Bruno O. David

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

Abstract 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 ...

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.

Spatial organisation and behavioural interaction of giant kokopu (Galaxias argenteus) in two stream pools differing in fish density

Abstract The spatial organisation and behavioural interactions between giant kokopu (Galaxias argenteus) of varying sizes were investigated in two stream pools which varied in fish density. The spatial distributions offish in Pool A were more exclusive, exhibited less overlap, and appeared to be more stable than those for fish in Pool B. The distinct difference observed between the two pools may have been influenced by fish density which was lower in Pool A (0.27 fish/m2) than in Pool B (0.51 fish/m2). A linear, size (weight) related dominance hierarchy appeared to exist within both pools whereby the heaviest individual was the most dominant. Though primarily nocturnal in habit, the social structure and behaviour of giant kokopu (when active during the day) was comparable to that exhibited by other drift‐feeding fish in the Northern Hemisphere.

Carbon sources supporting large river food webs: a review of ecological theories and evidence from stable isotopes

Abstract Quantifying the contributions of carbon sources that support food webs in large rivers is an important and growing field of ecological research with implications for future management and rehabilitation. Here we review theoretical concepts and recent empirical evidence that address carbon flow through aquatic food webs in large rivers. The literature reviewed focuses on studies using stable isotope analysis, which is a tested framework for identifying the origin of carbon sources that are assimilated by primary consumers and subsequently transferred through the food web to support higher consumers. Theoretical concepts addressing carbon flow in large river food webs have tended to stress the importance of organic matter originating from different sources, such as floodplains (Flood Pulse Concept), local riparian and aquatic primary producers (Riverine Productivity Model), or leakage from upstream processing of terrestrial organic matter (River Continuum Concept). Recent empirical evidence from a range of studies has highlighted the importance of autochthonous carbon, especially in the form of benthic algae and phytoplankton, to food webs in a variety of large rivers. However, some flexibility is apparent within food webs and several studies have identified a range of secondary carbon sources that can also be consistently important, depending on the temporal and spatial patterns of hydrogeomorphic conditions. The geographic spread of studies addressing carbon flow in large river food webs is steadily increasing, although long term data sets remain sparse. Despite this, opportunities exist to improve our understanding of historical changes in river food webs and to develop predictive models of future responses to environmental change through the use of museum collections and rehabilitation case-studies.

Movements of Radio- and Acoustic-Tagged Adult Koi Carp in the Waikato River, New Zealand

Abstract The movement of koi, a highly colored variant of common carp Cyprinus carpio, was monitored for 18 months in the Waikato River, New Zealand, with both radiotelemetry and acoustic telemetry. Koi had large total linear ranges (mean, 39 km), and most fish (74%) monitored for more than 250 d traveled between the Waikato River and lateral habitat. Differences in total linear range and mean daily movement between years suggest a behavioral response associated with reduced habitat availability during periods of low flow. The movements of koi were highly variable and infrequent, suggesting that important long-range movements are missed in short-term studies (<250 d), resulting in underestimations of total linear range. Our data suggest that large numbers of koi could have been intercepted traveling between lateral habitat and the Waikato River during 1 of 2 years, indicating that point source removal would be highly effective. Received June 12, 2009; accepted January 20, 2011

Acoustic and radio-transmitter retention in common carp (Cyprinus carpio) in New Zealand

Common carp (Cyprinus carpio) are notoriously difficult to monitor in water temperatures above 20°C using telemetry owing to transmitter expulsion. To reduce transmitter loss, radio transmitters were anchored to the pelvic girdle and a polymer coating was applied to acoustic transmitters to reduce tissue irritation in two tank trials. Ten dummy transmitters were surgically implanted in each of four groups of adult koi carp, a highly coloured strain of C. carpio. Water temperatures ranged between 7 and 24°C. After 365 days, the control and test groups of each trial had similar expulsion rates (P ≥ 0.30; two-tailed Fisher’s exact probability test). Expulsion rates for uncoated acoustic transmitters were 60% (n = 6), coated acoustic transmitters 50% (n = 5), unanchored radio transmitters 60% (n = 6) and anchored radio transmitters 90% (n = 9). Expulsions occurred 15–362 days after implantation as a result of ulcers at or near the surgical wound. Bacterial infection of the wound appears to be the primary mechanism for transmitter expulsion.

