Conservation status of New Zealand freshwater fish, 2009

Abstract

The threat status of 74 freshwater and estuarine fish present in New Zealand was determined. Fifty-one native taxa were ranked of which 67% were considered Threatened or At Risk. A single species was classified as Extinct, the New Zealand grayling, which has not been observed since the 1920s. Four taxa were classified in the highest threat category, Nationally Critical, and a further 10 taxa as Threatened (Nationally Endangered or Nationally Vulnerable). Twenty taxa were ranked in the At Risk group with the majority ranked as Declining. Endemic galaxiids (Galaxiidae) dominated the Threatened and At Risk taxa. The majority (68%) belonged to the Galaxias genus, comprising 81% of recognised taxa in this genus and all five species in the genus Neochanna were also ranked as Threatened or At Risk. In addition to 51 native taxa, a further three fish species were considered colonists and 20 introduced species were classified as naturalised, although two of these are considered rare. The majority of the Threatened species occur in the Canterbury and Otago regions where a suite of rare non-migratory galaxiids exist. Threat mechanisms that were identified as causal in the decline of freshwater fish species were the impact of introduced fish species, declining water quality, effects of water abstraction, loss of habitat via land-use change and land-use activities, and river modifications.

Keywords:

• threatened fish
• endangered fish
• uncommon fish
• extinct fish
• conservation status
• New Zealand
• threat classification

Introduction

For more than 30 years, the International Union for the Conservation of Nature (IUCN) has produced an international Red List of threatened species. This list is designed to detect rarity and decline at global and continental scales using rule-based methods (IUCN 2001; Mace et al. 2008). Since many New Zealand species are naturally very restricted in distribution, the IUCN criteria have sometimes exaggerated their threat status. To address this concern, the New Zealand Department of Conservation (DOC) has led a process to develop a species threat classification system designed specifically for New Zealand taxa. That is, for native taxa within New Zealand, with the intent that the New Zealand system will provide finer detail for the threat status than that provided by the globally applied IUCN Red List system (Townsend et al. 2008).

The DOC ranking process was first conducted using the system developed by Molloy & Davis (1992). This initial method was replaced a decade later by a system that listed taxa purely according to risk of extinction (Molloy et al. 2002) and Molloy et al.'s (2002) method was revised in 2007 (Townsend et al. 2008).

With each revision of the ranking, refinements to the methodology and changes to the terminology used for classifying the threatened or declining species have been introduced. The underlying objective with the early rankings (using the Molloy & Davis system) was to determine priorities for conservation management and the criteria included cultural aspects. The system of Molloy et al. (2002) was designed as a threat ranking system that excluded cultural elements; thus rankings from this system were focused solely on an assessment of the threat status. Similarly, the revision by Townsend et al. (2008) also focuses on threat status but includes some upgraded methodological changes and hence was used in the current assessment.

The earliest threat rankings in 1992 classified 10 species as threatened or having conservation priority. The subsequent ranking process in 2002, using the system of Molloy et al. (2002) classified four species as acutely threatened, 12 species as chronically threatened, four species at risk and five species as data deficient, which prevented their classification (Hitchmough 2002). In 2004, the rankings process classified six species as acutely threatened, 14 species as chronically threatened, six species at risk and three species as data deficient and again unable to be classified (Hitchmough et al. 2007). Since 1992, the threat rankings have seen an increase in the number of threatened freshwater fish species. The increasing number of threatened fish taxa is related in part to taxonomic revisions that have identified new taxa but also to the continuing decline in the abundance and distribution of freshwater fish.

Townsend et al. (2008) used a reduced set of categories to describe the threat status of species, although most of the underlying decline rates and areas of occupancy (key threat descriptors) remain the same as those described by Molloy et al. (2002). This paper reports the results of the 2009 threat ranking process applied to indigenous and introduced freshwater fish in New Zealand as at June 2009. The rankings presented here supersede the rankings conducted under the system of Molloy et al. (2002) as listed in Hitchmough (2002) and Hitchmough et al. (2007).

Methods

All indigenous and introduced freshwater fish taxa present in New Zealand and thought to be reproducing naturally in the wild are listed. The list includes all described species, and genetically distinct but undescribed taxa. For all colonising or introduced species, only the populations in New Zealand were assessed.

