Ian G. Jowett

A method for objectively identifying pool, run, and riffle habitats from physical measurements

Abstract Visual assessments of habitat type (pool, run, riffle) and physical measurements at 1112 points in a gravel‐bed river were used to derive an objective method for distinguishing pool, run, and riffle habitats. Water depth, velocity, and substrate composition were measured at each point and were used to calculate average substrate size, relative roughness, velocity/ depth ratio, and Froude number. Water surface slope was measured between each of 59 cross‐sections. The velocity/depth ratio, Froude number, and slope were the best determinants of habitat type. Velocity/ depth ratio and Froude number showed the most significant differences between habitat types. In the study river, pool habitat was associated with velocity/ depth ratios of less than 1.24 and Froude numbers less than 0.18, riffles with velocity/depth ratios of more than 3.20 and Froude numbers in excess of 0.41, and run habitat with intermediate values. Riffle habitats were characterised by slopes greater than 0.0099 and run and pool ha...

Microhabitat preferences of benthic invertebrates and the development of generalised Deleatidium spp. habitat suitability curves, applied to four New Zealand rivers

Microhabitat preferences of 12 benthic invertebrate taxa were investigated in four New Zealand rivers. Most taxa showed significant habitat preferences. Generally, taxa were more abundant in water ...

Flow variability in New Zealand rivers and its relationship to in‐stream habitat and biota

Abstract How variability indices were determined for 130 sites on New Zealand rivers and the sites were divided into groups based on these indices. Univariate and discriminant analyses were used to identify the catchment characteristics which contributed to flow variability. Climate, as determined by topography, geographic location, and the composition of the regolith (especially water storage capacity and transmissivity characteristics), accounted for a broad regional distribution of groups. Flow variability decreased with catchment size and area of lake and, to a lesser degree, with catchment slope. Relationships were found between flow variability, and morphological and hydraulic characteristics. The longitudinal variability of water depth and velocity increased with flow variability, indicating a more pronounced pool/riffle structure in rivers with high flow variability. Mean water velocity at mean annual low, median, and mean flow was higher in rivers of low flow variability than in rivers of high fl...

Microhabitat preferences of benthic invertebrates in a New Zealand river and the development of in-stream flow-habitat models for Deleatidium spp.

Abstract Microhabitat preferences of seven groups of New Zealand benthic invertebrates (Deleatidium spp., other mayflies, cased caddisflies, uncased caddisflies, beetles, Diptera, and stoneflies) were investigated and habitat suitability functions for use with the instream flow incremental methodology (IFIM) developed for the predominant group, Deleatidium spp. All invertebrate groups except uncased caddisflies and Deleatidium spp. exhibited significant preferences for at least two of the three habitat variables (substrate, water velocity, and depth) when each habitat variable was considered independently. Significant relationships were found between invertebrate size and at least one habitat variable for all groups except stoneflies. Models of Deleatidium spp. abundance were poor (r = 0.50–0.58) and generally predicted biomass better than numbers. The best models used all three habitat variables together with an index of the amount of periphyton. Deleatidium spp. abundance in the Waingawa River was most ...

Ecological characterisation, classification, and modelling of New Zealand rivers: An introduction and synthesis

Abstract A programme of research to characterise, classify, and model New Zealand rivers according to hydrological, water quality, and biological properties is introduced. The results are detailed in the accompanying eight research papers. These studies provide the first national perspective on water quality and biology in New Zealands rivers using a consistent methodology. They are also the first step toward providing managers with robust models for predicting the effects on aquatic biota of changes in flow regimes and catchment land use. A synthesis of the results is given in this paper together with recommendations for riverine ecoregions in New Zealand.

Habitat preferences of common, riverine New Zealand native fishes and implications for flow management

Abstract Habitat use of eight native fish species was determined by electroshocking depth‐stratified lanes < 0.125 m, 0.125–0.25 m, 0.25–0.5 m, and 0.5–0.75 m. Two runs and two riffles were sampled in 34 rivers. Water depth, velocity, and substrate size were measured. Bluegilled bullies (Gobiomorphus hubbsi), upland bullies (G. breviceps), common bullies (G. cotidianus), longfinned eels (Anguilla dieffenbachii), and shortfinned eels (A. australis) made up over 80% of the total number and biomass of fish sampled. Overall, fish densities were highest along river margins in depths of less than 0.25 m, and higher in riffles than in runs. The fish species could be classified into four habitat guilds: a fast‐water guild that occupied central portions of riffles, an edge‐dwelling guild, an intermediate guild, and finally a guild that was ubiquitous. Minimum flow requirements based on habitat for the edge‐dwelling and fast‐water guilds would be conflicting, with one benefiting from low flows and the other from hi...

