Frogs are amphibians, evolutionary intermediates between fish and reptiles. We now know that New Zealand had at least seven native frogs when humans arrived with their rats and fire-sticks. Three species subsequently became extinct and the remaining four were heavily reduced. The survivors are: Archey's frog; Hochstetter's frog; the Stephens Island frog and the Maud Island frog, the latter two of which, until recently, were classified as members of a single species, Hamilton's frog (Daugherty et al., 1994; Bell, 1994).
Since European settlement last century, three species of Australian tree frogs were introduced to New Zealand to provide duck food and eat mosquito larvae (Druett, 1983; Sharell, 1966). One species, the Golden Bell frog (Litoria aurea), preys on native frogs and, together with another species, L. raniformis, may compete with them for food and habitat (Bell, 1994). Both of these species are widely distributed.
All the native New Zealand frogs belong to a single genus, Leiopelma, which is found nowhere else in the world (Green and Cannatella, 1993). Members of this genus are almost the same as extinct fossil frogs which existed in late Jurassic times 140-160 million years ago, when New Zealand was still under the sea. These primitive frogs were ultimately driven to extinction in Gondwana but, before they had disappeared, a number found sanctuary on the newborn New Zealand landmass where they quietly founded a small dynasty of unique species.
Unlike other frogs, the leiopelmids do not croak, having neither vocal sacs nor eardrums. The surviving species are very small, less than 5 cm in length, though at least one of the extinct species grew up to 9 cm. Three of the four species live on dry land where they breed under logs, rotten stumps or loose stones. Only Hochstetter's frog prefers an aquatic habitat, but survives well on dry land. None of the New Zealand frogs has a free-swimming tadpole stage. The tadpole phase occurs mostly inside the egg and the young hatch as tiny froglets. Nevertheless, adult frogs retain the fish-like tail-wagging muscles associated with tadpoles throughout their lives.
By the time Europeans arrived, the frogs had become so rare that local Māori appear to have had little knowledge of them. According to Arthur Saunders Thomson, who witnessed the first discovery of a native frog by Coromandel gold-panners in 1852: "The frog was shown to many of the natives and was carefully examined by several intelligent old men. None of these individuals had ever seen the animal before, nor could they give any name to it." (Sharell, 1966).
Sub-fossil skeletal remains show that New Zealand's frogs were widespread before the first Māori canoes arrived. Their bones have been found by the tens of thousands in some places, suggesting that the mossy forest floor was alive with them (Flannery, 1994). Hochstetters's, Archey's and Hamilton's frogs occurred in both the North and South Islands (Worthy, 1987; Towns and Daugherty, 1994; Bell, 1994). Since then, the frogs have disappeared entirely from the South Island and from the lower half of the North Island. Archey's frog is now limited to the Waikato region, where widely separate populations are found in the Whareorino Forest and on the Coromandel Peninsula (Bell, 1994).
The only surviving Hamilton's frogs are restricted to 2 islands in Cook Strait. On Stephens Island a tiny population of about 170 frogs clings to a small, severely deforested, habitat of about 600 square metres (Brown, 1994). On Maud Island about 19,000 frogs survive in fragmented forest partially restored by the Department of Conservation and the former Wildlife Service (Bell and Bell, 1994; Brown, 1994).
Although they are similar to look at, the Hamilton's frogs on Maud and Stephens Islands have been isolated from each other for so long that they have become genetically distinct species (Daughertyet al., 1994; Bell, 1994). This raises the question of whether the Hamilton's frogs that became extinct in the North and South Islands were genetically distinct species as well. If so, the toll of extinct frog species would rise from three species to five. It would rise even higher if the extinct South Island populations of Archey's and Hochstetter's frogs were also genetically distinct from their North Island counterparts.
|Taxonomic name||Common name||Conservation Priority*|
|Leiopelma archeyi||Archey's frog||B|
|Leiopelma hochstetteri||Hochstetter's frog||B|
|Leiopelma hamiltoni (Stephens Is)||Stephens Is. frog||A|
|Leiopelma n. sp. (Maud Island)||Maud Island frog||B|
* Department of Conservation (1994b)
Hochstetter's frog is now the most widespread of the surviving frogs, though it covers only a fraction of its former range. It probably escaped the worst impacts of rats and fire by its preference for streams. However, the streams provided no escape from the Norway rat, which is an adept swimmer, nor from the siltation and stream degradation caused by deforestation. Hochstetter's frog survives in at least 12 distinct populations scattered through the upper North Island from Gisborne to Northland. Some of the populations are very vulnerable, being cut off by hostile farmland, areas of volcanic activity or arms of the sea (Green, 1994; Bell, 1994).
The native frogs were first granted 'absolute' protection in 1922 but this has not protected them from rat, cat and mustelid predation and the effects of habitat fragmentation. Seventy years on, the Stephens Island frog is ranked as a Category A threatened species and the other frogs are ranked as Category B threatened species (Department of Conservation, 1994b) (see Table 9.24). Of the Category B species, the Maud Island frog is the most vulnerable, followed by Archey's frog and then Hochstetter's (Bell, 1994).
Although the dinosaurs and their many close relatives have gone, four orders of reptiles remain on Earth. They are: the ancient Sphenodontida ('wedge-toothed' reptiles whose fossils are found all over the world, but whose sole surviving members are the tuatara); the Squamata (lizards and snakes); the Chelonia (the shell-covered reptiles, namely turtles and tortoises); and the Crocodilia (crocodiles, caimans and alligators).
New Zealand has two of the four reptile orders. They are represented by the tuataras (2 species) and the lizards (at least 29 gecko species and 30 skinks) (Daugherty et al., 1994). Tens of millions of years ago there were many more reptiles. Prehistoric tortoises and turtles swam around our coasts and, before them, large plesiosaurs and mososaurs did the same. Dinosaurs stalked the land and pterosaurs flew above it (Cox, 1991; Hyde, 1993). However, New Zealand has never had terrestrial snakes, these having evolved from burrowing lizards after the split with Gondwana. Nor has it had crocodilians.
Although the tuatara has become well-known, the diversity of our lizards has been described as one of New Zealand's best kept secrets, making them part of our 'forgotten fauna'. Few people realise that New Zealand has more lizard species per thousand hectares than any other temperate country, including Australia (Daugherty et al., 1994). All the native lizards are endemic. Only one alien, the Australian Rainbow skink (Lampropholis delicata) has become established here.
Some of our lizards have adapted to the alpine region, which is one of the coldest reptile habitats on Earth, but most are forest dwellers, whose populations have shrunk with the lowland forests. All are at risk from introduced predators such as rats, stoats, ferrets and even wild pigs. The cat is also a prime offender. Though they were once abundant on the mainland, about 40 percent of our lizard species are now confined to small predator-free islands (see Tables 9.25 and 9.26). Both tuatara species are also confined to islands.
In all, more than 40 percent of our surviving reptiles are now threatened with extinction. One tuatara species is highly endangered. The other is still abundant but is considered threatened because the number of independent populations has declined by 25 percent this century. Among the lizards, half the skinks (15-17 species) and a quarter of the geckos (7-8 species) are threatened (Daugherty et al., 1994; Department of Conservation, 1994b) (see Tables 9.25 and 9.26).