The threat panel (the authors) conducted the ranking using the methodology of Townsend et al. (2008). The process was conducted following public notification of intent to conduct the ranking in December 2008 and, a 6-month notification period was provided to interested parties enabling submissions to be lodged for consideration by the threat panel. Submissions were requested to provide information on the distribution, life history and decline rate for taxa. Eight submissions from the public were received via the Department of Conservation website. These were collated and reviewed along with data submitted by the Department of Conservation freshwater fish recovery groups. Data (meeting minutes and population decline predictions) from previous rankings (Hitchmough 2002; Hitchmough et al. 2007), distribution and survey information from the New Zealand Freshwater Fish Database (NZFFD), together with the expert opinion of the authors were also used to complete the threat classification process. Unpublished data from the Department of Conservation freshwater fish survey and monitoring programmes associated with freshwater fish recovery plans (Department of Conservation 2003, 2004, 2005) were used for developing rankings for galaxiid taxa with limited distributions. The information in submissions was considered with the threat panel's knowledge of life history, distribution, current abundance and distribution trends for each fish taxon. Where information was lacking, the threat panel used their expert opinion to make their best estimate for the ranking. While this creates some uncertainty with respect to the individual parameters for area occupied, adult population size and decline rate, this only became critical for species where the uncertainty in a parameter straddled a critical value that delineates between different threat rankings. For all taxa, apart from Canterbury mudfish, this uncertainty did not lead to difficulties with the ranking process. For Canterbury mudfish, submissions indicated an estimated decline rate of either 70% or 80% and these straddle the nationally vulnerable (<70% decline) and nationally endangered (≥70% decline) rankings. The threat panel was unable to determine which decline rate was most likely but, in line with the ranking process requirement to take a precautionary approach to the ranking, the higher rate and hence more threatened ranking was utilised.

The full list of fish species and undescribed taxa to be assessed was developed using all available taxonomic and genetic data for freshwater fish. Undescribed taxa are included in the full listing process, but listed as ‘Taxonomically Indeterminate’. Genetic criteria (as described below) were used to guide the threat panel on whether to rank undescribed taxa as populations within currently described species, or as separate taxa. Morphological information was also considered, although many of the non-migratory galaxiids considered here have yet to be distinguished morphologically (McDowall 2006a). Indeed, the ranking includes a number of undescribed (but evolutionarily significant) lineages that are inferred to have been genetically isolated for many hundreds of thousands of years. These undescribed taxa are defined using a genetic ‘barcoding’ approach—based on high mtDNA divergence values observed between phylogeographically distinct populations of Galaxias gollumoides (Waters et al. 2001). The substantial mtDNA divergence (∼3%) detected between Southland and Nevis River populations of G. gollumoides—reflecting 300,000–500,000 years of geological isolation (Waters et al. 2001)—was used as a broad benchmark for delineating evolutionarily distinct lineages of Galaxias. Importantly, this level of genetic divergence is comparable with or greater than divergence values detected between other pairs of morphologically distinct sister species (Waters et al. 2001; Waters & Wallis 2001a, b).

The threat classification process is fully described in Townsend et al. (2008) (Fig. 1; Table 1) and has the following threat categories:

1. Extinct;

2. Threatened (including Nationally Critical, Nationally Endangered, Nationally Vulnerable);

3. At Risk (including Declining, Recovering, Relict, Naturally Uncommon);

4. Not Threatened;

5. Non-resident Native (including Coloniser, Migrant and Vagrant);

6. Introduced and Naturalised (self-sustaining populations exist in the wild); and

7. Data Deficient.

This classification does not use the Gradual Decline, Serious Decline and Range Restricted categories of Molloy et al. (2002) and includes the new categories of Declining (that replaces gradual and serious decline), Recovering, Relict and Naturally Uncommon. Range restricted is now one of the possible qualifiers applied to taxa ranked in the new Naturally Uncommon category. The classification system of Townsend et al. (2008) also has minor differences compared with the previous system with the inclusion of the full range of population status and trends. Townsend et al. (2008) also included the super category of At Risk to group the categories of Declining, Recovering, Relict and Naturally Uncommon—replacing the At Risk category and most of the Chronically Threatened super category of Molloy et al. (2002).

Fig. 1  New Zealand threat classification system (after Townsend et al. 2008).

Table 1  Primary categories for ‘Threatened’, ‘At Risk’ and ‘Not Threatened’ taxa for all population trends using population size (A) or area occupied (B).A.

	Total number of mature individuals
Total population trend^a	<250	250–1000	1000–5000	5000–20,000	20,000–100,000	>100,000
>10% increase		NV/NU	NU/Rec		NT/NURR/Rel
Stable±10%		NE/NU	NV/NU	NU/Rel
10–30% decline		NE		Declining
30–50% decline			Nationally	Vulnerable
50–70% decline	Nationally Critical		NE
>70% decline
B.
	Total area occupied (ha)
Total population trend^a	≤1	10	100	1000	≥10,000
>10% increase		NV/NU	^b/Rec		^b
Stable±10%		NE/NU	NV/NU	^b
10–30% decline		NE		^b/Declining
30–50% decline			Nationally	Vulnerable
50–70% decline	Nationally Critical		NE
>70% decline
Note: ^aPredicted and ongoing trends related to ongoing threats and management action. ^bMore than one threat category available and additional information required to complete classification. Abbreviations: NV, Nationally Vulnerable; NC, Naturally uncommon; NE, Nationally Endangered; Rec, Recovering; Rel, Relict; RR, Range Restricted

In the classification process (Fig. 1, Table 1), two main parameters were used to assign the threat status: either total adult population size or area occupied, and population trend (Townsend et al. 2008).

