Estimating the abundance of banded kokopu (galaxias fasciatus gray) in small streams by nocturnal counts under spotlight illumination

The abundance of banded kokopu (Galaxias fasciatus Gray) in small streams has usually been determined by the labour intensive and invasive method of electric fishing. Recently, nocturnal counts under spotlight illumination have been used to determine presence or absence and relative abundance of banded kokopu, but the proportion of the population seen was unknown. We compared 20 spotlight counts of banded kokopu in approximately 20 m reaches in streams in the North Island, New Zealand, to population estimates determined by removal electric fishing in the same reaches. Spotlight counts were related to population estimates over a range of densities, and on average, spotlight counts were 64% of the population estimates. Though we tried to separate age-0 fish from older fish visually in the spotlight counts, the size frequency distribution of the fish caught by electric fishing showed that the visual separation was not reliable. In addition, visual counts were generally inefficient for age-0 fish (40-70 mm total length), as only about 40% were observed. Banded kokopu were also recorded in streams using time-lapse video recordings with a camera sensitive to low light levels. Diel activity showed two major peaks, one in the early morning from 0400 h to 0900 h, and the other in the afternoon and evening from 1300 h to 1900 h. Fish were less disturbed by the observer.s approach after dark than during the day, so we suggest that from dusk to about 2200 h is the best time for visual counts of banded kokopu by spotlight in summer months

Gravel galore: Impacts of clear-cut logging on salmon and their habitats

Timber harvest may have both direct and indirect effects on salmon, and with a few exceptions those effects result in lowered survival of salmon in their stream habitats compared with unlogged forest (Hicks et al. 1991b). Some impacts may be seen immediately or shortly after logging, whereas others can take decades to be expressed. Central to analyzing these effects is the context of the freshwater environment in which salmon are spawned and reared, and the life histories of the salmon species. This chapter will examine the effects of timber harvest on the freshwater habitat and life stages of salmon. It will also investigate the hypothesis that the salmon species least affected by timber harvest are those with the least reliance on stream habitats

Biology and potential impacts of rudd (Scardinius erythrophthalmus L.) in New Zealand

Rudd (Scardinius erythrophthalmus) is a cyprinid fish native to Europe that was illegally introduced into New Zealand in 1967. Between the 1960s and 1980s rudd were illegally spread to a number of lakes, ponds, and rivers in New Zealand, principally from the Waikato north. They now also occur in the Wanganui, Manawatu, Nelson, and Canterbury regions. Rudd undergo ontogenetic changes in diet as they grow. Young-of-the-year rudd (58–65 mm mean fork length (FL)) ate a mixture of planktonic cladocerans and chironomid pupae, and potentially competed for these foods with common smelt (Retropinna retropinna). Larger rudd (100–149 mm FL) were primarily benthivorous, and potentially competed with perch (Perca fluviatilis) of the same size, brown bullhead catfish (Ameiurus nebulosus), and probably common bullies (Gobiomorphus cotidianus). Rudd of still larger sizes were increasingly herbivorous, until at >200 mm FL their diet was >80% plant material. As rudd prefer native species of aquatic macrophytes to the introduced species, they can probably modify native plant communities and aid the invasion of introduced aquatic weeds. They may also have contributed to the switch of Hamilton Lake from a macrophyte-dominated state to a phytoplankton-dominated state. It is time for the threats posed by rudd to be recognised, and for an education campaign to be mounted. As past rudd introductions have been done outside the law, increasing the severity of penalties for further illegal transfers is unlikely to be effective, and the coarse angling community should instead be included in management decisions concerning rudd

Macroinvertebrates and water quality: a teaching guide

Streams support a diverse community of plants and animals on or in the stream bed. These organisms comprise the benthos. Among the benthos are worms, molluscs, crustaceans, and larval insects. Insect larvae are usually the most numerous animals of the benthos. Collectively the animals of the benthos are known as benthic macroinvertebrates because of where they live, and their large size (often 10-35 mm)

Food webs in forest and pasture streams in the Waikato region, New Zealand: A study based on analyses of stable isotopes of carbon and nitrogen, and fish gut contents.

Stable isotopes of carbon (C) and nitrogen (N) were studied in 11 stream communities in the Waikato region of New Zealand. From comparisons of mean d13C and d15N values, food webs in the shaded, forest streams were clearly based on allochthonous material (conditioned leaf litter and terrestrial invertebrates). Autotrophs in forest streams were not a significant C source for the food webs. However, the C source of food webs in the unshaded pasture streams appeared to be a mixture of allochthonous and autochthonous material. Conditioned leaf litter appeared to contribute to the pasture stream food webs, and the d13C and d15N of some samples of epilithic diatoms indicated their consumption by invertebrates in pasture streams. Fish ate a wide range of aquatic invertebrates; longfinned eels (Anguilla dieffenbachiai) and banded kokopu (Galaxias fasciatus) also had a large proportion of terrestrial invertebrates in their diet. Filamentous green algae were found only at pasture sites, where they were sometimes abundant. The wide range of d13C values of filamentous green algae (-18.8 to -29.7[[perthousand]]) complicated understanding of their role in the stream food webs. The d13C values of Cladophora were related to water velocity, with more 13C-enriched values in pools than in runs (-23.2[[perthousand]] in pools, mean velocity 0.12 m s-1; -28.1[[perthousand]] in runs, mean velocity 0.24 m s-1). Crayfish and the gastropod mollusc Potamopyrgus appeared to be the only invertebrates to eat filamentous green algae

Influence of open and closed river systems on the migrations of two northern New Zealand populations of banded kokopu (Galaxias fasciatus)

