Being big bony animals, humans tend to forget that the vast majority of animals are tiny and have no bones at all. These boneless animals, or invertebrates (i.e. animals which lack a backbone), make up 34 of the world's 35 animal phyla and have more species than all other domains and kingdoms put together.
The most primitive phyla, the Porifera (sponges), Cnidaria (jellyfish, anemones and corals) and Echinodermata (sea stars and sea urchins), each have 5,000-10,000 known species around the world and live exclusively in the ocean. Many other invertebrate phyla consist of worm-shaped animals which live mostly in the sea, though a few have also colonised the land, namely: the Nematodes (roundworms, threadworms), which have 25,000 described species, but may number in the millions; the Platyhelminths (flatworms), which have 20,000 known species; and the Annelids (segmented worms, such as polychaetes, leeches and earthworms), which have 12,000 identified species (Hawksworth et al., 1995).
Two of the most advanced invertebrate phyla are the Arthropods and the Molluscs. The arthropods are mostly land and shore dwellers, except for the crustacean group, while the molluscs are largely confined to the sea, except for some land-dwelling slugs and snails. The main mollusc groups are the cephalopods (e.g. squid and octopuses), the gastropods (those with one shell, such as periwinkles, paua and snails), and thebivalves (two-shelled molluscs, such as cockles, mussels, oysters, scallops and toheroa). In total, about 70,000 mollusc species are known, though many more remain to be discovered in the mud of the ocean floor.
Of all the invertebrates, only the arthropods have flourished on land. Without a water-proof skin, most other invertebrates tend to dehydrate on dry land. They also have difficulty getting about without jointed legs or wings. Burrowing worms, parasitic worms and slippery slugs and snails have all found answers to these problems, but are nowhere near as successful as the arthropods with their hard skin, or exoskeleton, jointed legs and, in some cases, wings (e.g. beetles, crickets, flies, bees, mosquitoes, butterflies etc.). The four main arthropod classes are the myriapods (e.g. millipedes, centipedes), the insects (e.g. beetles, flies, etc.), the arachnids (e.g. spiders, mites, scorpions) and the crustaceans (e.g. crabs, crayfish or lobsters, shrimp, copepods, slaters).
The most diverse arthropods are the six-legged ones, the insects, which have 950,000 described species. Many insect groups are well known: beetles, fleas, flies, mantids, grasshoppers, crickets, locusts, wetas, earwigs, cockroaches, termites, aphids, mosquitoes, sandflies, butterflies, moths, bees, wasps, ants and many more. The beetles are the most diverse insect order, with more described species than all other insects combined. And among the beetles, weevils have more species than any other group. The eminent biologist J.B.S. Haldane is said to have replied, when asked if his research had told him anything about God: "He has an inordinate fondness for beetles." Recently, however, it has been suggested that bee and wasp species, most of which are still unidentified, may have more species than the beetles (Emberson,1995).
The total number of invertebrate species is not known and even the best guesses vary widely. In New Zealand about 21,000 invertebrate species (mainly insects) have been described, but about 50,000 may exist, almost half of them insects. Of the insect species, about 10,000 have been described, but there are good grounds for assuming that the total number is in the range 17,500-20,400, with the most likely figure being close to 20,000 (Emberson, 1994, 1995). One group alone, the tiny parasitoid wasps, is now believed to contain several thousand species, nearly all of which are undescribed.
Nematode worms are also highly diverse, though estimating the number of species is particularly difficult. Only about 400 species have been described to date, but scientists believe that 11,000-12,000 may exist here (see Table 9.1). About half of these are parasitic roundworms which live inside animals. Most are specific to particular insects, spiders and crustaceans. About 3,000 species may live in marine mud and about 2,500 may live in the soil and on plants. The deforestation of large areas of New Zealand has probably reduced many soil-dwelling nematode populations and may even have eliminated several species. Similarly, the extinction of more than 60 native vertebrates probably wiped out at least as many parasitic nematodes.
Other invertebrate groups well represented in New Zealand are myriapods (millipedes and centipedes), arachnids (spiders and mites), molluscs and flatworms. The myriapods are related to the insects and arachnids. Their distinguishing feature is having a large number of legs. The most diverse myriapods are the millipedes which have about 200 described species and perhaps 600 unidentified ones. This compares to only 35 described centipedes. The known arachnid species suggest that New Zealand has an unusually large number of spiders and mites. About 2,600 have been described and many more remain to be identified. This is about 24 arachnid species for every 100 insect speciesthree times the global figure of 8 arachnids per 100 insects (Hawksworthet al.,1995).
New Zealand's flatworms are also diverse by world standards. Whereas Europe has only 6 native species, New Zealand has an estimated 200. Only about 50 of these have been named and described. Like most native invertebrates, the flatworms were badly affected by the vegetation changes that accompanied human settlement. One species which became confined to relic gardens and woodlands in the centre and south of the South Island isArtioposthia triangulata. This particular species received an unexpected new lease on life when it was accidentally exported with garden plants to Britain and Ireland. Now it is a major pest there, devastating earthworm populations wherever soils are damp and cool enough for it to become established.
About 2,000 marine molluscs have been described, and at least a thousand more have yet to be identified. On land, about 500 species (nearly all snails) have been described, with perhaps 200 more to be identified. Our land snails are among the most diverse in the world, but the larger species have been heavily reduced by vegetation change and introduced species.
Most of our known invertebrates are land and freshwaterspecies (mostly insects, but also including spiders, mites, slaters, slugs, snails, nematodes, flatworms and earthworms). The rest are marine species, such as molluscs (e.g. shellfish and squid), various marine worms (most notably estuarine, coastal and parasitic nematodes), echinoderms (e.g. seastars, sea urchins), cnidarians (e.g. corals, sea anemones, jellyfish), poriferans (e.g. sponges) and the only class of sea-going arthropods, the crustacea (which includes crabs, lobsters, shrimps, prawns and tiny shrimp-like creatures called copepods).
Based on known species, at least 90 percent of New Zealand's land and freshwater invertebrates are likely to be endemic and, in many cases, confined to very small parts of the country. The number of alien land and freshwater invertebrates introduced since human occupation is believed to be about 2,000. Over 300 recognised invertebrate taxa (species and subspecies) are listed by the Department of Conservation as threatened or possibly extinct. More than half of these (177) have so little known about them that their priority cannot be ranked (Department of Conservation, 1994b). Others, such as our native slugs, are not listed at all because information is so sparse. Given the lack of information on most species, and the limited distributions of many of them, the true number threatened is probably several times greater than the number currently recognised.
With so many species unknown, and likely to remain so for a long time, many may disappear before they have even been identified as threatened. This has led some scientists to the view that single-species recovery programmes for invertebrates are too piecemeal and should be replaced by habitat protection programmes which scoop up many species at once. However, others have argued that simply protecting habitats is not sufficient on its own because representative habitat for many threatened species no longer exists, or is infested with predators. Towns and Williams (1993) propose a balanced approach, in which habitat protection and restoration is integrated with species recovery programmes. Because they are so small, habitat protection for land and freshwater invertebrates can be much simpler than for birds, bats and other large species. A successful invertebrate reserve may require as little as a hectare of native forest, scrub or tussock.
The luckiest of the unlucky threatened invertebrates are those whose identities are known, enabling them to receive special attention. The Department of Conservation lists 26 in Category A of its top priority threatened taxa. They comprise: 13 insects (8 beetles, 2 moths, 1 grasshopper, 1 tusked weta and 1 cave-dwelling bug); one arachnid (a mite); 11 molluscs (2 giant snails, 1 kauri snail subspecies, and 8 sub-species of flax snail); and one annelid (a leech).
Little information exists on how many invertebrates might have become extinct since human settlement because, being small and boneless, they leave few remains. The remains of beetle exoskeletons and snail shells, however, indicate that several species have become extinct or been eliminated from large areas of their former range. A dozen species are listed as possible recent extinctions (Category X) by the Department of Conservation (1994b).
The vast majority of our invertebrates are forest-dwellers, so it is likely that some unknown species with localised distributions literally went up in smoke as forests were cleared. The impacts of rats and introduced birds would have added to this. TheAmychus click beetles, for example, were once abundant throughout New Zealand, but are now confined to a few rat-free islands.
