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Galaxias postvectis 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Actinopterygii Osmeriformes Galaxiidae

Scientific Name: Galaxias postvectis Clarke, 1899
Common Name(s):
English Shortjawed Kokopu, Shortjaw Kokopu
Synonym(s):
Galaxias charlottae Whitley & Phillipps, 1939

Assessment Information [top]

Red List Category & Criteria: Endangered A2bc; B2ab(iii,v) ver 3.1
Year Published: 2014
Date Assessed: 2014-08-14
Assessor(s): West, D, David, B., Hitchmough, R., Champion, P., Ling, N., Allibone, R & Crow, S.
Reviewer(s): Closs, G. & Gibson, C.
Facilitator/Compiler(s): Gibson, C. & Buley, K.
Justification:
The Shortjaw Kokopu (Galaxias postvectis) is a large, nocturnal migratory galaxiid species, endemic to New Zealand. It is considered that it was probably once widespread, but has been regarded as very uncommon for some time and is considered to be the rarest of the whitebait galaxiids. The area of occupancy (AOO) is calculated at 18.5 km2 and extent of occurrence (EOO) as 7,077 km2. The population of this species is sparsely distributed and concentrated at a few sites of suitable adult habitat in many areas. It is notably absent from most of the east coasts of both the North and South Islands. Although this species penetrates well inland in many catchments, it appears to be restricted to specific habitats with fast flowing streams located in native forest catchments, featuring pools and large boulder substrates with large interstitial spaces. It is known to have become locally extirpated at specific sites. Sometimes the species may not be found in neighbouring habitats, even though they appear to be very similar. G. postvectis lives to at least 15 years, maturing at about 2-3 years with a generation time of about 10 years. This species was probably once widespread but has been regarded as very uncommon for some time and is considered to be the rarest of the whitebait galaxiids. The number of mature individuals is estimated to be 500-10,000. The population is considered to be declining and although there are few presence/absence records of this species in the national New Zealand Freshwater Fish Database, the small numbers of records have indicated declines over a prolonged period (more than 20 years), despite more targeted and efficient sampling effort in their preferred habitats over this time. The population of this species is sparsely distributed but concentrated in suitable adult habitat. The majority of records are of low numbers of large adults and the predominance of large, old adults and the lack of juveniles is of concern. The high proportion of adults and evidence of poor recruitment at many sites also suggests that the current population is declining and that it is severely fragmented. According to the New Zealand Department of Conservation's national threat classification system, this species is assessed as Threatened - Nationally Vulnerable, based on a moderate to high ongoing or predicted population decline. Of the large galaxiids, this species has the most specific habitat requirements and is least adaptable to habitat modification. Historical rapid and extensive deforestation is considered to have been the biggest threat to this species and is likely to have significantly reduced and fragmented its distribution and abundance. Most remaining suitable adult habitat exists in protected high county locations, however some suitable habitat at lower altitudes is susceptible to further development for agriculture and forestry. Evidence of poor recruitment suggests migratory juveniles are particularly susceptible to impacts within the lower catchment and /or are limited by a sparse, highly fragmented adult population. Impacts on the population resulting from the harvest of whitebait are possible, but unquantified. This species is assessed as Endangered based on a suspected population decline of at least 50% over the past 30 years (3 generations) based on observed, but un-quantified declines at known sites and ongoing declines in area of occupancy, extent of occurrence and habitat quality caused by deforestation and development in lowland areas where suitable habitat currently still exists. If specific trend data were available, it is suspected that the actual rates of decline could be higher than this and the species may qualify as Critically Endangered. Additionally, the area of occupancy (AOO) for this species is less than 500 km2. The population is suspected to be severely fragmented and there is a continual decline in area, extent and quality of habitat and the number of mature individuals, meaning this species also meets the Endangered category under the geographic range criteria.
Previously published Red List assessments:

Geographic Range [top]