An additional process available to the threat panel, under the Townsend et al. (2008) process, was to designate a threat ranking where it was believed that other factors not included in the ranking scheme were affecting the conservation status of a taxon.

For each species, key threats were identified if known and the likelihood that these threats would continue into the future was assessed. Threats known adversely to affect native and introduced fish include declining water quality, habitat loss, the impact of introduced species, water abstraction and land-use change (e.g. conversion of tussock to pasture or plantation forestry). Additional threat processes considered for this ranking, and not considered previously (Allibone, personal observation) were the presence and potential effects of Didymosphenia geminata (didymo) on benthic dwelling fish, particularly longjaw galaxiid species for which recent unpublished research on didymo has been conducted (NIWA, DOC unpublished data) and the possible effects of climate change on long-lived species (e.g. eels) for which three generations are likely to exceed 50 years. Limited data is available on the possible effects of climate change although the general expectation of the threat panel is that greater climate variability including more intense storm and drought events could be expected to create greater potential for species decline However, for the current ranking, it was also apparent to the threat panel that uncertainty around didymo and climate change restricted our ability to predict their effects and thus other known threat issues were considered sufficient to conduct the ranking.

Key population metrics in the assessment of threat status (Table 1) were the number of mature individuals estimated to be in the population and/or the area of occupancy for the species. Area of occupancy was estimated from river length and average width information (when available) for species with localised distributions. It is important to note that, for instance, 10 km of 1-m-wide stream is required to comprise a hectare of habitat. Terrestrial areas between stream courses were ignored. For the widespread migratory species that occur throughout New Zealand, area of occupancy was always considered greater than 100 km². For species where key life cycle activities occur in more limited areas than other life history stages, the key limitation was considered. For instance, Galaxias maculatus (inanga) has a distinct spawning habitat at small sites in tidal reaches. The threat panel considered this a potential limiting factor and the effect of spawning habitat loss was considered a significant limiting factor for the species. Large adult populations of inanga with no spawning habitat or spawning habitat impacted by land-use activity have little or no reproductive output and cannot be considered to support the species.

For the categorising procedure, the current rate of decline for species is required for a period of 10 years or three generations, whichever is longer. The expert knowledge of the threat panel was used to set the three-generation time period when it was agreed three generations exceeded 10 years. For each species, key threats were identified if present and the likelihood that these threat processes would continue into the future was considered in assessing ongoing decline rates.

An estimation of the predicted rate of decline for species was also required. For species subjected to continuing pressure from land-use change and the effects of declining water quality and quantity, the rate of decline is expected to be relatively continuous when averaged over the 10-year or three-generation timeframe.

For species for which key aspects of their life histories are unknown, some potential decline effects could not be estimated and hence some degree of caution was recognised as appropriate and the decline rate was set at a precautionary level as required by the method. This is most apparent in the eel species with respect to their semelparous spawning biology. While spawning is known to occur in ocean areas of the south Pacific, it is unknown what minimum number of eels is required to reach the spawning grounds to achieve successful spawning and recruitment. Unless the eels all home to a specific spawning location, there exists a risk that a minimum number of eels is required to migrate in any year to ensure eels encounter one another at the ocean spawning sites. For the longfin eel, where concern exists over the survival of females in freshwater (Jellyman 2009), the females that do reach the spawning area must encounter males and spawn. There is an unquantifiable level of risk that if the number of eels in the spawning migration declines to a critical level, then Allee effects (negative feedback factors such as inbreeding depression or inability to find suitable breeding partners that increase the rate of decline of a species; Allee et al. 1949) will drive reductions in spawning success and juvenile recruitment as eels fail to encounter other eels in the ocean.

Results and discussion

Taxonomic list

The freshwater fish ranking process determined a threat ranking for all described species of freshwater fish in New Zealand, and included an additional 11 indeterminate taxa and 20 introduced taxa (Table 2). In total, 74 taxa were ranked using the Townsend et al. (2008) method. Fifty-four native or colonising freshwater and estuarine fish species and 20 introduced fish species were ranked.

Table 2  Threat classification rankings for freshwater fish, 2009, status criteria defined in Townsend et al. (2008).