Distribution of fish in tributaries of the lower Taieri/Waipori rivers, South Island, New Zealand

Abstract The distribution of fish within eight small streams feeding into the lower Taieri and Waipori Rivers on the east coast of New Zealands South Island was examined. A total of eight native and two introduced species were recorded. Eels (Anguilla spp.) and giant kokopu (Galaxias argenteus Gmelin) were the most widely distributed species being located in all streams surveyed. Common bullies (Gobiomorphus cotidianus McDowall) and brown trout (Salmo trutta Linnaeus) were also widely distributed being detected in seven and six of the streams respectively. Three streams of potential conservation significance were identified. These were Picnic Gully Creek which contained a significant population of banded kokopu (Galaxias fasciatus Gray), a Category C threatened species, and Cullens and Alex Creeks which contained significant populations of giant kokopu, a Category B threatened species. The population of giant kokopu in Cullens and Alex Creeks currently represents the largest known population of this species on the east coast of New Zealand (excluding Southland). It has been suggested that brown trout may influence the distribution of native galaxiids. The longitudinal distribution of giant kokopu and brown trout in streams was examined at night using a continuous spotlight sampling approach. Distributions of these two species rarely overlapped at a local scale. Coarse habitat use data indicated that brown trout regularly occupied a variety of habitat types including modified agricultural channels. In contrast, giant kokopu rarely used agricultural channels being predominantly located in pool habitats.

Mussel spat ropes provide passage for banded kokopu (Galaxias fasciatus) in laboratory trials

Abstract The use of mussel spat ropes to enable the passage of banded kokopu (Galaxias fasciatus) past perched culverts was tested under laboratory conditions. A 0.5 m high simulated perched culvert was fitted with one of two UV stabilised polypropylene rope types: “Russet Loop” and “Super Xmas Tree”. Four randomised replicate trials using each rope type were conducted to test their respective abilities to provide passage for “fresh‐run” banded kokopu whitebait (migrating post‐larval juveniles). There was no statistical difference in performance between the two rope types, with both performing equally well over each 3 h trial. A high proportion of fish used the ropes to successfully negotiate the structure (mean >85% individuals per trial irrespective of rope type). The high rate of successful passage over a short time period suggests that these ropes may be an effective, affordable and potentially easy retrofit to perched culverts, particularly for native species with similar climbing capabilities to banded kokopu.

A standardised sampling protocol for robust assessment of reach-scale fish community diversity in wadeable New Zealand streams

Abstract The New Zealand fish fauna contains species that are affected not only by river system connectivity, but also by catchment and local-scale changes in landcover, water quality and habitat quality. Consequently, native fish have potential as multi-scale bioindicators of human pressure on stream ecosystems, yet no standardised, repeatable and scientifically defensible methods currently exist for effectively quantifying their abundance or diversity in New Zealand stream reaches. Here we report on the testing of a back-pack electrofishing method, modified from that used by the United States Environmental Protection Agency, on a wide variety of wadeable stream reaches throughout New Zealand. Seventy-three first- to third-order stream reaches were fished with a single pass over 150–345 m length. Time taken to sample a reach using single-pass electrofishing ranged from 1–8 h. Species accumulation curves indicated that, irrespective of location, continuous sampling of 150 stream metres is required to accurately describe reach-scale fish species richness using this approach. Additional species detection beyond 150 m was rare (<10%) with a single additional species detected at only two out of the 17 reaches sampled beyond this distance. A positive relationship was also evident between species detection and area fished, although stream length rather than area appeared to be the better predictor. The method tested provides a standardised and repeatable approach for regional and/or national reporting on the state of New Zealands freshwater fish communities and trends in richness and abundance over time.

Diel patterns of feeding and prey selection in giant kokopu (Galaxias argenteus)

Abstract We examined diel variation in prey selection by giant kokopu, Galaxias argenteus, in relation to diel variation in the abundance of drifting invertebrates in a second order stream in Otago, New Zealand in summer. Clear differences in both the quantity and composition of prey consumed was evident. Greater numbers of aquatic insects were consumed at night relative to the day, whereas more terrestrial insects were consumed by day relative to the night. Giant kokopu were selective in the prey consumed. Trichoptera dominated giant kokopu diet at night even though drift samples collected at night were dominated by Deleatidium mayflies. Results suggest that giant kokopu feed actively during night and day in summer, and that prey selection is influenced by interactions between factors including prey availability, prey characteristics and light.