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State of NZ's Environment 1997

Opening Section

1: Introduction

2: The Place and the People

3: Production and Consumption Patterns

4: Environmental Management

5: The State of Our Atmosphere

6: The State of Our Air

7: The State of Our Waters

8: The State of Our Land

9: The State of Our Biodiversity

10: Conclusions on the State of New Zealand's Environment

The State of Our Fish

Fish are the most ancient of the five vertebrate classes. Their (and our) ancestors, the earliest vertebrates, were tiny eel-like animals called conodonts which first introduced teeth and backbones to the world during the Cambrian Explosion 520 million years ago (Janvier, 1995; New Scientist, 1995; Palmer, 1995c). Conodonts gave rise to the first true fish about 485 million years ago and these subsequently diversified into so many species that the Devonian period, from 355 to 410 million years ago, is referred to as 'the age of fishes' (Dayton, 1993).

Today, fish are by far the most diverse vertebrates on Earth with at least 20,000 species worldwide. They are also the most heavily harvested wild animals on Earth. According to the UN Food and Agriculture Organisation, 70 percent of the world's fish stocks are now 'either fully-exploited, over-fished, depleted, or are rebuilding from previous over-fishing' (FAO, 1995; Hagler, 1995; Pearce, 1995a).

Global fish and shellfish catches peaked six years ago, averaging 98 million tonnes per year through 1989-91 (plus about 27 million tonnes of discarded bycatch and about 13 million tonnes of farmed fish and shellfish). By 1993, the global catch had declined to just under 86 million tonnes, with marine yields falling by 6 percent to 78.8 million tonnes and freshwater yields falling by 52 percent to 6.9 million tonnes (Alverson et al., 1994; FAO, 1995; Welcomme, 1995). Most of the decline in marine catches occurred in northern oceans.

New Zealand's annual marine catch peaked in 1992 at more than 650,000 tonnes, made up of more than 530,000 tonnes of fish and nearly 120,000 tonnes of invertebrates, principally squid. This excludes discards, illegal catches, recreational catches and catches for customary Māori food-gathering. The year before, the total marine catch had been 608,000 tonnes and, the year after, it fell to 590,000 tonnes. Marine fish make up 99.8 percent of the total catch because we have only a small number of freshwater fish species. Apart from freshwater eels and farmed salmon, oysters and mussels, New Zealand's fisheries are almost totally based on wild populations of marine species.

Besides the commercial fish catch, a large number of inshore fish and shellfish are taken by non-commercial fishers and gatherers. About 390,000 people (16 percent of the population) engage in recreational sea fishing (Teirney and Kilner, 1995). An unknown number catch freshwater fish, both native fish fry (whitebait) and introduced trout and salmon. A smaller but unknown number of Māori engage in customary or cultural harvesting of fish, crustaceans and shellfish for household consumption and social gatherings.

Freshwater fish

New Zealand has 29 identified species of native freshwater fish. One of these, the grayling, became extinct earlier this century, and 10 of the remaining species are considered threatened. However, new species are still being identified (e.g. Mitchell, 1995). The number of identified species is expected to rise in the near future as a result of recent genetic research. Geneticists have found that some fish currently classified as sub-populations of a single species are really genetically distinct species that happen to look alike. As more 'new' species are discovered, or uncovered, the final species count could reach 35 or 36, and the threatened species count may, accordingly, rise to 15 or 16.

Although the total number of native fish is low compared to other countries, nearly 90 percent are endemic. Their Gondwana origins are obvious from the fact that most have close relatives at the genus or family level in other Gondwana countries, notably south-eastern Australia (McDowall, 1990). This is best reflected in the distribution of our most diverse genus, the galaxiids (Galaxias spp.) which are found not only in New South Wales, Victoria and Tasmania, but also throughout southern South America and even the southern tip of South Africa.

About 20 alien species of freshwater fish have been introduced since European settlement. They include trout, salmon, koi carp, catfish, tench, rudd and perch. Another six marine species often stray into New Zealand rivers from the sea (McDowall, 1990). In all, this brings the number of fish species that either inhabit or visit New Zealand's rivers and streams to between 55 and 60.

