Lake Waahi Research Articles

First observations and early life-history aspects of lake rearing galaxiid larvae in the lower Waikato River Basin, New Zealand

ABSTRACT Larval behaviour for many of New Zealand’s diadromous freshwater fish is inadequately described. Diadromy for many amphidromous species is not obligatory however, and where conditions are suitable, freshwater larval rearing may be facilitated. Where this occurs in lakes, opportunities to document the composition and conditions supporting larval rearing exist. Boat trawling was undertaken across nine lowland lakes in the Lower Waikato over four consecutive winters with a focus on larval galaxiids. Galaxiid larvae were captured in surface water habitats in all but one lake, with banded kōkopu (Galaxias fasciatus) and giant kōkopu (Galaxias argenteus) the most common species detected. One lake, Lake Waahi, consistently resulted in the most galaxiid captures for effort expended. Analyses of larvae from this and other lakes indicated that two sizes predominated in catches and that larger, older larvae were predominantly G. fasciatus while smaller, younger larvae were predominantly G. argenteus. Stomach contents indicated that two non-native zooplankton species predominated in the diet of larvae, the Holarctic daphnia, Daphnia galeata, and the Australian calanoid copepod Boeckella symmetrica. This study provides new information regarding the timing, movement and predicted recruitment of native fish species in this river basin that has important implications for lake and river management.

Long-term zooplankton composition data reveal impacts of invasions on community composition in the Waikato lakes, New Zealand

Data collected on zooplankton community composition over longer time periods (> 10 years) are rare. We examined among-lake spatial and temporal trends of zooplankton communities from a monitoring programme undertaken in the Waikato region, New Zealand. A total of 39 lakes were sampled over a period of 12 years, between 2007 and 2019, with varying degrees of temporal effort. We focussed particularly on eight lakes, considered here as ‘long-term lakes’, where samples were collected with greater regularity (including 5 with 12 years of data). Among lakes, suspended sediment concentrations and indicators of lake trophic state were inferred to be important in determining the zooplankton distributions; as this region is dominated by shallow lakes, the relative importance of suspended sediments was high. Among the long-term lakes, the greatest dissimilarities in zooplankton community composition among years were in Lake Waahi, where the Australian Boeckella symmetrica was first detected in 2012. That is, the greatest temporal changes to zooplankton composition during the study period were due to the invasion by non-indigenous species, rather than changes in trophic state or other environmental variables; non-native species commonly dominated the individual counts of species through much of 2014 and 2015, with most samples since 2016 being again dominated by native species. Following this lake, the largest and shallowest lakes in the dataset—Whangape and Waikare—exhibited the greatest variability in community composition among years.

To sea or not to sea? Multiple lines of evidence reveal the contribution of non‐diadromous recruitment for supporting endemic fish populations within New Zealand's longest river

Abstract Otolith microchemistry was used to identify marine‐ versus freshwater‐derived recruitment of three native freshwater fish species belonging to the southern hemisphere family Galaxiidae, in New Zealand's longest river system, the Waikato River. Water chemistry data for trace elements and 87Sr/86Sr isotope ratios were collected from five lentic and 10 lotic water bodies throughout the lower river floodplain. Potential spawning sites for galaxiids were compared with values obtained by laser ablation inductively coupled mass spectrometry (LA‐ICPMS) depth profiling of young‐of‐the‐year otoliths sampled from fish in nine lower river catchment sites. Otolith chemical signatures from the larval rearing period indicated that catchment‐scale recruitment for two species, Galaxias argenteus (Gmelin, 1789) and Galaxias fasciatus Gray, 1842, was driven predominantly by non‐diadromous recruitment from one lake (Lake Waahi). In contrast, diadromous recruitment appeared to be more common for Galaxias maculatus (Jenyns, 1842); however, non‐diadromous specimens were also identified for the first time from a New Zealand river. Reversing lake outlet flows linked to river stage appears be important in facilitating the dispersal of rheotactic larvae out of lakes, suggesting that lake outflow management at key times could be used to sustain this ecologically important function. This study highlights that some water bodies can supply a disproportionately large number of recruits to support fish populations within the wider riverscape. Identifying these water bodies and managing them to sustain recruitment is key to the conservation of non‐diadromous Galaxiidae in this modified lowland environment

First identification of the cylindrospermopsin‐producing cyanobacterium Cylindrospermopsis raciborskii in New Zealand

Cylindrospermopsis raciborskii is a planktonic freshwater cyanobacterium that is becoming increasingly prevalent in water bodies worldwide. During a survey of toxic cyanobacteria in New Zealand, C. raciborskii was identified in a sample collected from Lake Waahi (Waikato). This is the first identification of this species in New Zealand. Liquid chromatography‐mass spectrometry and liquid chromatography‐tandem mass spectrometry were used to confirm the presence of the cyanotoxins cylindrospermopsin (CYN) and deoxy‐cylindrospermopsin (do‐CYN). Detection of CYN and do‐CYN demonstrates that C. raciborskii is a now a species of concern in recreational, stock drinking, and potable water supplies in New Zealand.

