Diadromous Freshwater Fishes (Families Geotriidae, Anguillidae, Galaxiidae, Retropinnidae, Eleotridae, Pinguipedidae and Pleuronectidiae)
Jody Richardson, Robert McDowall, and Taoho Patuawa
General Description
New Zealand has a sparse but unique freshwater fish fauna. There are only about 35 native species, of which most are endemic and of which almost half are diadromous, meaning that they undertake obligatory, regular, and seasonally timed migrations between the sea and fresh water to complete their life cycles. Depending on the species, this life cycle may involve a passive migration from fresh water to the sea as eggs or freshly hatched larvae, or juveniles and adults actively swimming to or from the sea.
The lamprey is the only species from the primitive Geotriidae family in New Zealand, but is also found in Australia and South America. This fish spends its adult life in the open ocean, where it uses a circular sucker to attach itself to other animals and feeds by rasping a hole in their flesh. After migrating into fresh water during winter and spring, lamprey spawn in small rocky tributaries. Juvenile lamprey spend about four years in fresh water before they migrate to the sea to adopt the marine, parasitic life style. Adults probably range throughout the southern Pacific Ocean. Freshwater eels (Anguillidae) occur in Europe, North America, and throughout the eastern Pacific and Indian oceans. There are about 16 species, of which two are native to New Zealand: the shortfin and the longfin eel. Longfin eels are one of the largest Anguillidae, reaching over 20 kg in weight. Shortfin eels occur throughout the South Pacific. Adult eels breed hundreds of kilometres away from New Zealand, probably in deep ocean trenches somewhere near Tonga. The larvae are called leptocephalus and look nothing like an eel, being transparent, flat, and leaf-shaped. They reach New Zealand after more than a year drifting on ocean currents. Before entering fresh water the leptocephalus change into the more familiar eel shape, although they remain transparent for up to a week after leaving the sea. These tiny "glass" eels enter fresh water between July and November each year, often in very large numbers. Eels take many years to grow and it could be decades before an individual is ready to undertake the long migration back to the tropics. The adults never return as they die after spawning.
The Galaxiidae family is the largest family of freshwater fishes in New Zealand with over 25 species divided into two genera, the galaxiids, Galaxias spp., and the mudfish, Neochanna spp. Galaxiidae occur throughout the southern hemisphere. Only five of the New Zealand galaxiid species are diadromous, and all have a similar life cycle. Newly hatched larvae are swept out to sea on river currents and spend their first six months at sea. Where they live in the sea is not known, but larvae have been found up to 700 km from New Zealand. Juvenile galaxiids re-entering fresh water in spring are harvested as the highly sought local delicacy whitebait. The adults spend their whole lives in fresh water and prey on aquatic and terrestrial insects.
The most common diadromous galaxiid is the inanga, a species also found in Australia and South America. Koaro are present on the mainland, Chatham Island, and Stewart Islands, on the subantarctic Campbell Island and Auckland Islands, and in Australia. The other three diadromous galaxiids are endemic. They are relatively widespread at low elevations, and two are present on offshore islands. Life expectancy ranges from one year for inanga to several years for the other species.
Southern hemisphere smelts (Retropinnidae) are restricted to Australia and New Zealand. Two endemic species in two genera, Retropinna retropinna and Stokellia anisodon, occur in New Zealand. The common smelt is widespread throughout the country, including Stewart Island and the Chatham Islands. Very little is known about the life of smelt at sea, but large shoals of juveniles migrate to river mouths in spring and are often caught with whitebait. Stokells smelt is found only on the east coast of the South Island and never very far inland. This species probably spends most of its life in the marine environment, only entering fresh water to spawn in late spring and summer. Most smelt only live one year.
Members of the Eleotridae (bully) family occupy marine and fresh waters in the tropical Pacific and Southeast Asia. Most species are found in the tropics, and bullies reach their worldwide southern limits in Stewart Island. There is just one freshwater genus in New Zealand, Gobiomorphus, with seven species, of which three are strictly diadromous (bluegill, redfin, giant), three are non-diadromous (Crans, upland, Tarndale), and one (common) that can be either. All are endemic. The eggs of all Gobiomorphus species are laid in fresh water, and the larvae of the diadromous species passively washed to sea. The juveniles probably drift on ocean currents, migrating into fresh water in late winter and spring, with the adults occupying a variety of freshwater habitats.
The torrentfish is the only freshwater member of the Pinguipedidae in New Zealand, and is closely related to the more familiar blue cod. Torrentfish can be found in many New Zealand rivers that have easy access to the sea, but have never been reported from Fiordland, Stewart Island, or Chatham Island. Looking just like tiny replicas of the adults, juvenile torrentfish enter fresh water in the spring and autumn, and after a few weeks in the estuaries, begin moving upstream to the adult habitat.
The black flounder is the only member of the flatfish family, or Pleuronectidae, that is a truly freshwater species. The larvae are undoubtedly marine, but where and when spawning takes place is unknown. Black flounder are primarily a coastal species, although they can penetrate well inland if the river gradient is not too steep; specimens have been recorded more than 100 km inland in some river systems.
Status
An analysis of over 275 freshwater fishing records showed that elevation greatly affects the abundance of diadromous species at riverine sites. At elevations less than 50 m above sea level, densities of diadromous fish (fish per 100 m2) needed to exceed 60 to be as classified as high, whereas densities of more than five qualified as high at sites more than 150 m above sea level. In terms of diversity, more than five species present was considered diverse at low-elevation sites, whereas only two were needed for a high classification further inland.
The Department of Conservation has classified three diadromous freshwater fish (giant and shortjaw kokopu, and longfin eel) as in gradual decline, while lamprey is listed as sparse. Proposed recovery plans focus on the freshwater habitats, but because all the diadromous species spend part of their lives in the ocean or in near-shore environments, protection measures may need to consider aspects of both the larval and the adult phases.