Common name	Formal name	Threat classification	Status criteria	Qualifiers^a
Taxonomically determinate
Grayling	Prototroctes oxyrhynchus	Extinct
Canterbury mudfish	Neochanna burrowsius	Nationally Critical	C	CD, EF, RR, Sp
Lowland longjaw galaxias (Kakanui River)	Galaxias cobitinis	Nationally Critical	A(1)	CD, EF, OL
Dusky galaxias	Galaxias pullus	Nationally Endangered	A (3)	CD
Eldon's galaxias	Galaxias eldoni	Nationally Endangered	A(3)
Roundhead galaxias	Galaxias anomalus	Nationally Vulnerable	D (3)	EF
Bignose galaxias	Galaxias macronasus	Nationally Vulnerable	C (3)	RR
Upland longjaw galaxias (Rangitata, Rakaia Rivers)	Galaxias prognathus	Nationally Vulnerable	C (3)	DP
Northland mudfish	Neochanna heleios	Nationally Vulnerable	D (3)	RR
Longfin eel	Anguilla dieffenbachii	Declining	C (2)
Torrentfish	Cheimarrichthys fosteri	Declining	C (1)
Dwarf galaxias (West Coast)	Galaxias divergens	Declining	B (2)	DP, RR
Giant kokopu	Galaxias argenteus	Declining	B (1)	PD
Koaro	Galaxias brevipinnis	Declining	C (1)
Gollum galaxias	Galaxias gollumoides	Declining	B (2)	DP
Inanga	Galaxias maculatus	Declining	C (1)	CD, DP
Shortjaw kokopu	Galaxias postvectis	Declining	A (1)	DP
Lamprey	Geotria australis	Declining	B (1)	DP
Bluegill bully	Gobiomorphus hubbsi	Declining	C (1)	DP
Redfin bully	Gobiomorphus huttoni	Declining	C (1)
Brown mudfish	Neochanna apoda	Declining	C (1)	PD
Black mudfish	Neochanna diversus	Relictual	B
Dwarf inanga (North Kaipara Head Dune Lakes)	Galaxias gracilis	Naturally Uncommon		DP, EF
Tarndale bully	Gobiomorphus alpinus	Naturally Uncommon		RR
Chatham Island mudfish	Neochanna rekohua	Naturally Uncommon		RR, St
Stokell's smelt	Stokellia anisodon	Naturally Uncommon		RR
Yelloweyed mullet	Aldrichetta forsteri	Not Threatened
Shortfin eel	Anguilla australis schmidtii	Not Threatened
Flathead galaxias	Galaxias depressiceps	Not Threatened		CD
Banded kokopu	Galaxias fasciatus	Not Threatened
Alpine galaxias	Galaxias paucispondylus	Not Threatened		RR
Canterbury galaxias	Galaxias vulgaris	Not Threatened		DP
Crans bully	Gobiomorphus basalis	Not Threatened
Upland bully (East coast South Island)	Gobiomorphus breviceps	Not Threatened
Common bully	Gobiomorphus cotidianus	Not Threatened
Giant bully	Gobiomorphus gobioides	Not Threatened		DP
Estuarine triplefin	Grahamina nigripenne	Not Threatened
Grey mullet	Mugil cephalus	Not Threatened		SO
Common smelt	Retropinna retropinna	Not Threatened
Black flounder	Rhombosolea retiaria	Not Threatened		DP
Bridled goby	Arenigobius bifrenatus	Introduced and naturalised		DP, Inc
Brown trout	Salmo trutta	Introduced and naturalised
Rainbow trout	Oncorhynchus mykiss	Introduced and naturalised
Brook char	Salvelinus fontinalis	Introduced and naturalised
Mackinaw	Salvelinus namaycush	Introduced and naturalised
Atlantic salmon	Salmo salar	Introduced and naturalised
Chinook salmon	Oncorhynchus tshawytscha	Introduced and naturalised
Sockeye salmon	Oncorhynchus nerka	Introduced and naturalised
Perch	Perca fluviatilis	Introduced and naturalised		Inc
Tench	Tinca tinca	Introduced and naturalised		Inc
Rudd	Scardinius erythrophthalmus	Introduced and naturalised		Inc
Orfe	Leuciscus idus	Introduced and naturalised
Goldfish	Carassius auratus	Introduced and naturalised		Inc
Koi carp	Cyprinus carpio	Introduced and naturalised
Guppy	Poecilia reticulata	Introduced and naturalised
Gambusia	Gambusia affinis	Introduced and naturalised		Inc
Sailfin molly	Poecilia latipinna	Introduced and naturalised
Swordtail	Xiphophorus helleri	Introduced and naturalised
Caudo	Phalloceras caudimaculatus	Introduced and naturalised		DP
Brown bullhead catfish	Amerirus nebulosus	Introduced and naturalised		Inc
Australian longfin eel	Anguilla reinhardtii	Coloniser
Glass goby	Gobiopterus semivestitus	Coloniser		DP, OL
Goby	Parioglossus marginalis	Coloniser
Taxonomically indeterminate
Lowland longjaw galaxias (Waitaki River)	Galaxias aff. cobitinis ‘Waitaki’	Nationally Critical	A(3)	CD
Teviot galaxias (Teviot River)	Galaxias ‘Teviot’	Nationally Critical	A(3)	DP, RR
Alpine galaxias (Manuherikia River)	Galaxias aff. paucispondylus ‘Manuherikia’	Nationally Endangered	B (3)	DP, OL
Smeagol galaxias (Nevis River)	Galaxias aff. gollumoides ‘Nevis’	Nationally Vulnerable	B (3)	DP, RR
Upland longjaw galaxias (Waitaki River)	Galaxias aff. prognathus ‘Waitaki’	Nationally Vulnerable	B (3)	DP, RR, Sp
Clutha flathead galaxias	Galaxias sp. D	Nationally Vulnerable	C (3)
Dwarf galaxias (Nelson, Marlborough, and North Island)	Galaxias aff. divergens ‘northern’	Declining	C (1)	DP
Northern flathead (Marlborough)	Galaxias ‘Northern sp.’	Naturally Uncommon		RR
Dune lakes galaxias (Kai Iwi lakes)	Galaxias sp	Naturally Uncommon		EF
Southern flathead	Galaxias ‘Southern sp.’	Not Threatened		DP
Upland bully (West Coast South Island, North Island)	Gobiomorphus aff. breviceps	Not Threatened
Note: ^aQualifiers: CD, Conservation Dependent; DP, Data Poor; EF, Extreme Fluctuations; EW, Extinct in the Wild; OL, One Location; RF, Recruitment Failure; SO, Secure Overseas; TO, Threatened Overseas; St, Stable; De, Designated; IE, Island Endemic; Inc, Increasing; PD, Partial Decline; RR, Range Restricted; Sp, Sparse.