Otolith microchemical analysis by laser ablation inductively coupled mass spectrometry (ICP-MS) was used to investigate the migratory life histories of banded kokopu (Galaxias fasciatus) in two streams on the North Island of New Zealand. Known differences in marine and freshwater chemistry were used as a premise to document the migratory life strategies of banded kokopu between these environments. More specifically, temporal trends in high and low strontium/calcium ratios (Sr/Ca) identified in fish otoliths were used to determine evidence of migration between fresh and saltwater environments. Trace element analysis of fish captured above the Whau Valley Reservoir reflected non-migratory life histories and exhibited consistently low Sr/Ca ratios across the entire otolith. However, one fish from above the reservoir indicated unusually high Sr/Ca ratios in early adulthood. These high Sr levels were attributed to localised inputs from mineral-rich seepages associated with past mining practices in the region and low calcium availability within the Pukenui Stream. Otoliths from banded kokopu collected from Komiti Stream were shown to be migratory with a marine larval stage (high Sr/Ca ratio levels at the otolith nucleus), followed by a freshwater adult phase (low Sr/Ca ratio levels towards the edge) indicating their amphidromous origins. The study provides further evidence of non-diadromous recruitment for banded kokopu as a consequence of a large in-stream barrier and will add to the known distribution of landlocked species in New Zealand

Habitat requirements of black mudfish (Neochanna diversus) in the Waikato region, North Island, New Zealand.

Black mudfish (Neochanna diversus) were found at 39 of 80 sites in the Waikato region, New Zealand, ranging from large wetlands to small swampy streams. Of the sites with mudfish, 87% were dry at some time during summer. Sites with mudfish also generally had emergent and overhanging vegetation and tree roots, and showed low to moderate human impact. Black mudfish coexisted at some sites with juvenile eels or mosquitofish, but were absent from all sites with common bullies (Gobiomorphus cotidianus) or inanga (Galaxias maculatus). Sites with mudfish had almost exclusively semi-mineralised substrates or peat; only one site had mineralised substrate. Geometric mean catch rate for the 39 sites with mudfish was 0.70 fish per trap per night. Mean summer water depth was only 2.1 cm at sites with mudfish, compared to 22.6 cm at 41 sites without. Winter and maximum water depths were also less at sites with mudfish than at sites without mudfish. Mean turbidity was 11.5 nephelometric turbidity units (NTU) at sites with mudfish, but 21.3 NTU at sites without mudfish. Mudfish catch rates were negatively correlated with summer water depth, winter water depth, disturbance scale rating, and turbidity. A discriminant function model based on these variables successfully predicted 95% of the sites with mudfish. Habitat preference curves are also presented

Otolith chemistry, stomach contents and stable isotope analysis of a snapper (Pagrus auratus) caught in the Waikato River at Ngaruawahia

Analyses of stomach contents, stable isotopes and otolith microchemistry were carried out in order to ascertain the length of freshwater residence of a snapper (Pagrus auratus) caught in the Waikato River at Ngaruawahia in a net set for grey mullet(Mugil cephalus). Results of all analyses suggest that the snapper had spent all of its life in a marine environment with no evidence of freshwater residence in the otolith. Stable isotope analyses (δ15N = 17.0‰, δ13C = –17.1‰) indicated an entirely marine diet, and the stomach contents (two New Zealand screwshells, Maoricolpus roseus, and a hermit crab, Pagurus novizelandiae), suggested that the fish had not fed while in freshwater. However, this does not preclude the possibility that the snapper quickly travelled up the river, without eating, and was caught very soon after

Physical environment, nutrient budget, and ecology of Lake Moana-nui, Tokoroa

This report is based on fortnightly monitoring data collected over a 14 month period from November 2000 to January 2002 and a survey of the lake bathymetry and vegetation distribution. The project also included a detailed investigation into the associations between macroinvertebrates and the native and exotic plants in the lake, and experiments evaluating the effects of the large populations of the water flea Simocephalus vetulus that the lake maintains on algal concentrations and therefore water clarity. The aim of this report is to present and discuss the results of the monitoring, surveys, and experiments in order to make recommendations for the future management and health of Lake Moana-nui

Age and growth of longfinned eels (Anguilla dieffenbachii) in pastoral and forested streams in the Waikato River basin, and in two hydro-electric lakes in the North Island, New Zealand

Growth rates of New Zealand endemic longfinned eels (Anguilla dieffenbachii) from streams in pasture and indigenous forest, and from two hydroelectric lakes (Lakes Karapiro and Matahina), were estimated by otolith examination. Habitat-specific growth was further investigated with measurement of widths of annual bands in otoliths. Longfinned eels 170-1095 mm in length ranged between 4 and 60 years old (N=252). Eels in pastoral streams grew faster (mean annual length increment ±95% CL = 24 ± 3 mm to 36 ± 7 mm) than eels in streams in indigenous forest (annual length increment 12 ± 2 mm to 15 ± 3 mm). Eels from the hydro-electric lakes had growth rates (annual length increments 19 ± 4 and 19 + 7 mm) similar to eels from pastoral streams. Otoliths of most eels showed annual band widths that indicated growth in several different habitats, corresponding to growth during upstream migration, and limited movement among adult habitats. Estimated age at marketable size (220 g) ranged between 7 and 26 years. The particularly slow growth of longfinned eels in streams in indigenous forest has considerable implications for management. The fast growth rates of eels in hydro-electric lakes provides evidence for the potential of increased eel production by stocking. The probable selective production of female eels in these lakes may be nationally important to allow enhancement of breeding stocks