Zealand Rivers Research Articles

Male Dominance in the New Zealand Longfin Eel Population of a New Zealand River: Probable Causes and Implications for Management

AbstractThe endemic New Zealand longfin eel Anguilla dieffenbachi (hereafter, longfin eel), is overfished, and in southern South Island, New Zealand, rivers have recently become predominated by males. This study examined length and age at sexual differentiation in male eels in the Aparima River catchment (area, 1,375 km2; mean flow, 20 m3 · s−1) and the sex ratio and distribution of eels throughout the catchment. Longfin eels differentiated into males mostly at lengths from 300 to 460 mm and ages from 10 to 25+ years. Females were rare: Of 738 eels examined for sexual differentiation, 466 were males and 5 were females, and a few others, not examined, were large enough to be female. These counts suggest a male : female ratio among differentiated longfin eels of 68:1. Of 31 differentiated shortfin eels A. australis, less common in the Aparima River, 26 were females. Male longfin eels were distributed throughout the main stem and tributaries; undifferentiated eels were more prevalent in lower and middle reaches and in the main stem than in upper reaches and tributaries. In other studies, male longfin eels predominated commercial catches in the Aparima and four other southernmost rivers, by 2.4:1 to 13.6:1 males to females. The Aparima River had the most skewed sex ratio. Longfin eel catches from the Aparima River will become more male predominated because few sublegal‐size females were present. The length‐frequency distributions of eels in the present samples and in the commercial catches were truncated just above minimum legal size (about 460 mm), showing that few females escape the fishery. Historically, females predominated these rivers. The recent change in sex ratio is attributable partly to selective harvest of females, and partly to changes in the structure of the population from fishing, such that differentiation into males has been favored. Longevity, delayed sexual maturity, semelparity, and endemism with restricted range make the longfin eel particularly vulnerable to overfishing.

New Zealand River Management: Economic Values of Rangitata River Fishery Protection

An individual travel cost model of recreation behaviour was applied to the Rangitata River fishery in New Zealand's South Island. Results from the model were used to help inform decisions about whether a water conservation order should be placed on the river. Travel cost results showed the high value of the Rangitata River compared with other premier New Zealand fisheries. Fishery benefits were dependent upon the distance to substitute and complementary fisheries. Failure to model the influence of other sites would have resulted in underestimation of Rangitata River use benefits. Results were also sensitive to assumptions about cost perceptions. This case study illustrates the method's potential for informing decision-makers about resource allocation decisions.

Relationships between drifting and benthic invertebrates in three New Zealand rivers: Implications for drift‐feeding fish

We assessed whether taxonomic structure and density of aquatic drift could be predicted from the benthos in three New Zealand rivers. The three main orders contributing to both the benthos and drift were Ephemeroptera, Diptera, and Trichoptera. Drift and benthic densities for all taxa and all rivers combined were not significantly correlated (adults inclusive and exclusive). There were significant positive correlations between benthic and drift densities for the three main drifting orders—Ephemeroptera, Diptera, and Trichoptera when data from all rivers were combined. However, these relationships were not always detected in individual rivers. The propensity for Deleatidium to drift was negatively related to chlorophyll a concentration; suggesting density‐dependent drift mediated by food limitation. Drift was reduced when periphyton chlorophyll a concentration was high in relation to benthic Deleatidium density. This highlights an unexpected effect of periphyton proliferation on invertebrate drift and drift‐feeding fishes. Despite finding some correlations between benthic and drifting communities, defining general relationships between benthic and drifting communities is challenging given the complexity of density‐dependent and density‐independent mechanisms that influence invertebrate drift.