Debate continues about the number of geckos, skinks and tuataras that became extinct after humans arrived in New Zealand. A species of tuatara which was described in 1886 from bones on the East Coast of the North Island (Sphenodon diversum) has been accepted as valid and listed as extinct (Daughertyet al., 1990). It is hard to tell, without genetic analyses, whether other tuatara bones from various parts of the country belong to existing species or to unrecognised extinct ones.
A firm case can be made for the recent extinction of a large skink, Cyclodina northlandi, whose bones have been found in Northland (Worthy, 1991). Two other lizards, known only from museum specimens, are listed as possible extinctions. One of these, a skink classified as Oligosoma gracilicorpus, may belong to a living species. The other, a large gecko namedHoplodactylus delcourti, was found in a French museum and assumed to have come from New Zealand, but firm evidence of its origin has not been established (Towns and Daugherty, 1994).
While examples of extinction are few, the evidence of drastic population declines is overwhelming. Lizard bones found in caves, dunes and middens show that many of the species now threatened on the mainland or confined to small islands were once widespread (Towns and Daugherty, 1994). Species which once had continuous populations are now absent from large areas or limited to isolated populations hundreds of kilometres apart. In the northern North Island, for example, 10 (56 percent) of the 18 resident lizard species have gone. Most of the remaining 8 species persist in low numbers and in scattered localities (Towns and Daugherty, 1994).
Human predation probably played little direct role in the decline of the lizards, though it may have affected the tuataras, first by reducing the seabird populations on whom coastal tuataras preyed, and second by reducing the tuataras themselves. Tuatara bones are common in Māori middens. Several lizard species are also found in middens but were probably trapped there while scavenging (Towns and Daugherty, 1994). Lizards were viewed with fear by Māori because of their presumed magical powers. They were generally avoided, though some were killed when encountered because of their evil powers, while others were called on for protection, some species more than others. Lizard and tuatara carvings sometimes guarded sacred places (Buck/Hiroa, 1949; Sharell, 1966).
European settlers had little interest in hunting lizards, but museum collectors in the late 1800s harvested tuataras intensively and may also have put pressure on some lizard populations. The collectors appear to have eliminated one tuatara population (on East Island) before legislation stopped the trade (Towns and Daugherty, 1994).
Habitat loss has had a significant impact on the reptiles. In recent decades, for example, two species of South Island 'giant' skinks (Oligosoma grande and O. otagense) declined when their native tussock habitat was converted to exotic pasture grasses. Another skink, O. striatum, has been seldom seen since forests in the western central North Island were cleared for grazing. Not all reptiles respond negatively to habitat modification, however. Tuataras on some islands, for example, can reach artificially high densities when areas of forest are converted to pasture - provided predators are not present (Towns and Daugherty, 1994). In such circumstances, hungry tuataras may be a threat to other endangered species confined to the islands with them, such as giant wetas and click beetles.
Predatory mammals appear to have taken the greatest toll of New Zealand's reptiles. The first predator onslaught occurred when the Pacific rat arrived. The tuatara, the Robust skink (Cyclodina alani) and McGregor's skink (Cyclodina macgregori) were among the first reptilian casualties. By the time Europeans reached New Zealand, these species had disappeared from the mainland, where they were once widespread (Towns and Daugherty, 1994).
The second onslaught occurred about 500 years later when Norway rats arrived in European ships. They were accompanied by pigs, which also eat lizards and tuataras. Norway rats are bigger and more aggressive than Pacific rats and can swim up to 1.4 km in salt water, making them a threat even to lizards on some islands close to the coast. The dense tuatara population on Whenuakura Island off the Coromandel coast was wiped out within two years of being invaded by these rodent Vikings (Newman, 1986).
The third onslaught came in the late 1880s. This time even tree-dwelling skinks and geckos became victims as ship rats, stoats and cats joined the chase. The lizards most vulnerable to the predator onslaughts were the larger ones and those which were active at twilight or at night (Whitaker, 1978). Today, predator-free islands carry much greater species diversities and population densities than are found on the mainland or on islands where rats are still present. Lizard populations on islands where rats have been eradicated have shown rapid increases in numbers and habitat range (Towns and Daugherty, 1994).
A good example of what skink and gecko life must have been like on the mainland before human settlement can be seen on Middle Island in the Mercury Islands group where 11 reptile species co-exist in an area of just 13 hectares. A study site in native tussockland in central Otago also shows how a relatively small area can support a dense and diverse population of lizards. Eight species live together, but they occupy very specific niches, vary considerably in size, and have slightly different tastes in food (see Table 9.26) (Towns and Daugherty, 1994). On island sanctuaries the tuataras, skinks and geckos are relatively safe, though their populations often remain small and, hence, vulnerable. On the mainland, however, several of our reptiles are at considerable risk, even in reserves.
Since 1955, the number of known lizard species has more than doubled, from 29 to 61, as scientists have discovered new ones or reclassified old ones. More rare species are probably awaiting discovery but, given their small populations and the threats facing them, identification will be a race against time. In late 1995 the Department of Conservation began investigating reports from forestry workers that large lizards had been seen in the Bay of Plenty. To many people, however, one lizard looks the same as any other, a perception which herpetologists are trying to dispell. Not only are geckos and skinks quite different from each other, the species themselves show considerable diversity.
Geckos are distinguishable from skinks by their wide eyes, benign smile and slightly baggy skin. They are seen less often than skinks because few geckos inhabit urban areas. Well camouflaged, and with excellent hearing and eyesight, they can easily avoid detection. Geckos are long-lived; some are known to live for more than 40 years. The ancestors of both the skinks and the geckos have been established in New Zealand for more than 15 million years (Patterson and Daugherty, 1995).
New Zealand's 29 gecko species are all unusual in the way they produce their young. They give live birth to baby geckos, almost always twins, instead of laying eggs. Only one other gecko, a New Caledonian species, is known to bear live young. Recent research indicates that some geckos may play a significant role in plant pollination. Pollen, which smears the lizard's chin when it sips the nectar from the flowers of flax bushes and pohutukawa trees, can stay there for up to 24 hours (Higham, 1995). The most notable pollinators are the Pacific gecko (Hoplodactylus pacificus) and New Zealand's largest lizard, Duvaucel's gecko (H. duvaucelii).
Skinks are the streamlined members of the New Zealand lizard fraternity. The 30 known species are all endemic, and all but one give birth to live young instead of laying eggs. The one exception is known as the egg-laying skink (Oligosoma suteri). Skinks are faring much worse than geckos at present, with twice as many on the threatened species list. One of the rarest species is Whitaker's skink (Cyclodina whitakeri) a 20 cm lizard once found throughout lowland forest areas of the North Island. It is now reduced to one tiny mainland population, and two small island populations with a total occupied area of less than 20 hectares (Towns, 1992; Towns and Elliott, 1996).
Among the rare species is New Zealand's largest and longest skink, the Chevron skink (Oligosoma homalonotum). With its pale head and brown body bearing 'lance corporal' markings, the Chevron skink measures up to 30 cm. It has a Category A ranking in the Department of Conservation's threatened species list and is found only on Great Barrier and Little Barrier Islands. Their feeding habits and behaviour are still largely a mystery. Cats are thought to be the Chevron skink's main predator, but pigs, ship rats, Pacific rats, and even mice, all add to the pressure. Habitat loss and degradation through residential subdivision and tourist development, and forest browsing by feral goats and cattle, have placed added pressure on the Chevron skink's survival on Great Barrier Island (Towns and McFadden, 1993; Close, 1994a).
