G. J. Glova

Potential Effects of Reduced Flows on Fish Habitats in a Large Braided River, New Zealand

Abstract To predict the effects of reduced flows on potential rearing habitat for fish in a large braided river (the lower Rakaia River on South Island, New Zealand), water depth, velocity, and substrate data were collected along transects in two representative reaches at five discharges ranging from 69 to 146 m3/s during 1981–1982. From these measurements and habitat-suitability curves, weighted usable area (WUA) was computed for each of six species of fish. Within both reaches WUA declined with decreasing discharge for each of the native fish species, although variably so in space and time (2–33%), whereas for the two exotic salmonid species there was no consistent and appreciable change. The overall decrease in WUA was attributed primarily to the loss of habitat in minor channels (<1 m3/s). Weighted usable area ranged from approximately 20,000 m2/km of river for juvenile chinook salmon Oncorhynchus tshawytscha, which prefer relatively deep, slack water with cobble-bedded substrates, to 80,000 m2/km for...

Factors associated with the distribution and habitat of eels (Anguilla spp.) in three New Zealand lowland streams

Abstract The distributions of shortfinned eels (Anguilla australis) and longfinned eels (A. dieffenbachii) of all sizes in three New Zealand coastal streams were investigated during summer by sampling stratified, randomly chosen pool, run, and riffle sites from tidal to upper reaches. In all streams, both species were widespread, although a greater proportion of the total population of shortfinned eels was present in the lower reaches and small eels (<300 mm total length (TL)) had advanced further up stream than longfins in two of the streams. The biomass (g m‐2) of longfinned eels <300 mm TL was greatest in riffles, whereas that of comparable‐sized shortfinned eels was evenly distributed across habitat types in all streams; in contrast, eels ≥300 mm TL of both species showed no consistent pattern of habitat use between streams. Multiple regression analysis of species biomass (g m‐2) for four size groups (<100; 100–199; 200–299; ≥300 mm TL) against 16 habitat variables, indicated that the distribution of ...

Comparison of fish and macroinvertebrate standing stocks in relation to riparian willows (Salix spp.) in three New Zealand streams

Abstract The distribution of fish and benthic invertebrates in relation to riparian willow (Salix spp.) concentrations was investigated in three New Zealand streams. In each of the streams, representative sites were sampled quantitatively in willowed and non‐willowed sections. The abundance (m‐2) and biomass (g m‐2) of brown trout (Salmo trutta L.) were significantly greater in the willowed than in the non‐willowed sections in two streams; the third stream showed the same trend but any differences were not significant. Mean size of trout was greater in the willowed than in the non‐willowed sections, but size of fish varied greatly and the differences were not significant. Eels (Anguilla spp.) showed no consistent pattern in population characteristics between streams; however, their abundance in one river and biomass in another were significantly greater in the willowed than in the non‐willowed sections. Distribution of other fish (e.g., Galaxias spp. and Gobiomorphus spp.) appeared not related to riparian...

Prey availability and diet of juvenile brown trout (Salmo trutta) in relation to riparian willows (Salix‐spp.) in three New Zealand streams

Abstract Macroinvertebrate benthos and drift and the diet of juvenile brown trout (Salmo trutta) were investigated in willowed and non‐willowed sections of three New Zealand streams during summer. The abundance and biomass of the principal macroinvertebrate taxa in the benthos and daytime drift differed in relation to riparian willow (Salix spp.) density, but the trends were not consistent across all three streams. Crustacea, Ephemeroptera, Trichoptera, and Diptera comprised a major proportion of the diet of juvenile trout. Diets of trout from non‐willowed and willowed sections were dissimilar in three of five pair‐wise comparisons. In all three streams, juvenile trout fed selectively, with the amphipod Paracalliope fluviatilis, ephemeropteran Deleatidium, and trichopterans Aoteapsyche and Hydrobiosidae being the preferred prey. Their avoidance of the gastropod Potamopyrgus antipodarum, trichopteran Oxye‐thira albiceps, coleopteran Hydora, and drift of terrestrial origin appeared to occur in all streams. ...

Behavioral Interaction between Chinook Salmon and Brown Trout Juveniles in a Simulated Stream

Abstract The behavioral interaction between underyearling Chinook salmon Oncorhynchus tshawytscha and brown trout Salmo trutta, both exotics in an unnatural sympatry in New Zealand, was tested during spring and summer in a simulated stream containing natural food. Both species were highly territorial and actively defended preferred drift-feeding sites and resting areas in the pool. Species dominance differed with season and was influenced by prior residence. In spring, Chinook salmon were larger (because of their earlier emergence) and socially dominant, but they did not dominate when brown trout had prior residence. In summer, interspecific differences in size no longer existed, and brown trout were always socially dominant, although dominance required more time to establish when Chinook salmon were prior residents. Most aggressive attacks of both species were initiated and won by the dominant fish in both spring and summer. Yearling brown trout in the pool in summer did not influence the interaction bet...