Generally, New Zealand's indigenous fish are small, well-camouflaged, bottom-dwellers (Richardson and Jowett, 1994). Only 4 species (the 2 eels, the giant kokopu, and the extinct grayling) exceed 2 kg in body weight (McDowall, 1980). Although they are freshwater dwellers most of the time, many species have a marine stage in their life-cycles. This peculiarity may be related to New Zealand's long period of inundation during the Oligocene drowning.

One of the most distinctive of the sea-going freshwater fish is the torrentfish (Cheimarrichthys fosteri) - the 'black sheep' of a sea-dwelling family called the Mugiloididae. Other species in this family are exclusively marine dwelling, living in the oceans around Africa, Asia and various parts of the Pacific (McDowall, 1990). The wayward torrentfish, however, evolved into a freshwater species whose only acknowledgment of its oceanic heritage is a brief sea visit soon after hatching. Details are still sketchy, but it is believed that the torrentfish larvae are swept downstream to the sea where they develop into fry before returning to fresh water. On their way home, the maturing fry undergo an important rite of passage when they enter the river estuary. Vital developmental changes take place to equip them for freshwater life, including alterations to their body shape, colour, eating and escape behaviour and internal fluid regulating mechanisms (Glovaet al., 1995).

Though closely related to blue cod, torrentfish are much smaller, growing to about 10-12 cm. They live in open-bedded rivers and streams, using their large ventral fins, like hands and feet, to anchor themselves to the river or stream bed. Their pointed, flattened heads cut easily through fast-flowing water. Though rarely seen, the torrentfish is one of our more common species. Others have fared less well.

Today, a third of our native fish are threatened and several others are rare. A recent survey of the larger rivers found 16 native species and 3 introduced species (Richardson and Jowett, 1994). Only 8 native species were described as common. They included eels, torrentfish, various bully species and the common river galaxiids. Eels alone accounted for two-thirds of the biomass. The most abundant introduced species was the brown trout.

The National Institute of Water and Atmospheric Research (NIWA) maintains a freshwater fish database which now has about 13,000 records of fish sightings from all over the country (Richardson, 1993). The database gives some idea of the relative abundance of fish species. Whereas longfinned eels have been found at 48 percent of sites, the five migratory galaxiids are far less abundant. Inanga have been found at only 15 percent of sites, koaro at 10 percent, the banded kokopu at 8 percent, the giant kokopu at 4 percent and the short-jawed kokopu at a mere 2 percent of sites. All but the inanga were limited to heavily forested catchments.

The threats to our native fish come from introduced species and from human activities that have removed or altered their habitats. These activities include: forest clearance, pastoral farming, effluent discharge, nutrient pollution, water abstraction, barriers to migration, channels and drains and changes to river courses and banks, and possibly even whitebaiting.

No fish are known to have become extinct in the five or six centuries of Māori exploitation that preceded European settlement. For inland tribes in particular, freshwater fish were very important. Efforts were made to conserve and sometimes enhance fish stocks (McDowall, 1990). Eels, smelt, koaro and possibly bullies and banded kokopu were actively transferred to land-locked lakes to boost fish stocks (Strickland, 1993). One chief even tried to introduce 70 snapper to Lake Rotorua. A team of slaves carried the fish in a huge patua (a watertight vessel made of totara bark). A hundred more slaves were stationed along the way to replenish the saltwater from calabashes. Only one snapper survived the journey but died as soon as it was put in the lake (Mair, 1923).

Today, exotic species have displaced or become important predators of some of our native fish. The most widespread exotic intruders are brown and rainbow trout (Salmo trutta and Oncorhynchus mykiss) which were introduced, along with the closely related salmon (Salmo andOncorhynchus spp.), as sports fish and are still protected as such. Their introduction had a serious impact (see Box 9.9). As an example of the pre-trout abundance of native fish, Buck/Hiroa (1921) described a feast at Lake Ohinemutu in 1873 where the guests dined on 4,000 baskets of dried koura (freshwater crayfish) and inanga (a name then applied to several different galaxiid species). Such abundance apparently declined after trout entered the lake.

Māori tribes petitioned government on several occasions to stop further introductions of exotic fish, but without success (Strickland, 1993). However, not all fish introductions were unwelcome. Goldfish (Carassius auratus), which multiplied rapidly in some parts of the central North Island lakes, became a popular food fish with local Māori who protested when the Government temporarily prohibited the taking of goldfish in the early 1900s (McDowall, 1990).