Tuatara are the oldest and best known of New Zealand's reptiles. They are also the most long-lived, with some individuals having reached their 100th birthday. The order to which they belong, the Sphenodontida, had species in many parts of the Earth about 200 million years ago, but they were gradually driven to extinction as the closely related dinosaurs became more dominant. Most were gone or on the way out by 130 million years ago, except the tuataras which found a haven in the new-born New Zealand landmass.
Once abundant throughout the North and South Islands, both in forests and among coastal seabird colonies, the tuataras became extinct on both main islands after humans arrived. Today, two species survive on about 30 rat-free islands. Gunther's tuatara (Sphenodon guntheri) is limited to a small island in Cook Strait where about 300 adults and their young share a 1.7 hectare patch of scrub. In late 1995, 50 individuals were transferred to another island as part of an effort to extend the species' range (Holmes, 1995).
The common tuataras (Sphenodon punctatus) number about 60,000 and are divided into a Cook Strait sub-species and a Northern sub-species, the latter located on islands in the Bay of Plenty and the Hauraki Gulf. Though tuataras have been fully protected since 1895, the number of populations has fallen from 40 to 30 in the past century. Apart from rats and cats, tuataras are also threatened by international wildlife smugglers (Ansley, 1995).
In addition to the land-based reptiles, four species of marine turtles regularly visit with New Zealand. One of them, the leatherback turtle, is the heaviest reptile on Earth and can reach weights of nearly a tonne (the record-holder weighed 961 kg). Two species of highly venomous sea-snakes also slip in from time to time but, as denizens of warmer waters in tropical climes, their visits are probably accidental.
Although New Zealand's birds are a well-researched group, it is not possible to say with precision how many species and sub-species have lived and died here. New genetic studies and newly discovered bones continually revise our count of existing and extinct species. Such revisions improve our knowledge of the birds' story but, unfortunately, they do not make it read any better. Each newly identified species merely adds to the extinction list or the currently threatened list.
Apart from taxonomic revisions, the statistics on New Zealand birds can be confusing for other reasons. Many species are divided into several subspecies, or geographically isolated populations, some of which have their own distinctive characteristics. These populations are often treated as separate taxonomic units (or taxa) thus adding to the overall bird count. Further sources of confusion arise when whole groups of birds are excluded from the statistics, such as seabirds, or introduced birds, or non-endemic native birds (i.e. those native to both New Zealand and Australia).
If all New Zealand's bird taxa (species plus additional subspecies) are counted, including seabirds, non-endemics and introduced species, the total number of bird taxa currently in New Zealand comes to 231, comprising 33 alien species, 126 native land species and subspecies, and 72 native seabird species and subspecies. The threat of extinction is not spread evenly among them, however. The taxa most at risk are those which happen to be the most unique - the endemics. All our extinct species and nearly all our threatened species are endemic.
In contrast, the introduced and non-endemic birds tend to be mobile and adaptable. Most of the introduced birds were brought from Europe or Australia within the past 150 years and are well-adapted to the open landscape humans have created here. Most of the non-endemic natives are also open-space birds. Some are migratory species, for whom New Zealand is a necessary part of their international range. Others are accidental tourists that flew or blew here within the last few thousand years from Australia or the Antarctic. They include such successful species as the harrier hawk, the pukeko and the black-backed gull. As if their success in modern New Zealand were not enough, the introduced and non-endemic species are also buffered from extinction by having secure populations overseas. In contrast, the endemic birds are on their own.
Most of the following discussion is concerned with the state of our endemic birds. Land and sea-going species are discussed separately. Where relevant, statistics are given for both species and taxa (i.e. species plus additional subspecies). The species classification generally follows the Ornithological Society's 1990 checklist (Turbott, 1990), but also includes four extinct seabirds yet to be formally described and named.
Ignoring subspecies, it appears that, when humans reached New Zealand, they found at least 131 full species of land birds (that is birds whose primary habitat is on land, freshwater or the coast) and 65 species of seabirds (e.g. gulls, albatrosses, petrels and penguins). More than two-thirds of the land birds (93 species) and one-third of the seabirds (22 species, including the four unnamed ones) were endemic or unique to New Zealand (see Tables 9.28 and 9.29).
Today, 43 of the endemic land species (46 percent) are extinct, and 4 of the endemic seabirds (18 percent). A further 7 subspecies of land birds are also extinct. In the towns and farmland of New Zealand it is hard to imagine the scale of the country's bird losses because birds still seem plentiful. Sparrows, starlings, blackbirds, chaffinches, song thrushes and magpies are everywhere. Asian mynas dominate the road verges in the upper North Island. Introduced pigeons form dense clusters in city centres. Rooks have become closely watched agricultural pests in Canterbury and the Wairarapa. But all these birds, 33 species in total, are interlopers brought here in the past 150 years. They bear little resemblance to the giants they have replaced - the great Haast's eagle, the giant swan, the pelican, the rails and, of course, the moas.
By the time Europeans arrived, 34 species and 1 subspecies (35 taxa) of endemic land birds had gone. Following European settlement 9 more species and their constituent subspecies (13 taxa in all) were wiped out and a further 6 subspecies were lost. This leaves 50 surviving endemic species (comprising 102 taxa), of which 37 (comprising 66 taxa) are now listed as threatened (Department of Conservation, 1994b).
Overall, then, 84 percent of New Zealand's endemic land bird species have become extinct or threatened since human occupation. Of today's 50 surviving species, 74 percent are threatened (see Figure 9.7). These statistics are only likely to worsen in the foreseeable future as palaeontologists and archaeologists bring more evidence of extinct species to light, and as pests and habitat degradation push more birds onto the threatened list or into oblivion.
The irony of this is that the thing which makes the endemic birds unique and globally important - their evolutionary isolation - is also what has rendered them so vulnerable (Holdaway, 1989; Anderson and McGlone, 1992). They evolved no defences against humans and other hungry mammals (see Table 9.28). For the first time they faced predators that could hunt by smell at night and that could follow them into their tunnels and hollows. Many had little or no ability to fly, so they could not escape forest fires and hunters, nor emigrate to safer habitats.
In the face of such pressures and limitations, the survival to date of some species is nothing short of remarkable. Among the threatened land birds are most of our flightless species, such as the takahe (see Box 9.19), the kiwi (see Box 9.20), the weka, the Auckland Island and Campbell Island teals, and the desperately endangered kakapo.
The takahe (Porphyrio mantelli) is a flightless blue bird belonging to the rail family. It looks like a heavier version of its close cousin, the pukeko, or Purple Swamphen. In fact, the takahe is a descendant of stray pukekos which landed here from Australia several million years ago. In the placid New Zealand environment they lost the power of flight, put on weight, and prospered. Now they are in danger of dying out. The takahe were already rare when Europeans arrived and, for the first half of this century, were thought to be extinct. In 1948, however, about 500 survivors were found in the rugged and remote Murchison Mountains in Fiordland. Several pairs have been transferred to predator-free islands and have had some breeding success. But in the wild their plight is worsening. The Fiordland population is down to about 115 birds.