Distribution and abundance of freshwater fish in New Zealand rivers

The distribution and abundance of fish at sites in 38 medium to large New Zealand rivers were examined. Fish density varied from 5 to 200 fish per 100 m2, with an average of 53 fish. Our study sites contained a greater species richness and abundance than records stored on the New Zealand Freshwater Fish Database, where the average density was 28 fish per 100 m2. The average number of species at the study sites was 5, compared to 3 in the national database. Comparison of first-pass catches with multiple-pass population estimates showed that there was no difference in capture probability between species and that on average 51% of the population was captured on the first pass. The diadromous habit of many native species, and their ability to penetrate inland, was an overwhelming influence on their distribution. There was little regional variation in species composition, apart from the presence or absence of three non- diadromous species. Two distinct fish communities were evident: lowland and upland. Lowland communities typically contained the highest density and diversity offish, whereas upland communities were dominated by one or two species. Many river sites were intermediate between lowland and upland, both in species composition and fish density, and showed a gradual reduction in abundance and change in community structure with elevation, as those fish less able to penetrate inland disappeared and non-diadromous species began to appear. Elevation was the most important discriminating factor, with physical habitat and

A comparison of composite habitat suitability indices and generalized additive models of invertebrate abundance and fish presence-habitat availability

Abstract Generalized additive models (GAMs) offer an alternative approach to developing habitat suitability functions; these models may resolve some of the criticisms that have been made of conventional habitat suitability criteria and the associated composite suitability index (CSI). The potential advantages of GAMs include the ability to (1) account for correlation among habitat variables, (2) include interactions among variables, (3) make quantitative predictions of abundance or probability of occurrence at given flows, and (4) identify sharp thresholds in habitat selection. We developed CSIs and GAMs for two data sets—abundance of benthic invertebrates (mayflies Deleatidium spp. and caddisflies Aoteapsyche spp.) and habitat selection of large brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss—and applied them in an instream habitat analysis. The GAMs performed only slightly better than CSIs. The GAMs for two of the four taxa examined (Deleatidium and brown trout) had strong negative veloci...

Relative effects of in-stream habitat and land use on fish distribution and abundance in tributaries of the Grey River, New Zealand

Abstract The distribution and abundance offish was investigated over 2 years at 78 sites in Redjacks Creek and adjacent tributaries draining native, exotic, and mixed forest catchments within the Grey River system, South Island, New Zealand. The abundance of diadromous fish decreased with altitude and distance from the sea, whereas the abundance of non‐diadromous fish species, especially dwarf galaxias (Galaxias divergens), increased with altitude and distance from the sea. Species abundance varied with average stream depth and velocity, generally in accordance with micro‐habitat preferences. The relative influences of diadromy, land use, and physical habitat on fish distribution and abundance were difficult to separate. Differences in fish abundance in the three land‐use categories were often attributable to differences in physical habitat. Nevertheless, there were indications that land use and its effect on the stream environment was influencing the distribution of some fish species. Ammocoetes (Geotria...

Effects of deposited sediment on invertebrate drift: An experimental study

Abstract The effect of deposited sediment on invertebrate drift was experimentally assessed by adding fine sediment to three of six cobble‐lined artificial channels. One invertebrate species, Deleatidium spp., was added to the channel after the addition of sediment, whereas other taxa had colonised the channel naturally before the addition of sediment. Invertebrate drift was collected from each channel after the added sediment had worked its way into the interstitial spaces of the cobbles. Drift was collected every evening and morning for 3 days, after which time benthic densities in the channels were assessed. The percentage of benthos in the drift was significantly higher from sediment‐treated channels than from untreated channels for Paracalliope fluviatilis, Oxyethira albiceps, Hydrobiosis sp., and chironomid larvae. Drift of these animals from sediment‐treated channels was more than double that from untreated channels, with an average of over 5% of the benthos drifting from the sediment‐treated channels per day. Although there was no difference in the percentage of Deleatidium in the benthos that drifted from treated or untreated channels, significantly more individuals drifted from treated channels. Deposition of fine sediment had no significant effect on chironomid emergence or diurnal drift patterns for the taxa in the experiment. Periphyton communities in sediment‐treated channels were characterised by reduced chlorophyll a and increased inorganic content. We could not determine whether increased drift caused by deposited sediment reflected decreases in suitable habitat, reductions in food quality of the algae, or both.