A significant conservation problem continues to be the unauthorised liberation of fish. Current law requires, among other things, an environmental impact assessment before fish can be released or transferred. The requirement applies to both native and introduced species. Furthermore, some introduced species are designated as noxious and must be killed if caught. The noxious fish regulations were introduced in the 1970s after the deliberate release of exotic fish by irresponsible anglers (or 'biological hooligans' according to one commentator) who were trying to re-create an English-style 'coarse' fishery here (McDowall, 1990). Coarse fish are those with large scales compared to trout and salmon. Their release began in the upper North Island in the late 1960s with rudd. Then came tench and perch and, most recently, European carp and orfe. In the early 1970s, there were also misguided moves to introduce several smaller exotic species, such as European dace, minnow, roach and gudgeon as forage fish for trout.

The distribution of noxious coarse fish has gradually became more widespread. All are threats, not only to native fish and stream ecology, but also, in some cases, the waterways themselves. None is a greater problem in this regard than the European carp ( Cyprinus carpio) which is now well-established in the upper half of the North Island, particularly the Waikato catchment, despite firm Government policy to contain its spread. This fish is a native of Europe, the Mediterranean and western Asia but has become widespread throughout Asia where it is a popular aquaculture species bred for food and ornamental purposes. The brightly coloured variety living in New Zealand was developed by Japanese fish-breeders who refer to it as koi. European carp are closely related to goldfish and can hybridise with them. They are mud-feeders, which can undermine stream banks, turn clear waters muddy brown and cause significant damage to aquatic ecosystems. Controlling them is a priority for the Department of Conservation.

Other designated noxious fish which could cause damage if released here include three species of the ferocious and much feared South American piranha (Serrasalmus spp.), and the predatory walking catfish (Clarias batrachus), an African species which has been troublesome in Florida and is popular with anglers and fish fanciers. At present, the only known piranha in New Zealand are in captivity at the Napier Aquarium and Kelly Tarlton's Underwater World in Auckland. The only catfish species to have become established in the wild here is the North American brown bullhead (Ictalurus nebulosus). It is becoming more abundant in the lower Waikato and Lake Mahinapua, where it is accused by fishers of competing with the eel population (McDowall, 1990). Though not designated as noxious, it is considered to be a nuisance species. Another nuisance species is the mosquitofish ( Gambusia affinus), which preys on insect larvae.

Introduced plants have also had an impact on our native fish, altering their habitat and food distribution. At least 200 introduced wetland plants have been identified. In addition, nutrient pollution from run-off and waste discharges have caused algae and cyanobacteria to proliferate on stony river bottoms changing the invertebrate communities on which fish feed. Pressures on native fish have probably been mildest in north-west Nelson, Westland, Fiordland, and Stewart Island, where large river systems are still surrounded by unmodified catchments. Even there, however, most riverine plant and animal communities contain introduced species.

So far, only one native fish, the grayling (Prototroctes oxyrhynchus) has been exterminated by these pressures. It was abundant when Europeans first arrived, and died out in the 1930s. Forest clearance and pasture development probably contributed to its sudden decline, with trout giving it the final nudge (McDowall, 1990). Of the remaining 28 species, 10 (36 percent) are listed as threatened (see Table 9.18). Top of the list is the short-jawed kokopu (Galaxias postvectis), the only Category A fish on the Department of Conservation's threatened species list. Not much is known about this fish. It has been found at a small number of locations from Northland to Fiordland, suggesting a wide distribution in earlier times. Sightings have usually been made in smallish streams surrounded by unmodified broadleaf/podocarp forest, and in pools with very thick vegetation cover.

The brown mudfish (Neochanna apoda) and the Canterbury mudfish (Neochanna burrowsius) are also high on the threatened species list, but, fortunately, not as high as they were just a few years ago. Listed in 1992 as Category A species, the mudfish have now been downlisted to Category B, thanks largely to progress with habitat protection (Department of Conservation, 1994b). The mudfish are 10-15 cm in length and appear to be relic populations from former swampy wetlands and wet riverbanks. As the wetlands disappeared and the riparian tree cover was removed, the mudfish were relegated to weedy drains, irrigation ditches and shallow muddy creeks. They spawn in mud and, if this dries, the newly hatched mudfish wriggle down into the soil in search of moisture. They have sometimes been found more than a metre underground, to the amazement of early settlers.