For a long time it was believed that the takahe's preferred habitat was the high tussock country where the survivors were found (Mills et al., 1984). Although takahe bones have been dug up in many parts of New Zealand, these were assumed to date from Ice Age times when tussock grasslands were more extensive. Today, however, the bones are believed to be more recent. Far from being tussock dwellers, it now seems that the takahe were most at home stepping and pecking their way along the edges of lowland streams and forests. The Murchison Mountains are merely their last inhospitable refuge from the onslaught of humans, rats and fire (Bunin and Jamieson, 1995).
Until recently, red deer (Cervus elephus) were blamed for steadily reducing takahe numbers by competing for what was assumed to be the birds' favorite food, snow tussock. However, after an intense deer eradication programme, the snow tussock has recovered, but not the takahe. The latest research suggests that the birds face the same problems as other small populations trapped in ecological 'islands'. The takahe are not prolific breeders and, faced with stoats and the harsh and changeable weather of the Murchison Mountains, the species is on a knife edge.
Having adapted to an environment free of mammalian predators, the takahe are not 'street wise' like their pukeko cousins. They appear to lack the know-how to recognise and avoid enemies. In contrast, the pukeko, which arrived here from Australia about 1,000 years ago, is one of our most common native birds, in spite of the best efforts of human hunters, rats, stoats and other predators. The pukeko has the advantage of being able to fly, albeit reluctantly and briefly, but another flightless New Zealand bird, the weka, has proved that you don't have to fly to survive. The knack may simply be in knowing when to run and what to run from.
Researchers recently tested this theory in a cross-fostering experiment with pukeko. Takahe eggs were slipped into a pukeko nest to find out whether the pukeko would be effective foster parents (thus freeing the takahe parents to produce more chicks) and also to see whether the takahe chicks may pick up a few survival skills from their foster family (Bunin and Jamieson, in press). The research was limited by a shortage of viable eggs. Over two breeding seasons, only 12 takahe eggs could be given to the pukeko, of which only eight hatched and only two produced chicks that survived. One of these chicks was used in a predator defence experiment with a model stoat. The chick appeared to respond more to the stoat than did another takahe chick reared by takahe parents. It was also more likely to leave the danger area.
With such a small sample, the behavioural experiment was far from conclusive, but the exercise did show that pukeko will hatch and raise takahe chicks, and that takahe will lay more eggs if the first clutch is removed. At the same time, it also confirmed that takahe eggs often fail to hatch, and that takahe chicks are often frail. Until scientists can find ways to solve these problems, the takahe will struggle to survive.
The kakapo (Strigops habroptilus) is a large flightless ground-dwelling parrot that managed to stay abundant in areas far away from Māori hunters and fires but declined dramatically after night-hunting mammals, such as cats, were introduced (Holdaway, 1989). A mere 50 survivors are known today. As part of the effort to save them from extinction, they have all been shifted from Stewart Island, where they were clinging to existence, onto three stoat- and cat-free island sanctuaries.
Since the intensive kakapo conservation programme began in 1989, only 13 chicks had hatched by 1995, and almost all had died as a result of predation or starvation. The Pacific rat, or kiore, is now generally accepted to be a major threat to nesting kakapo. Intensive research continues into the parrot's diet and how to improve it. On top of these concerns is the growing fear that the birds' biological clocks may be running out. Of the 50 surviving parrots, only 19 are females and most are more than 30 years old. They may be nearing, or at, the end of their reproductive lives.
Prior to Polynesian arrival in around 1300AD, there were over 90 endemic land and freshwater bird species. Prior to European arrival in around 1800AD, over 30 species were extinct and nearly 10 more were threatened. Today over 40 endemic species are extinct, and nearly 40 more are threatened.
To Californians, a 'kiwi' is the fat brown Chinese gooseberry now marketed around the world as 'kiwifruit'. To Australians, it is the national nickname and marketing symbol of their New Zealand neighbours. To New Zealanders, it is both of these things but it is still, first and foremost, a bird. The question is, for how much longer? Introduced predators, loss of habitat and a measure of public complacency have reduced once flourishing populations to remnants. It is a strange way of repaying the bird that has helped put us and our products 'on the map'.
Kiwis are forest dwellers. At night they seek spiders, earthworms, and larger creatures such as frogs, fallen fruits and seeds. Kiwi couples tend to pair for life. Some are known to have been together for more than 30 years. Having evolved in a land without ground-dwelling mammals, the kiwi became a sort of pseudo-mammal. It is flightless and ground-burrowing. It has hair-like feathers and a body temperature closer to mammals than birds. It is the only bird known to have external nostrils at the end of its bill and a keen sense of smell to match. Even laying an egg is more like a mammalian birth. Only one egg is laid and it is an astounding 20 percent of the females' bodyweightthe largest egg-to-bodyweight ratio of any bird. With such a huge investment in just one offspring, both the male and female are devoted egg sitters and parents.
The kiwi genus (Apteryx spp.) is New Zealand's most ancient group of living birds, and one of Earth's oldest. The ancestral kiwi evolved shortly after the New Zealand landmass broke away from Gondwana about 80 million years ago. It belonged to the ancient ratite group of birds whose handful of large, flightless, species include Australian emus, Papuan cassowaries, South American rheas and tinamous, African ostriches and New Zealand's extinct moa. During New Zealand's Oligocene drowning, the early kiwi populations evolved into four separate species: the great spotted, the little spotted, the northern brown, and the recently identified southern brownor tokoeka.
The Department of Conservation further divides the northern brown into the North Island and the Okarito varieties, and the southern brown into the southern tokoeka (in Stewart Island and Fiordland), and the Haast tokoeka.
About 25,000 great spotted kiwis are thought to exist. Since European settlement their range has diminished by about one-third. They now occupy high rainfall areas in north Westland and Nelson where the surviving population may be stable because stoats are less prevalent in very wet habitats. The much rarer little spotted kiwi is lucky to be here at all. It would almost certainly be extinct were it not for island sanctuaries. Its population is now estimated to be about 1,500 birds, and growing. The most threatened kiwis are probably the northern browns, despite being the most numerous and widespread. Their population is declining at a rate of 5.8 percent per year but could be halted if predation on young kiwis by stoats and cats were cut by a third (McLennan et al., 1996). In Northland the spread of ferrets and possums into the remaining pockets of lowland forest is placing them under extreme threat (Miller and Pierce, 1995). At the other end of the country, the southern browns appear to be holding their own on Stewart Island, probably because there are no stoats there, but the Haast population of about 200-300 birds is regarded as a remnant colony whose habitat is almost confined to the top of one range.
Efforts are being made, as resources permit, to slow the kiwis' decline in key areas and prevent their extinction. The Department of Conservation, the Royal Forest and Bird Protection Society, and the Bank of New Zealand, have joined forces in 'The Kiwi Recovery Programme'. Funds from the programme are being used to educate the public about the kiwis' plight and to support captive breeding programmes in which birds that face extinction in their natural environments are moved to predator-free 'museum environments' on offshore islands.
The flightless Campbell Island teal (Anas aucklandica nesiotis) is our most threatened native duck. Only 50 to 100 of these small, almost cocoa-coloured, birds survive. After 10 years of trying to breed in captivity, four ducklings hatched in 1995. They, and any others bred by conservationists, will probably end up on another of New Zealand's island sanctuaries. Plans are under way to clear the rats from Centre Island in Foveaux Strait to make a teal refuge. The Campbell Island teal is a close relative of another highly threatened duck, the Auckland Island teal (Anas aucklandica). It, too, has lost the ability to fly and uses its small wings mainly to help it scramble out of the seaweed kelp forests where it feeds. It lives on coastal rocks in sheltered bays.
