Galaxias Argenteus Research Articles

Complete versus partial macrophyte removal: the impacts of two drain management strategies on freshwater fish in lowland New Zealand streams

AbstractComplete macrophyte removal to maintain drainage performance in lowland streams can have a negative effect on resident fish communities, but few studies have quantified this impact. Moreover, limited research has been carried out exploring alternative approaches for macrophyte removal that minimise the impact on the resident fish community. The aims of this study were (i) to determine how the current practice of removing almost 100% of available macrophyte cover affects native fish populations in lowland New Zealand streams and (ii) to see whether this impact can be reduced by limiting macrophyte removal to alternating 50‐m sections of the waterway. Native fish populations were surveyed before and after experimental macrophyte removal for the following three treatments: (i) complete macrophyte removal, (ii) macrophyte removal from alternating 50‐m reaches and (iii) control with no macrophyte removal. Radiotelemetry was used to monitor the behavioural response of individual giant kokopu (Galaxias argenteus) to the different treatments. The results of this study suggest that current drain management practices reduce CPUE of fish by 60%. Although limiting macrophyte removal to alternating 50‐m sections did not minimise the community impacts of drain clearing, large giant kokopu did benefit from this strategy. All tagged giant kokopu remained in stream reaches partially cleared of macrophytes, while in completely cleared reaches all individuals were displaced. These results demonstrate the threat current drain management practices pose to New Zealand native fish and highlight the value of trialling alternative methods of macrophyte removal.

A review of radio and acoustic telemetry studies of freshwater fish in New Zealand

Radio and acoustic telemetry have been used in 24 studies of freshwater fish in New Zealand. Although most native species are too small to carry these tags, studies using telemetry have been carried out on four of the larger species, i.e. lampreys (Geotria australis), shortfin and longfin eels (Anguilla australis and A. dieffenbachii) and giant kokopu (Galaxias argenteus). Among the introduced species, telemetry has been used to study movements of brown and rainbow trout (Salmo trutta and Oncorhynchus mykiss) in both rivers and lakes, chinook salmon (Oncorhynchus tshawytscha), koi carp (Cyprinus carpio) and bullhead catfish (Ameiurus nebulosus). To date, studies have almost exclusively been of short-term movements and seasonal migrations. Study objectives range from measuring microhabitats and home ranges to determining the extent of seasonal spawning migrations. The advent of progressively smaller tags will provide increased opportunities to use this technology on a wider range of fish species. Management implications of several studies are presented. Although biotelemetry studies have not yet been used in New Zealand, there are considerable opportunities for using such technology to increase understanding of fish energetics and also stress associated with catch-and-release practices in recreational fishing.

Effects of riparian manipulation on stream communities in small streams: Two case studies

The effects of riparian manipulation in New Zealand are described for two case studies, one a short‐term study of the effects of the removal of riparian vegetation on fish, and the second, a long‐term study of the effect of re‐establishment of riparian vegetation on fish and benthic macro invertebrates. The first case study was an experiment carried out between November 2001 and May 2002. Overhanging bank vegetation and in‐stream wood were removed from short reaches of a small pastoral stream that had intact riparian margins, resulting in a change in stream structure with the formation of shallow uniform runs rather than pool and riffle structures as in unmodified reaches. The removal of bank cover and consequential instream habitat changes reduced inanga (Galaxias maculatus) densities by a factor of four within months of vegetation removal, showing the importance of instream cover and habitat to inanga. Adult longfin eel (Anguilla dieffenbachii) also became less abundant in the cleared reaches, but elvers (Anguilla spp.) became more abundant. In the second case study, pastoral sections in two small streams draining from native forest catchments were restored in 1995/96 by planting riparian vegetation and preventing stock access. After 10 years, the restoration efforts had more than doubled the numbers of giant kokopu (G. argenteus) and redfin bullies (Gobiomorphus huttoni), slightly increased numbers of banded kokopu (G. fasciatus), and decreased shortfin eel (A. australis) numbers by about 40%. The macroinvertebrate communities changed so that they became more similar to those at upstream native forest reference sites. These two case studies show that riparian margins can influence the composition of the fish and macroinvertebrate communities in small streams through the effects on cover, instream habitat and probably water temperature. Riparian restoration was most effective for the fish species that use cover and pool habitat.

Is diel activity determined by social rank in a drift-feeding stream fish dominance hierarchy?