Habitat preferences of shortfinned eels (Anguilla australis), in two New Zealand lowland lakes

The habitats used by shortfinned eels (Anguilla australis (Richardson)) in Lakes Ellesmere (Canterbury) and Waahi (Waikato), New Zealand, were determined using a variety of capture techniques during the summers of 1994/95–1997/98. The most successful technique used to catch juvenile eels (<300 mm total length (TL)) in Lake Ellesmere was a 2‐m wide beam trawl; larger eels were captured mainly by fine‐meshed fyke nets. Trawl catches during the night exceeded catches during the day by a factor of 2.4. In Lake Ellesmere, juvenile eels were mainly caught in the depth range 0.6–1.2 m, on a gravel and/or mud substrate, and within 1 km of the shore. In contrast, larger eels (>300 mm) preferred sandy substrates, but showed no marked preference for particular depths or distances offshore. The spatial distribution of both size groups was non‐random. Although water temperature did not influence catch rates (CPUE, catch‐per‐unit‐effort) of either size group, catches of the smaller eels were greater during the new moon phase than during the other phases—catches of larger eels were unaffected by lunar phase. Length‐frequency distributions of eels from Lake Ellesmere were strongly bimodal, with eels 200–300 mm poorly represented—this probably reflects poor recruitment for several years, either because lake opening times did not coincide with the availability of glass eels, or because overall numbers of glass eels were low. Juvenile eels in Lake Waahi, caught in fine‐meshed fyke nets and in special brush collectors, were also inshore residents; unlike Lake Ellesmere, juvenile eels could be caught at the lake margins, probably because Lake Waahi is not subject to the same wind‐induced water level fluctuations as Lake Ellesmere. Recruitment into Lake Waahi commenced in mid December, but there was evidence of low recruitment in past years for this lake also. An important outcome of this research is that estimates of the number of juvenile eels to be transplanted during stocking programmes should be made using the area of the shallow littoral rather than the area of the whole lake.

Mouth gape, food size, and diet of the common smelt Retropinna retropinna (Richardson) in the Waikato River system, North Island, New Zealand

The feeding ecology of the common smelt, Retropinna retropinna, was determined at several locations on the Waikato River system. The mean size of the dominant prey was found to increase as smelt mouth gape increased. Smelt smaller than 40 mm total length fed mostly on zooplankton. Chironomid larvae, pupae, and adults were the dominant foods of larger fish from most sites, although mysids and amphipods were the major prey in Lake Waahi and the Waikato River estuary. Algae were the dominant food in many smelt but ingestion was probably incidental. Seasonal and annual differences in dominant foods were minor. Common smelt are generalists, capable of feeding on the majority of smaller organisms present in their different environments; however, they may grow faster and achieve a larger adult size when food of optimal size and nutritive value is present.

Avoidance of suspended sediment by the juvenile migratory stage of six New Zealand native fish species

The avoidance response of the migratory juvenile stage of six species of diadromous fish to different levels of suspended solid (SS) was determined in the laboratory using a two‐choice avoidance tank. Trials were mostly conducted with resuspended sediment from the outlet of Lake Waahi, New Zealand, but a series of tests was also conducted with kaolin for comparison. Banded kokopu (Galaxias fasciatus) was the most sensitive species, displaying a 50% avoidance response to kaolin and Waahi silt at 17 and 25 NTU, respectively. Koaro (Galaxias brevipinnis) and inanga (Galaxias maculatus) were found to be less sensitive than banded kokopu, with a 50% avoidance response to Waahi silt at 70 and 420 NTU, respectively. Shortfinned and longfinned elvers (Anguilla australis and/1, dieffenbachii), and redfinned bullies (Gobiomorphus huttoni) showed no avoidance behaviour, even at the highest turbidities (1100 NTU) tested. Based on these laboratory results, and until field testing is undertaken, a limit of about 15 NTU in otherwise clear waterways should ensure that the upstream migration of some of the most common New Zealand native freshwater species will not be affected.

