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Galaxias argenteus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA ACTINOPTERYGII OSMERIFORMES GALAXIIDAE

Scientific Name: Galaxias argenteus
Species Authority: (Gmelin, 1789)
Common Name(s):
English Giant Kokopu
Synonym(s):
Esox alepidotus Forster, 1801
Esox argenteus Gmelin, 1789
Galaxias forsteri Valenciennes, 1846
Galaxias grandis Haast, 1873
Galaxias kokopu Clarke, 1899

Assessment Information [top]

Red List Category & Criteria: Vulnerable A4ac ver 3.1
Year Published: 2014
Date Assessed: 2014-07-07
Assessor(s): West, D, David, B., Franklin, P., Ling, N., Allibone, R, Crow, S. & Hitchmough, R.
Reviewer(s): Closs, G. & Gibson, C.
Facilitator/Compiler(s): Gibson, C. & Buley, K.
Justification:
The Giant Kokopu (Galaxias argenteus) is the largest of the galaxiid species and is endemic to New Zealand. It is primarily a coastal species that does not usually penetrate very far inland and is mainly found in low altitude areas close to the south and west coasts of both main islands. G. argenteus is migratory, but it can form land-locked populations and therefore has the capacity for both diadromous and non-diadromous recruitment. This species has undergone significant population declines since European settlement times and it has been locally extirpated in parts of its former range. Loss and degradation of habitat through activities such as drainage of wetlands and straightening of river channel systems are the biggest threat to this species. Current and historic land-use change and intensification has resulted in an incremental loss of habitat. Around 85% to 90% of New Zealand's wetlands have been lost in the last 100 years and this species is now essentially absent from most of New Zealand's intensively utilised lowland plains. There is a continuing expansion of dairy farming and associated drain management practices in stronghold areas for this species. The mechanical clearance of drains causes direct mortality through the removal and stranding of fish on banks. Drain clearing occurs extensively in the Waikato and Southland and is increasingly occurring on the West Coast, as land use changes to more intensive dairy farming. Here, the impacts on the Gargenteus are expected to be severe. Although specific data on the rates of population decline are unavailable, it is reasonable to assume on the basis of past and on-going habitat loss and human pressures that the population has experienced at least a 25% decline over the past 20 years (2 generations). Furthermore, a confounding aspect of this species' life history is that large, old fecund specimens could be sustaining the population in the face of habitat loss and drain clearing mortalities and a 10-20 year lag may be weakening the current observations of a decline. It is therefore reasonable to suspect that that the population will experience further declines of at least 5% over the next 10 years (1 generation). Based on these suspected population decline rates in the past and the predicted future population declines, this species has been assessed as Vulnerable, where the cause of declines are due to a decline in the area of occupancy, extent of occurrence and habitat quality.
History:
1996 Vulnerable

Geographic Range [top]

Range Description: The Giant Kokopu (Galaxias argenteus) is endemic to New Zealand where it occurs in areas of suitable habitats in the North and South Islands and Chatham and Stewart Islands, but not the sub-Antarctic islands or Kermadecs (McDowall, 1990). The extent of occurrence (EOO) is calculated as 9,654 km2 using an intersection of New Zealand Freshwater Fish Database records and spatial representations (polygons) of Freshwater Ecosystems of New Zealand 3rd-4th order river catchments and lakes (NZFFD 2011, FENZ 2010). The area of occupancy is as 348 km2, calculated from the sum of the lengths x estimated stream widths of river reaches in which this species was recorded the New Zealand Freshwater Fish Database (NZFFD 2011; Ministry for the Environment 2013). This calculation includes lake areas where this species occurs, but it is unlikely to use the entire lake as habitat, so the AOO is an over estimation (West pers. comm. 2014).
Countries:
Native:
New Zealand (Chatham Is., North Is., South Is.)
FAO Marine Fishing Areas:
Native:
Pacific – southwest
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: This species is nationally assessed as 'At risk - declining' according to the New Zealand Department of Conservation's threat classification system (Goodman et al. 2014). It has experienced significant population declines since European settlement times. The population has never recovered however the rate of decline appears to have slowed. The loss of around 85% to 90% of New Zealand's wetlands (Ministry for the Environment 1997) in the last 100 years has severely impacted on the population and distribution of this species. For example, historically this species was well known from south Canterbury streams and wetlands, but it is now absent from most of this region. This species remains in areas of suitable habitat and in areas where habitat is unimpaired. In areas where introduced predatory salmonids do not occur (e.g. Stewart Island), this species can be locally abundant. However, inland populations predominantly consist of adults with low apparent recruitment, which could be indicative of population declines in these areas. There are also likely to be localised declines as a result of loss of river connectivity. Additionally, despite occurrence of suitable habitat, this species is rare north of Auckland (probably due to unsuitable water temperatures). It is therefore inferred that there is still an overall slow, gradual decline in the population of G. argenteus. Although specific data on the rates of decline are unavailable, it is reasonable to assume on the basis of past, existing and continuing human pressures that the population has experienced at least a 25% decline over the past 20 years. Furthermore, a confounding aspect of this species' life history is that large, old fecund specimens could be sustaining the population in the face of habitat loss and drain clearing mortalities and a 10-20 year lag may be weakening the current observations of a decline (D. West pers. comm. 2014).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: G. argenteus is the largest of the galaxiid species, reaching a total length of 580 mm, but is now uncommonly seen greater than 400 mm. This is primarily a coastal species that does not usually penetrate very far inland. It is mainly found in low altitude areas close to the south and west coasts of both main islands. Preferred habitat includes small-medium size, slow-flowing streams, although it can also occur in non-flowing aquatic habitats such as wetlands, ponds and lake margins. They are also usually found in habitats with good cover from overhanging vegetation, undercut banks, logs or debris clusters. This large galaxiid is migratory but, like Koarao (Galaxias brevipinnis) and Banded Kokopu (Galaxias fasciatus), it can form land-locked populations and therefore has the capacity for both diadromous and non-diadromous recruitment. They are cryptic, mostly nocturnal fish that mature at 2-3 years of age, with the oldest recorded specimen aged at between 21-27 years of age (McDowall 1990). Generation time is estimated at 10 years (B. David pers. comm. 2014). Spawning occurs in autumn/winter during elevated flows, with eggs deposited in riparian vegetation. Eggs develop terrestrially before hatching 3-6 weeks later when re-inundated by high flows. Anecdotal evidence suggests that in some streams short-term downstream migrations may occur for spawning (Franklin pers. comm. 2014). Larvae typically rear at sea and return after 4-6 months to freshwater as whitebait. Whitebait are able to climb, but not as well as some other whitebait species. This species has a diverse diet including terrestrial and aquatic invertebrates, freshwater crayfish and sometimes other fish (McDowall 1990, Department of Conservation 2010, NIWA 2013).
Systems: Freshwater; Marine