Genetic distances observed amongst G. gollumoides (Waters et al. 2001) and Galaxias cobitinus and Galaxias prognathus populations (Waters & Craw 2008) led the threat panel to list lineages within each of these currently recognised species as separate undescribed taxa. No judgement is implied on the likely taxonomic rank of these taxa. In addition, upland bully, Gobiomorphus breviceps, was assessed as two taxa, split as eastern and western forms according to the deepest parapatric divergence found by Smith et al. (2005).

The current ranking has recognised an additional six taxa (Smeagol galaxias from the Nevis River; upland and lowland longjaw galaxias, from the Waitaki River; alpine galaxias from the Manuherikia River; dwarf galaxias from all areas apart from the West Coast and upland bully from the West Coast, Marlborough and North Island) as undescribed, or indeterminate taxa that had not been recognised or ranked in 2005. Three taxa—the Von River galaxias, Shag River galaxias and an undescribed Cran's bully taxa—included in the 2005 ranking process have, in the light of recent research (Burridge et al. 2007) or lack of data, been regarded in the current ranking as belonging to more widespread described taxa.

Threat rankings

The threat status of all taxa is listed in Table 2. For the native freshwater fish (51 taxa excluding colonists), one species, the grayling (Prototroctes oxyrhynchus), was classified as Extinct, but there were no additional extinct taxa since the previous 2005 ranking process. Of the extant taxa, four (8%) were classified as Nationally Critical, three taxa (6%) as Nationally Endangered and seven taxa (14%) as Nationally Vulnerable placing a total of 28% of the extant native freshwater fish taxa in the Threatened categories. Within the At Risk categories, 13 extant taxa (26%) were ranked as Declining, six (12%) as Naturally Uncommon and one (2%) as Relict, comprising 40% of the extant native taxa considered. Sixteen extant taxa (32%) were considered Not Threatened. Excluding the one extinct taxon, 68% of native freshwater fish in New Zealand were classified as Threatened or At Risk, compared with 53% (25 extant taxa) in 2005.

The 20 introduced taxa were ranked as Introduced and Naturalised. Two of these species, Atlantic salmon and mackinaw, are now rare and restricted to the Waiau River system (M. Rodway Southland Fish & Game, personal communication) and Lake Pearson (McDowall 1990; B. Webb Central South Island Fish and Game, personal communication) respectively, and can be considered declining towards extinction in New Zealand. Seven introduced species were also noted as increasing in range either via natural colonisation of new areas or as a result of deliberate (and generally illegal) introductions to new waterways.

The previous listing of freshwater fish (that included only indigenous and endemic species) in 2005 (Hitchmough et al. 2007) ranked six taxa in the Acutely Threatened categories (equivalent to Threatened here) and 14 in the Chronically Threatened (equivalent to At Risk here) categories. Taxa not ranked as Threatened in the 2005 ranking but now ranked include the five new taxonomically indeterminate entities and the riffle and run dwelling species bluegill bully, koaro, torrentfish and redfin bully. Analysis of the NZFFD records showed significant declines in the presence of these four species in database records in the last 10 years (Table 3) with all being rarest in the last decade. Two additional whitebait species, inanga and shortjaw kokopu, were also classified as declining because of loss of habitat for both species (e.g. via land-use change on the West Coast with farm development) and evidence of loss of peripheral populations of shortjaw kokopu in the Wellington region (Allibone personal observation), Kaikoura (NZFFD data) and western Southland (DOC unpublished data) that indicate range contraction for this species is occurring.

