Martin L. Bonnett

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 ...

Seasonal arrival patterns of juvenile freshwater eels (Anguilla spp.) in New Zealand

Abstract The arrival season of glass eels of both New Zealand species of freshwater eel, the short‐finned eel (Anguilla australis (Richardson)) and the longfmned eel (A. dieffenbachii (Gray)), was studied by electric fishing of 13 streams/rivers throughout east and west coasts of both North and South Islands at 14‐day intervals. Sites were usually located at the most downstream riffle exposed at low tide, and sampled by single‐pass electro fishing. The species composition was dominated by shortfins, with exceptions being west coast sites, one in the North Island and two in the South Island. From a comparison of species proportions in adjacent catchments, it was concluded that glass eels make choices about entry in particular water‐types. As the stage of pigmentation advanced during the arrival season, “early stage” glass eels were defined and densities of these compared to show seasonal arrival patterns—densities were generally low in August, highest in September‐October, and declined during November‐Dece...

Does one size fit all? An evaluation of length–weight relationships for New Zealand's freshwater fish species

Length–weight relationships are a fundamental tool for assessing populations and communities in fisheries science. Many researchers have collected length–weight data throughout New Zealand, yet parameters describing these relationships remain unpublished for many species of freshwater fish. We compiled 285,124 fish records from researchers and institutions across New Zealand to parameterise length–weight equations, using both power and quadratic models, for 53 freshwater species belonging to 13 families. The influence of location and sex on length–weight relationships was also assessed. Location, in particular, generated different length–weight relationships for 65% of the species examined. Length–weight equations were validated by comparing predicted weights against independently measured weights from 25 electrofished sites across New Zealand and the equations were highly accurate (R2>0.99). Recommendations are made about how to robustly apply this new resource which should assist freshwater fisheries researchers throughout New Zealand.

Variability in spatial and temporal abundance of glass eels (Anguilla spp.) in New Zealand waterways

Abstract The regional and annual variability in the abundance of newly arrived glass eels, Anguilla australis (Richardson) and Anguilla dieffenbachii (Gray), were examined using glass eel densities (n = 100 m–2) from electric‐fishing samples collected at 14‐day intervals over 5 years from 13 streams/ rivers throughout New Zealand. Although the density of shortfin eels exceeded that of longfin eels for any one year, the annual trends for both species were generally similar. Both species behaved independently, but significant factors affecting density were “year” and “region”, with the pronounced regional effect for longfin eels attributed to “coast” (east or west), but not “island” (north or south). There was no evidence of declining recruitment for longfin glass eels.

Habitat preferences of giant kokopu, Galaxias argenteus

Abstract 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.

Diet of giant kokopu, Galaxias argenteus

Abstract 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.

Age and growth of alpine galaxias (Galaxias paucispondylus Stokell) and longjawed galaxias (G. prognathus Stokell) in the Rangitata River, New Zealand

Abstract The age and growth of alpine galaxias (Galaxias paucispondylus) and longjawed galaxias (G. prognathus) were determined from samples of fish collected from the Rangitata River, Canterbury, New Zealand. Both species are small (total length up to 112 mm and 87 mm respectively), slender fish with entirely freshwater life histories. Aged from sagittal otoliths, the majority of fish were age 0+ and age 1+, although alpine galaxias up to age 4+ and longjawed galaxias up to age 3+ were found. Growth of both species was greatest during their first year of life. Alpine galaxias continued to grow in subsequent years, but fish of ages 2+, 3+, and 4+ were exclusively females. Longjawed galaxias showed little increase in length after their first year of growth, but for all ages > 0+ the females were significantly larger than males. Overall, both species are not only similar to each other, but also similar to the dwarf galaxias (G. divergens) and the common river galaxias (G. vulgaris), particularly in terms of...

The influence of juvenile brown trout (Salmo trutta) on habitat use of inanga (Galaxias maculatus) in a stream simulator

Abstract Introduced salmonid fishes may have affected native galaxiid fishes in New Zealand by forcing alterations in their use of spatial resources. A stream simulator was used to test the effects of juvenile brown trout (Salmo trutta) (fork length range 66–115 mm) on habitat use of inanga (Galaxias maculatus) (fork length range 51–100 mm) during autumn. The stream simulator consisted of a single run‐riffle‐pool sequence lined with gravel and cobble substrates, and c. 8 m3 of untreated artesian water was recirculated through the stream simulator at a rate of 3 litres s‐1. Stream invertebrates were introduced into the stream simulator to provide food for the fish. Four experiments were run, each consisting of three 1‐day trials using either 10 inanga, 20 inanga, or 10 inanga and brown trout. Counts of inanga visible in each of 12 designated habitat zones were made throughout the day, and proportions of visible inanga were used in repeated measure ANOVAs to test whether the proportion of fish visible varied according to the time of day, the density of inanga, or the presence of trout. Our experiments showed that neither the presence of juvenile brown trout nor the density of inanga had significant influence on inanga habitat use in the stream simulator. We conclude that in New Zealand streams any influence of brown trout on inanga is more likely to result from predation and/or competition for food by larger brown trout.

Spatial and temporal variability in length of glass eels (Anguilla spp.) in New Zealand

Abstract The spatial and temporal trends in length and pigmentation of glass eels for the shortfinned eel (Anguilla australis (Richardson)) and the longfinned eel (A. dieffenbachii (Gray)), were investigated by electric‐fishing 13 New Zealand streams/rivers on both the east and west coasts, at 14‐day intervals between July and December, from 1995 to 1998. A total of 11 479 glass eels were individually identified, measured, and assigned a pigmentation stage. On the basis of pigmentation, 67% were described as “newly arrived”. Modal pigmentation stage advanced over the arrival season for both species, and on arrival, longfinned glass eels were usually more pigmented than shortfinned glass eels. For any given time, North Island glass eels were consistently more advanced in pigmentation than were their South Island counterparts. Few very early pigmentation stages were recorded from the North Island samples, probably because sample sites were above estuaries and harbours. Longfinned glass eels were generally longer than shortfinned glass eels from the same river. Length of both species declined during the arrival season. Regional differences in mean length provides some indication of arrival patterns—predominantly from the north in an anti‐clockwise dispersal around New Zealand. Recruitment also showed annual variation, which appeared to be influenced by the El Niño Southern Oscillation, with the arrival route appearing to be more strongly from the north‐west during the El Niño phase (persistent westerlies) and from the north‐east during the La Niño phase (more persistent north‐easterlies). The mean length of new arrivals increased in the north and in the south‐west between 1995 and 1997, and decreased in all regions between 1997 and 1998, which could have been the result of changes in the duration of migration. Possible reasons for this include spatial and temporal changes to spawning, and oceanic variations in production.

Distribution and freshwater residence of Stokell's smelt, Stokellia anisodon (Stokell), in the South Island, New Zealand

Abstract Stokells smelt are restricted to some rivers on the east coast of the South Island, New Zealand, mainly in the Canterbury region. Migrations of Stokells smelt into fresh water occur mostly from October to March. Analysis of samples taken from the Rakaia River at intervals during this period suggests that there are successive migrations of maturing fish, which continue to develop sexually during freshwater residence. The duration of residence could not be determined, but the presence of females containing relatively small eggs implies that some smeltremain in fresh water for weeks, or even months. Spawning occurs throughout the season, as ripe and spent fish were found in all the samples examined.