Most of the other threatened fish are, like the short-jawed kokopu, galaxiids. Adult galaxiids are rarely seen, but the juveniles are familiar to most New Zealanders as whitebait - once readily available in fish shops, but these days an increasingly rare and expensive treat. Whitebait are caught in river mouths each Spring, as the teeming shoals of fry enter freshwater from the sea. Inanga (Galaxias maculatus) juveniles make up most of the highly prized catch, but on the West Coast of the South Island, up to 5 species are involved, including the koaro, the short-jawed kokopu and the giant kokopu. In the whitebait stage, koaro and short-jawed kokopu are difficult to distinguish from the other species, but the giant kokopu is more recognisable. Smelt fry may also occur in the whitebait catch.

As its name suggests, the giant kokopu (Galaxias argenteus) is larger than other galaxiids, with adults growing to half a metre in length. Loss of preferred habitat, nutrient pollution and competition with trout are some of the factors believed to have contributed to the decline in giant kokopu numbers. In 1994, the Government considered introducing regulations to reduce the whitebaiting pressure on the giant kokopu. Because the juveniles enter West Coast rivers in November, a little later than other whitebait, the regulations would have brought the 6 week season forward so that it ended on 31 October instead of 14 November. However, following submissions from West Coast whitebaiters on the timing of the juvenile giant kokopus' return to the rivers, the regulations were not introduced.

Until recently, the most resilient of the native fish were the eels. New Zealand has two native species. The larger of these, the longfinned eel (Anguilla dieffenbachii), is endemic, while the smaller shortfinned eel (Anguilla australis) is also found in South Australia, Tasmania and New Caledonia. Although longfin and shortfin habitats overlap, longfins predominate in stony rivers and high country lakes, while shortfins are more abundant closer to the coast in the lowland lakes (e.g. Ellesmere or Waihora) and muddy rivers.

Average eel life-spans are almost the same as the pre-industrial human life-span - in the 20-40 year range - and, as with humans, very old individuals have been recorded. Female eels are longer-lived and bigger than the males, with the oldest on record being a 60-year-old shortfin and a 106-year-old longfin. They breed only once and leave New Zealand to do it. Their spawning grounds appear to be several thousand miles away, in the tropical waters to the north of Fiji and Western Samoa (Castle, 1995).

After spawning, the parent eels never return, but their tiny young elvers drift back on the ocean currents that sweep in an arc through the western Pacific, past New Caledonia and Australia and on to New Zealand. Once in our waters, the elvers randomly enter rivers as they encounter them. Recently the Australian longfinned eel (Anguilla reinhardtii) has been discovered here, presumably because its elvers were swept down on the same currents and missed their usual stop. Our native shortfin probably arrived here in a similar way thousands of years ago.

Though still abundant, eel biomass has fallen in some areas, particularly Lake Ellesmere and the lower Waikato River, as a result of habitat decline (i.e. pollution, wetland drainage) and human predation (i.e. commercial fishing). Eels are the only commercially significant native freshwater fish. Although they have always been harvested for food by Māori communities, commercial harvesting for export markets by Europeans only began in the late 1960s.

The estimated annual catch peaked in the 1970s, exceeding 2,000 tonnes several times. Since the early 1980s, the catch has settled to an average of just under 1,400 tonnes (see Figure 9.4). Concerns about declining biomass in Lake Ellesmere (Waihora) led to it being declared a controlled fishery in 1978. The number of eel fishers was cut from 30 to 17, and the total allowable catch (TAC) quota was set at 256 tonnes. In following years, both the fishers and TAC quota were progressively reduced to the current 136.5 tonnes distributed among 11 fishers.

Consideration is being given to bringing all eel fishing under the Quota Management System. Regulation at present is through restrictions on entry, gear limitations and a minimum size limit on eels caught. Amateur fishers are restricted to six eels a day, regardless of size. For commercial fishers, a new national minimum size of 220 g took effect in April 1993, replacing the previous 150 g size limit. However, the minimum size for eels in Lake Ellesmere was set at 140 g, reflecting the extent to which the lake's large old eels have been reduced. The Lake Ellesmere limit will be incrementally raised each year to bring it into line with the national size limit.