Table 3  The percentage occurrence for four migratory native fish (data from NZFFD, June 2009).

	1960–1969			1970–1979			1980–1989			1990–1999			2000–2009
Species	Total^a	<100 m^b	Ef, <100 m^c	Total	<100 m	Ef, <100 m	Total	<100 m	Ef, <100 m	Total	<100 m	Ef, <100 m	Total	<100 m	Ef, <100 m
Redfin bully	18.0	27.7	n/a	14.8	22.3	32.3	15.8	23.8	35.2	16.0	23.9	29.3	11.0	18.7	21.9
Bluegill bully	6.1	10.1	n/a	7.0	10.8	19.2	4.8	6.4	9.8	4.3	6.7	10.5	1.7	3.2	5.2
Torrentfish	9.2	15.0	n/a	9.1	12.2	19.8	9.4	11.9	16.6	8.8	12.3	18.6	4.5	6.9	10.8
Koaro	16.0	9.5	n/a	10.4	9.6	9.7	10.8	9.4	11.9	10.0	6.9	8.5	6.5	4.3	4.9
Note: Percentages in bold indicate the lowest percentage of occurrence for each species. ^aOccurrence recorded in all database records for the decade. ^bOccurrence recorded in all database records at an altitude of 100m or less. ^cOccurrence recorded in all database records at an altitude of 100m or less where electric fishing was a sampling method.

Since 2005, eight taxa—the Canterbury mudfish, Teviot galaxias, dusky galaxias, roundhead galaxias, bignose galaxias, upland longjaw galaxias (in the Rangitata and Rakaia River catchments), Eldon's galaxias and Galaxias spD—have become more threatened and their ranking upgraded. In all cases, these are non-migratory species for which incremental habitat and population loss is occurring. Four species, dune lakes galaxias, dwarf inanga, flathead galaxias and southern flathead were downgraded, although still at risk, because no further decline has been apparent over the last 4 years (DOC unpublished data). The net comparison with 2005 includes 14 additional taxa now considered threatened or at risk (including five of the six newly recognised taxa), and an overall increase in taxa richness from 48 to 51.

The majority of threatened fish are galaxiids with 23 taxa from the Galaxias included in the Threatened and At Risk groups. This genus makes up 68% of all taxa considered threatened. Mudfish, Neochanna, are the second most threatened genus with all five recognised species classified as Threatened or At Risk and contributing 15% of the taxa considered threatened. This is in accordance with the previous threat classifications where Galaxias and Neochanna species have been the most commonly threatened taxa. Gobiomorphus are the third most threatened genus with three species listed as Declining or Naturally Uncommon. In addition, one species from each of the genera Anguilla, Cheimarrichthys, Geotria and Retropinna have been classified as Declining.

Nationally Critical taxa

Four taxa have been ranked as Nationally Critical—Neochanna burrowsius, the Canterbury mudfish; Galaxias cobitinis, lowland longjaw galaxias from the Kakanui River; Galaxias aff. cobitinis, the Waitaki River lowland longjaw from the MacKenzie Basin; and Galaxias ‘Teviot’ from the Teviot River catchment in Otago.

All four taxa are characterised by few extant populations and multiple threats. While the lowland longjaw galaxias in the Kakanui River catchment is the subject of significant conservation effort, no secure populations exist. For the two indeterminate taxa, conservation effort is limited although active management of the Waitaki lowland longjaw galaxias is occurring to prevent salmonid invasion at two locations. Canterbury mudfish continues to decline mainly because of loss of natural habitat, and because very little legally protected habitat exists this decline is expected to continue. It is further threatened by changes throughout Canterbury to the management of irrigation canals, an artificial habitat utilised by Canterbury mudfish. It is likely that this species will retreat to core populations in the Wainiwaniwa Valley and Hororata River areas, as current development continues to eliminate small remnant populations. Teviot galaxias is restricted to three tributaries of the Teviot River (Clutha River catchment) and monitoring has indicated that substantial decline has occurred at monitoring sites in recent years (Department of Conservation unpublished data). Although the reasons for the observed decline are unknown, a continuation of the observed trend is of significant concern. For all four taxa, the lack of formal protection for their habitat is of concern and, if habitat and population losses continue, all four taxa are expected to continue to decline towards extinction.

Regional occurrence of threatened fish

The diversity and distribution of the Galaxias genus has a strong influence on the regional distribution of threatened fish taxa with the majority of the threatened taxa in Otago and Canterbury (Table 4). In these areas, there are a number of locally endemic non-migratory galaxiid taxa, almost all of which are Threatened or At Risk. It is also notable that the majority of the taxa that have increased their threat status are present in these two regions. The status of these threatened fish is exacerbated by the increasingly high demand for water in Central Otago and Canterbury, including the development of the Clutha, Taieri and Waitaki River catchments for hydro-electricity generation, increases in irrigation and changes in land-use activities.