Testing a model of drift-feeding using three-dimensional videography of wild brown trout, Salmo trutta, in a New Zealand river

We tested the assumptions and predictions of a foraging model for drift-feeding fish. We used three-dimensional videography to describe the foraging behavior of brown trout, Salmo trutta, mapped water depth and velocity in their foraging area, sampled invertebrate drift to determine length class specific drift densities, and captured trout to determine the size composition of their diet. The model overestimated the fish's prey capture rate and gross energy intake rate by a factor of two. Most of this error resulted from the fact that prey detection probabilities within the fish's foraging area averaged only half the expected value. This was the result of a rapid decrease in capture probability with increasing lateral distance from the fish's focal point. Some of the model's assumptions were accurate: equations for predicting reaction distance and minimum prey size supported reliable predictions of the shape and size of the fish's foraging area and the size composition of the diet. Other assumptions were incorrect: fish detected prey within the predicted reaction volume, not on its upstream surface as expected, fish intercepted prey more slowly than the expected maximum sustainable swimming speed, and fish captured about two-thirds of their prey downstream of their focal point, rather than upstream.

Fish communities in New Zealand rivers and their relationship to environmental variables

Fish abundance data from selected electric‐fishing records in the New Zealand Freshwater Fish Database (NZFFD) were used to identify riverine fish communities and to examine their relationship to environmental variables included in the NZFFD. Only 21 fish species, 18 native species, and three introduced salmonids, were present at 1% or more of the sites. We defined 12 fish communities characterised by a dominant species: two salmonid communities, two non‐diadromous native communities, and eight communities characterised by diadromous native species. Altitude and distance inland were the two most significant variables, reflecting differences between communities dominated by diadromous and non‐diadromous species. The next most important variables were related to the geographic location of the site. Other environmental variables that were highly correlated with the fish community assignments were stream width and percentage of native forest or farming land use in the catchment upstream of the site. Of the local habitat variables, percentage of cascade habitat and percentage of sand substrate were the most important discriminators between communities. Despite having only a limited set of broad‐scale environmental variables, we achieved 47% success in the prediction of community membership using multiple discriminant analysis, with another 21% of sites being near misses. A greater knowledge of barriers to migration of diadromous species and fine‐scale variables describing in‐stream habitat would probably increase the predictive ability of the model, although collection of such data is time consuming and therefore impractical on a national scale.

Benthic community dynamics during summer low‐flows in two rivers of contrasting enrichment 2. Invertebrates

We examined the effects of summer low‐flow on invertebrate communities in two New Zealand rivers of contrasting enrichment and associated periphyton development. Quantitative benthic samples were collected and hydraulic measurements made from three runs in each river over a 6‐week period. Although hydraulic conditions and time since last flood disturbance were similar in both rivers, invertebrate communities were dissimilar. This dissimilarity reflected differences in periphyton communities within each river. The invertebrate community in the low enrichment river (Okuku River) was dominated by high numbers of “clean‐water” insect taxa, and this community changed little over time. Periphyton biomass was low here, and the community was composed of diatoms. Major changes occurred to the invertebrate community in the high enrichment river (Waipara River) over the summer, where the relative abundance of dominant invertebrate taxa changed from insects and snails to ostracods. Periphyton biomass was high in this river, which was originally dominated by diatoms and cyanobacteria but which became dominated by filamentous green algae. Changes to invertebrate communities were linked to this increase in filamentous green algae. Multiple regression analysis showed that changes to the invertebrate community in the enriched river were strongly correlated with the number of days at low flow, suggesting that successional processes occurred during the low‐flow period. Such changes may occur naturally during summer low‐flows in enriched rivers or could be exacerbated if velocities are reduced by abstraction. Our results suggest that a river's degree of enrichment should be considered when assessing minimum flows for consents or for the development of flow management guidelines.

