Galaxiids–stars of the Māniatoto
Galaxias are a group of small freshwater fish native to New Zealand. They were originally called Galaxias because of their markings, which are made up of fine spots and patterns that resemble stars in the galaxy.
Whitebait are the most well-known galaxiids, there are five different whitebait species. Whitebait larvae develop in the ocean and migrate back to freshwater as adults to lay their eggs in estuarine environments. However, New Zealand also has many non-migratory species which do not go out to sea as larvae, remaining in freshwater for their entire lifecycle.
The non-migratory galaxiids are some of New Zealand’s most threatened species. Although they are not as well-known as rare bird species such as kākāpō, many species are just as rare.
Many non-migratory galaxiids have naturally restricted geographic ranges, and some are confined to a single catchment. In combination with their restricted ranges, the threat posed by introduced species and land use changes has resulted in many non-migratory galaxiids becoming endangered. These taonga species are endemic to New Zealand, being found nowhere else in the world and must be protected for future generations.
The Māniatoto region is home to several species of non-migratory Galaxias, prominently the Taiari flathead, Galaxias depressiceps, and the Central Otago roundhead, Galaxias anomalus. These species belong to two different lineages of Galaxias: the flatheads and the roundheads and can be distinguished by the shape of their heads.
Otago non-migratory Galaxias life histories
The life history phases of non-migratory galaxiids in Otago can be summarised as having a spring spawning period, a late spring larval hatching, a late spring – late summer juvenile growth period, a spring – late summer gain in adult condition and development of reproductive cells, and a late winter reproductive cell readiness for spawning.
Central Otago roundhead Galaxias
Like many other non-migratory galaxiids, Central Otago roundheads reproduce over the late winter to early spring period. They lay their eggs within cobble or gravel bars and the banks of braided streams in relatively low velocity areas. Central Otago roundheads lay eggs around 2.3 mm in size and may lay between 500 – 1000 eggs per season.
The eggs hatch between 3-6 weeks after spawning depending on water temperature. After hatching, larvae swim into the stream current to prevent getting washed downstream, they then develop into juveniles in slow flowing margins or backwaters. They are relatively short lived compared to other non-migratory Galaxias, living for up to 4 years.
The Central Otago roundhead is one of the most threatened Galaxias species in New Zealand being listed as nationally endangered. Within the Maniototo, the Kye Burn River and its tributaries is a major habitat stronghold for the species. Spec Gully forms an important sub-population within the Kye Burn system, providing a substantial amount of habitat for the species.
Like other Galaxiids, Central Otago roundheads are small, scaleless fish. They are typically between 60 – 100 mm long as adults, but can reach up to 150 mm. They are olive coloured with disjointed brown markings along their body and have a light covering of gold speckles.
Central Otago roundhead are generally found in Otago at lower altitudes than Taieri flatheads, the other Galaxias commonly occurring in the Maniototo. They are generally found in shallow, relatively slow flowing streams, with gravel or cobble bottoms. They have an estimated habitat range of less than 100 hectares. Their population status is considered to be nationally critical.
Like other Galaxias species, they are generalist predators, feeding on small stream invertebrates. This includes the aquatic larvae of insects such as mayflies and midges, as well as terrestrial insects which fall into streams.
Taiari Flathead Galaxias
The Taieri flathead Galaxias depressiceps is the other most commonly seen galaxiid in the Maniototo region. The Taieri flathead generally occurs at higher altitudes than the Central Otago roundhead, living in small headwater streams. Due to the lower temperature and productivity of these small headwater streams, Taieri flathead are longer lived and slower growing than Central Otago roundhead, living up to 8 years. They produce fewer larvae which are larger at hatch to enable them to eat a wider variety of foods and survive in the lower productivity streams.
Taieri flathead are endemic to Otago but less threatened than the Central Otago roundhead, occurring in several other catchments including the Waikouaiti and Shag Rivers. However, they are still at risk and are classed as nationally vulnerable. Their estimated habitat range is less than 100 hectares.