Table 4  Distribution of threatened fish by Department of Conservation Conservancy.

Fish species	Northland	Auckland	Waikato	East Coast Bay of Plenty	Taupo Turangi	Wanganui	Wellington Hawke's Bay	Nelson Marlborough	West Coast	Canterbury	Otago	Southland
Grayling
Canterbury mudfish										X
Lowland longjaw galaxias (Kakanui River)											X
Lowland longjaw galaxias (Waitaki River)										X
Teviot galaxias (Teviot River)											X
Alpine galaxias (Manuherikia River)											X
Dusky galaxias											X
Eldon's galaxias											X
Smeagol galaxias (Nevis River)											X
Upland longjaw galaxias (Waitaki River)										X
Roundhead galaxias											X
Bignose galaxias										X
Upland longjaw galaxias (Rangitata, Rakaia Rivers)										X
Clutha flathead galaxias											X
Northland mudfish	X
Longfin eel	X	X	X	X		X	X	X	X	X	X	X
Torrentfish	X	X	X	X		X	X	X	X	X	X	X
Dwarf galaxias (Nelson, Marlborough, and North Island)				X		X	X	X		X	X
Dwarf galaxias (West Coast)									X
Giant kokopu	X	X	X	X		X	X	X	X	X	X	X
Koaro	X	X	X	X	X	X	X	X	X	X	X	X
Gollum galaxias											X	X
Inanga	X	X	X	X		X	X	X	X	X	X	X
Shortjaw kokopu	X	X	X	X		X	X	X	X			X
Lamprey	X	X	X	X		X	X	X	X	X	X	X
Bluegill bully	X	X	X	X		X	X	X	X	X	X	X
Redfin bully	X	X	X	X		X	X	X	X	X	X	X
Brown mudfish						X	X	X	X
Black mudfish	X	X	X
Northern flathead (Marlborough)									X	X
Dwarf inanga (North Kaipara Head Dune Lakes)	X
Dune lakes galaxias (Kai Iwi lakes)	X
Tarndale bully									X
Chatham Island mudfish							X
Stokell's smelt										X

Threat processes and patterns of decline

A number of threat processes have been identified including land-use change especially agricultural and forestry effects (Hanchet 1990; Rowe et al. 1999 , 2000), predation and competition by introduced fish (e.g. McIntosh et al. 1992; McDowall 2006; Baker et al. 2004) and other native fish (e.g. Allibone 1999), and water abstraction (e.g. Allibone 2000). These factors have been recognised over the last 20 years and the impact of these threats is becoming more apparent on the New Zealand freshwater fish fauna, as more taxa are classified as threatened. However, despite an increasing concern over the state of freshwater (e.g. Parliamentary Commission for the Environment 2004) and increased recognition of impacts, little success has been made in halting the decline of threatened fish taxa. Similarly, little progress has been made in restoring or improving threatened fish populations. The expectation of decline predicted in 2005 for a number of non-migratory species has been realised with the loss of a number of small populations of lowland longjaw, Eldon's, roundhead and dusky galaxias, and Canterbury mudfish (DOC, NIWA unpublished data).

However, decline of some non-migratory galaxiids with limited distributions is related to episodic invasion by predatory salmonids (Townsend 1996; McDowall 2006) and larger native fish (e.g. koaro; Allibone 1999). For many streams, the probability of invasion is related to the loss of a downstream barrier (usually a waterfall where key rock sections are moved or eroded during high flows) or the introduction of predatory fish to areas upstream of the barrier. Some of the non-migratory galaxiid populations remaining today occur in stable and relatively pristine high country streams where land-use and water quantity and quality effects are negligible or stable. The process of invasion for these galaxiid streams is episodic, with stable populations of fish residing upstream of barriers until an invasion event occurs followed by a rapid decline after any invasion event. As the failure rate of such barriers is unknown, the decline rate for species can only be estimated from observations of invasions made over 10–15 years of intensive survey work.

We also recognised that in some cases barrier failure would lead to the loss of only a few metres of stream, because the next barrier was a short distance upstream, whereas in other cases many kilometres of stream would be exposed to invasion if a key barrier were lost. Therefore, it was concluded that for populations in refugia above barriers the decline rates are non-linear, and currently unpredictable in magnitude and frequency. However, for the purposes of this ranking process, populations upstream of large bedrock waterfalls were considered secure, whereas populations upstream of small barriers and boulder barriers were considered insecure. Background waterfall data for this assessment were provided by Allibone & Townsend (1997) and DOC (unpublished data).