Riparian land use and accessibility to fishers influence size class composition and habitat use by longfin eels in a New Zealand river

Riparian land use and accessibility to fishers influence size class composition and habitat use by longfin eels in a New Zealand river

Riparian land use and accessibility to fishers influence size class composition and habitat use by longfin eels in a New Zealand river

Fyke nets were used to sample longfin eels Anguilla die.enbachii in fourth order stream sites with contrasting riparian land use (native tussock, exotic pasture and pasture plus willows Salix spp.) in Lee Stream, a tributary of the Taieri River, New Zealand. Total lengths (LT) of longfin eels from locations inaccessible to eel fishers were normally distributed whereas those from accessible locations had a non‐normal, positively skewed distribution. Mean LT and body condition were higher in inaccessible than accessible sites, consistent with considerable fishing exploitation in the latter. Mean LT of the fish was greatest in pasture, intermediate in willow and smallest in tussock sites. Larger longfin eels (≥535 mm) were associated with a riffle‐type habitat consisting of shallow, faster‐flowing water with coarse, variable sediment and were taken farther from cover. In contrast, smaller longfin eels were associated with a pool‐type habitat consisting of slower‐flowing, deeper water, with fine, homogenous sediment and were captured closer to cover. This pattern of habitat use differed from some previous reports and probably reflects differences in methodology: fyke nets set over 48 h to sample actively moving longfin eels compared to daytime electric fishing, which samples longfin eels that are more likely to be at rest.

Habitat use by juvenile lampreys (Geotria australis) in a large New Zealand river

Ammocoetes (larvae) of Geotria australis Gray, were sampled in a large South Island, New Zealand, river during summer to determine their distribution and habitat associations. Ammocoetes were widely distributed along the length of the river, being present at 66 of the 95 sites sampled. They ranged in density from 0 to 180 m–2, and were associated with habitat type (mainly runs), overhead shade, and substrate features (depth or the proportion of fine sand). The amount of particulate organic matter was negatively correlated with ammocoete abundance.

Effects of flow regulation and sediment flushing on instream habitat and benthic invertebrates in a New Zealand river influenced by a volcanic eruption

AbstractI sampled five sites above and below a dam in the central North Island of New Zealand on five to six occasions to examine the effects on benthic substrates, periphyton and invertebrate communities of (i) degree of flow regulation and (ii) flushing of sediment stored behind a dam. A series of volcanic eruptions during the course of this study provided the opportunity to investigate the effects of a period of high sediment delivery on this regulated river. The operation of the dam prior to sluicing of stored sediment appeared to have little impact on substrate size distribution or fine suspendable sediment levels. Periphyton biomass was markedly higher below than above the dam when sampling was preceded by a period of stable baseflow, but over all sampling dates biomass and inorganic content of periphyton did not appear to be related to degree of flow regulation. The taxonomic richness, biomass and density of invertebrate communities were lowest directly below, rather than above, the dam on most dates, and the site below the dam differed significantly from some of the downstream sites. However, changes in invertebrate abundance and diversity generally did not follow the expected gradient of flow regulation impacts except for the mayfly Deleatidium. Multiple regression analyses implicated substrate size and the biomass and inorganic content of periphyton as significant predictor variables for invertebrate density, biomass and taxonomic richness on sampling dates not influenced by recent sediment flushes, whereas degree of flow regulation was a significant predictor for densities of the dominant chironomid Cricotopus. The volcanic eruption led to deposition of fine silt that had passed through the dam with the residual flow and coarser sediments released during subsequent dam flushes. Flushing of stored sediment during large floods increased levels of sand and gravel directly below the dam and upstream of a large island in the middle reaches of the river, and also appeared to increase scouring of periphyton and associated invertebrates downstream. Overall, invertebrate communities in the study reach appeared to be structured more by periphyton accrual patterns, changes in substrate composition, the occurrence of large floods and natural longitudinal gradients than degree of flow regulation. These findings suggest that site‐specific and large‐scale factors can obscure generalized reach‐scale patterns expected along regulated rivers. Copyright © 2002 John Wiley & Sons, Ltd.