Dominance hierarchies among pool-dwelling drift-feeding fish can determine spatial and temporal segregation of feeding territories. We tested the hypothesis that primarily nocturnal, dominant giant kokopu, Galaxias argenteus, force smaller, primarily diurnal, subordinate giant kokopu to feed by day. To test whether subordinate fish would become more nocturnal in the absence of dominant fish, we temporarily removed dominant fish from stream pools in which stable dominance hierarchies operated. Removal of the dominant fish resulted in a significant increase in the number of smaller giant kokopu active in stream pools at night; however, no change in activity was detected by day. The results indicate that large dominant fish control diel activity of subordinate fish, excluding them from stream pools at times (night) when invertebrate drift densities are at their highest.

Habitat use by banded kokopu (Galaxias fasciatus) and giant kokopu (G. argenteus) co‐occurring in streams draining the Hakarimata Range, New Zealand

Habitat selection by banded kokopu (Galaxias fasciatus) and giant kokopu (G. argenteus) was examined in three first‐ and second‐order restored streams draining the Hakarimata Range, Waikato region, New Zealand. Longitudinal distribution surveys were undertaken recording physical habitat dimensions and cover selection at the location of each banded and giant kokopu. The main habitats used by both species were pools or backwaters, and both species strongly selected debris dams and undercut banks over other types of in‐stream cover. The key features discriminating banded kokopu and giant kokopu habitat were elevation, habitat size, and riparian cover. Banded kokopu were found at higher elevations than giant kokopu, where habitats had smaller dimensions and higher proportions of native bush as riparian cover. Within the study streams, in‐stream debris, in the form of debris dams, was strongly selected as cover by both species and therefore could be an important feature in habitat restoration within the Waikato region, especially in streams where undercut bank cover is scarce.

Diel activity and home range size in relation to food supply in a drift-feeding stream fish

Individuals within a species often compete for resources in both space and time. In dominance hierarchies individuals with the greatest competitive ability will occupy prime locations during optimal periods. We compared spatial and temporal use of habitat, aggression, and feeding success among giant kokopu (Galaxias argenteus) in dominance hierarchies under normal and reduced food supply. Under normal food supply conditions dominant fish were predominantly nocturnal and maintained large home ranges at night. Conversely, subdominant fish were diurnal and occupied large home ranges by day but were generally not observed at night. When the food supply was limited, the utilization of pools was determined by social rank. Dominant fish from each pool increased diurnal activity, home range size, aggressiveness, and the capture of food items offered by day while simultaneously reducing the spatial and temporal activity and habitat use of subdominant fish. These results indicate that behavioral changes in large dominant fish influence and reduce the amount of resources available to subdominant fish. Copyright 2005.

EVIDENCE FOR GIANT KOKOPU MIGRATION BETWEEN FRESHWATER ENVIRONMENTS FROM MICROPIXE MEASUREMENTS OF SR IN OTOLITHS

The giant kokopu, Galaxias argenteus, is a native New Zealand freshwater fish which optionally undergoes a marine larval phase after hatching near a river mouth. The marine phase is indicated by a high Sr : Ca ratio in the core of the otolith of the adult fish. Elemental scanning for Sr and Ca with a proton microprobe is one of the most useful techniques for identifying and quantifying the presence of the marine core. However, many individuals, whether or not they show the marine core, exhibit one or more concentric rings of slightly elevated Sr levels outside the core. Examples of this behaviour are given and quantitative estimates of the degree of elevation of the Sr levels are made from both area and line scans using high efficiency detectors for Sr detection. It is suggested that these Sr variations reflect adult fish migration within a freshwater habitat, perhaps seeking a brackish zone in which to spawn.

Seasonal variation in diel activity and microhabitat use of an endemic New Zealand stream‐dwelling galaxiid fish