Ironically, the minimum legal size limit is probably threatening the sustainability of the eel stocks rather than helping them. It offers total protection to shortfinned males, which normally migrate when they weigh between 140 and 160 g, and has redirected the fishing effort onto the rarer longfins and the female shortfins. To counter this, a maximum legal size of 4 kg now covers the whole of the South Island. This was introduced to offer some protection for the larger longfin females, which are at the greatest risk because they remain in the river systems the longest.

One obstacle to successful eel quota management is the lack of good data. Eel stock size and levels of exploitation cannot be assessed accurately for several reasons: stocks are replenished from the ocean rather than from resident populations; commercial catch data are of poor quality; and non-commercial catch data are nonexistent.

Besides fishing, eels, like other native fish, are affected by environmental pressures, such as pollution, loss of overhanging vegetation, river straightening, lake lowering and wetland drainage. Another source of pressure is the increasing number of river obstructions impeding their migrations. With more than 400 dams of 1.8 m or more in height and thousands of smaller dams and weirs, returning elvers now run a formidable obstacle course. The Electricity Corporation (ECNZ) has assisted with feasibility studies on installing passes for incoming elvers in the Waikato, Waitaki, Clutha, and Waiau rivers.

Sometimes, Government, industry and iwi have cooperated to physically transfer elvers to headwaters, lakes or farm dams. This can involve up to a dozen people working over several consecutive nights with boats, buses, tankers and collectors. When eels are transferred to landlocked waterways they are effectively taken from the ocean-going breeding population so a special permit from the Ministry of Fisheries is needed for transfers, even small ones. Freshwater fishing regulations now prohibit the taking of more than six eels (of any size) per person per day. Technically this applies to elvers, 1,000 of which weigh less than a kilogram.

Marine fish

More than 1,000 species of fish have been identified within 200 nautical miles (320 km) of our coast - our Exclusive Economic Zone (EEZ) (Paulin et al., 1989). A further 200 or so have yet to be formally identified. Each fortnight another unidentified species is added to the list. About 110 marine fish (11 percent) are endemic to New Zealand waters, but less than half of these live in the open sea. Most of them (61) are confined to coastal rockpools where 62 percent of species are endemic. The most diverse rockpool species are the triplefins (or cockabullies) with their distinctive line of three fins on the back. New Zealand's rockpools have 21 species, accounting for a third of the world's known triplefins and making our region a biodiversity 'hotspot' for cockabullies (Paulin and Roberts, 1993; Roberts, 1994).

Although little is known of the status of most marine fish in the EEZ, an assessment has been made of the rockpool fishes. Eleven are listed as threatened, all of them endemic (Paulin and Roberts, 1994). None are endangered, but they are rare and vulnerable to habitat disturbance (see Table 9.18). The threatened species represent 12 percent of all rockpool fish and 18 percent of the endemic ones. Away from the coastline, only two of the sea-dwelling fish species are known to be threatened and neither is endemic. The great white shark (Carchardon carcharias) and the basking shark (Cetorhinus maximus) are threatened in all oceans (Department of Conservation, 1994e; IUCN, 1990).

Only 5 percent of the marine fish living beyond the rockpools are endemic (50 out of about 1,100 species). Most, nearly 60 percent, are found throughout the world and a further 30 percent are found elsewhere in the Southern Hemisphere. Many arrived here by a gradual process of migration and expansion over long periods of time, while others are recent or intermittent arrivals. Orange roughy, for example, have probably been here for a long time. They are also found as far away as the North Atlantic, where they were first discovered. Peruvian jack mackerels, however, are recent immigrants. They were first noted in 1987 and now are caught far more frequently than the two endemic jack mackerels. Tuna are migratory visitors which come and go every year, covering vast areas of ocean. In many cases, 'foreign' fish arrive as stragglers which remain rare in our waters but abundant elsewhere.

Most fishing in New Zealand is confined to places where the water is less than 1 km deep. Such areas cover approximately a third of the EEZ. Scientists and fishing companies are continually exploring these waters to find new stocks and new species which may be exploitable. Trawl surveys have found more fish species in the north than in the south and more species in deep rather than shallow water. The areas of greatest species diversity are concentrated along the margins of the Chatham Rise and are associated with the subtropical convergence of cold and warm waters (McClatchie, 1995).