Distribution and abundance of zooplankton in the Waikato River, New Zealand

Potamoplankton is often a well developed component in large lowland rivers, yet little is known about its structure in New Zealand's longest river, the Waikato River. To redress this gap we sampled bimonthly at seven sites along the length of the river over 12 months. Rotifers were the dominant zooplankton in the Waikato River making up 85% of the total densities. Cladocerans represented 9% and copepods only 6%. Rotifers were also the most taxonomically rich group with 41 species in 20 genera identified throughout the study. Thirty rotifer species and nine genera represent new records for the river – two cladoceran species were also recorded for the first time. The highest densities of crustaceans and rotifers were found in the hydro lakes. Densities of crustaceans decreased with increasing distance downstream and densities of rotifers were on average 15 times greater than crustaceans in the lower river. The seasonality of Crustacea was similar to that in New Zealand lakes and rivers with high densities in summer and minimum densities over the winter period. Total rotifer densities showed a similar trend although there were marked seasonal differences between individual species.

Longitudinal distribution of macroinvertebrates in two glacier‐fed New Zealand rivers

1. Environmental variables, benthic algal biomass and macroinvertebrate fauna were examined from September 1999 to January 2000 (austral summer) along two glacier‐fed rivers in South Island, New Zealand.2. The rivers were characterized by high flow variability, high turbidity and physically disturbed beds. Water temperature ranged from <1 °C near the glacier margin to 10 °C further downstream.3. Epilithic algal biomass was very low (<0.1 mg m–2) in months characterized by heavy rainfall, but ranged from 1.1 to 14.4 mg m–2 following an extended period with negligible precipitation.4. Abundance and diversity of invertebrates in both rivers was low. Dominant taxa were Chironomidae (Orthocladiinae, Podonominae, Diamesinae), although mayfly species (Deleatidium: Leptophlebiidae) also occurred at most sites. A species of Eukiefferiella (Orthocladiinae) was collected at all sites and was the most abundant invertebrate close to the glacier margins. No meiofauna were found in either river.5. Faunal diversity increased at the lowermost stations where species of Plecoptera, Trichoptera, Coleoptera and non‐chironomid Diptera also occurred.6. The faunas of the two New Zealand rivers conformed to the conceptual model of Milner & Petts (1994) in that taxon richness increased downstream with water temperature. However, invertebrate abundance increased downstream in only one of the two rivers. Also in contrast to the model predictions, Leptophlebiidae and Orthocladiinae, rather than Diamesinae, dominated the fauna at the coldest sites.

Spatial and temporal variation in the abundance and composition of ichthyoplankton in a large South Island, New Zealand river estuary

Larval and juvenile fish drifting on ebb tides were collected from early summer to mid autumn at various locations in the Taieri River and Waipori River estuary, South Island, New Zealand. A total of seven species of fish were recorded, however only three species were regularly collected. These were the larval common bully (Gobiomorphus cotidianus McDowall), larval inanga (Galaxias maculatus Jenyns), and postlarval cockabully (Tripterygion nigripenne Valenciennes). Common bully densities were highest in mid January, with the highest densities being recorded drifting out of Lake Waihola. Inanga densities were highest in March and April, with the highest densities being recorded in the channels draining wetland areas where extensive tidal inundation of riparian vegetation occurred. Cockabully were recorded from February to April, mostly at more downstream sites. Inland penetration by marine species was considerable, with two marine species, clingfish (Trachelochismus pinnulatus Forster) and smooth leatherjacket (Parika scaber Forster), being recorded c. 12 km upstream in late summer.

Reduced abundance of banded kokopu (Galaxias fasciatus) and other native fish in turbid rivers of the North Island of New Zealand

Laboratory experiments demonstrated that migrant juvenile banded kokopu (Galaxias fasciatus Gray) were more sensitive to suspended sediment (SS) than other native fish species. If juvenile migrants avoid waters made turbid by SS and their recruitment to adult habitats up stream is reduced, then adult abundance may decline in turbid rivers. To test this, we compared the abundance of diadromous native fish between turbid and clear rivers. The duration (% time) for which SS concentrations exceeded 120 mg litre‐1 (a critical level from laboratory experiments) during the migration season (August‐December) was estimated for over 150 New Zealand river sites. Turbid rivers were defined as those where SS concentrations exceeded 120 mg litre‐1 for over 20% of the time and clear rivers as those where SS concentrations exceeded 120 mg litre‐1 for less than 10% of the time. Eight turbid rivers and seven clear ones were identified where sufficient data on SS and native fish populations existed to permit a comparison. The mean occurrence of banded kokopu was reduced by 89.5% in turbid rivers and, although other diadromous fish species were also less common, banded kokopu was most affected. Densities of adult banded kokopu were also significantly lower in optimal stream habitats in three turbid compared with three matched clear rivers. We therefore concluded that the abundance of adult banded kokopu was reduced in turbid rivers and propose that this is because of reduced recruitment of juveniles in turbid rivers.