Range Description:The Shortjaw Kokopu (Galaxias postvectis) is endemic to mainland New Zealand and off-shore islands except Chatham, Stewart and the sub-Antarctic islands (McDowall 1990). It is notably absent from most of the east coasts of both the North and South Islands (McDowall et al. 1996, NZFFD 2011). The area of occupancy (AOO) is calculated at 18.5 km2 using reach lengths x estimated stream widths of species occurrence from the New Zealand Freshwater Fish Database records (NZFFD 2011). Extent of occurrence (EOO) is calculated as 7,077 km2, using an intersection of New Zealand Freshwater Database records and spatial representations (polygons) to 3rd-4th order river catchments and lakes of Freshwater Ecosystems of New Zealand (NZFFD 2011, FENZ 2010). This species is sparsely distributed and is only known from a few sites in many areas (D. West pers. comm. 2014, S. Bowie pers. comm. 2014). It is only found in specific habitats and is sometimes not found in neighbouring habitats, even though they appear very similar (S. Bowie pers. comm. 2014). This species has also experienced local extirpations (e.g. from the Katikara stream) (S. Bowie pers. comm. 2014).
Countries occurrence:
Native:
New Zealand (North Is., South Is.)
FAO Marine Fishing Areas:
Native:
Pacific – southwest
Additional data:
Estimated area of occupancy (AOO) - km2:18.5
Upper elevation limit (metres):500
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:This species was probably once widespread (McDowall 1990), but has been regarded as very uncommon for some time and is considered to be the rarest of the whitebait galaxiids (NIWA 2013). The number of mature individuals is estimated to be 500-10,000 (J. Goodman pers. comm. 2014). The population is considered to be declining and although there are few presence/absence records of this species in the national New Zealand Freshwater Fish Database, the small numbers of records indicated declines over a prolonged period (more than 20 years), despite more targeted and efficient sampling effort in their preferred habitats over this time (NZFFD 2011). The population of this species is sparsely distributed but concentrated in suitable adult habitat. The majority of records are of low numbers of large adults and the predominance of large, old adults and the lack of juveniles is of concern (Department of Conservation 2005). The high proportion of adults and evidence of poor recruitment at many sites suggests that the current population is declining and also that it is severely fragmented (D. West pers. comm. 2014, G. Closs pers. comm. 2014, B. David pers. comm. 2014). According to the New Zealand Department of Conservation's national threat classification system, this species is assessed as Threatened - Nationally Vulnerable, based on a moderate to high ongoing or predicted population decline (Goodman et al. 2014).
Current Population Trend:Decreasing
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:G. postvectis is a large, nocturnal galaxiid species that occurs in foothill streams upwards to altitudes of about 500 m above sea level. Although it penetrates well inland in many catchments, it appears to be restricted to fast flowing streams located in native forest catchments, featuring pools and large boulder substrates with large interstitial spaces (NIWA 2013, McDowall et al.1996). In-stream cover and shading are key habitat features. This species was formerly considered obligatorily diadromous, but in 2009 the first land-locked population was discovered in an Auckland reservoir. As this species has been so rarely encountered, little is known about its life history. G. postvectis lives to at least 15 years, maturing at about 2-3 years (McDowall 2000) with a generation time of about 10 years (B. David pers. comm. 2014). Spawning occurs during autumn/winter and close to typical adult habitats. Eggs develop terrestrially after being deposited in riparian vegetation during high water events, hatching after reinundation. Larvae are carried downstream to rear in marine environments and return to freshwater after 4-6 months as whitebait (Charteris et al. 2003). This species feeds extensively on terrestrial and aquatic invertebrates (McDowall 2000).
Systems:Freshwater; Marine
Generation Length (years):10
Movement patterns:Full Migrant

Use and Trade [top]

Use and Trade: Although G. postvectus is one of the five galaxiid species harvested as a component of the domestic whitebait fishery, the proportion made up by this species alone is unknown and is likely to vary geographically (Department of Conservation 2005). However, considering this is one of New Zealand's least known freshwater fishes and its apparent rarity, G. postvectis probably makes up a relatively small part of the whitebait run.

Threats [top]

Major Threat(s): Considering its habitat preferences, the historical rapid and extensive deforestation is considered to have been the biggest threat to this species and is likely to have significantly reduced and fragmented its distribution and abundance. Most remaining suitable adult habitat exists in protected high county locations; however some suitable habitat at lower altitudes is susceptible to further development for agriculture and forestry. Evidence of poor recruitment suggests migratory juveniles are particularly susceptible to impacts within the lower catchment and /or are limited by a sparse, highly fragmented adult population. Other potential threats include predation and competition by introduced salmonids, primarily Brown Trout (Salmo trutta). Impacts on the population resulting from the harvest of whitebait are possible, but unquantified (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 time-period of the plan has now passed.

Citation: West, D, David, B., Hitchmough, R., Champion, P., Ling, N., Allibone, R & Crow, S. 2014. Galaxias postvectis. The IUCN Red List of Threatened Species 2014: e.T8813A3147213. . Downloaded on 18 December 2017.
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