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NEW ZEALAND ECOLOGY |
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NATIVE GALAXIID FISH |
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The giant kokopu Galaxias argenteus belongs to the Galaxiidae family of the Osmeriformes order, and is only found in New Zealand.
Giant kopopu was the first galaxiid identified, by Gmelin from specimens collected by naturalists in the 1773 expedition of Captain James Cook. Gmelin described it in 1789 as a pike Esox argenteus. George Cuvier later recognised it wasn't a pike and it became Galaxias argenteus.
The genus name Galaxias refers to the giant kokopu's distinct but varied pattern of golden rings, blotches and crescents as found in the galaxy of stars, on dark olive to brown colouring.
It is the largest of all the 34 Galaxias species worldwide, and the Galaxiidae family, with the longest recorded body length of 58 cm and weighing 2.7 kg. Adults may exceed 40 cm and weigh a kilogram, however, a large giant kokopu is anything in excess of 30 cm and 500g.
The threatened giant kokopu is listed as 'vulnerable' on the IUCN Red List of Threatened Species, and in 'gradual decline' on the 2005 New Zealand Threat Classification System.
Giant kokopu are not climbers like the closely related shortjaw kokopu. They do not penetrate very far inland, preferring flatter, slower flowing water, and riparian cover and instream plants. It is attracted to the still water of heavily vegetated swampy lagoons and lakes, and there are many landlocked populations. |
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The giant kokopu is the largest of all 34 Galaxias species worldwide, and the Galaxiidae family, with a body length of 58 cm and weight of 2.7 kg. |
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Giant kokopu probably take three years to reach maturity [Rasmussen, 1990], and may live for many years; a large adult fish (400 mm long and weighing 1.05 kg) was estimated from otolith growth rings to be between 21 and 27 years old [McDowall, 1990].
Distribution is normally within the range of 170 km inland, up to an elevation of 250m. It is rare in Northland, and on the east coasts of both mainland islands from East Cape to Otago.
On the west coast in the South Waikato region, giant kokopu were found from DoC fish surveys in 2003 in Nukuhakari Stream west of Moeatoa, and in 2008 in Paparahia Stream and a tributary south of Waikawau. Both of these small streams flow directly into the ocean.
It was also found in a 1986 NIWA survey, further south in Kuriwera Stream south of Awakino Gorge.
These three survey locations, are the only recorded places in the New Zealand Freshwater Fish Database for giant kokopu on the west coast of the North Island between the Awakino River, and the Waikato River catchment where the strongest populations occur.
Giant kokopu are found in Taranaki, Bay of Plenty and Wellington in the North Island; and in the South Island in the Marlborough Sounds, the west coast down to Fiordland, and Southland. It is on Stewart Island and the Chatham Islands.
The extent of giant kokopu distribution known from the New Zealand Freshwater Fish Database, may be under-represented because of the limited number of surveys, and insufficient reporting. It is hard to catch and mainly cryptic, hiding in places difficult to observe and feeding at night.
As with all galaxiids, a large rounded single dorsal and an anal fin are set back close to the large square caudal fin. Giant kokopu do not have scales, but have a leathery, thick skin covered with mucus.
Giant kokopu mostly feed on invertebrates that either live in the stream bed or fall into the water, and will move into the open at night for feeding.
The most common co-inhabitant is the longfin eel Anguilla dieffenbachii, that will prey upon young giant kokopu. Reduction of large eels by fishing may have helped giant kokopu populations. |
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A young adult giant kokopu Galaxias argenteus.
Photo Stephen Moore, Crown Copyright © Department of Conservation.
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The amphidromous migration cycle of giant kokopu .....
Athough there are many landlocked populations in lakes, giant kokopu are mainly diadromous, growing from lava in the first stage of their life in salt water, before returning to freshwater as whitebait, where they spend the remainder of their life.
Little is known about the spawning habits of giant kokopu - its' eggs have never been found. It has a similar amphidromous breeding cycle to the four other whitebait galaxiids, but spawning locations remain a mystery.
Giant kokopu are a small part of the whitebait run. This is difficult to determine without expert identification, as it can be hard to distinguish giant kokopu whitebait from koaro, banded kokopu and shortjaw kokopu. Giant kokopu whitebait migrate later in the spring and may avoid the fishing pressure.
Sampling of whitebait from migrations in the Heaphy, Orowaiti, Buller, Hokitika, Wanganui, Okarito, and Mataura Rivers of the North Island West Coast, Westland, and Southland showed that giant kokopu whitebait migrate late in the spring and early summer, entering the rivers in early November and continuing into December.