Grazer Control of Stream Algae: Modeling Temperature and Flood Effects

A computer model for epilithic algae and grazer biomass in streams is modified to better predict the effects of temperature and is calibrated for diatoms and mayflies. Mayflies are predicted to maintain low diatom biomass provided that (1) temperatures remain within their preferred range (10-207C); and (2) mayfly populations are not adversely affected by floods. Algal blooms are predicted to occur in mayfly-dominated streams above 207C—temperatures common in pasture streams over summer. We hypothesize that mobile bed streams are susceptible to blooms during summer low flows following floods because (1) they usually lack temperature tolerant snail grazers; and (2) mayfly recovery lags behind algal regrowth, and there is a short period when algae escape from ''top-down'' grazer control. Proliferations of periphytic algae (algal blooms) have been documented in a number of New Zealand rivers with stoney beds draining agricultural catchments (Biggs and Price 1987) and adversely affect ecosystem structure and function, river aesthetics, and some water uses. Most conspicuous are blooms of filamentous green algae, although proliferation of diatoms and blue-green algae are also of management concern. Algal blooms only occur sporadically, when the rates of accrual (au- totrophic fixation plus colonization) exceed the rates of loss (sloughing, flow disturbance, and consumption by grazers). Benthic macroinvertebrate grazers (principally aquatic in- sects) have a significant negative effect on algal biomass; for example, Welch et al. (1992) showed that 3,000 grazers m 22

Development and Test of a Whole-Lifetime Foraging and Bioenergetics Growth Model for Drift-Feeding Brown Trout

We developed and tested a combined foraging and bioenergetics model for predicting growth over the lifetime of drift-feeding brown trout. The foraging component estimates gross energy intake within a fish- and prey size-dependent semicircular foraging area that is perpendicular to the flow, with options for fish feeding across velocity differentials. The bioenergetics component predicts how energy is allocated to growth, reproduction, foraging costs, and basal metabolism. The model can reveal the degree to which growth is limited by the density and size structure of invertebrate drift within the physiological constraints set by water temperature. We tested the model by predicting growth based on water temperature and on drift density and size structure data from postemergence to age 12, and we compared the predictions with observed size at age as determined from otoliths and scales for a New Zealand river brown trout population. The model produced realistically shaped growth curves in relation to the observed data, accurately predicting mean size at age over the lifetime of the trout, assuming 24-h maximum rations and including diurnal drift-foraging costs (predicted versus observed weight r2 = 0.94; length r2 = 0.97). The model predicted that, within a given water-temperature regime, growth is limited primarily by reproduction costs but also by increasing foraging costs as trout grow (a phenomenon that is associated with the increasing foraging time that is required in order to feed to satiation on small invertebrate drift prey). Invertebrate drift size structure significantly influenced predicted growth, especially maximum size, through its effect on foraging time. The model has potential in terms of the exploration of growth-limiting factors and has associated use as an environmental-impact tool and as an aid for hypothesis generation in studies of salmonid growth processes.