Not all of the indigenous invertebrates have suffered, however. A review of land use effects on land invertebrates noted that some indigenous species responded positively to the removal of forest and the advent of exotic plants and animals (Yeates, 1991). Species which appear to have benefited include:
- the native bees (about 40 species) which have adapted well to pastures and crops as sources of nectar and pollen, and which, despite losing out to the European wasps in beech forests, are competing successfully in other habitats with the seven alien bee species (Donovan, 1980; Scott, 1984);
- two indigenous parasitic wasps (Pterocormus promissorius and Lissopimpla excelsa), which became widespread by parasitising the pasture pest, armyworm (Mythimna separata), until an alien parasitic wasp (Apanteles ruficrus) was introduced in 1972 to successfully control the armyworm population;
- several species of small black field crickets (Pteronmobiusspp.) which may have been reduced in their native tussock habitat by the effects of grazing, but have been able to increase their range by exploiting lightly grazed exotic pasture previously under forest;
- the native shorthorned grasshoppers (15 species belonging to the family Acridiidae), which are restricted to the tussock grasslands, but appear to have benefited from the modifications caused by grazing to the extent that they may be considered pests (Scott, 1984);
- the compressed weevil (Irenimus compressus) which is endemic to New Zealand and appears to have become widespread in pasture and crop soils where its larvae feed on roots;
- the endemic grass grub moths (Costelytra zealandica) and porina weevils (Wiseana spp.), whose larvae have become successful pasture pests; and
- plant-feeding nematodes of the genus Paratylenchus, which are abundant in pasture but not in natural forests.
On the other side of the ledger, many invertebrate species have been negatively affected by the land use changes of the past 150 years and by the many introduced species which now prey on them or destroy their remaining habitat. The negatively affected species include:
- all 178 native earthworms which have disappeared from deforested soils throughout the country and been replaced by about 25 species of European earthworms;
- most species of large land snails, which were reduced by the removal of their forest habitat as well as by predation from rats, birds and pigs, and perhaps competition from the 26 introduced slugs and snails;
- several chafer beetles (Prodontria spp.), especially the Cromwell and Alexandra chafers, which are restricted to very small habitats and are preyed on by a number of introduced animals;
- all but one of the dozen giant wetas (Deinacrida spp.) and all three of the known tusked wetas ('Hemiandrus'spp.), whose forest and scrub habitats have been greatly reduced, and which are preyed on by rats (Meads, 1990);
- several ring nematodes, especially species of the genusCriconemoides, which are found in 60 percent of forested soils but in only 2 percent of pasture soils, and whose range has been reduced along with the forest (Yeates, 1991);
- Amychus click beetles, which are now limited to a few small islands, such as the Three Kings, the Chathams group and a few rat-free islands in Cook Strait;
- the large weevils, which are now less numerous and diverse in the lowlands than in the mountains, and whose depleted species include: Anagotus stephenensis, A. Rugosus, and Ectopsis ferrugalis, all of which have been greatly reduced since the arrival of rats and mice; and Hadramphus tuberculatus which appears to have gone extinct about 80 years ago through the combined impacts of introduced predators and pasture development (Kuschel and Worthy, 1996); and
- at least 250 other known species of small invertebrates, particularly beetles, which live in indigenous forests and are listed as threatened.
Among this last group are many species which are presumed threatened or extinct but on whom little information exists (Department of Conservation, 1994b). Until recently, Fiordland's bat-winged fly (Exsul singularis) was one example (Patrick, 1996). About the size of the common house fly, it has disproportionately large, black wings - as big as a butterfly's. It is carnivorous and changes its flight pattern when hunting to mimic a butterfly. It was regarded as the world's rarest fly (Meads, 1990), but a recent review of its distribution has recommended that it be removed from the threatened list because it appears to be widespread in the high mountain grasslands of Fiordland and the southern Alps, particularly around alpine streams (Patrick, 1996).
Another unique New Zealand insect which is presumed threatened is the wingless bat fly (Mystacinobia zelandica). It is so ancient that it has no close relatives and lives its entire life with the rare native short-tailed bat. The bat flies share their hosts' roosts, feed off their droppings and use the bats' fur for public transport. The bat fly's only close relative became extinct in 1965 after the rat invasion of Big South Cape Island when its host, the larger short tailed bat, was wiped out.
Even more ancient than the bat fly is a small group of invertebrates called the Onychophora or velvet worms which are often referred to as 'living fossils' (Gleeson, 1996). With their many pairs of sac-like legs they are something of an evolutionary enigma. Some scientists consider them to be primitive arthropods, a sister group to the centipedes and millipedes, while others regard them as an even more primitive 'missing link' between the arthropods and the annelid worms (Poinar, 1996). They live in moist habitats under stones, leaves and rotting logs, and have probably become more rare as the world's forests have declined.
Velvet worms have been identified internationally as 'vulnerable' (Wells et al., 1983) and as warranting priority for conservation (New, 1995). Until recently, 5 species were known in New Zealand, 4 of them endemic. Two are widespread and 3 have restricted distributions. Several new species have come to light and these also appear to have restricted distributions. They include a new genus from the Leith Valley and Caversham regions of Dunedin and a new species from Birch Island in the lower Clutha River, a habitat which is under threat of inundation for hydroelectricity development (Gleeson, 1996).
The chafer beetle group contains species whose status is still being investigated. All of the 15 or so known species are endemic to Otago, Southland or Stewart Island, and all live in restricted habitats (Emerson, 1994). Their best known member is the Cromwell chafer (Prodontria lewisii), which is among the species on the Department of Conservation's top priority list. It is found in only one area - an 80 hectare reserve near Cromwell in Central Otago where it lives among silver tussock (Poa laevis) and scabweeds (Raoulia spp.). Its original range was just 500 hectares, but this was reduced to 100 hectares by the activities and construction of the Clyde dam and the reconstituted Cromwell township (Meads, 1990; Watt, 1979).
The reserve was established for the Cromwell chafer in 1983, but humans are not the little beetle's only enemies. The chafer is eaten by hedgehogs (Erinaceous europaeus), blackbirds (Turdus merula) and song thrushes (Turdus philomelos), and is a particular delicacy of the little owl ( Athene noctua). These alien predators were introduced from Europe; the hedgehog to control introduced snails which had become a garden pest, and the owls to control other introduced birds which had become orchard pests. Cromwell chafers make up 10 percent of the little owl's summer diet (Meads, 1990).
|Taxonomic name||Common name|
|Asaphodes stinaria||a geometrid moth|
|Brachaspis robustus||robust grasshopper|
|Confuga persephone||a cave dwelling bug|
|Dorcus auriculatus||Te Aroha stag beetle|
|Dorcus ithaginis||Mokohinau stag beetle|
|Dorcus 'Moehau'||Moehau stag beetle|
|Hirudobella antipodum||Open Bay Island leech|
|Mecodema costellum subsp. costellum||Stephens Island carabid beetle|
|Mecodema laeviseps||Ida Valley carabid beetle|
|Paryphanta busbyii subsp. watt||kauri snail|
|Pianoa isolata||a mite|
|Placostylus ambagiosus (8 subspecies)||flax snails|
|Powelliphanta gilliesi subsp. brunnea||a giant land snail|
|Powelliphanta traversi subsp. otakia||a giant land snail|
|Prodontria bicolorata||Alexandra chafer beetle|
|Prodontria lewisi||Cromwell chafer beetle|
|Has not yet been described||Middle Island tusked weta|
|Xanthorhoe bulbulata||orange cress moth|
|Xylotoles costatus||Pitt Island longhorn beetle|
Source: Department of Conservation (1994b)
Habitat destruction has had a big impact on many other insect species. The effects of deforestation on beetle diversity have been studied in Auckland (Kuschel, 1990) and Wellington (Crisp, 1995). Both studies found that the number of beetle species living in grass or other exotic vegetation is much lower than the number living in native bush. The only long-term study of the relationship between habitat destruction and insect biodiversity was a survey of 150 moth species in an area of South Island tussock grassland (White, 1991).