Summary1. Seasonal variation in microhabitat use and activity of 14 giant kokopu Galaxias argenteus, a drift‐feeding galaxiid fish, was compared using radiotelemetry.2. During winter giant kokopu predominantly used low velocities and intermediate depths by night and day. Activity recorded during 24 and 72 h periods indicated that fish were consistently active at night and inactive during the day. Activity data corresponded with point‐in‐time habitat use data, both of which indicated that fish were concealed amongst cover during the day and used open water habitats at night.3. During summer, giant kokopu used higher water velocities, shallower depths and coarser substrata, particularly at night but also occasionally during the day relative to winter. Giant kokopu were active by both day and night in summer, although periods of activity were less defined and less predictable than during winter.4. Adults used predictable home reaches at base‐flow, with most individuals repeatedly using of one or two cover locations within their ‘home’ reach. Reaches used by fish were relatively short (rarely exceeding 26 m) irrespective of season and always included a single pool‐riffle sequence.5. Diel and seasonal behaviour of giant kokopu was generally comparable with that exhibited by other drift feeding fish species in small temperate streams. However, the nocturnal activity of giant kokopu contrasts with activity patterns in various salmonids, indicating that the impact of predation by different drift feeding fish may vary considerably.

Ontogenetic shift in nocturnal microhabitat selection by giant kokopu in a New Zealand stream

Nocturnal microhabitat selection in relation to size was examined for a New Zealand drift‐feeding freshwater fish, the giant kokopu Galaxias argenteus in three coastal Otago streams. Evidence for ontogenetic shifts in microhabitat selection were observed, particularly with respect to water velocity and depth. Small (<80 mm) giant kokopu tended to occur in shallow backwaters adjacent to fast flowing water. In contrast, larger individuals (≥80 mm) were most commonly observed in deeper, slower flowing pools. These patterns of habitat selection are most likely associated with the trade‐offs involved with the selection of optimal habitats for drift feeding combined with avoidance of intra‐specific competition and the threat of predation from larger conspecifies.

Ontogenetic shift in nocturnal microhabitat selection by giant kokopu in a New Zealand stream

Ontogenetic shift in nocturnal microhabitat selection by giant kokopu in a New Zealand stream

Behavior of a Stream-Dwelling Fish before, during, and after High-Discharge Events

The movements of giant kokopu Galaxias argenteus were recorded before, during, and after high-discharge events in two small streams using radiotelemetry. Giant kokopu remained within defined stream reaches during base flow conditions. During high-discharge events, individuals either stayed within their home reach, moved and settled elsewhere, or moved and returned to their home reach as flows subsided. The variable behavior exhibited by individual giant kokopu suggested that reasons for moving during floods are complex. Reasons that may have influenced movement during floods included reproduction and mate searching, lack of adequate refugia, or some combination of these. In many instances, individual giant kokopu appeared to exhibit adaptive behaviors in response to high discharges. Behaviors supporting this view included fish not moving during the highest floods, fish moving upstream during the peak discharge period, and fish making purposeful “micromovements” (movements <5 m) into low-velocity habitats. This study shows that high-discharge events may play an important role in organizing populations of fish in small streams by providing opportunities for individuals restricted during base flow conditions to move to other stream locations.

Diet of giant kokopu, Galaxias argenteus

The stomach contents of 105 preserved specimens of giant kokopu, Galaxias argenteus (Gmelin 1789), collected from various locations around New Zealand between c. 1963 and 1994, were used to investigate giant kokopu diet. A total of 76 food taxa, predominantly invertebrates, were identified and categorised as either of aquatic or terrestrial origin from the 91 stomachs that contained food items. Aquatic Trichoptera, Gastropoda, and Hemiptera comprised 29.1, 12.6, and 14.4% by abundance respectively, and terrestrial Coleoptera 12.2% by abundance. Adult terrestrial Coleoptera were the most commonly occurring taxa, and were found in 59% of the stomachs that contained food. Food items of aquatic origin occurred in 94.5% of the giant kokopu stomachs that contained food and comprised 74.9% of the items by abundance. Although fewer items of terrestrial origin were encountered, they nevertheless appeared to be a significant component of the diet, and occurred in 83.5% of the giant kokopu stomachs that contained food, and comprised 25.1% of the items by abundance. Items of terrestrial origin occurred slightly more frequently in giant kokopu from lotic habitats than from lentic habitats. The significance of terrestrial food may be associated with giant kokopu preference for habitats with riparian cover. Fish also appeared to be a significant component of the diet, as 26% of the giant kokopu examined contained fish remains. Giant kokopu are probably best described as generalist feeders, as they utilise a wide range of foods of both aquatic and terrestrial origin.