The Teviot flathead galaxias Galaxias ‘Teviot’ is one of New Zealand’s most endangered animals with the highest conservation listing of Nationally Critical. They are endemic to Otago and occur only in the headwaters of the Teviot River on the edge of the Maniototo with an estimated known habitat of only one hectare.
There are many measures we can take to help save galaxiids from extinction.
Introduced species such as trout threaten Galaxias through both competition for food resources and predation. Central Otago roundhead have had at least 12 confirmed local population extinctions due to the invasion of trout, and the majority of remaining populations are at risk from trout invasion.
A pragmatic approach to managing species interactions is to manage larger river and stream ecosystems for multi-species (sports fish such as trout, eels, and bullies) and actively exclude (or reduce) trout populations in smaller tributary streams.
In select small streams trout can be maintained at low levels using methods such as electric fishing (to remove selected fish) and the addition of trout barriers to reduce recolonisation. In larger water bodies it is not practical to control trout numbers and they also provide a sportfish resource many members of the public enjoy. This approach allows for the conservation of both Galaxias populations in smaller streams and enjoyment of trout fisheries.
Protecting and enhancing habitat
Historic gold mining, intensification of land use with over stocking of stream banks also threatens Galaxias. These practises can cause increases in sediment input to waterways. When streams become sedimented, the spaces between the gravel or cobble substrate become blocked with fine particles. This causes loss of habitat for stream invertebrates and may reduce food resources for galaxiids. Many Galaxias also require the space between cobbles to spawn in, and sedimentation can reduce available spawning habitat.
In many areas of Central Otago, galaxiid populations have been protected by farmers using extensive farming practices (light stocking rates) to avoid bank damage and sedimentation of waterways. Riparian fencing is being used to exclude heavy stock such as cattle from waterways. Often some sheep grazing along waterways is used to manage long grass and control willows - which can smother waterways if left unchecked. Riparian planting with native species such as the sedge, Carex secta, can also provide cover and shade for fish species.
Human induced flow manipulation can have a negative impact on galaxiid numbers, and fragment remaining populations. The provision of carefully considered environmental flows when abstracting water from streams can also help enhance galaxiid populations. Non-migratory galaxiids require quiet slow-moving water for spawning and juvenile habitat, but if flows become too low and slow, oxygen levels can decrease and have a negative impact on egg survival. In some cases, a continuous flow of shallow water helps to maintain galaxiid numbers by reducing the numbers of larger predatory fish.
Education and awareness
Many people are unaware of the existence and plight of non-migratory galaxiids. Please inform your friends and family. Better still - bring them to Spec Gully Stream.
This project is dedicated to Matthew Hickey and the Kyeburn community who worked together to achieve improved environmental flows and outcomes in the Kyeburn catchment. This legacy of Matt’s work is continuing with ongoing efforts between the farming community and agencies such as Otago Regional Council, Department of Conservation, Fish and Game and Tiaki Maniototo to protect galaxiid populations.
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Allibone, R. M., & Townsend, C. R. (1998). Comparative dietary analysis of a recently described fish species complex (Galaxiidae) in a New Zealand river. New Zealand Journal of Marine and Freshwater Research, 32(3), 351-361.
Dunn, NR. (2021) Evidence of Dr Nicholas Rex Dunn on behalf of the Director-General of Conservation/ Tumuaki Ahurei dated 5th February 2021
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McDowall, R. M. (2003). Impacts of introduced salmonids on native galaxiids in New Zealand upland streams: a new look at an old problem. Transactions of the American Fisheries Society, 132(2), 229-238.
Robertson, H.; Bowie, S.; Death, R.; Collins, D. (Eds) (2016). Freshwater conservation under a changing climate. Proceedings of a workshop hosted by the Department of Conservation, 10–11 December 2013, Wellington. Department of Conservation, Christchurch. 87 p.