The moth study found that, between 1962 and 1989, the tussocks and herbs on which half the moth species feed, had been replaced over about 30 percent of the study area by the exotic grass browntop (Agrostis capillaris). Although no species had disappeared, the populations of many of them had halved. If the browntop continues to spread, it is expected that moth populations will continue to fall until some species are lost (White, 1991).
Fifteen species of native land snails and 59 additional sub-species feature in the Department of Conservation's threatened species list. For its size, New Zealand has more kinds of land snails than almost any other country. About 500 species have been identified and up to 700 may exist. They range from tiny species with shells no larger than a few mm to giant species as long as a person's forearm. Several species, known only from shells, are considered to be extinct. More than half of our threatened snails are from one genus, Powelliphanta, the giant land snails. Other hard-hit genera are the kauri snails, Paryphanta, and the flax snails,Placostylus. Many more species of smaller snails may be threatened but have yet to be identified.
The larger snails are preyed on by such animals as Pacific, Norway and brown rats, possums, pigs, hedgehogs, blackbirds and song thrushes, but the greatest threat to their existence has been the destruction of their habitat (Meads et al., 1984). Land snails usually live in the deep, moist, non-acidic leaf mould that accumulates under forest and scrub where shelter, food and moisture are readily available. Deforestation and drainage have drastically reduced such areas, and many snail populations have declined accordingly. The effect of forest degradation on native snail biodiversity was studied on Manakau Peninsula. In undisturbed forest, 57 species were found. The number fell to 48 in regenerating forest which had been fenced off from stock animals, and fell further to 32 in forest stands that were not fenced off and which had been either burnt or cut over (Solem et al., 1981).
Habitat loss also threatens some of our unique slugs. Slugs are actually snails which have lost their shells. New Zealand has about 30 species, all endemic (Burton, 1962, 1963). Like the snails, they have some close relatives in eastern Australia, New Caledonia, Vanuatu and other Pacific Islands, and, also like the snails, they need a moist shady environment. They are often found under logs, in leaf mould and in the leaf bases of flax bushes and nikau palms.
They are easily distinguished from introduced slugs, such as the common grey European slug, by the fact that they have two tentacles instead of four, and are more attractively coloured. Some of the native slugs are also considerably larger than the imports, with one species growing up to 15 cm. The natives do not have a mantle or saddle on their bodies and often have a leaf-like shape with venous lines fanning out from a centre-line which runs down their backs. The New Zealand slugs are unique in having a tiny pinhole on their backs which, like a whale's blowhole, leads to the slugs' most distinctive feature - a highly developed lung found in no other mollusc (Burton, 1982).
Some native slugs are widespread throughout New Zealand. The euphoniously named Athoracophorus bitentaculatus, for example, is found throughout the North and South islands (Barker, 1978). The olive green Green Gherkin Slug (Pseudaneitea papillata) is also widely distributed and is common on flax bushes and even toitoi. Others are rare and seem restricted to specific locations. Five species known from four subantarctic islands (the Snares Islands, Auckland Island, Campbell Island, and Macquarie Island) have yet to be found on the mainland.Pseudaneita dendyi has been found only in mid-Canterbury,Pseudaneita schauinslandi is restricted to the Marlborough Sounds (Burton, 1962) and Pseudaneita multistriatais confined to two tiny islands off Stewart Island.
Three slug species found in the Chatham Islands may be lost before they are formally described. Two of them are restricted to forest remnants on the main island, the third to a similar habitat on the smaller Pitt Island. Several more species in Northland, again formally undescribed, are also dependent on habitat conservation for their survival. As with snails and birds, habitat loss is the main threat to our slugs. Predation adds to the pressure, as does competition from the 26 or so species of introduced slugs and snails. Some of the introduced species may even eat native species or pass on protozoan diseases to them. Because information on their status is so scant, no slugs are currently listed as threatened by the Department of Conservation.
About 450 formally identified insect species and at least 200 other kinds of invertebrate (e.g. crustaceans, molluscs and various worm phyla) live in streams and other freshwater habitats (Collier, 1993). A recent review of their status and distribution found that 154 species (mostly flying insects) that live in or on surface waters have 'restricted' distributions in New Zealand, as do a further 20 species (mostly molluscs) which live in underground waters, and a further 36 species known only from offshore islands (Collier, 1993).
Not all of these restricted species are necessarily threatened, but several are of sufficient concern to be included in the Department of Conservation's threatened species list. The main threats come from habitat degradation by catchment clearance, removal of riverbank vegetation, wetland drainage, diffuse and point source pollution, channel engineering works, mining, and the regulation of flow regimes (Collier, 1993). In some cases (e.g. freshwater crayfish) predation by introduced fish is also a threat.
A third of the invertebrates with restricted ranges are known from specimens, but have not been formally described and named (Collier, 1993). Without taxonomic descriptions it is not possible to assess distributions or accurately target species for recovery programmes. Because time may be running out for some species, it has been argued that, instead of waiting for scientific descriptions and assessments of individual species, the immediate priority should be to protect representative freshwater habitats (Collier, 1993).
Many of our larger marine invertebrates are well known to shellfish gatherers, divers and beach-combers, but many of the tiny species are never seen. 'Meio-fauna' is a catch-all term for animals which are barely 1 mm long. They are bigger than single-celled micro-organisms (bacteria, protozoans and micro-algae) but too small to be classed with the crabs, snails and seaweeds as 'macro-organisms'.
Ninety-five percent of the meio-fauna in our estuaries are either threadworms (nematodes) or tiny, shrimp-like crustaceans called copepods. They are vital parts of the food chain, eating bacteria and micro-algae before being eaten in turn by baby flatfish which, in turn, are eaten by wading birds. Although they are apparently sensitive to environmental disturbances, and have even been suggested as environmental indicators of estuarine health, nothing is known of their status (Dickison, 1992).
The larger marine invertebrates are more familiar to most people. They include several species which are gathered or fished, and many which are not. The better known groups are: crustaceans (e.g. crabs, shrimps, barnacles and rock lobsters or marine crayfish); molluscs (e.g. abalone or paua, pipi, mud snails, scallops, catseyes, tuatua, oysters, toheroa, cockles, mussels and many more, plus, in deeper waters, squid and octopus); echinoderms (e.g. seastars and sea urchins or kina); poriferans (sponges); cnidarians or coelenterates (corals, jellyfish, sea anemones); bryozoans (e.g. lace corals); and brachiopods (lamp shells).
Many of the molluscs are taken recreationally as well as commercially, and have traditionally formed a large part of the Māori diet. In fact, evidence from middens suggests that every available form of shellfish was eaten by pre-European Māori - even barnacles, which are small shell-like crustaceans (Foster, 1986). A typical West Auckland midden, for example, contained the shells of 32 mollusc species, 2 barnacle species and one sea urchin (kina). The most abundant species were cockles (67 percent), pipi (13 percent), mussels (11 percent) and tuatua (2 percent). In some coastal areas, middens show that local shellfish populations declined in size or disappeared altogether by about a.d. 1500 (Davidson, 1984). In most areas, however, particularly harbour flats, they remained abundant.
Today, several of the larger marine invertebrates are harvested commercially. Most of the harvesting is controlled by catch limits imposed by the Ministry of Fisheries (see Table 9.12).
|Cockles||Catch limits on permits|
|Dredge oysters||Controlled fishery - individual quotas|
|Mussels||Ban on all commercial fishing|
|Octopus||No catch limit (but very small fishery)|
|Paddle crab||Competitive TAC|
|Queen scallops Competitive||TAC|
|Sea cucumber||Catch limits on permits|
|Spider crab||Catch limits on permits|
|Surf clams||Catch limits on permits|
|Toheroa||Ban on all commercial fishing|
|Whelks||Catch limits on permits|
* Competitive TAC = a total allowable catch (TAC) limit which is not divided into individual quotas.
Harvesting continues competitively until the total allowable tonnage has been reached.
** QMS = the official Quota Management System, in which total allowable catch (TAC) limits are divided into individual quotas (see Box 9.14)
A few species are subject to the Quota Management System (QMS) which regulates catches through annual quotas (see Box 9.14). Many others are subject to competitive quotas or catch limits specified on permits. These controls are necessary because many invertebrate species are of very high commercial value and are extremely vulnerable to overfishing. Good stock assessment information is available for only a few species.
