River and study site descriptions

Data were collected from sites located on Tongariro, Manganuiateao, Ikawetea and Makaroro Rivers. Each river had a resident population of blue ducks and all contained trout. Ikawetea and Makaroro Rivers each had large waterfalls which obstructed upstream migration of trout. On both of these rivers blue ducks were present above and below the waterfalls.

The study sites on Tongariro and Manganuiateao Rivers were located in the middle sections of the two systems where both rivers were characterised by large width, deep water, high flow and stable boulder /

Chapter Three Methods 36

cobble substrate. Conversely, the sampling sites on the two Ruahine rivers were located in the headwaters which were characterised by unstable cobble / gravel substrate, relatively low flows, shallow water and narrow channel width. Due to the similarity in the nature of Tongariro and Manganuiateao Rivers, and Ikawetea and Makaroro Rivers, the discussion of the data from the similar rivers is often combined in the following sections.

A description of each of the four rivers follows.

Tongariro River

Tongariro River originates in the Kaimanawa Ranges. In addition to collecting water from the Kaimanawas, Tongariro River also drains the eastern flanks of the central North Island volcanos, before flowing into Lake Taupo. The river's flow dynamics have been substantially altered since the early 1970s when it became part of a large hydropower scheme. In the area where I collected my samples, the river was approximately 20-30 m wide and fast-flowing with a predominantly boulder / cobble substrate. The riparian forest bordering the river in this regIOn IS dominated by silver beech (Nothofagus menziesii).

There is a population of blue ducks in the middle and upper reaches of the river while the lower section contains a world-renowned trout fishery. In the middle section of river, where I conducted my study, the trout population is mainly composed of rainbow trout.

From this river I collected trout, blue duck faecal droppings and benthic macroinvertebrate samples at two sites. The first s ample site was located immediately upstream of the Pillars of Hercules (8 39° 09' 05", E 175° 49' 02/1, elevation 620m) while the second was located approximately 0.5 km downstream of Tree Trunk Gorge (8 39° 10' 04", E 175° 48' 05") (Fig. 3. 1).

Monitoring of the Tongariro River blue duck population indicates that the adult ducks occur at a density of approximately 1 . 3 birds per km although numbers have declined by approximately 40% since 1983 (Don 1992 unpublished). Little information exists on the density of juvenile trout in the study area. However, work by Stephens ( 1989) reported

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juvenile trout densities in the lower river increased rapidly in spring to a maximum in December before declining slowly throughout the summer and autumn. As with Stephens ( 1989), I found by electrofishing that juvenile densities were highest in summer with fish occurring in the

littoral substrate at approximately 1 per m2 .

Manganuiateao River

Manganuiateao River originates in the southwest snow fieldd of Mt Ruapehu, in the central North Island (Fig 3 .2). It flows southwest for approximately 80 km to its confluence with Wanganui River and has a catchment area of 620 km 2 (Cudby & Strickland 1986). In the middle section of the river from which I collected my samples, the river is characterised by a well defined pool / riffle system. The river substrate is composed of large rounded andesitic boulders and is relatively stable in nature. Mean annual water flow recorded at Ruatiti downstream of my sampling sites is approximately 18.2 m3 s�1 and water quality has been reported as uniformly high (Williams 1991). The river in the vicinity of my study area is flanked by pasture and, in places, regenerating native bush.

There is a population of blue ducks in the middle and upper reaches of the river while both rainbow and brown trout occur throughout the river. Samples for my study were collected from three sites in the middle reaches of the river. These were named Top site (S 39 19' 06" E 175 14' 00"), Camp site (S 39° 19' 05" E 175° 14' 03"), and Flying fox (S 39° 19' 05" E 175° 15' 0 1") which was the most downstream site. Resident pairs of blue ducks occupied territories encompassing each of the sampling sites.

Adult blue ducks within the study area occur at a density of approximately 1 pair per kilometre of river (Williams 1991). Adult trout (FLI > 0.2 m) densities have been reported by Cudby & Strickland (1986) to be in the order of 5 fish per pool in the reach from which samples were collected. No published information is available on juvenile trout density in the study area. From my electro-fishing, densities of juvenile trout appeared to be low, being in the order of 0.2 fish per m2 .

Fig. 3. 1 Location of Tongariro River and sampling sites. o t:J""

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Chapter Three Methods 40

Ikawetea River

Ikawetea River originates in the Northern Ruahine Ranges and flows north to join Taruarau River and ultimately Ngaruroro River (Fig. 3.3). The river drains two large valleys, the Ikawetea and the Apis which combined have a catchment area of approximately 80 km2 . The lower valley slopes are dominated by red beech (Nothofagus fusca ), the upper slopes by mountain beech (N. cliffortioides) and the open tops by leather wood scrub ( Olearia colensoi) and tussock (Chionochloa sp. ) . The headwaters are relatively devoid of riparian vegetation other than tussock.

The stream bed is composed of a mixture of cobble and gravel-sized material with outcrops of bed rock prominent in upper gorge sections. Mean annual flow was estimated (based on stream width x depth x velocity estimates) to be 0.5 m 3s-1 with the stream's flow pattern being punctuated throughout the year by high flow events. A waterfall of approximately 20 m height is situated in the middle section of the river

(8 39° 35' 08" E 176° 12' 05").

Benthic, faecal and trout samples were collected from a total of six sites, three sites below the falls and three sites above. The below-fall sites were spaced approximately 1 . 5 km apart with the first being 300 m downstream of the falls. The first of the three upstream sites was located approximately 100 m above the falls. The second upstream site was approximately 2 kms upstream while the third was 3.5 kms above the falls and 100 m downstream of Rockslide Bivouac (8 39° 37' 03" E 176° 13' 07").

Thirteen blue ducks were recorded between the lower and upper benthic macroinvertebrate sampling sites on the Lower Ikawetea and Apis Rivers during the 1991/92 data collection period. This equates to a density of 1 .9 birds per km of river. From visual counts of adult trout in Ikawetea River below the waterfall I estimated trout density to be in the order of 1 - 2 fish per pool.

Chapter Three Methods 42

Makaroro River

Makaroro River, like Ikawetea, originates in the Northern Ruahine Ranges and drains a catchment of approximately 67 km 2 (Fig. 3.4). The vegetation of the catchment is much the same as that of Ikawetea. The upper reaches of the river flow in a southerly direction before flowing west to join Waipawa River. The stream has a substrate composed predominantly of cobble and gravel-sized material. I estimated the mean annual flow to be in the order of 0.5 m 3s-1 . A waterfall of approximately 10 metres height is located in the middle section of the river (8 39° 40' 06" E 1760 14' 0 1").

I collected benthic, faecal and trout samples from three sites below the waterfall and benthic and faecal samples from three sites above the waterfall. Benthic sample collection sites were spaced at approximately 1

km intervals both above and below the falls.

Eight blue ducks were counted between the upper and lower macroinvertebrate sampling sites in 1991/92 equating to a density of 1.6 birds per km of river. The smaller size of trout occurring in Makaroro River made visual trout counts less accurate and the highest density of trout recorded was 0.75 fish per pool.

Fig. 3. 4 . Location of Makaroro River and sampling sites. o P"' Pl "d c-t­ CD '1

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Chapter Three Methods 44