ABSTRACT1. The Falkland Islands, in the cool-temperate south-western Atlantic Ocean, have an impoverished freshwater fish fauna, with only two indigenous species certainly present there: the Falklands minnow, Galaxias maculatus, and the zebra trout, Aplochiton zebra. Additional species whose presence there is uncertain are the southern pouched lamprey, Geotria australis, and the Patagonian puyen, Galaxias platei. Brown trout, Salmo trutta, were introduced in the mid-20th century, and sea-migratory (diadromous) populations are widespread.2. Distributions of zebra trout and brown trout, particularly, are complementary, suggesting that brown trout are having detrimental impacts on zebra trout. Zebra trout have suffered massive decline over the past few decades and remain largely in restricted areas that brown trout have not yet invaded.3. Owing to their sea-migratory habits, it can be expected that brown trout will eventually invade all significant streams on the Falkland Islands. This raises issues of serious concern since zebra trout are also probably sea-migratory, and therefore need access to and from the sea to complete their life cycles. Therefore, any streams accessible to zebra trout are potentially accessible also to brown trout, raising the spectre that eventually brown trout will invade all the streams where zebra trout persist.4. The existence of landlocked populations of zebra trout provides some form of protection from brown trout invasion, though a landlocked stock does not represent the full behavioural and genetic diversity of zebra trout in Falkland's waters, and must be regarded as a last resort means for conservation.

We examined genetic variation at 13 isozyme loci in three diadromous and two non-diadromous species of galaxiid fish from streams in South and Stewart Islands of New Zealand. Analysis of allele frequency data revealed higher F,, and Nei's D values among conspecific populations of the nondiadromous species. We propose that the genetic structurings of these species are affected by their migratory behaviours. We suggest that the derived condition of non-diadromous behaviour may increase scope for speciation, but also the probability of extinction. This is exacerbated by population fragmentation over the last century.

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.

We examined genetic differentiation among 23 samples of non-migratory river galaxias from 17 streams in the Taieri River system, South Island, New Zealand. Four major genetic types were found, two of which occur in narrow sympatry in one location. These were compared with topotypical material representing Galaxim anomalus from the Clutha system (Otago) and G. vulgaris from the Waimakariri system (Canterbury) in order to establish identity.Morphological examination of these four major genetic types revealed consistent concomitant differences. The results suggest that there are at least three species of river galaxias in the Taieri system: G. anomalus, G. vulgaris and at least one previously undescribed species. We propose that the genetic structuring and subsequent speciation of this group has been promoted by the absence of the marine juvenile phase that is found in five other members of the genus native to New Zealand. This structuring may be exacerbated by population fragmentation over the last century owing to the negative influence of introduced trout. The phylogenetic diversity within the river system mirrors the diverse flora and invertebrate fauna of the region, and has conservation implications that parallel those resulting from our improved knowledge of the New Zealand herpetofauna through the application of genetic analysis. UJ 1!)0(1 The Linnean Society of london ADDITIONAL

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Life-history theory predicts that the optimal strategy in the trade-off between egg size and number varies in relation to resource availability and environmental disturbance. We assessed interspecific differences in egg size, fecundity and other life-history traits in a species complex of stream-resident galaxiid fish, which are distributed across a range of contrasting habitat types on the South Island, New Zealand. Oocyte size, fecundity and reproductive effort were measured from gravid females collected immediately before spawning. Proxy measures of stream productivity, flow variability and predation pressure were extracted from modelled data sets. A suite of different egg sizes were identified across species within the Galaxias vulgaris complex, with mean oocyte volume differing by up to 133% between species. The species with the smallest eggs showed mean size-relative fecundities 246% higher than the species with the largest eggs. A significant negative relationship was found between species' mean egg size and size-relative fecundity, suggesting a trade-off between these traits. Species with larger eggs had larger maternal body size, lower reproductive effort and delayed maturity compared to 'small-egg' species. Consistent with the predictions of life-history theory, species with larger eggs, lower size-relative fecundity, lower reproductive effort and delayed maturity were associated with low productivity, stable streams, whereas species exhibiting the opposite set of traits occurred in relatively productive but disturbed systems.

Distribution, abundance, and habitat preferences of native fish were investigated down the length of a relatively pristine, medium-sized, fourthorder stream on Stewart Island, New Zealand. A limited fish fauna was recorded (six species), including three threatened large galaxiid species (Galaxias argenteus, Galaxias fasciatus, and Galaxias brevipinnis), which have restricted distributions on mainland New Zealand. Results indicated that these large galaxiids occupy diverse habitats including pools and backwaters within the mainstems of this stream. Their extensive distributions and wide habitat usage were attributed to factors such as the intact catchment vegetation, unmodified stream channel, and the absence of introduced fishes, particularly salmonids. Results suggest that some native species have been excluded from mainstem habitats elsewhere in New Zealand. It was also evident that interactions among the native species influenced habitat use; G. brevipinnis avoided backwaters, runs, and pools in reaches occupied by G. fasciatus and Anguilla dieffenbachii; whereas G. fasciatus appeared to avoid habitats occupied by G. M98035Received 30 June 1998; accepted 30 January 2000 argenteus and A dieffenbachii. Maximum densities and biomass of galaxiids and eels occurred in deepwater habitats (>0.75 m). Furthermore the fish inhabiting these deeper waters were larger and more likely to be female. These findings have significant implications for the design and application of sampling protocols for native New Zealand fishes and for the protection of their habitats. If deeper waters are not sampled then species, sex, and size biased data may result.

Genetic differentiation among populations of the Tarndale bully and three other Gobiomorphus species was investigated with mitochondrial DNA sequence variation. Sequences from parts of the mitochondrial cytochrome b gene and control region were obtained for 70 bullies. Specimens of Tarndale bully, known from only five small tarns in the northern South Island of New Zealand, clustered with specimens of common bully from both North Island and South Island locations, and not upland or Cran's bullies. The molecular results are discussed in relation to the morphometric and meristic variation, and the origin of the Marlborough tarns. It is concluded that populations of bullies in the Marlborough tarns are a lake-locked ecophenotype of the common bully and not a phylogenetic species.