Habitat associations of juvenile shortfinned eels (Anguilla australis) in shallow Lake Waahi, New Zealand

Abstract Small meshed G‐minnow traps were used to assess the habitat associations of juvenile shortfinned eels in Lake Waahi, a shallow mesotrophic lake in the lower Waikato River basin, New Zealand. Five distinctive marginal habitats (raupo, aquatic macrophyte, reed, willow, exposed clay, and mud), and five offshore positions at various depths through the water column and distances from the margin (1–3 m and 50–500 m, respectively) were compared. Eels smaller than 400 mm were closely associated with marginal habitat. The highest catch per unit effort (CPUE) of juveniles occurred in raupo, the most complex cover. CPUE in marginal habitats declined in autumn particularly in the willows which corresponded to defoliation. Offshore sampling revealed that eels smaller than 350 mm were almost exclusively in the margins, and that larger eels were mostly offshore. Beyond 50 m from the margin, the size of eel did not change with increasing distance offshore. Eels were not caught in suspended traps (other fish were...

Effects of suspended solids on the establishment and growth of Egeria densa

To identify levels of suspended solids (SS) in Lake Waahi (Huntly, New Zealand) favourable for the re-establishment of Egeria densa Planchon, shoots were grown in 2 m deep tanks filled with water transported from the lake and maintained at selected SS loadings between 5 and 40 g m−3 (predominantly compromised kaolinitic clays). Plant growth was measured over periods of 44–47 days in spring, summer and autumn. Highest relative growth rates (RGR) were recorded in summer (maximum 40 mg g−1 daytt-1). Egeria propagules growing from a depth of 1.85 m showed positive growth responses at SS levels up to approximately 25 g m−3 (Kd ≈ 1.75) in spring and autumn, and approximately 35 g m−3 (Kd ≈ 1.95) in summer. At SS levels up to 15 g m−3 (Kd = 1.5 m−1), growth was little affected during summer, while during spring and autumn biomass accumulation was reduced to about 60% and RGR values to about 70% of the maximum seasonal values recorded. Egeria shoots showed maximum elongation at about 10–20 g m−3 SS (Kd = 1.3−1.65). Plant architecture became less branched with increasing SS and the number of roots produced decreased. Implications for the establishment of Egeria in turbid waters are discussed.

Effects of elevated turbidity on shallow lake fish communities

We compared the fish communities of two shallow lakes in the lower Waikato River basin, North Island, New Zealand, to determine the effects of elevated suspended solids (SS) and collapse of submerged macrophytes. Lake Waahi was turbid (20–40 g m-3 SS) and devoid of submerged macrophytes whereas Lake Whangape was clearer (5 g m-3 SS) and dominated by submerged macrophytes. The lakes had similar fish species richness and had nine major species in common; representing eight families including Anguillidae, Retropinnidae, Galaxiidae, Eleotridae, Mugilidae, Ictaluridae, Poeciliidae, and Cyprinidae (two species). The only major fish that was absent from Lake Waahi was a lacustrine form of the common smelt, Retropinna retropinna, which disappeared after the lake became turbid in the late 1970s. CPUE, condition, and size of most species in Lake Waahi were similar to, or greater than, those in Lake Whangape. Lake Whangape clearly exceeded Lake Waahi only for CPUE of two species. Within Lake Whangape two species displayed significantly greater condition, and one species greater size, in a turbid arm of the lake than in the main basin. Apart from lacustrine Retropinna retropinna, the fish in these lakes appear well adapted to cope with, or to avoid, the direct toxic effects of suspended and settleable solids on sensitive early developmental stages. In Lake Waahi loss of cover and food provided by submerged macrophytes appears to have been compensated for by increased turbidity and an associated increase in the biomass of the mysid, Tenagomysis chiltoni (a major prey item).

Relationship between turbidity and fish diets in Lakes Waahi and Whangape, New Zealand

Abstract Stomach contents of Gobiomorphus cotidianus,Retropinna retropinna, Gambusia affinis, and Anguilla australis were compared between two shallow lakes in the lower Waikato River basin, to examine the relationship between turbidity and diet. Lake Waahi and the south arm of Lake Whangape had been turbid (20–40 g suspended solids (SS) m−3) and devoid of submerged macrophytes since the late 1970s and early 1980s, respectively. The main basin of Lake Whangape had been generally clearer (5 g SS m−3) with dense beds of submerged macrophytes, but at the time of sampling (1987) water clarity had deteriorated (> c. 10 g SS m3) and submerged macrophytes had declined. The mysid Tenagomysis chiltoni was an important prey for all species of fish from turbid water bodies but was less important in stomachs of fish in the main basin of Lake Whangape. Apparently, mysids were not an important prey in Lake Waahi before it became turbid. Chironomid larvae and pupae dominated the diets of small fish in the main basin of ...