Use and Trade [top]

Use and Trade: Historical accounts indicate this species was a food source for Maori (Department of Conservation 2005). This species is currently harvested as a component of the domestic whitebait fishery, the proportion of which varies seasonally and geographically. Officially, there are no 'commercial' catches - superficially it is a recreational fishery, but there are no restrictions on then on-selling 'surplus' catch and no reporting of catches is required (G. Closs pers. comm. 2014). Over the scale of decades, there has clearly been a decline in catches from the early twentieth century to the present day. It is apparent that the catches that were achieved (even if many of the reports are anecdotal and allowing for overestimates), were massive 100 years ago relative to what they are today. However, there is currently no known data being collected in a sufficiently rigorous way that could confidently allow the direction of trends on a more recent year from year basis to be stated (Closs pers. comm. 2014). Available information suggests that abundance of this species is unlikely to be controlled by juvenile recruitment under existing conditions of fishery-induced mortality (McDowall 1999).

Threats [top]

Major Threat(s): Loss and degradation of habitat through activities such as drainage of wetlands and straightening of river channel systems are the biggest threat to this species. Current and historic land use change and intensification has resulted in an incremental habitat loss for this species. Around 85% to 90% of New Zealand's wetlands have been lost over the last 100 years (Ministry for the Environment 1997) and this species is now essentially absent from most of New Zealand's intensively utilised lowland plains. Mechanical clearance of drains causes direct mortality, where this wide scale drain 'management' is known to directly remove and strand fish on the banks. There is a continuing expansion of dairy and associated drain management in stronghold areas (e.g. Waituna Lagoon complex area and Lake Brunner area) for this species. In some regions (e.g. Waikato), on-going drain management is continually suppressing the potential for these areas to be recolonised. There is on-going pressure to increase efforts to clear drains in these key regions and the impacts on the population here will be severe (Greer et al. 2012). Also, areas that have been recolonized (following long periods of no drain disturbance) are subjected to being uprooted and this has been observed on numerous occasions in the Waikato region, since about 2002 (David pers. comm. 2014). Crucially, on top of the direct removal of fish, the remaining habitat is insufficient to support the species, which increases the loss of suitable habitat and reduces area of occupancy (David pers. comm. 2014). Additionally, the loss of riparian vegetation (potential spawning habitat) is likely to change the water temperature and reduces the terrestrial food supply. Other threats include artificial barriers to migration (which disrupt river connectivity and access to adult habitats, thereby negatively affecting the distribution of Galaxias argenteus) and predation and competition by introduced salmonids, primarily brown trout Salmo trutta. Impacts on the population resulting from the harvest of whitebait are possible, but are currently un-quantified (McDowall 1990, Department of Conservation 2005, NIWA 2013).

Conservation Actions [top]

Conservation Actions: This species was included in New Zealand's Department of Conservation large galaxiid recovery plan 2003-2013 (Department of Conservation 2005), which outlined a number of options for recovery. This document is expected to be updated in the near future, as the period of the plan has now passed. Many Protected Areas within New Zealand consist of high-altitude uplands (outside of this species' range), meaning the waterways are unsuitable for this species. There are however, stronghold populations in Rakiura National Park, Stewart Island, which are secure. Recent conservation measurement techniques include 'within bank' habitat augmentation and assessment within agricultural drains, which is being carried out in the Waituna wetland complex and also by the Waikato regional council within urban streams and at a number of regularly 'cleaned' modified channel sites. Trial translocations of captive reared fish to areas within the species natural range have also occurred. Additionally, the whitebait season on the West Coast has been shortened in an effort to reduce the vulnerability of this species to the fishery. More research and monitoring is required to better understand the population size, distribution and trends for this species and also the impact of threats such as fishing, on the population.

Citation: West, D, David, B., Franklin, P., Ling, N., Allibone, R, Crow, S. & Hitchmough, R. 2014. Galaxias argenteus. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 24 November 2014.
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