Not all our threatened ducks are flightless. The attractive blue duck (Hymenolaimus malacorhynchos), for instance, can fly but this has not prevented it from being reduced to a few small populations on remote fast-flowing rivers in the North and South Islands. Another teal, the brown teal (Anas chlorotis), can also fly but has experienced a similar reduction in numbers and range. Once common on swampy streams and tidal creeks shaded by overhanging trees, they were often killed for food by the early European settlers. As wetlands were turned into farmland, their numbers dropped dramatically. They now survive in the wild mainly in Northland.
Of the 22 endemic seabird species (encompassing 39 taxa) which were here when people arrived, 18 survive (Turbott, 1990). Fifteen of the surviving species (83 percent), or 26 of the surviving 35 taxa (74 percent), are now listed as threatened (Department of Conservation, 1994b). These include 5 penguins (among them the world's rarest, the yellow-eyed penguin), 7 mollymawks, 4 albatrosses (including the royal albatross which nests at Taiaroa Head, near Dunedin), and 4 petrels. Threats include predation on nests and eggs by ferrets, stoats, rats, cats and humans, incidental capture by longlines and setnets, long-term changes to feeding grounds as sea temperatures rise, and localised pressures from pollution and toxic algal blooms.
The Chatham Islands are home to six of our most threatened seabirds. Several seabirds became extinct there following human settlement and today 24 seabird species still breed in the islands. Top of the threatened seabird list are the Chatham Islands taiko ( Pterodroma magentae) and the Chatham petrel (Pterodroma axillaris). The other four threatened birds are the Northern royal albatross (Diomeda epomophora sanfordi), Northern Buller's albatross (Diomeda bulleri platei), Chatham Island albatross (Diomeda cauta eremita), and the Chatham Island shag (Leucocarbo onslowi) (Bell and Robertson, 1994).
The taiko or magenta petrel is a large bird, with a deep brownish-black head, neck and throat. It is one of the 'gadfly' group of petrels, named for their airy drifting flight punctuated by startlingly abrupt free-falls (Falla et al., 1979). For more than a century the taiko was considered extinct. Breeding in burrows on the main island, it was easy prey for human hunters and the many bones found in middens indicate that it became a major food source for the Moriori people. The spread of predators such as rats and ferrets all but sealed the bird's fate.
The taiko was rediscovered on New Years Day 1978 and the population now has between 50 and 150 birds. Only four burrows are known to harbour breeding pairs, but the discovery of pairs of birds in another two burrows in 1993 has raised hopes that the number of breeding couples may rise to six. In 1994, the best breeding year so far, four known breeding pairs produced a chick each. All four died, however, even though intensive predation control was carried out.
Captive rearing of petrels has rarely been attempted and the rearing of seabirds in general without parental involvement is rare. To determine the requirements for captive rearing of the taiko, a trial is now in its second season at the Mount Bruce Reserve using eggs from the grey-faced petrel. One chick has survived, providing valuable information on such things as incubation temperature and feeding strategies. Predator numbers are still high, and twice-yearly trapping is carried out as part of the taiko conservation effort. The principal threats to the survival of the threatened birds are mammalian predation, destruction of ground nesting habitat by pastoral farming, occasional recreational and customary hunting, and possible climatic and oceanic changes or cycles (Bell and Robertson, 1994).
A significant threat to some seabird species is the risk of getting hooked on tuna longlines. Nearly 20 seabird taxa from 14 different species, 5 of them endemic, have been recorded among the longline bycatch. All these birds are legally protected and, under recent amendments to the Wildlife Act 1953, this protection now extends to the limit of New Zealand's Exclusive Economic Zone (EEZ). Among the victims are the wandering albatross, the snowy albatross, the southern black-browed albatross, the grey petrel and several threatened species, namely: the New Zealand black-browed albatross, the grey-headed albatross, the New Zealand white-capped albatross, the black petrel and the Westland black petrel.
Government observers on foreign tuna boats have recorded seabird bycatch since the late 1980s. However, the quality of the observer data is uneven, with marked fluctuations in some years (e.g. 16 observed captures in 1992 and 215 observed captures the following year). The observed catch rate per hundred sets has varied from 7 to 196 in the northern tuna fishery and from 4 to 80 in the southern fishery. While most of these fluctuations reflect uneven observer coverage, they may also reflect variations in fishing effort (e.g. the number of lines and hooks set in a given year); the use of mitigation measures by the boats carrying observers (e.g. the percentage of properly deployed tori lines); the choice of areas for setting longlines; and the degree of visibility during night sets (Duckworth, 1995).
Most seabirds are caught in the brief period between the longline being thrown overboard (setting) and it sinking out of diving reach (soaking). The baited longline provides a tempting meal and, once a bird has become hooked or entangled, it is dragged under and drowned. Observers are generally sleeping during this part of the operation, their main role being to record fish species during the 10-17 hour hauling-in phase. Most seabird deaths are therefore recorded hours after they occur, when the lines are pulled in, by which time an unknown number may have been eaten by sharks, become detached from the line, or died elsewhere from injuries sustained in tearing free (Brothers, 1991).
The scale of the seabird bycatch has been hotly debated. Estimates refer only to the Japanese tuna boats operating in New Zealand waters. Information from the domestic tuna fleet has been too limited to make estimates. In 1990, when the Japanese fleet was four or five times larger than it is today, one unofficial estimate put the seabird toll at 5,000-25,000 deaths (Tennyson, 1990). Official estimates for the same year, based on Government observer data, have ranged from more than 9,000 captures, with perhaps 5,000 deaths (Murray et al., 1992, 1993) to 1,200-3,600 captures (Baird, 1996). The official estimate for 1995 is 90252 seabird captures by Japanese longliners in New Zealand waters (Baird, 1996).
Bycatch estimates are dependent on both the level and quality of observer coverage and the level of fishing effort. Betweeen 1987 and 1992, Government observers witnessed only 1-7 percent of the Japanese longline sets. The percentage increased dramatically after 1992 as the Japanese tuna fleet was severely reduced. In New Zealand's southern bluefin tuna fishery, for example, the Japanese fishing effort fell from about 12 million hooks in 1990 to less than 3 million hooks by 1995, and the estimated number of seabird captures has declined accordingly (see Table 9.31). Conversely, the unrecorded bycatch of 10-15 years ago must have been much greater than it is today. In the period 1979-1983, nearly 22 million hooks were set each year in the southern bluefin fishery. This may have been a crucial factor in driving some species onto the threatened list.
As late as 1990, the 32 Japanese boats catching southern bluefin were accompanied by only 2 New Zealand longliners. By 1995, however, the number of Japanese vessels had declined to 9, while New Zealand longliners had multiplied to 25. The bycatch from these domestic vessels is not known, but conscientious efforts are being made by the local industry to reduce the problem. However, beyond New Zealand waters, other longline tuna fisheries encircle the Antarctic, both on the high seas and in other countries' exclusive economic zones. Together, these longline fleets may catch as many as 40,000 or more seabirds each year, including many New Zealand birds whose flight paths are not limited to New Zealand waters (Tennyson, 1990; Brothers, 1991; Close, 1994b).