Amongst 70 whitebait samples containing nearly 9,000 whitebait there were only 231 giant kokopu whitebait, all of these taken later than 4 November [McDowall 1990]. All except four of the giant kokopu whitebait were taken from Buller River and Hokitika River, where most of the samples were taken. |
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The difficulty of galaxiid protection .....
Restrictions on fishing meet fierce opposition, and nothing could be more so than whitebaiting controls.
The whitebait catch season is presently from 15 August until 30 November, and previously mid-November. A shorter season would help protect giant kokopu because of their later entry into estuaries during early November and into December.
Data indicating that most giant kokopu whitebait migrate after the end of the first week of November formed the basis for the Department of Conservation implementing control measures on the West Coast whitebait fishery with the intention of providing additional protection of giant kokopu (Tisdall 1994).
Regulations were introduced to close the whitebait fishing season in November, to minimise the giant kokopu whitebait catch. A season that is two weeks shorter would not severely reduce the total whitebait catch, because only a small proportion of all whitebait species are taken during November.
Later analysis by McDowall in 1994, suggested that in most years, less than ten percent of the catch was in the first two weeks of November.
The West Coast Whitebaiters Association strongly objected to earlier closure regulation. The matter went before the Regulations Review Committee of the New Zealand Parliament, which supported the whitebait fishers, and the 14 November closure was resumed.
The whitebaiters argued that the information supporting closure, that most giant kokopu whitebait are caught after early November, was by 1993, old and unreliable, but did not establish that the migration season had changed since the late 1960s and early 1970s.
There is no daily catch limit, and a whitebaiter can fish every day of the 14 week season. For many baiters it is a significant income with whitebait selling for up to $180/kg. That's not bad if you bring in 20 kg in a day, but catches vary during the season, and from year to year.
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The Galaxias genus throughout the southern hemisphere
New Zealand's freshwater fish fauna is sparse with 41 native species in 9 families, but unique with the predominance of 17 species of the genus Galaxias, and 5 species of the genus Neochanna in the Galaxiidae family. Another 7 unamed possible new non-diadromous Galaxias species are being taxonomically described.
More than half of the freshwater fish fauna is diadromous, moving between fresh and salt water during their life.
The five whitebait galaxiids, shortjaw kokopu, giant kokopu, banded kokopu, inanga and koaro are amphidromous, a form of diadromy relating to breeding in freshwater.
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Fishes of the family Galaxiidae are primitive teleosts of salmoniform relationships with origins likely dating back to Mesozoic times. |
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Longer, fatter giant kokopu bear some resemblance to smaller shortjaw kokopu, but little to other small, sleak and slender galaxiids.
The 34 described Galaxias species are fishes of the southern hemisphere. New Zealand has more species than any other region, with half of the total species worldwide.
There are 9 Australian and Tasmanian Galaxias species, of which two, inanga and koaro are not endemic. Chile has one endemic species and the widely distributed inanga, and South Africa and New Caledonia each have one endemic species.
Despite the wide distribution and long evolutionary history of Galaxias fishes, fossils have only been reported in New Zealand.
Fish fossils are not common, and only rarely preserved. The small size of galaxiids, the fragility of fish bones, and movement through freshwater habitats do not provide very good conditions for preservation of fossils.
A fossil of Miocene age from the Manuherikia group, from a site near Bannockburn in Central Otago, is identified as a galaxiid, probably genus Galaxias. The fish was large, estimated at 383 mm, and thus larger than all extant New Zealand Galaxias except G. argenteus, which is known to reach 580 mm.
However, it appears to have been of quite slender form. There was, therefore, in Miocene times, a large, slender, perhaps lacustrine Galaxias in Palaeo-lake Manuherikia in Central Otago [McDowall, Pole, 1997].
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References
Bonnett, M.L., McDowall, R.M., Sykes, J.R.E. 2002. Critical habitats for the conservation of giant kokopu, Galaxias argenteus (Gmelin, 1789), Science for Conservation 206, Department of Conservation.
McDowall, R.M. 1999. Migration season of whitebait of giant kokopu, Galaxias argenteus, Department of Conservation.
McDowall, R.M. 1990. New Zealand freshwater fishes: A natural history and guide, Heinemann-Reed, Auckland.
McDowall, R.M., Pole, M. 1997. A large galaxiid fossil (Teleostei) from the Miocene of Central Otago, New Zealand, Journal of the Royal Society of New Zealand, Vol 27:2, June 1997, pp 193-198.
Rasmussen, A.G. 1990. Certain aspects of the biology of a landlocked population of giant kokopu (Galaxias argenteus, Gmelin, 1789). A dissertation in partial fulfilment of requirements for the Postgraduate Diploma in Science, University of Otago. |
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CLICK IMAGE GO TO FIRST
SEE "WHITEBAIT AND THE MIGRATION CYCLE OF DIADROMOUS GALAXIIDS"