Two-thirds of our fishing zone is considered commercially barren, consisting of deep low-nutrient waters which plunge more than a kilometre down. Though many species live in the deep water, few are considered fishable at present, with the significant exception of orange roughy. Few surveys have been done to identify species living at depths greater than 1.5 km, which is roughly the lower limit of the orange roughy trawl. In some areas, such as the subduction zone of the Kermadec Trench, the water is more than 10 km deep and its inhabitants are unknown.

A little over 100 marine fish species are harvested commercially - 10 percent of our known fish species. Stock assessments are made on the 42 species harvested for Maximum Sustainable Yield (MSY) under the Quota Management System (QMS). Stock assessments are also made on species such as Southern Blue Whiting, which are fished commercially, although they are not part of the QMS. Provision exists for a further 117 species to be brought into the system.

The QMS species are not all assessed separately. Some are lumped together into groups (such as the jack mackerels, the oreos, and the flatfish) bringing the number of assessed fish 'species' down to 30. These are subdivided into 179 stocks (150 if the little-fished Kermadec area is excluded). Large amounts of data on many other species have been collected in trawl surveys. The information is stored in huge databases, but has not been analysed because a limited number of fishery scientists are available to do the work. As a result, low priority species and those which are only lightly harvested are not assessed.

Migratory species, such as tuna and billfish, are also fished commercially, but they are not covered by the Quota Management System. Because they range so widely across the world's oceans, these fish are caught in many different waters and need to be managed under an international system, rather than by different sets of national regulations. So far, the only such system in operation is the Convention for the Conservation of Southern Bluefin Tuna (CCSBT). Under this trilateral agreement between New Zealand, Australia, and Japan, separate southern bluefin quotas are set for each nation (see Table 9.23). Management regimes for other migratory species have recently been the subject of a United Nations-brokered agreement on the management of straddling stocks.

Because fish stocks are wild populations living in inaccessible environments, population data and models are often uncertain or inadequate. This is particularly true for species living in areas not suited to trawling. Data for these species are sparse and often limited to commercial catch/effort data. However, in areas that are more suited to trawling, good quality data are collected from regular trawl surveys by NIWA's fishery research vessels. This information, along with data derived from the commercial fishery, is used to make assessments on 74 of the 161 QMS stocks. Sufficient data are also available to assess many non-quota stocks, but resource constraints have prevented this to date.

Many of the stocks whose status is unknown are either unexploited or only lightly exploited and are assumed to be in the fishing-down phase or fluctuating within natural limits. What is unknown, however, is whether those natural limits are changing in response to fishing activities and other environmental disturbances. Commercial fishing can alter predator-prey relationships and habitat quality through such practices as: significantly reducing the biomass of prey or predator species; dumping waste; stirring up sediment clouds; and killing non-target species of fish, marine invertebrates, seaweeds, seabirds and marine mammals through bycatch, bottom trawling or dredging.

There is often a noticeable decline in the invertebrate animals brought up by trawls when new deep-water fishing grounds are exploited. Because no records are kept, the extent of these effects has not been quantified and their possible contribution to fishery declines has generally been ignored in fisheries management literature. Some marine biologists believe there is an urgent need to carry out trawling impact studies in water deeper than 500 m because this is where the effects could be severe with flow-on impacts on the fisheries themselves (Jones, 1992).

Non-commercial fishing can also be a source of pressure on commercial species, such as snapper and blue cod, and non-commercial species, such as red moki. As much as a third of the annual snapper catch is taken by recreational fishers. Set-netting and spear-fishing have forced some stocks of reef-dwelling red moki (Cheilodactylus spectablis) into a decline. On some Northland reefs, stocks have been almost wiped out. Because they are long-lived (60 years) and slow-growing, their recovery is likely to be slow.

Of the 74 QMS fish stocks which have been scientifically assessed, most are thought to be near or above the level of Maximum Sustainable Yield (MSY) and still in the fishing-down phase (e.g. all stocks of hoki). Among those thought to be at or near the MSY level are most stocks of barracouta, blue moki, blue warehou and groper. Other species with at least some stocks above, at or near, the MSY level are alfonsino, blue cod, bluenose, hake, jack mackerels, ling, orange roughy, red gurnard, southern blue whiting, stargazer, tarakihi and trevally.

