pacific oysters grow best in open water, where tem­peratures are less variable, oxygen levels are higher and amounts of gill-clogging sediment are less. Oyster farmers look for areas where strong water flows bring a plentiful supply of food and where wave action stops mud from building up around the shells. However, greater exposure puts racks and crop at risk, so grow­ing sites just inside estuaries are sought as the prime areas for oyster culture. The height of the growing racks is set at about the level of neap low tide (the highest of the low tides). At these times of the lunar cycle, when there is least difference between high and low tide, the oysters are barely ex­posed in air at low water. The description of oyster farming which follows is based largely on the methods used at Bio-Marine in the Mahurangi Estuary, one of the first farms set out specifically for growing Pacific oysters. To grow oysters, first you must catch the spat. Essentially this is very simple, as oysters will grow on al­most any hard, cleanish surface. In harbours, estuaries and sheltered bays where sediments accumulate, suitable natural substrates are fairly scarce. The spat will therefore settle very readily on any artificial hard surfaces provided. Sticks put out for this purpose are usually nailed to­gether in bundles and wired to 'catching racks'. Spacers are placed between the sticks so that water car­rying the oysters' swimming veliger larvae is able to circulate freely, en­suring an even settlement. Before use, new sticks are dipped in a thin slurry of sand and cement which dries to give a rock-like film over the surface of the wood, ideal for the settlement of oyster spat. Locally de­veloped and manufactured PVC sticks are also used. Pacific oysters breed by the sepa­rate males and females releasing their spawn of sperm and eggs into the water simultaneously. Spawning is initially stimulated by a rise in sea­water temperature to about 22°C, but spawning by one individual also serves as a strong stimulus to neigh­bouring oysters to join in too. Spawning may occur at any time from December through to March, but the peak is generally around new year. Getting the right number of spat on a stick is tricky. An ideal density is between six and eight dozen, but it is possible for 10,000 spat to settle on a single stick. To prevent such over-settlement (which results in mal­formed, undersized oysters) some farmers delay putting out their spat-collecting bundles until the peak of spawning has passed. This approach has its risks because all spawning may suddenly cease with a sharp change in weather conditions, leav­ing the farmer with insufficient spat on the sticks, and hence wasted space. To a certain extent variations in settled spat densities can be accom­modated by good management. Sticks with a lower density of oysters can be placed closer together on the growing racks. Alternatively, the catching sticks can be kept in their bundles to limit growth. There is in­sufficient water flow through the stick bundles to support active growth and juveniles soon reach a small size plateau. At this size (about 20mm in diameter) they are, so to speak, kept 'on hold' — healthy, but unable to grow further. This arrangement is very conven­ient for harvest management because active growth only commences after the catching sticks have been broken out of their bundles and laid out on the growing racks. By setting out sticks at regular intervals from the reservoir of bundled sticks, the oys­ter farmer is able to spread his har­vest of marketable-sized oysters through the year. Moreover, forecast peaks in demand can be accommo­dated by increasing the number of sticks set out in advance to corres­pond with an expected growth rate. As with most farming ventures, growing conditions vary from year to year, affecting the crop quality and time to reach maturity. With the warm temperatures that persisted through the late summer and autumn this year, oysters have grown much faster than normal. As a conse­quence, some oysters set out to be ready for the 1989 Christmas market will reach optimum size too soon. These will have to be harvested at a time when there is less demand, and careful management of remaining stocks will be required to ensure suf­ficient numbers for the festive season. At Bio-Marine the process of set­ting out the thousands of collecting sticks is speeded up by the use of a nailing gun. The thin steel nails or staples slowly rust away, but hold well enough to secure the sticks until the oysters are ready to harvest. During harvesting, sticks with mature oysters are lifted from the racks and loaded into cradles or 'frames' on a flat-decked barge for transport back to a landing. There the cradles are hoisted on to a truck to be taken to the processing factory. To release all the oysters from each stick requires only a few stout blows along its length with a piece of iron waterpipe. The oysters are given a crude wash to remove the worst of the mud that accumulates over and between the tightly packed, frilly shells. Any clumped oysters are bro­ken apart by hand as they pass along a conveyor belt to a rotating tumble-washer with high pressure water jets. The cleaned oysters are then size sorted. About half are of standard marketable size, with a quarter being of premium size and the remainder undersized. The latter are packed loosely into plastic mesh bags which are returned to the growing racks for about four months, until the oysters reach marketable size. Bio-Marine markets its oysters in three ways. Some, in good-shaped shells, are sold alive and unopened. Many are exported live to New Caledonia, where restaurant diners are prepared to pay premium prices to have the living animals opened in front of them at the table. A large proportion of the oyster harvest is sold in the 'half shell'. The flat upper shell valve is removed after cutting its connection to the large, central shell-closing muscle, leaving the succulent mollusc lying in a deli­cate serving dish that it grew itself. As food presentation is all-important, it is critical that oysters in the half shell are not