The decline of the native freshwater fish is related to a variety of sometimes compounding factors. The widespread migratory species appear to be declining in abundance and distribution throughout their range. Little targeted survey information is available but analysis of the NZFFD indicates that the reported occurrence of some species is declining. For these migratory species, it is highly likely that metapopulation dynamics are an important factor that supports populations of fish even in relatively poor habitat and the species exist as a series of interconnected ‘source and sink’ populations for which the dynamics of recruitment and survival are unknown. In this lies an inherent risk of rapid regional or national decline once sink populations dominate the species and recruitment failure has the potential to occur widely. The extinction of grayling in the 1920–1930s was a possible example of this effect where even though much of the country at this time was unmodified, detrimental effects created by development, salmonid introductions and harvest of grayling likely overwhelmed the fish's reproductive capacity in the secure habitat leading to rapid decline and extinction of this species. The decline now being observed in the NZFFD for what are considered common species indicates that other species are also potentially vulnerable to rapid declines. The general decline in fish abundance and diversity is also evident in a recent review by Joy (2009) of fish communities and diversity in areas of differing land-use. This review indicated that fish diversity is declining in agricultural and urban areas as habitat is degraded and sensitive species are lost.

For longfin eel, there exists an additional risk that the population of migrant eels might drop below a minimum threshold required for successful recruitment. Recruitment of heavily exploited northern hemisphere species of eels has declined markedly over recent decades (Dekker et al. 2003), although there is considerable debate over the reasons. However, despite heavy commercial harvest, eel species overseas have continued to spawn successfully, although there are management initiatives to increase total spawner biomass. Should these initiatives be unsuccessful, it is likely that at some unknown population size, Allee effects will reduce spawning success and recruitment failure is likely. Although the most recent elver monitoring data at dam trap and transfer sites throughout New Zealand indicate recent increases in elver numbers, indicating higher levels of recruitment (Martin et al. 2006 , 2007), this follows a long decline (Jellyman 2009) and it is not apparent if this represents increasing recruitment related to better adult survival, as a result of regulatory changes in the commercial fishery, or is the result of stochastic variations in recruitment. Accordingly, the declining ranking is still warranted until sustained increases in recruitment are apparent together with stable or increasing adult migrant populations.

The second pattern of decline is the incremental loss of populations as evident in the non-migratory galaxiids. The majority of non-migratory galaxiids and mudfish in small streams and wetland habitats are slowly being lost as land-use effects, changes in water quality and quantity, drought and flood effects, and predator invasions continue to impact on these species. A number of species such as Canterbury mudfish, Teviot galaxias, lowland longjaw and Eldon's galaxias now appear to be rapidly declining to a few core areas. A key conservation concern with these declining distributions is that few, if any, key core areas for these threatened fish are protected and that protection mechanisms, such as conservation or reserve status, do not eliminate some substantial threats (e.g. invasion by exotic species, drought and floods). Therefore, without actions to maintain and expand these species, they are expected to become increasingly threatened and the possibility of extinction becomes likely in the near future.

Some populations of non-migratory galaxiids have hitherto been protected by their remote or high altitude locations that have isolated them from effects of land-use change, from didymo invasions, and have been isolated above waterfall barriers that prevented invasion by introduced species (particularly salmonids). However, increasing demand for water is increasing the pressure to utilise freshwater resources from previously unmodified catchments. Land development for dairy farming, both in traditional farming areas (e.g. Southland and Otago) and in areas with more recent dairy conversions (e.g. Westland, inland Canterbury, Buller) is leading to increased water demand, increasing habitat modification and potential declines in water quality. For Canterbury mudfish, the issue is now acute with the loss of habitat related to drainage and habitat modification (e.g. The Press 2008; Canterbury Aoraki Conservation Board 2008) rapidly leading to the species being lost from many of the areas that sustained remnant populations in the 1990s (NIWA unpublished data). It is likely that this species will retreat to core sub-populations in the Wainiwaniwa Valley and Hororata River areas as current developments continue to impact on the small remnant populations. Similarly, populations of other Threatened taxa present in the Waitaki River's MacKenzie Country basin are in areas proposed for development that have the potential to lead to the further decline of these threatened species.

In summary, it is apparent from this threat ranking process that no genus of freshwater fish in New Zealand is immune from the processes of decline and furthermore, since the last review of the status of freshwater fish in 2005, both the abundance and distribution of an additional seven established species have declined, resulting in these species being added to various threat categories. An a dditional five indeterminate taxa have been added to the list, four of which are in the Threatened group. It is apparent that more serious effort is now required to reverse the decline in native freshwater fishes and to manage the instrumental causes of their decline that are ongoing, and in some cases increasing, if the extinction of further freshwater fish is to be prevented.

Acknowledgements

We thank all the parties that contributed submissions to the panel and additional experts, who responded to our requests for further information on aspects of the life history and current population sizes for some species. The manuscript was also improved by the comments of two anonymous reviewers. Fig. 1 was reproduced with the permission of the Department of Conservation.