Apart from harvesting pressure, some marine invertebrates are vulnerable to environmental disturbances, particularly sediment washing down from rivers, pollution, changes in sea temperatures, and fishing activities, such as the scraping of heavy nets and dredge buckets along the sea bottom (Jones, 1992; Pain, 1996a).
As pressure has intensified on some wild populations, shellfish 'farms' (aquaculture) are increasing in number because they give much greater control over populations and harvest rates. Green-lipped mussels and the introduced Pacific oysters are farmed in this way. Paua farms have recently been established, along with freshwater prawn farms, such as the Machrobrachium rosenbergii farm associated with the Wairakei geothermal fields. There are seaweed farms, whose 1995 output came to about 70 tonnes, in Bluff Harbour and Tory Channel. And aquaculture is also likely to be developed for dredge oysters, scallops, and rock lobsters.
Toheroa (Paphies ventricosa) are large endemic clams which live in groups, mostly on the wave-pounded beaches of Northland's and Wellington's west coast and a few beaches at the bottom of the South Island. In the past, massive toheroa shells, measuring up to 33 cm (13 inches) could be found, but these days most toheroa are about half that size (Heath and Dell, 1971). They are considered a delicacy and their habit of burrowing into the sand for protection makes them easy prey for determined shellfish gatherers.
Commercial harvesting began in the late 1800s, and the successful canning of toheroa soup and toheroa tongues was achieved in the early 1900s. The main effort was on the west coast beaches of Northland. At one stage, four factories were operating on a 20 km stretch of North Kaipara Beach (Dargaville Beach). Three closed after a few seasons, but the fourth remained in operation until 1969 when it, too, was forced to close down because of the dwindling number of toheroa. Another cannery which operated on Ninety Mile Beach from 1923, closed in 1945 because of the depleted stocks. It reopened again in 1962, but shut down for good in 1964. Other commercial harvesting occurred for brief periods at Muriwai Beach near Auckland, the west coast beaches of Wellington, and Bluecliffs Beach in Southland. Restrictions on recreational toheroa gathering were introduced in 1932, with a two-month season (OctoberNovember), a daily bag limit of 50 toheroa per person for non-Māori gatherers, and a minimum legal size of 3 inches (7.5 cm) shell length.
In 1941, a daily bag limit of 80 toheroa per person was introduced for Māori gatherers. In 1950, ethnic distinctions were revoked and all gatherers were subject to a daily bag limit of 20 toheroa per person, or 50 per vehicle. Although fisheries regulations now give special consideration to fish and shellfish gathering for Māori gatherings and funerals (hui and tangi), these are still subject to conservation restrictions. Special legislation for cultural harvesting of fish and shellfish is now in preparation. Despite these measures, toheroa stocks continued to decline, so the controls were periodically tightened until, by the late 1970s, the season had been reduced to one week, the daily bag limit was down to 10 per person (still with a car limit of 50), and the use of digging implements had been banned. In 1980, the season was further reduced to 5 days, and the legal size limit was increased to 10 cm (just over 4 inches).
Since 1962, decisions on whether toheroa seasons should be held have been based on beach surveys which are now conducted about every 3 years. No toheroa seasons were approved during the 1980s, but in 1990 and again in 1993 seasons were approved at Oreti beach near Invercargill where, for a season to be held, the survey must indicate a beach population of at least 1 million toheroa.
The 1993 toheroa 'season' or open day lasted just 9 hours (roughly the period of low tide). It had a bag limit of 5 toheroa per person and a minimum shell length of 10 cm. An estimated 15,000-20,000 were taken. The other toheroa beach in Southland, Bluecliffs in Te Waewae Bay, has a population trigger value of 450,000, but the beach is eroding and has been unable to support a season in recent years.
Since 1986, our most commercially important marine species have been fished under the Quota Management System (QMS). New Zealand was one of the first countries to adopt this system in which catch limits for each stock are set by the Government and allocated to commercial fishers through individual quotas. Most species consist of several stocks which each inhabit different parts of our 200-mile Exclusive Economic Zone (EEZ). To help identify them, the EEZ has been divided into 10 Quota Management Areas (QMAs) (see Figure 9.5). Each stock has a unique label reflecting both its species name (e.g. SQU for squid) and its QMA address (e.g. SQU6 for those in QMA 6). The label may be further elaborated when several stocks of one species share the same QMA (e.g. the SQU6T stock occurs on plateaus accessible to trawlers, while the SQU6J stock occurs in deeper waters accessible only to jiggers).
Every year, fishery scientists analyse catch and trawler survey data to assess whether each stock is above or below its Maximum Sustainable Yield (MSY) level (see Box 9.15).
The results of the stock assessments are forwarded to the Minister of Fisheries who then consults with the fishing industry, Māori representatives, environmental and recreational groups, and other interested parties, before setting the annual Total Allowable Catches (TACs). A TAC specifies the total amount that may be taken from a stock by the combined efforts of commercial, recreational and Māori customary fishers. The objective in setting TACs is to reduce (or, in some cases, rebuild) stocks to their MSY level, and hold them there. This is largely done by controlling the commercial portion of the TAC, which is called the Total Allowable Commercial Catch (TACC). The commercial catch limits are set after an allowance has been made for the estimated recreational and customary catches. The commercial catch is divided among fishers in the form of Individual Transferable Quotas (ITQs). An ITQ permits the holder to catch a specified percentage of the TACC for a particular stock. The original ITQs were allocated in perpetuity to commercial fishers in 1986, based on their catch histories. Many fishing companies and independent fishers have since bought, sold or leased their ITQs in the same way as they might buy, sell or lease property. In fact, the ITQ is a kind of property right.
Shortly before opting for the ITQ system, the Government used a different method to reduce the inshore fishing pressure. In 1984, part-timers were excluded from the industry. This effectively halved the number of commercial fishers in a single year. Shore fishing permits were reduced from 550 to 261 and the fishing fleet was cut from 4,320 to 2,747 (Department of Statistics, 1985). Fleet numbers have remained at or below this level since. Many of the excluded fishers were Māori who, in 1986, sought a High Court injunction against the ITQ allocation process. In 1987 the Court made an interim declaration in their favour which led to long negotiations between Māori representatives and the Crown. The result was a two-stage settlement costing the Crown approximately $280 million. In the first stage, the Government purchased ITQs representing 10 percent of the existing TACC and allocated these to Māori fishers through the Māori Fisheries Act 1989. It also established the Māori Fisheries Commission to facilitate this process. In the second phase, following further negotiations, the Crown signed a Deed of Settlement which is reflected in the Treaty of Waitangi Settlement (Fisheries) Act 1992. Under this, the Government funded the purchase of a 50 percent share in Sealord Products Ltd for Māori interests, agreed to allocate 20 percent of the quota for any new QMS species to Māori interests, and also agreed to establish a regulatory framework for non-commercial Māori customary fishing. Through the Sealord purchase and the quota allocations, Māori commercial interests now control 40 percent of the commercial fishing quota. The relatively small customary catch is not subject to quota. Together with recreational fishing, allowance is made for it when the TACCs for each stock are set.
The overall success of the Quota Management System has still to be assessed. Economically, it has been hailed as very efficient, but, ecologically, the benefits are uncertain. The emphasis on scientifically based sustainable yield management is a distinct improvement on previous approaches and those used in many other parts of the world. However, it cannot, in itself, overcome some of the inherent difficulties affecting all fisheries management regimes. For a start, little is known about the extent and impact of illegal fishing practices, or the level of voluntary compliance with quotas and other restrictions. Illegal practices which are known to occur include bycatch dumping (i.e. discarding accidentally caught species for which the fisher has no quota), 'highgrading' (i.e. discarding less valuable fish in favour of more valuable ones), poaching, fishing out of season, and selling illegally caught fish and invertebrates on the blackmarket. In the 1993/94 season, for example, more than 60 enforcement operations by the Ministry of Agriculture and Fisheries (MAF) led to eight major prosecutions against people and companies involved in quota fraud. It has been estimated that up to 80 percent of domestically sold fish may have been funnelled through the blackmarket (Minister of Fisheries, 1992; Duncan, 1995). The compliance problem is a feature of fisheries worldwide and is being addressed by both Government and industry.