damaged or spoilt with broken fragments of shell, and look truly appetising. The skill of the oyster opener is therefore an important factor in the reputation of the processing house. Any oysters that are slightly damaged during opening, or specimens that do not look fully fat, or are over­sized, are taken out of the shell and sold to commercial and domestic ca­terers and fish shops as 'meat' oysters. Present-day oyster prices are as follows: At an ordinary restaurant half a dozen oysters in the half shell with a twist of lemon and little other prepa­ration cost about $10 (= $20 per dozen). The same dozen oysters would re­tail for $5 in a city shop which had purchased them from the processor/ packer for $2.60. Some packers are also growers, but many handle product from small operations whose proprietors receive only $1.65 per dozen for unopened oysters suit­able for marketing in the shell. Meat oysters are worth very little in com­parison: a grower is lucky to get 15 cents a dozen. There is considerable fluctuation in local demand for rock oysters throughout the year. Demand drops from March to August, when Bluff oysters are available, and is also af­fected by a period of low restaurant activity during winter. Low season demand is about 5000 dozen per week, but this increases to 25,000 dozen per week during the high sea­son from October to January. There­after supply drops off as spawning oysters lose condition. The domestic market is supplied mainly with oysters in the half shell and 'meat' out of the shell, chilled in plastic tubes or pots for the restau­rant trade and for private consumers inexpert at opening shelled oysters. The whole of the domestic market is worth a little over $4 million per annum. The export market commands slightly higher prices (about $4.50 per dozen from the packhouse) with three quarters being sent as oysters in the half shell. The live export of unopened oysters, a moderate part of this market, is available to grower-marketers who can ensure that their product reaches its overseas destina­tion within about 24 hours of har­vesting. As unopened oysters require much less processing they are a pro­fitable commodity at about $3 per dozen. [Chapter break] Most People Enjoy a good oyster, but to some they are nothing short of ambrosia. The Romans went to great trouble to ship the succulent shellfish from England to Italy packed in ice. (Though that is probably no more bizarre than us air-freighting consid­erable tonnages of oyster shell, with small amount of oyster meat inside, all the way to Japan, the United States and other distant countries.) In America a good many people have even been killed in disputes over rights to the prized beds of the Potomac River. The oyster is one of the few ani­mals that we eat live. Open the shell, drink the liquor and then let the slip­pery mollusc slide out of its shell straight into your mouth. Some like to chew them slowly while others just roll them around the palate for a while before swallowing the crea­tures whole. Oysters seem to have a special ap­peal that is found in few other foods, for they have frequently been assoc­iated with amazing exhibitions of gluttony and excess. In ancient Rome thousands were consumed in lavish Bacchanalian feasts. It was appar­ently normal etiquette for the re­vellers to gorge themselves until they could eat no more, and then retire to a vomitarium with peacock feathers or other throat ticklers. Thus relieved, they could return to the party and start all over again. Oysters are molluscs, like cockles, mussels, grazing snails, whelks, slugs and octopus, but they are much simpler than many of their relatives. Because they do not move, they have no need for eyes or tentacles to sense where they are going — in fact, no need for a head at all. They possess neither teeth nor jaws, for they eat only microscopic plankton filtered by their gills and swallowed in a mucus stream. A common feature of nearly all molluscs is a muscular foot. Slugs and snails crawl along on it, clams use it for burrowing into mud and sand and mussels use it to attach elastic anchor ropes called byssus threads to rocks. As the headless adult oyster does none of these things, it is not surprising to find that it also has no foot. The free-swimming larval oyster, however, does have an active foot that allows it to crawl about in search of the ideal site to settle. As soon as the shell is cemented it has no further use for the foot, which withers and is lost. This lack of a foot is such a diag­nostic feature that it can be used to distinguish oysters from other shell­fish even after they have been smoked and canned in oil. (Such diagnosis is required from time to time by importing authorities to verify that canned smoked oysters are true to label.) By looking for the foot — and not finding it— a biologist is easily able to complete the verification. Lewis Carroll appears to have known about this detail of the oys­ter's anatomy. In his poem "The Walrus and the Carpenter" from Through the Looking Glass we read: "But four young oysters hurried up, All eager for the treat, Their coats were brushed, their faces washed, Their shoes were clean and neat ­And this was odd, because, you know, They hadn't any feet." On the surface of it, oysters lead an idyllic life. They stay in their beds all day long; the only work they do is opening and shutting their shells; their meals are delivered to them, and they spend most of their lives drinking, putting away on average 180 litres a day. Of course, the problem with cementing your bed to the substrate and dispensing with the means to get out of it is that it is impossible to escape from stressful environmental changes, competition for a limited food supply, or from animals that try to eat you. Oysters can only defend themselves by adopting the siege strategies of medieval people who sought shelter in thick-walled castles. Such strategies often failed because the invaders eventually found a way in or penetrated the walls, or else the inhabitants died of starvation or disease. Life for the oyster contains similar difficulties. Sediment can choke