Source: Department of Conservation (1994b)
New Zealand has no native ground-dwelling mammals. Our few native mammals either fly or swim. The early ancestors of the mammals had not reached New Zealand when it split off from Gondwana about 80 million years ago. Before the ocean gap had become too wide, however, some bats flew or blew here and evolved into endemic species. The only other mammals to discover New Zealand without the aid of boats were marine onesseals, sea lions, whales and dolphins.
Our native bats belong to two very different families. The comparatively normal long-tailed bat (Chalinolobus tuberculatus) is part of a worldwide family called the Vespertilionidae. It has close relatives in Australia. The short-tailed bat (Mystacina tuberculata) is so different from other bats that it belongs to a family of its own, the Mystacinidae, which exists only in New Zealand. The short-tailed bats are believed to have arrived here more than 35 million years ago, whereas long-tailed bats arrived about 3 million years ago.
In their isolation the short-tailed bats evolved some rather unbat-like ways. They rummage around on the ground for food, climb trees and have even been seen walking nimbly over boulders near the sea, wings tucked under forearms, hunting for insects and small marine invertebrates. They also eat fruit and nectar and are important pollinators of the threatened plant, Dactylanthus taylorii (Ecroyd, 1996).
Two species of short-tailed bat lived here but the larger of these was wiped out 30 years ago when rats invaded its last island refuge. The remaining species, the lesser short-tailed bat is listed as a 'high priority' threatened species. It is divided into northern, volcanic and southern subspecies, all of which are threatened. The long-tailed bat is also on the threatened list.
Several times in the evolution of the mammals, different species took to the sea. In one case, about 50 million years ago, a wading relative of today's pigs, hippos and cattle evolved into a large otter-like animal, which gave rise to the world's whales and dolphins - the cetaceans (Thewissen et al., 1994). Much later, between 20 and 25 million years ago, a population of wading bears also became otter-like and eventually evolved into today's seals and sea lions - the pinnipeds (Janis, 1994).
Some 34 species of cetaceans and 7 species of pinnipeds have been sighted in New Zealand waters, but only two are unique to New Zealand: Hector's dolphin (Cephalorhynchus hectori) and the New Zealand sea lion, also known as Hooker's sea lion (Phocarctos hookeri). The native New Zealand fur seal (Arctocephalus forsteri) is not endemic, being also found in southern Australia.
The massive elephant seals (Mirounga leonina), which live throughout the subantarctic region, were almost eliminated from New Zealand waters in previous centuries but re-colonised Campbell Island and the Antipodes Islands this century. Recently, however, unknown factors have drastically reduced elephant seal populations in parts of their range. The Campbell Island population has fallen by at least 95 percent and the Antipodes population is also small, having less than 100 pups.
The most commonly seen cetaceans in our waters are common dolphins (Delphinus delphis), dusky dolphins (Lagenorhynchus obscurus) and bottlenose dolphins (Tursiops truncatus). Several toothed whales are also common, such as long-finned pilot whales (Globicephala melaena), which normally live far out at sea but frequently strand on sloping beaches. Orcas, or killer whales ( Orcinusorca) and pygmy sperm whales (Kogia breviceps) are also common and occasionally strand on New Zealand beaches.
A diverse but little-known group called the beaked whales is known mostly from strandings (Dawson, 1985). Nine species have been reported from New Zealand waters and they occasionally strand in ones and twos on our beaches. They seem rare in coastal waters but may be more common in the deep ocean. One of them, Shepherd's beaked whale (Tamacetus shepherdi), is rarely seen anywhere in the world, with only 30 or so specimens having been reported, most of them from strandings on New Zealand beaches.
The large whales which were most common around New Zealand were the southern right whale (Eubalaena australis), the humpback whale (Megaptera novaeangliae) and the sperm whale (Physeter macrocephalus). Right whales fed in the Antarctic during the summer and came north to breed in the winter. They bred close to the coast and were sometimes so abundant in places that ships had to avoid running into them. Their curiosity often drew them to ships and their protective instincts often led them to stay there after one of their number had been harpooned. They were easy prey and became almost extinct by about 1850, though a small remnant population still breeds in New Zealand's subantarctic waters.
Groups of 50-100 right whales have been seen in aerial surveys around the Auckland Islands and Campbell Island during the winter breeding season. Boat surveys have found an estimated 96 right whales around the Auckland Islands with 9 cow/calf pairs. New Zealand scientists are now studying genetic samples from the whales to identify their relationship to other right whale stocks.
Like the right whales, humpback and sperm whales were never permanent residents in New Zealand waters, but regularly passed through on their migrations between the tropical winter breeding grounds and the Antarctic summer feeding grounds. Though heavily depleted by whaling, a small humpback population still migrates past our coast. New Zealand scientists are investigating the relationship between this population, which breeds around Tonga, New Caledonia and Niue, and the rapidly recovering East Australian population.
Sperm whales are globally the most abundant of the large whales. The International Whaling Commission puts the total number of sperm whales at between 500,000 and 1,250,000. Although this is less than the pre-whaling population, they were not as heavily depleted as the other large whales. The main reason is that their breeding females are half the size of the males and were hunted less heavily. Because sperm whale society is polygynous, with one male having exclusive access to many females, most of the hunting impact fell on the reproductively 'surplus' bachelor males. In the other large whales, however, breeding females are bigger than males and so bore the brunt of the hunting.
Migrating bachelor sperm whales regularly stock up on squid and fish, including orange roughy, in the deep ocean trench off Kaikoura. In recent years a thriving whale-watch tourist industry has developed around them. Up to 20 or 30 whales may visit at a time, with some lingering for weeks or months. Several appear to be residents and are reasonably tolerant of the attention from the whale-watch boats.
Other large whales, such as the giant blue (Balaenoptera musculus), fin (B. physalus) and sei (B. borealis) whales, frequent polar oceans during summer months and are only rarely seen in New Zealand waters, but their smaller relatives, the 12 m Bryde's whale (B. edeni) and the 8 m minke whale (B. acutorostrata) are more common.
Unlike the cetaceans, pinnipeds spend a significant amount of their time on land. Before people arrived in New Zealand, fur seal colonies existed all around the coastline, from Northland to Bluff, though the largest populations were probably in the cooler southern regions and subantarctic islands. New Zealand sea lions (Hooker's sea lions) and elephant seals were less abundant than the fur seals but had a similar distribution (Smith, 1989). They were easy prey for the Māori settlers and their descendants and became the main meat source in many areas (Davidson, 1984). By 1600, pinnipeds had been eliminated from the North Island (Smith, 1989; Anderson and McGlone, 1992).
By 1800, when the commercial sealers from Europe and America arrived, the fur and elephant seals and the sea lions had been eliminated from most of the South Island, too. Fur seal colonies survived only in the sparsely populated far south of the South Island. Sea lions had disappeared from the mainland, but still survived on Stewart Island. Elephant seals had gone completely (Smith, 1989). By 1820, the sealers had almost eradicated the remaining fur seals and sea lions and drastically depleted the large populations on the subantarctic islands (Taylor, 1982; Mattlin, 1987).
Whales and dolphins fared much better than the pinnipeds in the pre-European era. Māori hunting of whales appears to have been negligible. Stranded whales were eaten as they became available, but were rarely hunted as far as the archaeologists can tell. Dolphins, however, were hunted (Davidson, 1984; Smith, 1989). Harpoons have been recovered with dolphin remains in midden sites. Dolphins may also have been driven ashore or caught in large beach seine nets.