A more fundamental question, however, concerns the impact of legal fishing. About half the QMS stocks are of unknown status, although most of these are the more lightly fished stocks. Of those whose status is known, most are still in the process of being 'fished down', so the system's ability to maintain them at the MSY level has yet to be tested. For stocks which were near or below the MSY level when the system was introduced, results have been mixed. Several stocks appear to have stabilised or begun rebuilding, but some have declined below the MSY level (e.g. some orange roughy stocks) or failed to rebuild to it (e.g. some snapper stocks). Quotas for these stocks have now been dramatically reduced and improvements are expected, though they may take some time.
The other important environmental question about the QMS concerns its impact on non-target species and their ecosystems. Until the recent passing of the Fisheries Act 1996, the QMS had been relentlessly single-species in its focus, with each stock managed in isolation from the other species in its environment. When, for example, a stock was reduced by two thirds to boost its yield, no account was taken of the possible impacts of such a reduction on the associated predator and prey populations. Little account was also taken of the effects of bycatch, or vessel and net disturbances, on non-target fish and invertebrates. Nor was any account taken of the need to maintain key ecosystems (such as coastal mangroves and deepwater seamounts) that act as nurseries, spawning grounds or feeding grounds for many target stocks. Now, however, this is all set to change. In line with the new Fisheries Act requirement to manage both the environmental impacts of fishing, as well as the yields, the Ministry of Fisheries is developing a long-term strategy entitled Fisheries 2010.The proposed cornerstone of the strategy will be a fundamental change of course away from resource management and toward ecosystem management (Ministry of Fisheries, 1996).
Rock lobsters or marine crayfish (Jasus edwardsii andJ. verreauxi) are one of the most important of the commercially fished marine invertebrates, and, until recently, one of the most over-fished (see Table 9.13). Jasus edwardsiiwas listed as a commercially threatened species by the International Union for the Conservation of Nature and Natural Resources (IUCN, 1990) and the Department of Conservation (1994e). However, rock lobsters are not a protected species. Instead, their harvesting is regulated by a combination of size limits and seasonal restrictions and, in the past four years, has come under the Quota Management System (QMS).
The status of the Chatham Island and Kermadec rock lobster stocks is unknown, but all eight stocks around the North, South and Stewart Islands are below the level of Maximum Sustainable Yield (see Box 9.15). The overall rock lobster catch was relatively stable from about 1960 until 1987, though signs of over-exploitation began to show as the effort required to catch them increased steadily over this time. The number of potlifts needed to catch a given amount of lobster doubled between 1979 and 1992. Then, between 1987 and 1992, the total commercial catch declined by half (Boothet al., 1994).
Fisheries scientists concluded in 1991, and again in 1993, that the fishing pressure had been too high for some time and that there was some risk of stock collapse (Breen, 1993). The Total Allowable Catch (TAC) was duly reduced by 20 percent in 1993 to 2,953 tonnes. Stocks now appear to be recovering, despite an illegal catch estimated at 650-700 tonnes. The recreational catch is estimated to be at least 160 tonnes. The Māori food-gathering catch is unknown but may be less than 20 tonnes (Booth et al., 1994; Breen, 1994; Ministry of Agriculture and Fisheries, 1995; Teirney and Kilner, 1995).
Scampi (Metanephrops challengeri) are small deep-water lobsters, 4-6 cm long, with natural lifespans of possibly 15-20 years. They began to be fished in 1987-88. Stock levels are assumed to be above the MSY level and in the 'fishing down' phase (Annala, 1995a)(see Table 9.13).
The Maximum Sustainable Yield (MSY) is the maximum tonnage of 'surplus' individuals that can be taken from a stock while still leaving a constant population of breeding individuals. It is a production-driven approach to fishery management, rather than an ecologically driven one, requiring fish stocks to be kept well below their natural size so that a large number of surplus offspring can be continually generated. In natural fish populations relatively few youngsters survive to adulthood. This is because food and territory are fully taken by the existing adults. However, when a population has been significantly reduced, the competition for territory and resources eases and many more offspring can survive to adulthood. Because food is more available they can also grow faster, reaching a harvestable size sooner. In nature, fish populations rarely remain at this level. Left to themselves, each year's crop of young adults become 'new recruits' to the breeding population and this causes the stock to expand back up to its natural saturation point where territory and food supplies once again limit survivorship and growth rates. Under fishery management, however, this population recovery process is interrupted by repeated harvesting, thus sustaining the population indefinitely at the MSY level.
A fish population is at the MSY level when it has reached the maximum size that will sustain peak rates of survivorship and growth. For most fish stocks this is between 25 percent and 60 percent of the population's pre-exploitation biomass. Above that size, 'habitat crowding' causes survivorship and growth rates to decline, taking the total yield down. Below that size, the total number of breeding females, and hence offspring, declines, again taking yields down. The first goal of fishery management, then, is to 'move' stocks to the MSY level by setting catch limits which allow stocks above that level to be 'fished down' and those below it to be 'rebuilt'. Once the MSY level has been reached, catch limits have to be finely tuned to match the tonnage of each year's new 'recruitment class' of young adults. Significant error either way can cause lower yields in following years. Getting it right, therefore, requires good scientific assessments and a precautionary approach in setting catch limits. If excessive catch limits are repeatedly set, stocks may eventually 'collapse' to the point of commercial or even biological 'extinction'. Although this has not happened to any QMS stocks, sectoral lobbying has sometimes overshadowed scientific advice in the TACC setting process, resulting in catch limits that have exceeded recruitment levels.
Setting sustainable catch limits is not the only difficulty associated with the MSY approach. Because it has the single aim of getting maximum sustainable yields from target stocks, the MSY method is blind to any adverse impacts on non-commercial fish, invertebrates and ecosystems. This presents a challenge for fishery scientists and managers now that the Fisheries Act 1996 and the proposed Fisheries 2010 strategy demand an ecologically sustainable approach to fisheries management. It remains to be seen whether the MSY method can be adapted to the new ecosystem management regime or whether entirely new techniques will be required to produce the Ecologically Sustainable Yields (ESY) of the future.
|Species||1990 1||1992 1||1994 1||1996 1||Stocks Status 1996|
|Packhorse rock lobster (Jasus verreauxi)||Quota||None||31||40||40||D|
|Red rock lobster (Jasus edwardsii)||Quota||3,699||3,616||2,913||2,913||B (Nth & Sth Is.)|
|Catch||3,113||3,061||2,765||2,510||D (Chatham Is)|
|Scampi (Metanephrops challengeri)||Quota||No quota||1,230||1,230||1,230||A|
|Squid (Arrow squid) (Nototodarus gouldo, N. sloanii)||Quota||166,250||118,571||122,875||123,332||D|
|Paua (Haliotis iris; H. australis)||Quota||1,287||1,287||1,238||1,254||D|
|Oysters (Tiostrea chilensis) (Challenger beds)||Quota||500||500||500||500||D|
|(Foveaux Strait beds)||Quota||46,000 sacks 2||18,400 sacks 2||Closed season||4,000 sacks 2,3||B|
|Catch||46,114 sacks 2||5,821 sacks 2,4||3,869 sacks 2,3|
Source: Ministry of Fisheries.
1 For rock lobsters, the fishing year is the 12 months up to December, while for other species it is the twelve months up to June.
2 1 sack = 0.079 tonne. Oyster quota was reduced from 115,000 to 46,000 sacks during the 1990-91 season whenBonamia was found to have spread.
3 The Foveaux Strait Dredge Oyster Fishery was opened between June and August 1996 for the first time since 1992
4 Fishing was only permitted in the outer areas of fishery because of Bonamia.
Stocks Status Key
A = Above Maximum Sustainable Yield (MSY) and being "fished down".
B = Below MSY level.
C = Currently at or near the MSY level.
D = Data deficient.