them, hot summer days coinciding with low tides can cook them, run-off from the land can bathe them in fresh water (causing internal stress) and they are a tasty target for predators. Tooth marks all over the bare sur­faces of oyster racks and sticks show that they are routinely grazed very thoroughly by fish. This would be sufficient to remove a large propor­tion of freshly settled oyster spat if the catching sticks were not kept wired up in bundles until the juve­niles had grown sufficiently to no longer be vulnerable to this inciden­tal predation. The oyster-borer Lepsiella scobina is a frequent killer of wild rock oysters on sheltered shores, but rarely attacks rack-cultured speci­mens. Also known as oyster-drills, these whelks are beautifully equipped for penetrating the oyster's armour. The rasping tongue with rows of hardened teeth (called the radula, and found in all snails) is modified in the whelks for drilling holes and mincing flesh. Each re­placeable row has just three multi-cusped teeth, and on the terminal row these are arrayed around the working tip like the three cutting wheels of a geological drill. The radula is held within a pro­boscis tube that extends down to the oyster surface. The proboscis holds the drill tip in position as it is rotated alternately clockwise and anticlock­wise to wear away a perfectly round hole. The whelk lubricates the abrad­ing tip with a mucus secretion that may contain an acid to dissolve or soften the limestone matrix of the oyster's shell. It may take from one to three days to bore right through, depending on the size of the whelk and the thick­ness of the oyster shell, but the preda­tor is rewarded with an enormous feast at the end. The proboscis and radula are squeezed through the hole to macerate the live oyster's soft tis­sues into a pulp which is sucked up through the proboscis into the whelk's mouth. If you were to put yourself in the position of the oyster, this would surely be one of the worst ways to die. Imagine listening to that inces­sant grinding for a couple of days, knowing that when the drilling was complete you would feel the toothed proboscis snaking across your body. It would then start mincing up only the less vital parts of the body to keep you, the victim, alive for as long as possible so that the shell did not gape to allow scavengers in to share the feast. Other predators include crabs, which break off the shell margins to gain access to the flesh inside, large starfish, which pull the shells open before smothering the whole animal and digesting it, and rays, which crush the shells with their powerful flattened teeth. The `mudworm' Polydora can be a serious problem on oyster farms, par­ticularly if oysters are too tightly clumped and mud accumulates be­tween the shells. Polydora is a small marine worm that lives in a tunnel that it bores chemically in chalky mollusc shells. The filter-feeding worm only seeks shelter from its host, but as it grows larger it must enlarge its living space, and narrow tunnels can become sizeable caverns partly filled with mud and mucus. Sometimes the worms bore right through the shell and the oyster re­sponds by secreting a thin patch of nacreous shell over the hole (the same process by which pearls are formed in the pearl oyster). The prob­lem with these internal shell blisters is that they are thin and easily broken. There is a danger that using a sharp blade to free an oyster from its shell may result in a blister being broken, and unsightly anaerobic mucus oozing out from the mud-worm's tunnel to taint the oyster. This year some farms have seen up to 80 per cent of their harvest spoiled by mudworm. Infections by fungi, bacteria and viruses are as common in the sea as they are to us and other organisms on land. Many infections are common in all marine shellfish, but are at a low level and generally go unnoticed. However, they can become serious in farmed populations where huge numbers are concentrated in small areas in conditions that allow very easy transmission between individ­uals. Fortunately for New Zealand oyster farmers there is no record of Bonamia, the scourge of the Bluff beds, affecting Pacific oysters. The oyster industry in New Zea­land faces other kinds of hazards too. With world oyster production in ex­cess of one million tonnes per year, our 4000 tonnes of exports relegates us to being a minor player competing against suppliers who are closer to the major markets (Hong Kong, USA,Singapore and Australia) and for whom labour costs are often much lower. Strong international price compe­tition and a depressed local economy have given New Zealand growers a hammering. For many growers profits have not been commensurate with the capital investment and sheer hard work of operating an oyster farm. To make matters worse, the influx of a whole range of new seafood products on to the market has provided stiff competition for the oyster. Once the pieces de resistance of any smorgasbord, oysters have be­come passé, just one more item in an increasingly cramped section of the food market. After a decade of strong expansion in the industry, production levels and prices have been static for the last few years. All is not gloom, however. With renewed interest in all aspects of shellfish cultivation (and govern­ment predictions that the country has the potential to earn $250 million from aquaculture) oysters are likely to be on the menu for a long time to come.

Geography

The obsidian island

Though it is little more than a speck in the ocean, Tuhua (Mayor Island) has a remarkable history of violent volcanic upheaval, bloody tribal warfare and legendary big game fishing. Buddy Mikaere tells the story of an island which ranks as one of the jewels of the Bay of Plenty. 

Science & Environment

The living carpet

Beneath the forest canopy lies a seamless living carpet of mosses, lichens and liverworts. These simple plants not only clothe the forest floor, they grow `wall-to‑ wall', adorning tree trunks, rocks and even rivers and pools with a spectacular array of colours, shapes and textures.

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