Two QMS species (blue moki and elephantfish) have stocks which are believed to be recovering from previous over-fishing and may be below the MSY level. Several other species (gemfish, grey mullet, rig) have one or more stocks whose catches are declining or are well below the allowable quotas. It is unclear whether the low catches are caused by economic or biological factors. Two species (smooth oreo and snapper) have one or more stocks which may be at risk of depletion given 1995 catch rates. Overall, only 7 of the 74 assessed fish stocks (10 percent) are considered to be below the MSY level. Four of these are orange roughy and 3 are snapper (see Table 9.23).

Snapper

Snapper (Pagrus auratus) are the dominant inshore species in the warmer waters around the North Island and the top of the South Island. Although several species occur in temperate and tropical coastal waters in all oceans, only one is known in New Zealand. They eat invertebrates, squid and small fish at, or near, the sea bottom and rarely go deeper than 200 m. They are most abundant above 60 m. Unlike orange roughy, they were already depleted before they came under the QMS. However, they do share some traits with their deeper-water cousins. They are long-lived (up to 60 years), have low natural rates of birth and death and, like roughy, their flesh commands high prices, particularly in Japan.

Snapper have been caught commercially for many years, and the fishery is one of the largest and most valuable coastal fisheries in New Zealand. It is also one of the largest recreational fisheries. Recent surveys indicate that up to one-third of all snapper caught are taken by amateurs (Teirney and Kilner, 1995). Snapper are also part of the bycatch taken by the tarakihi, gurnard and other inshore fisheries. The customary Māori catch is unknown.

Three of the four snapper stocks (SNA1, SNA7 and SNA8) have been reduced below the MSY level (see Table 9.22). These stocks surround the top and west coast of the North Island. The fourth stock (SNA2) extends along the east coast of the North Island from Gisborne to Wellington. Its status is unknown, but its TACC has constantly been exceeded since 1987-88 because of bycatch losses to the tarakihi and red gurnard fisheries.

The largest snapper stock (SNA1) consists of two separate populations, both of which have been heavily reduced. The east Northland population is now close to the MSY level, while the Hauraki/Bay of Plenty population is well below it (see Figure 9.6). In 1995, scientists predicted that, at prevailing catch rates, both sub-stocks would decline further over the next five years (Annala, 1995b). The Fisheries Minister responded to this new information by announcing quota reductions for SNA1 (Minister of Fisheries, 1995). A year earlier, the Minister had accepted proposals by the Recreational Fishing Council to reduce the take of juvenile snapper in SNA1 through measures other than quota reductions. These had included an increase in the minimum legal size from 25 cm to 27 cm for recreational fishers and a cut in the daily bag limit from 20 fish to 15.

Based on the new evidence, however, the estimated recreational catch was reduced to 2,300 tonnes by lowering the daily bag limit from 15 fish to 9. The commercial quota was reduced from almost 5,000 tonnes to 3,000, and an allowance was made for a Māori customary take of 300 tonnes. Additional measures, to reduce snapper bycatch, included a year-round minimum net mesh size of 12.5 cm in shallow waters and a six-month closed season to commercial fishing in the inner Hauraki Gulf. No changes were made to management controls for the other snapper stocks. Catch levels for the other depleted stocks (SNA7 and SNA8) were considered to be sustainable and at levels that would allow them to rebuild to the MSY level. A year after these measures were implemented, the catch limits for Hauraki snapper had to be reduced yet again.

Orange roughy

Orange roughy (Hoplostethus atlanticus) has been heavily fished since 1982. It is one of five roughy species found in our waters and is by far the most valuable. The first known New Zealand specimen was netted at the bottom of Cook Strait by scientists in 1957, but it was not properly identified until 1979. Adults range between a third and half a metre in length, and are highly valued. Although they make up less than 5 percent of the total marine catch by weight, orange roughy account for nearly 17 percent of the fishing industry's income - about $200 million.