Scallops (Pecten novaezelandiae) are dredged off Northland, the Coromandel Peninsula, and Nelson (see Table 9.14). These hermaphroditic shellfish are highly fecund and their populations are highly variable from one year to the next. This makes status assessments difficult, though it seems that commercial fishing at past levels poses no threat to the North Island stocks, each of which is managed by catch limits and seasons (Annala, 1993b).
Scallops are also sensitive to pressures other than direct harvesting. Bull (1986) found that the survival rate of scallop larvae after nine months was heavily affected by the presence or absence of fishing trawlers. In an area closed to trawlers, 20 percent of young scallops survived, compared to less than 1 percent where trawlers were working. Scallops are also highly sensitive to suspended clay particles and land use decisions which affect water run-off can have highly destructive consequences for scallop beds.
|Northern Fishery||Northland (Season: July 15 - February 14)|
|Quota||600kg greenweight (unopened) per boat per day||600kg greenweight (unopened) per boat per day||600kg greenweight (unopened) per boat per day||600kg greenweight (unopened) per boat per day||600kg greenweight (unopened) per boat per day||600kg greenweight (unopened) per boat per day||188 tonnes 2|
|Coromandel (Season: July 15 - December 21)|
|600kg greenweight (unopened) per boat per season per day||600kg greenweight (unopened) per boat per season per day||7 tonnes of meat per boat per season||6 tonnes of meat per boat per season||3 tonnes of meat per boat per season||Quota details not available||88 tonnes (2 tonnes of meat per boat)|
|Catch||143 t.||282 t.||230 t.||157 t.||202 t.||208 t.||200 t.|
|Southern Fishery 3||Nelson and Marlborough (Season: August-December with start date based on surveys of scallop size)|
|Quota||No fishery wide quota. Each vessel allocated a set catch.||No fishery wide quota. Each vessel allocated a set catch.||About 640 t.(meatweight) later increased to about 740 tonnes.||AAC 4 1,100 tonnes (meatweight) per season||AAC 4 850 tonnes (meatweight) per season||AAC 4 720 tonnes (meatweight) per season||AAC 4 720 tonnes (meatweight) per season|
|Catch||240 t.||672 t.||710 t.||805 t.||850 t.||521 t.||672 t.|
Source: Ministry of Fisheries
1 This table contains no assessment of stock status because scallop stocks vary markedly from year to year. Catch limits have been based on annual abundance surveys since 1992 in the Northern Fishery and since 1993 in the Southern Fishery.
2 For the 1995-96 fishing season, the quota allocation for the Northland Zone of the Northern Fishery was changed from a quota per boat system to an overall area system.
3 Since 1986, the Southern Fishery has been "farmed" with a rotational fishing strategy and stock from a seeding programme contributing to the annual yield.
4 The Southern Fishery has 48 licensed vessels whose catch limits were initially set on a per boat basis but, from 1993 on, have been subject to a fishery-wide Allowable Annual Catch (AAC) allocated through a transferable quota (ITQ) system.
The large Southern Scallop fishery, based near Nelson, is augmented by scallop farming, has a season based on annual surveys of scallop size (see Table 9.14) and is fished on a rotational basis. The fishery was placed under a transferable quota management system in 1992. In the late 1970s, it experienced a classic boom and bust phase and is now recovering.
From small beginnings in 1959, catches rose to 1,246 tonnes in 1975 then crashed to zero in 1981 and 1982. The stocks' recovery has been assisted by a re-seeding, or enhancement, programme. Although catches have increased throughout the 1990s, the 1995-96 quota had to be reduced from 850 tonnes to 720 tonnes because many scallops were small, probably due to a seasonal food shortage.
The most commercially important marine invertebrates are the two arrow squid species (Nototodarus gouldi and N. sloanii). By invertebrate standards, these ten-legged molluscs and their eight-legged relatives, the octopuses, are big and brainy. They are widely distributed around New Zealand, but population estimates are uncertain and vary widely from year to year. Because squid live for only one year, scientists cannot predict stock size nor determine if recent catch levels and quotas are sustainable (Annala, 1995a).
Commercial squid fishing began in the 1970s and peaked in the early 1980s when more than 200 vessels, mainly from Japan, fished in our deeper waters using spinning hooks on long-lines (jigging). The number of foreign jiggers has declined since the late 1980s, leaving most of the catch to New Zealand trawlers operating in the shallower continental shelf zones around the mainland and the Auckland Islands.
Since 1986-87, the annual squid catch has consistently been lower than the Total Allowable Catch (TAC), averaging 65,000 tonnes against an average TAC of 128,000 tonnes (see Table 9.13). Although the total catch has fluctuated widely over this period, from as low as 37,000 tonnes (1992-93) to as high as 114,000 tonnes (1988-89), it has shown no overall trend. Both the 1986-87 and 1993-94 catches were just over 74,000 tonnes (Annala, 1995a). The only example of a squid catch exceeding quota was in the southern squid fishery (SQU6T) in 1993-94 when 34,534 tonnes were caught - 14 percent above the TAC of 30,369. Whatever their impacts on the squid stock, high catches in this fishery pose a bycatch hazard to the rare New Zealand (Hooker's) sea lion (see Box 9.18 and Table 9.34).
Paua, or abalone, are gastropod molluscs and, hence, relatives of the snails and slugs. Two species are caught: the common black-footed paua (Haliotis iris) and the smaller and less abundant yellow-footed paua (H. australis). They are not differentiated in the fishing statistics, but 90 percent of the catch consists of black-footed paua. Paua have been commercially fished since the mid-1940s, at first only for the shells, but later for the meat as well. Commercial paua fishing must be done by hand without underwater breathing apparatus.
For most of the past decade, the annual commercial catch has been about 1,250 tonnes and the annual TAC has been slightly above this. In 1993-94, however, the total catch slipped to barely 1,000 tonnes, the lowest for more than a decade. Besides the commercial catch, an estimated 400 tonnes are taken illegally each year and a further 200 tonnes are taken by recreational gatherers (Teirney and Kilner, 1995). This is equivalent to half the commercial take and suggests that the overall TAC is regularly being exceeded.
Most of the catch is from the South Island, Stewart Island, and the Chatham Islands, with some off the Wairarapa coast. It is not known if recent catch levels or the current TACCs are sustainable, or if the overall population is increasing or declining (Annala, 1995a). Although stocks around the South Island appear to be abundant, they may be declining around Stewart Island and also on the west coast where "the fishery may be serially depleting an accumulated stock of presumably very old individuals" (McShane et al., 1994) (see Figure 9.5 and Table 9.13).
Dredge or Bluff oysters (Tiostrea chilensis) are Gondwana veterans which were native to New Zealand and Chile long before dredges or the city of Bluff were invented. Their wild populations have been commercially harvested for more than100 years and research is now under way to farm them commercially (Jeffs, 1995). The commercially farmed Pacific oysters (Crassostrea gigas) are not native, having been introduced here from Japan in the early 1970s. The two main stocks of dredge oysters are at the top and bottom of the South Island - the Challenger beds near Nelson and the Foveaux Strait beds near Bluff (see Table 9.13).
The TAC for the Challenger beds has been 500 tonnes since 1987 and has been reached or exceeded 7 times in the past 14 years. No information has been collected on customary and recreational fishing. Scientists do not know whether the catch is sustainable or whether the population is above or below the MSY level (Annala, 1995a).
The Foveaux Strait oyster beds were closed to fishing from 1993 after the spread of an infectious parasite called Bonamia which was first identified in 1986. By 1993, the combination of disease and harvesting pressure had reduced the stock to 20 percent of its 1975 level and 10 percent of its original level (Annala, 1993a). Since the oyster beds have been closed, the commercial fishers have been carrying out research to see if the population can be increased through an enhancement programme similar to that used for the scallop beds at the other end of the island. The 1995 oyster beds survey showed that the Bonamia infestation had declined, and oyster numbers had increased enough for the Minister of Fisheries to agree to a short commercial season during the winter of 1996.
Cockles (Austrovenus stutchburyi) have been commercially picked from tidal flats since the early 1980s. They have been collected for much longer in many areas by Māori and recreational shellfish gatherers. The commercial harvesters operate in three areas: Whangarei Harbour, Golden and Tasman Bays (near Nelson), and Papanui and Waitati inlets (near Dunedin).