Prey selection by Galaxias vulgaris in the Hawkins River, New Zealand

Abstract To determine the extent of prey selection by the nocturnally active fish Galaxias vulgaris, samples of fish, drift, and benthos were collected over a 24‐h period in summer in a stream draining the foothills of the Southern Alps in New Zealand. Feeding started after sunset, peaked by midnight, and virtually ceased by midday. Both drifting and benthic foods were consumed, and timing of peak feeding was synchronous with the period of greatest abundance of aquatic drift. Larvae of Austrosimulium spp., Deleatidium spp., and Aoteapsyche colonica comprised the major proportion of the prey eaten. Prey selection was indicated by the over‐representation of Austrosimulium spp. and under‐representation of both the smaller size classes of Deleatidium spp. and other aquatic invertebrates in the diet of fish. With the exception of the coleopteran Costelytra zelandica, terrestrial organisms were not eaten by fish, but several aquatic taxa were. Foraging by Galaxias vulgaris on drift and benthos may provide fish ...

Movements of shortfinned eels, Anguilla australis, in Lake Ellesmere, New Zealand: Results from mark‐recapture studies and sonic tracking

Abstract Movements of non‐migratory and migratory shortfinned eels in Lake Ellesmere, New Zealand, were studied from recaptures of streamer‐tagged eels and tracking of eels tagged with sonic transmitters. Of the 9956 streamer‐tagged eels, 1982 were recaptured by commercial fishers over 5 years, some as many as 7 times. Most non‐migratory eels were recaptured at, or adjacent to, their original capture site, although some eels had moved to 11 of 12 regions in the lake within 3 weeks of tagging. Transplanted non‐migratory eels showed a tendency to home to their original capture site. Although most eels do not appear to move more than a few kilometres they are capable of periodic extensive movements; we conclude that there is a single population in the lake. The mobile portion of the population will be important in repopulating areas where eel numbers have been reduced by commercial fishing. Migrating eels always congregated at Taumutu, the area where the lake is artificially opened to the sea. There was some...

Fish density variations in the braided Ashley River, Canterbury, New Zealand

Abstract To determine variation in abundance (m‐2) and biomass (g m‐2) of fish populations in the lower Ashley River, New Zealand, a representative reach was sampled by electric fishing during periods of low, stable flows in two consecutive summers (1981 and 1982). For nine species of fish combined, abundance and biomass in riffles differed by 50% and 41% respectively between the two summers. Size frequency distributions for three of the most common migratory species differed significantly between summers and may partly explain the variation in fish standing stock. Abundance of fish, mostly under 150 mm body length, was highest in riffles (3.0 m‐2), whereas biomass was highest in pools (46.5 g m‐2) owing to the presence of a few large eels and trout. Within riffles, there was no significant difference in the longitudinal and cross‐sectional distributions of the more common fish species present. Both abundance and biomass of fish were lowest in runs, the habitat with the least apparent cover for fish. Limi...

Spatio‐temporal distribution of fish in the Kakanui River estuary, South Island, New Zealand

Abstract The fish community of the Kakanui River estuary on the east coast of the South Island, New Zealand, was studied seasonally over 1 year by diel seine netting and nocturnal fyke (trap) netting. Twenty species were recorded, although nine of these together constituted 0.2% of the total number of fish caught. Marine species were represented by single individuals of four species. Brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) were the only species without an obligatory marine life‐history phase. Small benthic fishes, cockabullies (Tripterygion nigripenne), and common bullies {Gobiomorphus cotidianus) were the numerically dominant species and, together with a further nine species, were resident year‐round. Winter was the season of lowest abundance of most species. Spatial patterns of distribution were apparent with common bullies, giant bullies (G. gobioides), and longfinned eels (Anguilla dieffenbachii) occurring mainly in the upper estuary; common smelt (Retropinnna retropinna) ma...

Movements and habitats of adult lamprey (Geotria australis) in two New Zealand waterways

Abstract The spring upstream spawning migration of the Southern Hemisphere lamprey, Geotria australis Gray, was investigated by monitoring movements of radio‐tagged lampreys in two South Island, New Zealand, catchments of contrasting size (Okuti Stream, a small coastal stream and the Mataura River, a medium‐sized lowland river). A total of 65 lampreys were radio‐tagged and tracked by foot and helicopter between 1998 and 1999. Retention of the externally‐mounted tags proved a problem, and lampreys were tracked for a maximum of 56 days. Most movement was recorded within a few days of release; movement was generally up stream although a number of fish also periodically moved down stream. Maximum daily movement in the Okuti Stream was 0.45 km compared with 12.6 km in the Mataura River; upstream movement was stimulated by increased flow but curtailed by large floods. During the day, lampreys were generally associated with bankside debris cover. The seven fish that moved furthest up the Mataura River all entered the same tributary, presumably in response to odours of their conspecifics. Thirteen lampreys retained for a year and released as nearly sexually mature, moved little from their place of liberation and possible reasons for this are discussed.