Living at depths of 700 m to at least 1,500 m, the orange roughy's life is still somewhat mysterious. From gut contents, it is known to eat squid, crustaceans and other fish. It is also known to be eaten by larger species, such as sperm whales. Those that avoid being eaten are long-lived. Individuals can survive for up to 120-130 years and many which end up in fish fillets are far older than the people consuming them. They also have one of the longest childhoods of any species, not reaching sexual maturity until they are about 33 years old. By fish standards, they produce relatively few eggs each spawning season (40,000-50,000). The eggs are large and drift upward. Those not eaten by predators hatch after 10 days and begin the slow process of growing up in the ocean depths.

In just 15 years, from 1978 to 1993, the total biomass of known orange roughy stocks was reduced to an estimated 15-30 percent of its original size. The decline was greater for some stocks than for others, depending on their initial size and the intensity of the fishing. Some stocks live as isolated populations on underwater plateaus or in deep-sea canyons and valleys, while others are spread over wide areas. It is now clear that the actual stocks do not always correspond to the fishery stocks for which TACCs have been set in the past. At present eight stocks are recognised, four of which are below the MSY level.

The four depleted stocks are around the west, south and lower east of the South Island. They are: the Challenger Plateau stock (ORH7A); the West Coast stock (ORH7B); the Puysegur stock (ORH3B Puysegur); and the Chatham Rise stock (ORH3B Chatham). A fifth southern 'stock' (ORH3B Other) consists of separate populations which may be one stock and which are too poorly known to make an assessment (Annala, 1995a).

The two stocks still above the MSY level and being fished-down are the Northern stock (ORH1) to the north and west of the North Island, and the East Cape stock to the north of Gisborne (ORH2A North) (Annala, 1995a).

The only stock which is currently at the MSY level is the 'East Coast' stock extending from Cape Runaway in the North Island down to Banks Peninsula in the South Island. It was originally classified as three separate stocks (ORH2A, ORH2B and ORH3A) but is now assessed as a single stock. Since 1986, catches and quotas for this stock had averaged almost 10,000 tonnes. Following scientific advice, the TACC was reduced to 6,660 tonnes in 1994 and then 2,100 tonnes in 1995, barely a fifth of its original level (Annala, 1995a; Minister of Fisheries, 1995).

Because of its extremely slow growth, very high economic value and ecological remoteness, orange roughy has been a difficult test case for the Quota Management System, embodying some of the biological and economic extremes that make quota decisions difficult for scientists and politicians. The entire history of the fishery represents less than a fifth of one fish's lifespan. So far the QMS has not emerged with flying colours. The four depleted stocks were all driven below the MSY level under the QMS regime. The challenge now is to achieve stock recoveries while avoiding the same mistakes with the remaining stocks.

Recent quotas reflect this goal. Although the two 'new' northern stocks have had their quotas increased, all other stocks have had substantial quota decreases. The overall orange roughy TACC for 1995-96 was just over 21,000 tonnes, one third of its peak in 198889 when it exceeded 62,000 tonnes. However, stock sustainability is only part of the challenge facing the orange roughy fishery in this era of ecological sustainability. Trawler impacts on deep-sea ecosystems, such as seamounts and coral communities, also need to be assessed and addressed before it can be considered to be truly sustainable (Jones, 1992; Fisher, 1995; Probert, 1996; Probertet al., in press; Raloff, 1996).

Hoki

In contrast to snapper and orange roughy, hoki (Macruronus novaezelandiae), which is fished as a single widespread stock, is under no stress. In fact, it is the most abundant of our commercially fished species. Foreign vessels began catching hoki in the 1970s, and today it makes up nearly one-third of the industry's total catch of all species. The hoki stock is well above the MSY level and is still being 'fished down'. The TACC was reduced from more than 250,000 tonnes in 1989 to just over 200,000 the following year. Since 1994, it has been cautiously increased and, for the 1995-96 season, was 240,000 tonnes (Minister of Fisheries, 1995).

While scientists believe the current hoki catch and quota levels are sustainable during the fishing-down phase, the catch has a significant impact on other species which may be less sustainable. Some stocks of ling, hake and silver warehou have had their quotas exceeded because too many are taken as bycatch in hoki nets. The hoki fishery also has a significant effect on non-fish species, such as seals and sea lions (see Box 9.18) and on mud-dwelling corals and other sea-floor invertebrates (Grange, 1993).