In Whangarei Harbour, the overall number of cockles has not changed, but their age and size distribution has, with harvestablesized cockles down to a third of their original levels. Large old cockles have declined by more than 90 percent. Although small cockles appear to have increased, it is not known whether recent catch levels are sustainable. Catches have grown in the past decade, except for the 1992-93 year when toxic algal blooms caused a closure of the fishery (Annala, 1995a).
Commercial fishing of the Papanui and Waitati stocks is relatively light and fishing at current levels is unlikely to reduce the biomass of cockles to low levels, though some recreational cockle pickers have complained that the proportion of large cockles has decreased in recent years. This is a normal consequence of the 'fishing down' phase as older individuals are replaced by an increasing number of young ones (Annala, 1995a).
Besides the arrow squid and various shellfish species that are harvested commercially or recreationally, many more molluscs go unnoticed in our waters. These range from several other species of cephalopods (squids and octopuses) to several thousand species of marine snails and shellfish, many of which thrive in the marine mud 1-2 km below the ocean surface. Approximately 2,280 species and subspecies of marine molluscs have been recorded from the New Zealand region, and approximately 1,000 specimens held in the National Museum have yet to be described. At least as many species may still be awaiting discovery on the sea floor (Marshall, 1994).
The great majority of molluscan species are less than 1 cm in size and many of those are in the millimetre size range. Virtually all groups need taxonomic revision. Many species once thought to have limited distributions are now known to be more widespread. None of the unharvested species of marine molluscs is known to be threatened, though the habitats of some may be at risk (Marshall, 1994).
Although lobsters earn more money, crabs are probably the best known crustaceans. Lesser known crustaceans include the numerous, but tiny, copepods and amphipods. In total, New Zealand has about 1,500 known species of marine crustaceans, of which 93 are crabs. Half of our crabs are endemic, including 10 spider crabs and 12 pill-box crabs. Most species are widespread around our coastline and many are found elsewhere in the Pacific. Only two endemic species are considered rare (Elamena momona and Halimena aotearoa) and one subspecies (Leptomithrax tuberculatus mortenseni), which is confined to the Hauraki Gulf, is considered rare and potentially threatened by intensive fishing. Three other non-endemic natives have restricted distributions, as do two introduced species, but none are threatened (McLay, 1994).
New Zealand's only freshwater crab, Amarinus lacustrus, did not evolve here, but seems to have been introduced from Australia by migratory waterfowl. It is confined to the upper North Island and is listed by the Department of Conservation (1994b) as threatened in New Zealand but secure overseas. The main causes of its restricted distribution appear to be predation by trout and habitat destruction (McLay, 1994).
The sponges belong to the most primitive animal phylum of all, the Porifera. The cells which make up their bodies are almost identical to those of the single-celled choanoflagellates from which the animal kingdom seems to have sprung. Sponges vary in shape and size, but all have a simple body plan. They have no nervous system, no organs of any kind, and no limbs. What they do have is a body that is hollow on the inside and full of thousands of small holes everywhere else. Tiny food particles are caught in these pores as water continually filters through them into the central cavity.
Dead sponges were once standard bathroom items. Today they are of interest to drug companies prospecting for potentially useful biochemical compounds. Scientists from several institutions (e.g. NIWA and Canterbury University) have investigated the compounds that may be obtained from sponges found on the Chatham Rise and off Kaikoura. One species belonging to the genus Lissodendoryx holds the promise of a new anti-cancer drug (see Box 9.7).
At least 350 sponges have been identified in New Zealand, and several additional species are probably lurking among the 120 unnamed specimens which lie on museum shelves waiting for a taxonomist to describe and name them (Dawson, 1993). Being sessile (attached to the sea bottom), sponges are vulnerable to disturbances of the sea floor. Sediment and detritus can clog their pores. Dredging and trawling can uproot and kill them. At present, the status of New Zealand's sponges is unknown.
About 600 cnidarian species are known in New Zealand waters, about half of them 'corals' of one sort or another. Although they look very different, jellyfish, anemones and corals all spring from a common ancestor and share a similar body design - basically, a bag whose open end forms the mouth. In some species these 'bags' take on an upright tube-like shape with one end stuck to the sea bottom (a polyp). In others, they assume a free-swimming bell-like shape (a medusa). In either case, all cnidarians are hunters. Their mouths are fringed with tentacles armed with tiny stinging cells called cnidae. The phylum Cnidaria gets its name from these stinging cells which immobilise small animals, allowing the tentacles to draw them into the mouth.
Cnidarians are divided into three broad classes: the Scyphozoans (jellyfish); the Hydrozoans (hydroids, hydrocorals); and the Anthozoans (anemones, corals). They all start life as polyps. The jellyfish eventually grow into medusae, spending their adult lives roaming the oceans. The Hydrozoans contain some species that remain as polyps and some that develop into medusae. All Anthozoans remain as polyps, staying more or less permanently in one place all their lives. The colourful anemones prefer shallow water, and some can be found within the tidal zone, while most of the corals inhabit deeper water.
New Zealand's corals and other polyps are vulnerable to harvesting by divers for jewellery-making and curio-collecting. They are also at risk from disturbances of the sea floor by sedimentation, dredging and trawling (Saxton, 1980; Jones, 1992). Recent research into trawler bycatch on the Chatham Rise suggests that some of our deep water corals may be seriously affected (Probert, 1996; Probert et al., in press). Similar concerns have been raised in Australia over the damage inflicted on Tasmania's deep-water corals by orange roughy trawlers (Fisher, 1995).
'Corals' are not a united group. Almost any cnidarian that has hard body parts can be called a coral, though the term is usually restricted to Anthozoans. Hydrozoans with hard body parts are often called corals but, technically, they are referred to as hydrocorals. Most corals wear their hard parts on the outside, as a protective tube or exoskeleton, but many prefer to carry them on the inside, either as internal skeletons (e.g. black corals), quill-like backbones (e.g. sea pens) or small splinter-like spicules (e.g. soft corals).
Some cnidarians live independently as solitary polyps on the sea floor, but many others live in colonies where their tissues, nerves and skeletons become fused together. These colonies often look like trees or bushes whose branches are decorated by the colourful mouths and tentacles of many polyps living side by side. The individual polyps are generally small (i.e. no wider than 1-2 cm and no longer than 2-5 cm) but the colonies can be very large, forming underwater 'trees' which sometimes stretch to 5 m. In the tropics these colonies can become truly vast, grow into huge coral reefs. The corals which build these reefs have symbiotic algae living in their polyps. Because the algae need sunlight to survive, the corals tend to live in shallow waters where they spread out over wide areas. Hundreds of species compete in the same limited zone, building colonies on top of each other and on the skeletal remains of previous generations. Over thousands of years these colonies have grown into enormous reefs which are home not only to the corals and algae, but also to many fish and other organisms.
New Zealand has no coral reefs because our water temperatures are too cool for the algae-dependent corals to thrive here. Some 15-20 reef-building species have straggled into our waters, forming clumps on the sea floor around the northern Kermadec Islands, but they are very atypical of the 320 or so coral species found around New Zealand. Although they are not thriving, these stragglers are fortunate to have settled in a marine reserve.
They probably face a more secure future than many of their tropical relatives which are threatened by growing pressures from human development, particularly in the Pacific and Oceania. The pressures include: sediment washing down from deforested river catchments; nutrient pollution; fishing activities; blasting reefs for building materials; collecting of aquarium specimens; climate change; and disease. Already, in the past two decades, an estimated 10 percent of the world's coral reefs have been damaged, and a recent study predicts that about 60 percent will disappear within the next 2 to 4 decades (Pain, 1996a; Stone, 1995b).
New Zealand's 200 or so colonial corals do not form reefs but can form underwater 'gardens' and 'thickets' of red, white, pink, brown and black. The 100 or so solitary species scattered around the sea floor are less conspicuous but, in some cases, the individuals can reach lengths of nearly 20 cm (Cairns, 1995). New Zealand's corals belong to three major groups:
- the Hydrocorals (Hydrozoan corals) which are mostly colonial and have 62 known species (Cairns, 1991);
- the Hexacorals (Anthozoans whose tentacles are in multiples of 6) which include about 130 known coral species (mostly stony corals and a small number of black corals) as well as about 70 non-corals (various anemones); and
- the Octocorals (Anthozoans with eight tentacles) which consist of about 60 horny corals (or gorgonians) and about 60 other coral species (soft corals, sea pens, and related groups).