Animal and human faecal pollution in New Zealand rivers

Sentinel freshwater mussels (Hydridella menziesi) were immersed in rivers at sites impacted by faecal pollution. The indicator bacterium, Escherichia coli, was recovered from all mussels including those at a forest control site, but concentrations were highest at sites impacted by either treated sewage or treated meat‐processing waste water, or by inputs from dairy farms. The three pathogens sought were recovered from mussels, except those at the forest (control) site: Campylobacter jejuni and Campylobacter coli at treated sewage sites; Salmonella typhimurium and C. jejuni at treated meat‐processing waste water sites; and C. jejuni and Yersinia enterocolitica at sites impacted only by dairy farms. The FRNA bacteriophage concentration was high in mussels impacted by sewage or sheep‐processing waste water but was low when the input was only from dairy farms. Mussels up to 23 km from a sewage discharge contained a high concentration of FRNA suggesting that there could be a health risk due to viruses, although the water did not exceed recommended guidelines. Pathogens were also sought in untreated waste waters. C. jejuni and C. coli were recovered from both sheep‐processing and beef‐processing waste waters and the only sewage isolate identified was confirmed as C. coli. Salmonella spp. were recovered from all waste waters, with S. typhimurium phage type 135, isolated from a sample of meat‐processing waste water, and from mussels immersed 1 and 5 km down stream of that plant's discharge. Y. enterocolitica was recovered from most samples of animal waste water. It appears that pathogens are introduced into New Zealand rivers by all major sources of faecal contamination.

Hydraulic geometry of New Zealand rivers and its use as a preliminary method of habitat assessment

‘Downstream’ hydraulic geometry relationships describe the variation of water depth, velocity, and water surface width between rivers of different size at a characteristic discharge, whereas ‘at-a-station’ geometry describes the variation of hydraulic geometry with discharge within a reach. The instream flow incremental methodology (IFIM) also predicts the variation in water depth and velocity with discharge at a reach scale, so that hydraulic geometry relationships can potentially be used as a preliminary method of habitat assessment. Hydraulic geometry relationships were calculated from instream habitat surveys of 73 New Zealand river reaches with mean flows varying from 0.6 to 204 m3 s−1 and an average gradient of 0.0047. The exponents of both at-a-station and downstream hydraulic geometry relationships were within the range of values reported in other international studies, although the exponents indicated that New Zealand rivers tended to experience greater changes in velocity and less in depth than the international average, probably because of high average gradient. The frequency distributions of water depth and velocity were positively skewed in most rivers, and on average the modal velocity was 90% of the mean velocity and the modal depth was 80% of mean depth. The use of at-a-station hydraulic geometry relationships for instream habitat assessment was compared to depth and velocity predictions using habitat simulation techniques (IFIM) in two streams. Measurements of stream width and depth at five cross-sections at two calibration discharges were used to establish at-a-station hydraulic geometry relationships. These predicted mean depth and velocity within 8% of the reach average values of the IFIM surveys within the range of calibration discharges and within 10–15% of the IFIM reach average when extrapolated beyond the calibration discharges. Hydraulic geometry can be used to indicate whether hydraulic conditions approach a ‘threshold’ such as a minimum acceptable depth or velocity, thus predicating the need for more extensive habitat survey and analysis. © 1998 John Wiley & Sons, Ltd.

Comparative dietary analysis of a recently described fish species complex (Galaxiidae) in a New Zealand river

The diets of several populations of four recently described species of galaxiid with allopatric distributions were examined in the Taieri River, New Zealand. Comparisons of available prey items and prey consumed were carried out to examine whether the distributions of the galaxiid species might be influenced by food availability and preferences. Seventy‐three prey categories were identified. The availability of four of these (Deleatidium, Oligochaeta, Elmidae larvae and adults) differed among the streams occupied by different galaxiid species. Three differences in the frequency of prey consumption (Deleatidium, Oxyethira, and Elmidae larvae) were detected. Despite differences in diet it was concluded that all four fish species were generalist predators of invertebrates with similar diets that were influenced mainly by prey availability. Furthermore prey availability was not considered responsible for the allopatric distribution of the four species, rather, spawning habitat availability, physical nature of the streams, and prior geological history of the Taieri catchment are considered the controlling influences on galaxiid distribution.

Hydraulic geometry of New Zealand rivers and its use as a preliminary method of habitat assessment

Hydraulic geometry of New Zealand rivers and its use as a preliminary method of habitat assessment