Habitat preferences of giant kokopu, Galaxias argenteus

The giant kokopu (Galaxias argenteus (Gmelin 1789)) is endemic to New Zealand, and is regarded as threatened. A perceived decline of the species has been attributed mostly to the loss and degradation of its habitat. To determine habitat requirements, information from the New Zealand Freshwater Fisheries Database, and from field surveys in the South Island were analysed. These indicated that five habitat features are important: in‐stream cover, deep water, low water velocity, proximity to the sea, and overhead shade/riparian cover. These features were important in two distinct regions surveyed and for both juvenile and adult fish. The effects of different types of riparian and in‐stream cover were examined, but it appeared that the presence of some form of cover was more important than its composition. The conservation and management of giant kokopu will probably continue to be based upon management of their habitat, and these processes will be enhanced by the knowledge of the species’ habitat requirements.

Habitat use and longitudinal distribution patterns of native fish from a near pristine Stewart Island, New Zealand, stream

Distribution, abundance, and habitat preferences of native fish were investigated down the length of a relatively pristine, medium‐sized, fourth‐order 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. 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.

Date and age at migration in juvenile giant kokopu, Galaxias argenteus (Gmelin) (Teleostei: Galaxiidae) and estimation of spawning season

Juveniles of giant kokopu (Galaxias argenteus (Gmelin)) that had newly entered fresh water were captured, primarily from the Buller and Hokitika Rivers, New Zealand, between 5 November and 15 December (when sampling ceased). Age at migration estimated from otolith daily growth rings was mostly c. 104–140 days. There is a positive relationship between fish length and number of otolith growth rings at migration, though variation is broad. Back calculation to hatch indicated that hatching occurred 185–245 days after 1 January (4 July‐2 September); allowing 28 days for development, these data suggest that giant kokopu spawn between early June and early August.

Distribution, abundance and conservation status of native fish in some Waikato streams in the North Island of New Zealand

Abstract The distribution and abundance of native fish were investigated in 16 tributary streams of the Waikato River near Hamilton, in the region of Pirongia Forest Park and the Hakarimata Range , and two nearby coastal streams. We found a total of twelve species of native fish, and two introduced species (rainbow and brown trout), at study sites in upland native forest and lowland pastoral areas. At most sites the fish community was relatively depauperate, both in species diversity and in abundance. Only longfinned eel was found at the majority (92%) of sites, while other species were recorded from a minimum of 2% (inanga) to a maximum of 30% (common bully) of sites. Over half of all native fish species were recorded at fewer than 10% of all sites; species in the family Galaxiidae were recorded from only 7% of sites. Large galaxiid species (banded, giant and short-jawed kokopu and koaro) were very sparsely distributed and low in abundance at most sites, and were generally absent from lowland pastoral sites, where the fish community was dominated by eels and common bully. Rainbow and brown trout were quite widely distributed throughout the study area. We consider that only two species of native fish (longfinned eel and common bully) could be classified into the IUCN conservation status of common, while two species (redfinned bully, Cran's bully) were rare, and four species (banded kokopu, giant kokopu, shortjawed kokopu, koaro) appear to be either vulnerable or endangered. Habitat loss and degradation, mainly through deforestation and agricultural development, appear to be the main explanations for the decline of native fish in Waikato tributaries, but other factors, such as predation and competition from introduced species of exotic fish and overfishing of whitebait in the lower reaches of the river, may possibly contribute to the problem.

Effect of land use on the distribution and abundance of native fish in tributaries of the Waikato River in the Hakarimata Range, North Island, New Zealand

Abstract The effect of land use on fish community structure was examined at fifty‐five sites in tributaries draining exotic, indigenous forest and pastoral catchments in the Hakarimata range in March and April 1987. Using a model containing percentage woody debris, temperature, and substrate coarseness, 76% of the sites were classified into correct land uses by discriminant analysis. This indicated that differences in stream habitat, and hence of the fish fauna, were related to effects of changed land use rather than other confounding physical or geographical features of the streams in the catchments. Tributaries in indigenous forest were numerically dominated by banded kokopu (Galaxias fasciatus) and longfinned eel (Anguilla dieffenbachii), with redfinned bully (Gobiomorphus huttoni) and giant kokopu (G. argenteus) occasionally being caught. Pastoral streams below the forest generally supported higher densities and contained more species including the forested species above, Cran's bully (G. basalis), and shortfinned eel (A. australis). As the amount of indigenous forest in the catchment decreased the fauna became less abundant and less diverse and was dominated by both species of eel and Cran's bully.