Apart from a few remains which have been identified as common dolphins (Delphinus delphis), most of the dolphin bones in Māori middens have not been identified at the species level. Some may belong to Hector's dolphin, which would have been relatively easy to catch and has more Māori names than any other cetacean. Today this dolphin is far more rare around the North Island than the South Island, but it is not known if this was always the case. Genetic analysis of bone samples may eventually shed light on this.
Whale hunting began with the arrival of American and European whalers in the late 1700s. Many coastal whaling stations were established and the remains of some are now historic places. Whales were hunted from these shore stations until the 1960s, though the greatest impact on whale numbers came from the visiting whaling fleets that killed vast numbers of whales in open waters. Each of the large species was devastated in turn, beginning with the right whales, then the blues, fins and humpbacks. The more resilient sperm whales were hunted throughout.
From the 1960s, the industry was dominated by Russian and Japanese factory fleets whose main prey were sei and minke whales, though it is now known that large quantities of other species were taken illegally or in larger quantities than reported (Yablokov, 1994; Baker and Palumbi, 1994). In 1986 the world regulatory body, the International Whaling Commission (IWC) imposed a moratorium on commercial whaling and, in 1994, created the Southern Ocean Whale Sanctuary as a permanent refuge, even if commercial whaling is resumed.
Today, only one nation commercially hunts whales. Norway kills about 300 minke whales each year in the north-east Atlantic (Motluk, 1995a; Abdulla, 1995). However, under IWC rules, 'scientific' whaling is still allowed, even within the Southern Ocean sanctuary. Japan is the only country which takes advantage of this, killing about 300 minke whales in the Antarctic each year. The meat from these frequently ends up in supermarkets rather than laboratories (Baker and Palumbi, 1994).
The whaling nations, some indigenous groups in the Arctic circle, and some pro-whaling lobby groups, continue to push for an expansion or resumption of whaling. However, most countries support the whaling moratorium and have opted for more benign forms of marine mammal commercialisation, such as whale-watching and dolphin-diving. This reflects the strong public sentiment in many of those countries that whales and dolphins are intelligent creatures deserving of special protection.
New Zealand's direct involvement in the whaling industry had dwindled by 1963 to just one shore-based station in the Marlborough Sounds. Following a sharp decline in the south-west Pacific population of humpbacks in 1960-61 the IWC banned the hunting of humpbacks in 1963. The station switched to sperm whaling but abandoned this in 1964 when the international price of sperm whale oil dropped from more than £90 per ton to about half that in one season.
With the closure of its last station, New Zealand withdrew from the IWC, but in 1976, in response to appeals from the public and the scientific community, the Government rejoined, this time to lobby for a global end to whaling. This was followed in 1978 by the passing of the Marine Mammal Protection Act, which banned the hunting and cruel treatment of marine mammals within New Zealand and its waters (with an allowance for accidental capture in fishing nets) and also banned the importation of whale products.
With hunting now largely removed, most cetacean populations appear to be recovering or, at least, holding their own, though many are still only a fraction of their former abundance (see Table 9.33). Whales in New Zealand waters now face few dangers other than becoming stranded on shallow beaches. Strandings are a problem for several deep water species (particularly pilot whales, beaked whales, and sometimes sperm whales) whose echolocation systems sometimes fail to detect gently sloping beaches. A whale rescue network is coordinated by the Department of Conservation. Each year about 200 callouts are attended and about 60 percent of the stranded whales (200-500 animals) are rescued (Department of Conservation, 1994d, 1995).
The main direct threat to fur seals and sea lions, and also some dolphins, is drowning in fishing nets, particularly the large trawl nets used in the hoki, southern blue whiting and squid fisheries (see Box 9.18 and Tables 9.33 and 9.34). Fur seal and sea lion deaths were first noted in the late 1970s and early 1980s by Government fishing observers who were placed on foreign trawlers. Since 1990, an average of almost 1,000 fur seals and nearly 70 sea lions are estimated to have been drowned each year in trawl nets.
The New Zealand sea lion was widely distributed before people arrived, though the population size is unknown. Bones found in Māori food middens reveal that sea lions once ranged the length of New Zealand right up to Houhora in the far North. They had been almost exterminated on the mainland by 1500. When European sealers arrived, only the Stewart Island Māori were still able to hunt sea lions. The commercial sealers put a quick end to that. Although their main targets were fur seals, they killed large numbers of sea lions as well, leaving only remnant populations on several sub-antarctic islands.
Today, the species is still limited to those islands. The most recent population estimate is 10,000-15,000 (Cawthorn, 1993). Roughly 80 percent of all pup births occur on Dundas Island, a remote and almost inaccessible member of the Auckland Islands group. Another 10 percent are born on Enderby Island. Surveys on Enderby and Figure of Eight Islands have shown little population change in several decades. A small rookery exists on Campbell Island, and, until recently, a few pups were born at the Snares Islands each year.
New Zealand sea lions are now commonly sighted at Stewart Island, the Catlins coast and Otago Peninsula. Very rare sightings have been made at Banks Peninsula, and even the Kaikoura and Nelson coasts, with one sighting as far north as Plimmerton, near Wellington (Cawthorn, 1993). The Department of Conservation has recorded an influx of two-year-old males on the Otago Coast over the past 2 years. The presence of 3 females and a recent instance of breeding near Dunedin have led to speculation that the species may be re-establishing itself on the mainland after centuries in exile (Peat, 1993; Department of Conservation, 1995).
Squid trawling in the Auckland Islands began in the late 1970s and is a major fishery involving up to 40-50 boats during the summer and autumn. This is also the season when the sea lions are breeding and foraging for food on the Auckland Islands shelf. Each year squid trawl nets drown an estimated 20-140 sea lions (see Table 9.34). Sea lion bycatch data has only been systematically recorded since 1988. Although fishing industry observers have also recorded sea lion kills since 1993, official estimates use only Government observer records. Between 1988 and 1996, the percentage of trawlers carrying Government observers varied between 8 percent and 29 percent. In the 1995-1996 season the observers witnessed 557 trawl net tows and 13 sea lion kills. This represented 2.3 kills per hundred tows.
The number of sea lions killed before 1988 is not known, though concerns were expressed in the late 1970s by Government scientists on a large German research trawler. As a result, a 'no fishing' zone was designated around the Auckland Islands in 1982, extending out to the territorial sea limit of 12 nautical miles (22 kilometres). The zone became a marine mammal sanctuary in April 1993 but has been criticised as being too small in area (Bellingham, 1993a).
In 1992, the Ministers of Conservation and of Fisheries set a maximum allowable kill of 63 sea lions (including no more than 32 females). Meanwhile, the fishing industry decided to review the fishing operation of any vessel catching 3 or more sea lions and to voluntarily withdraw any vessel catching 4 or more. One boat was reviewed in 1993 when a freak incident led to three sea lions being caught in a badly deployed scampi net. Generally, the small nets used by scampi trawlers are far less of a threat to sea lions than the squid trawlers' huge pelagic nets (which can be larger than a 25-storey office block, stretching up to 80 m from top to bottom). Shortly before the end of the 1995 and 1996 seasons, the few remaining squid trawlers voluntarily withdrew from the fishing grounds after the Ministry of Fisheries estimated that the allowable sea lion kill had been exceeded.