New Zealand's 62 known hydrocorals are mostly colonial and tend to live at depths of 100 m or more (Cairns, 1991). They are sometimes referred to as 'red corals' because they look like the gorgonian 'red corals' which are harvested overseas and sold as jewellery. Despite their common name, they are not all red. Some are pink and white. Apart from several populations inhabiting shallow waters in Fiordland, little is known of their ecology and lifestyle. The Fiordland populations appear to be fragile and slow-growing and some colonies may occasionally be damaged by divers and boat anchors. The Department of Conservation has contracted NIWA scientists to study the damage caused by divers. Hydrocorals in deeper water may be vulnerable to trawl nets, but no research has been published on this. All species are legally protected, but their status is unknown.
The stony corals are our most diverse coral group. They are found throughout New Zealand's fishing zone, but most species can only tolerate the warmer northern waters. More than 100 species are found north of Cook Strait compared to only 20 or so south of there. Approximately 30 species are endemic (25 percent) while the remaining
90-odd are also found in other seas (Cairns, 1995). The stony corals' exoskeletons are usually white, sometimes mottled or streaked with black, brown or pink pigment, while their waving tentacles are often red.
About 80 species are solitary and 40-50 are colonial, including the 15-20 reef corals around the Kermadec Islands. Most stony corals live at depths of 200 m-1,000 m and some, particularly on seamounts, are vulnerable to deep-sea trawling along the seafloor. About 40 species are found in shallower waters and may be vulnerable to sedimentation and other forms of pollution. Some of the colourful, larger, branched species (such as Oculina spp.) may be threatened by scuba collectors in northern New Zealand. Little is known about most stony corals and they are not legally protected, except those lucky enough to live in marine reserves.
Black corals form coral 'trees' which range from 1 m-5 m in height. They are found on steep reef edges and rock faces in all oceans, generally in areas with reasonable currents at depths greater than 30 m. They cannot survive in estuarine waters or in areas where sedimentation is high. Growth rates are slow and large colonies are likely to be centuries old (Grange, 1994). Since ancient times, they have been exploited to make jewellery. Black coral amulets were once thought to ward off evil spirits and ill health. Now black corals around the world are regarded as threatened and are listed by the Convention on Trade in Endangered Species (CITES).
Because most of New Zealand's 13 known species have narrow geographic ranges, all have been legally protected since 1981. Four species have been recorded within scuba diving range, all of them endemic and all with restricted distributions. One is considered endangered and the other three are considered rare, though one of these is actually abundant within its limited range (Grange, 1994). The rare and endangered species are:
- Antipathes fiordensis, whose 5 m 'tree colonies' are known only from Fiordland and Stewart Island where an estimated 7 million trees are found at depths of 6 m-160 m;
- Antipathes lillei, whose 4 m tall trees are known from only a few sites around Northland and the offshore islands along the north-east coast, including the Poor Knights, Hen Island and Great Barrier Island;
- An unidentified species of Antipathes whose 1.5 m trees have been found at several sites in the Bay of Plenty; and
- The endangered Aphanipathes fruticosa whose only known colony, a 2 m tall tree at Kapiti Island, was damaged several years ago by a boat anchor (Grange, 1994).
Although they have no hard parts, anemones are closely related to the stony and black corals and are therefore classed among the Hexacorals. New Zealand has 73 known anemone species, 64 of them sea anemones (Actinarians). They are probably the cnidarians best known to school biology classes as they live close to the shore and are often brightly coloured. Despite this, little is known of their status. Their proximity to the coast is likely to make them vulnerable to sedimentation, pollution and other forms of habitat disturbance.
New Zealand's 61 known horny corals (sometimes called sea fans) form tree colonies. They are rare in shallow waters and relatively little is known about them. Their scientific name comes from gorgonin, the rubbery protein which makes up their internal skeleton. The 'red coral' gorgonians which are used in jewellery are not New Zealand species, but are harvested overseas. Like other large corals the horny corals are common on unexploited seamounts (underwater plateaus) but disappear where orange roughy trawlers are operating (see Chapter 7, Box 7.4). The main species affected is a large gorgonian called Paragorgia arborea which can grow to a height of 4 m. Horny corals are not legally protected.
The 63 known species in this group are related to the horny corals and, like them, have protein-based internal hard parts rather than exoskeletons. They are colonial and some grow very large. Nearly all the soft corals and sea pens are deep water species, though some are found in Fiordland at depths that can be reached by divers. The soft corals grow on hard bottoms, such as seamounts, while the sea pens occur in soft sediments. Both habitats are vulnerable to trawling. None of these corals are protected outside of marine reserves and little is known of their status.
Another phylum of sessile invertebrates which has attracted the attention of biochemists is the Bryozoa. Like the corals, these tiny tubular animals, each only a few millimetres long, encase themselves in exoskeletons. They form small colonies (1 mm-50 cm in size) which are often mistaken for seaweeds or corals. New Zealand has about 900 recognised species of bryozoa with some 200 still to be named and described. Only about 120 species are commonly encountered by divers and only a third of these are conspicuous enough to be noticed. Although none appear to be threatened, some of their habitats are, and one endemic species, the Scarlet Alcyonidium, is considered rare, being known from only one site in the world, the Leigh Marine Reserve (Bradstock and Gordon, 1983; Gordon, 1994).
In December 1980 an area of seabed in Tasman Bay was closed to power-fishing methods, such as trawling, Danish seining and dredging. The reason for the closure was to protect two endemic bryozoan species, Celleporaria agglutinans andHippomenella vellicata, whose tall, dense mounds served as important nursery grounds for commercial fish species, such as snapper and tarakihi. According to the Ministry of Agriculture and Fisheries the closure is permanent. Habitat restoration is not being monitored (Gordon, 1994).
New Zealand has about 400 known species of echinoderms with about 100 specimens awaiting description. Only one of the known species is listed as threatened by the Department of Conservation - a large starfish, or sea-star, called Eurygonias hyalcanthus.Described as one of the most spectacular and conspicuous of all New Zealand sea-stars, it is known from barely 20 specimens and has only been found around the lower North Island, Stewart Island and the Snares Islands, mostly at depths of about 10 m (Clark, 1994). Nothing is known of its biology.
Only one species of echinoderm is commercially harvested. This is the sea urchin or kina (Evechinus chloroticus). Kina look like spine-covered balls whose underside has a small mouth with large triangular teeth that munch on kelp and other seaweeds. They inhabit shallow coastal waters (generally less than 10 m deep), often forming dense populations on subtidal reefs. After larval settlement, kina are quite sedentary and rarely move more than 100 m in the rest of their life. Distributions tend to be patchy, and reproduction and growth rates vary markedly between local populations, probably reflecting the quantity and quality of the food in their immediate surroundings.
Kina are prized for their gonads, or roe, a traditional Māori food which is also sold on the domestic market. They are caught by diving, shorepicking, bottom trawling or dredging. At present they are managed as if they form a single stock with a quota set at 200 tonnes (Annala, 1995a). The fishery is small and does not seem to have affected local populations. An attempt to develop a large-scale kina industry in Fiordland has apparently been discontinued for commercial reasons.
Only about 300 lamp shell species are known worldwide and 30 of them are in New Zealand. Nine of these species occur at depths of less than 30 m, giving New Zealand a greater diversity and abundance of shallow-water brachiopods than any other comparable region in the world. Eight of the shallow-water species are endemic and one of these, Pumilus antiquatus, is considered rare. Most of the other species have extremely patchy distributions and some populations could be described as 'vulnerable'. Sedimentation, pollution and human interference, such as the removal of boulders, have been identified as risk factors for some populations. One population in Whangarei Harbour may have vanished between 1968 and 1990 and another, at Ripa Island in Lyttelton Harbour, appears to have been reduced (Lee, 1994).