Key Locations
Although diadromous freshwater fish are widespread in New Zealand, including the offshore islands, many species occupy specific habitats. Lowland rivers and streams with unrestricted access to and from the sea generally have the highest abundance of diadromous species, and such waterways are also important paths for species that migrate further inland. New Zealand has a wide variety of freshwater habitats and fish communities have evolved to occupy these. Benthic species such as torrentfish, bluegill bully and black flounder prefer open, gravel-bed rivers. Bush-covered streams provide habitat for lamprey, shortjaw kokopu, koaro, banded kokopu and redfin bully, whereas low-gradient, coastal rivers, streams, and lakes are inhabited by inanga, giant kokopu, shortfin eel, giant bully, and common smelt. Longfin eel and common bully are generalists that are found almost everywhere. Key locations during the marine phase are unknown.
Summary of Threats
Artificial structures such as dams, culverts, and floodgates that block the migration paths of diadromous species are a threat to their survival. Forest clearance followed by pastoral or urban development has caused significant habitat loss for many diadromous fish. Many lowland waterways and waterbodies now suffer from reduced water quality, also leading to habitat loss. In addition, introduced pest fish such as gambusia are aggressive toward native species, and their spread should be prevented. Estuarine degradation could affect the larval stage of some species, and changes to ocean currents as a result of global warming may have consequences for the diadromous fish.
Typical Habitats
Typical freshwater habitats utilised by diadromous fish include gravel-bed rivers, bush streams and low gradient, lowland waterways. Cover such as overhanging or undercut banks, overhanging bank vegetation, or large substrate particles, are often used as protection from river currents and predators. Eels, inanga, giant kokopu, common smelt and common bully are also commonly found in lakes. Oceanic, near-shore, and estuarine environments are probably utilised during the marine phases of the life cycles.
State of Information
Generally information on the freshwater phase of the diadromous species is good and there is a large body of published material. Few details are known about the marine phase of any of the diadromous fish.
Significance for Maori
Many diadromous species were an important food resource for Maori, including tuna (collective name for eels-although there were a vast array of different name for eels depending on where you were from and the species in question), inanga (whitebait, galaxiid or smelt), kaoro, and piharau (lamprey, also korokoro). Tuna were the most sought after of these fish, not only because of a taste preference, but also because tuna afforded a greater food supply than the other, smaller species. Traditional eel fishers had to be adaptive, and as such there were numerous harvest methods employed including the construction of elaborate weirs or nets (koumu), and traps (hinaki), as well as using spears (matarau), striking (patu tuna) and taking them by hand. Some of these traditional eeling methods are still practised today in many parts of New Zealand.
Inanga were traditionally caught with similar methods used for the tuna, however they were slightly refined to capture the smaller animals and thus were referred to differently; pa inanga (weirs), hinaki or kaka (traps), or kupenga hao (long, rectangular nets). Although small, inanga were caught in large quantities using these methods and were a delicacy for Maori. Inanga fishing is still conducted to this day using the kupenga hao method as well as using large scoop nets.
Key References
Best, E. 1929. Fishing Methods and Devices of the Maori. Reprinted by Te Papa Press 2005. 264pp.
Department of Conservation. 2004. New Zealand large galaxiid recovery plan, 2003-13: shortjaw kokopu, giant kokopu, banded kokopu, and koaro. Threatened species recovery plan 53. 45pp.
McDowall, R M. 1990. New Zealand freshwater fishes. A natural history and guide. Heinemann Reed, Auckland. 553pp.
Richardson, J. 2005. NIWA atlas of New Zealand freshwater fishes. www.niwascience.co.nz/rc/freshwater/fishatlas/
Table 15: Diadromous freshwater fishes (Families Geotriidae, Anguillidae, Galaxiidae, Retropinnidae, Eleotridae and Pinguipedidae) in New Zealand
| Taxon | Common name | Breeding species | Endemic species | Total species |
|---|---|---|---|---|
| Family Geotriidae | ||||
| Geotria australis | Lamprey | Yes | No | |
| 1 | 0 | 1 | ||
| Family Anguillidae | ||||
| Anguilla australis | Shortfin eel | No | No | |
| Anguilla dieffenbachii | Longfin eel | No | Yes | |
| 0 | 1 | 2 | ||
| Family Galaxiidae | ||||
| Galaxias argenteus | Giant kokopu | Yes | Yes | |
| Galaxias brevipinnis | Koaro | Yes | No | |
| Galaxias fasciatus | Banded kokopu | Yes | Yes | |
| Galaxias maculatus | Inanga | Yes | No | |
| Galaxias postvectis | Shortjaw kokopu | Yes | Yes | |
| 5 | 3 | 6 | ||
| Family Retropinnidae | ||||
| Retropinna retropinna | Common smelt | Yes | Yes | |
| Stokellia anisodon | Stokells smelt | Yes | Yes | |
| 2 | 2 | 2 | ||
| Family Eleotridae | ||||
| Gobiomorphus cotidianus | Common bully | Yes | Yes | |
| Gobiomorphus hubbsi | Bluegill bully | Yes | Yes | |
| Gobiomorphus huttoni | Redfin bully | Yes | Yes | |
| Gobiomorphus gobioides | Giant bully | Yes | Yes | |
| 4 | 4 | 4 | ||
| Family Pinguipedidae | ||||
| Cheimarrichthys fosteri | Torrentfish | Yes | Yes | |
| 1 | 1 | 1 | ||
| Family Pleuronectidae | ||||
| Rhombosolea retiaria | Black flounder | Yes | Yes | |
| 1 | 1 | 1 | ||
| Total | 14 | 12 | 17 |