The New Zealand fur seal could just as easily have acquired an Australian name. Although it lives around the South Island, lower North Island and various subantarctic islands, it is also found along the coast of Tasmania and the southern Australian coast from Victoria to Albany. Though officially classified as a single species, recent genetic research by scientists at Wellington's Victoria University indicates that the fur seals may actually belong to two very divergent sub-species, one of which is much rarer than the other (Chambers et al., 1996).
The original fur seal population in the New Zealand region is unknown. When the first European sealers arrived 200 years ago, the seals had already been eliminated from most of New Zealand's coastline, but were still abundant on the subantarctic islands. One estimate, based on historical sealing records, puts their population at this time at about 1.25 million (Richards, 1994). By the time the sealers were through, several decades later, the population may have been no more than 10,000. Fur seals began to be protected by the law from 1875 when the killing season was restricted to a short period every year. From 1894 hunters needed a permit to kill seals, except for a 3-month period in 1913 when there was an open season for anyone. Since then no fur seals have been killed legally, except on Campbell Island in 1922 and 1924, and in southern New Zealand in 1946 (Melrose, 1973).
The Australian population was recently estimated at about 27,000 and increasing (Shaughnessy et al., 1994). In New Zealand, a planned national census of fur seals in 199596 was postponed by the Department of Conservation but is among the draft research suggestions put forward for 1997-98 by the Ministry of Fisheries' Nonfish Species and Fisheries Interactions Working Group (Baird, 1996).
Current population estimates for the New Zealand region are based on data collected in the early 1970s and summarised by Wilson (1981), who put the total population at 30,000-50,000. Studies since then have found marked population increases in Cook Strait, Nelson-Marlborough, Otago and on some subantarctic islands (Baird, 1995; Crawley, 1990; Dix, 1993; Lalas and Harcourt, 1995; R.H. Taylor, 1992; Taylor et al., 1995). These studies suggest that the total population, though still just a fraction of its former size, may now exceed 50,000. As the population expands, new colonies are forming, and, for the first time in four centuries, the lower North Island is being recolonised.
An average of nearly 1,000 fur seals a year have been drowned by trawl nets in recent years (see Table 9.35). Most of the reported deaths occur in the southern blue whiting fishery on the Bounty Platform, the hoki fisheries off the South Island's West Coast and Puysegur Point, and the southern squid fishery (Baird, 1994a, 1996). Fur seal drownings began to be officially monitored in 1986 by Government observers on a sample of West Coast hoki trawlers. About 60-70 boats trawl for hoki off the West Coast during the winter and early spring, from June to September. In 1992 monitoring was extended to a sample of trawlers in other fisheries throughout the Exclusive Economic Zone.
Between 1990 and 1992, the estimated probability of catching one or more fur seals in one tow of the trawl net fell from 5.6 percent to 2 percent (Mattlin, 1994a). In 1994, the Fishing Industry Board estimated the encounter rate to be about 2-3 percent. However, even though the catch rate per tow has fallen, the actual number of deaths depends on other factors as well, such as the total number of tows in a season and their proximity to seal feeding grounds. As a result, annual bycatch figures continue to fluctuate (see Table 9.35).
Based on preliminary observer reports, the total fur seal bycatch for the Exclusive Economic Zone in 1994 was higher than in previous years, with 202 reported kills, 60 of them by hoki trawlers and 97 by southern blue whiting trawlers. If the ratio of observed to estimated kills was anything like previous years, this suggests approximately 1,600 kills, plus or minus 300 (see Table 9.35b). At present, NIWA scientists are reassessing fur seal bycatch estimates for 1992-95.
Hector's dolphins are easily recognised in coastal waters by their paddle-shaped black dorsal fins. They are the world's smallest marine dolphins and live in small family groups of 2 to 12. They are found only in New Zealand waters and generally stay within 5 km of the coastline (Dawson and Slooten, 1994, 1996). Their population size and distribution before human settlement in New Zealand are unknown.
These days most Hector's dolphins occur around the South Island and their total population has been estimated at 3,000-4,000, making them one of the world's rarest dolphins (Dawson and Slooten, 1988). As yet unpublished research at Auckland University suggests that the population consists of two genetically distinct sub-populations, one on the east coast and one on the west coast, which have no contact with each other.
Modern pressures on Hector's dolphins include entanglement in fishing nets and pollution from river mouths and harbours. Between 1984 and 1988, setnets, or gill nets, removed 130-230 dolphins from the Banks Peninsula population of about 600 (Dawson, 1991). These deaths were additional to those resulting from other causes. Fears for the impact on the Banks Peninsula population led to the area being made a marine mammal sanctuary with a restriction on the use of gill nets (Dawson and Slooten, 1993).
Because they are at the top of the marine food chain and feed near river mouths, Hector's dolphins are also at risk from anything which may reduce the quantity or quality of their food supply, such as excessive inshore fishing, sediment washing down from rivers, or the accumulation of toxic chemicals in fish. Dead Hector's dolphins which occasionally wash up on beaches or are drowned in setnets have had their blubber analysed for chemical residues. Although persistent organochlorines have been found, such as polychlorinated biphenyls (PCBs) and DDT residues, the concentrations are much lower than in Northern Hemisphere dolphins (Buckland et al. , 1990; Department of Conservation, 1992a; Jones, 1995).
PCB levels in Hector's dolphins are higher than in other cetaceans that live further from the coast (e.g. common dolphins, dusky dolphins, beaked whales) but are still below 5 parts per million (ppm). This compares to PCB concentrations of 37-80 ppm in US dolphins and 55 ppm in British harbour porpoises (Jones, 1995). Overseas research has linked high concentrations of organochlorines to reproductive abnormalities and immune deficiencies in a number of species, though the interpretation of such data is still controversial (Addison, 1989; Motluk, 1995b; Stone, 1994a, 1994b, 1995a; Sharpe, 1995; Tanabe, 1994). Even more controversial are claims that low organochlorine concentrations can interfere with reproduction and immunity through prolonged exposure or through a combined 'cocktail' effect (Colburn et al., 1996; Wilkinson and Dawson, 1996).
Because no data were collected on New Zealand dolphin populations or their chemical residues during the years of high organochlorine use (1950-1980) it is not known whether Hector's dolphins were adversely affected during this period. It is likely that they had higher concentrations of organochlorine residues than are found in today's dolphins, but the effects on their population, if any, remain unknown.
Other dolphin species in New Zealand waters have even lower concentrations of organochlorines than the Hector's dolphins and their populations seem large enough to cope with the limited bycatch pressure from setnets and trawlers. Probably the largest dolphin bycatch is associated with jack mackerel trawlers in the Taranaki Bight (see Table 9.36). Most of the victims are common and bottlenose dolphins. More than 90 percent of the drownings occur during night trawls.
The fishing industry has developed a code of practice for trawlers catching jack mackerel in this Quota Management Area (JMA 7). The relatively small number of dolphins caught and the lack of a controlled comparison makes it difficult to draw any conclusions about the effectiveness of the code of practice (Baird, 1996). During the 1994-95 season, after several bycatch incidents with dolphins, the jack mackerel trawlers were voluntarily withdrawn from the Taranaki Bight and their operations reviewed.