Age and growth of shortfinned eels(Anguilla australis)in the lower Waikato basin, North Island, New Zealand

Abstract Growth rates of shortfinned eels (Anguilla australis) from various locations in the Waikato basin, New Zealand, were determined by otolith examination. Two colour‐morphs from the Whangamarino Swamp exhibited different growth rates. Dark‐coloured eels (96% of the catch in low water levels) resided in the swamp; their growth was much slower than that of light‐coloured eels (40% of the catch in floods) which probably entered this habitat in flood waters from Lake Waikare, the Whangamarino River, or main wetland channels. Overall, growth rates were fastest in Lake Waikare followed by Lake Waahi, Lake Whangape, and Hakarimata pastoral streams. Dark‐coloured swamp eels were the slowest growing. Relative annual length increments ranged between 10 and 47 mm. Fast growth of eels in Lake Waikare may be the result of low densities owing to poor recruitment and heavy fishing pressure in recent years. Estimated age at threshold commercial size varied by 11 years throughout the Waikato.

The effects of recent environmental changes in Lake Waahi on two forms of the common smelt Retropinna retropinna, and other biota

Since 1977 open cast (open pit) coal mining has increased discharge of silt-laden wastes into Lake Waahi, a small shallow lake in the Waikato River system, New Zealand. Phenolic wastes from a coal carbonization factory on the major tributary also have entered the lake in high but variable concentrations since 1974. During and after the summer of 1978–1979 total suspended solids and turbidity were high, the formerly dense macrophyte beds disappeared, the summer phytoplankton community changed from dominance by blue-green algae to diatoms, the eel fishery failed and the black swan population decreased to low levels. The once abundant lake resident form of the common smelt declined drastically between 1975 and 1981 and apparently was extinct by 1983. The migratory form, although abundant until 1981, was scarce by 1983. Low water levels in the outlet stream and the malfunction of a fish pass in the flood control structure located near its mouth may have impeded upstream migration in the spring of 1982. The major cause for the changes in Lake Waahi was the addition of silt; however, the loss of macrophytes may have caused increased toxicity of phenols, particularly to eels, and also promoted continual resuspension of sediments by more effective wind-produced circulation. Remedial measures are considered.

Lake resident and migratory smelt, Retropinna retropinna (Richardson), of the lower Waikato River system, New Zealand

Retropinna retropinna occurred in two forms in Lake Waahi, North Island, New Zealand. One form was characterized by high mean gill raker counts (c. 28) and low mean vertebral counts (c. 52)—similar to those of non‐migratory, lake resident, native smelt in some other lakes of the lower Waikato River system. The other form had low mean gill raker counts (c. 21) and high vertebral counts (c. 60)—similar to migratory smelt at five sites along the lower Waikato River down to its estuary. The lake resident form was shorter but deeper bodied than the migratory form, as indicated by significant differences in mean length and in weight‐length regression analyses.The two forms overlapped in time of sexual maturity. As in other native lacustrine smelt populations of the lower Waikato system, the resident form had more but smaller eggs than the migratory form. The egg number to body length regression and the mean egg diameter of migratory Lake Waahi smelt were similar to those of lower Waikato River smelt. Evidence for reproductive separation of the two forms is presented and mechanisms controlling their meristic and other differences are considered.

The food of the grey mullet (Mugil cephalusL.) in Lake Waahi and the Waikato River at Huntly

Abstract The diet of the grey mullet (Mugil cephalus L.) was studied in Lake Waahi, and the Waikato River at Huntly —2 highly productive freshwater habitats in New Zealand. Grey mullet fed all year despite temperatures ranging from 7–26°C. Their diet was found to include a wide range of algal species, some macrophyte detritus, inorganic particles, and occasionally the snail Potamopyrgus antipodarum. The food items selected reflected their availability in the 2 habitats. The source of these food items is discussed and the environmental effects of mullet feeding activities are considered briefly.

Reproduction, growth and mortality of the common bully, Gobiomorphus cotidianus McDowall, in a eutrophic New Zealand lake

Gobiomorphus cotidianus in Lake Waahi, North Island, New Zealand, (37° 34'S; 175° 08'E) spawned continuously between July 1976 and March 1977. Length frequency data indicated that two, and briefly, three year classes, were present, each made up of three groups which were the progeny from successive peaks in spawning activity. Scale examination revealed checks to growth associated with spawning and stressful midsummer conditions. These and length frequency data were used in growth estimates which indicated that bullies reached 3·5‐4·0 cm after their first year, 5‐6 cm after their second but did not survive a third year. Mortality was associated with spawning and midsummer stress.