Ice in the Environment: Proceedings of the 16th IAHR International Symposium on IceDunedin, New Zealand, 2nd–6th December 2002International Association of Hydraulic Engineering and Research

EXPERIMENTAL STUDY ON BENTHIC FISH HABITATS IN ANICE COVERED RIVER

T. Nogami1, Y. Watanabe1, M. Nakatsugawa1, F. Nakamura2, K. Kamura2,H. Yamada2, S. Tsuchiya3, K. Watanabe4 and H. Iwase4

ABSTRACTFor fish living in cold, snowy regions, their wintering habitat is known to stronglyinfluence their survival rate for the following year. While some surveys have addressedthe wintering environment of high-value commercial fish such as salmon and trout, fewstudies have considered the wintering environment of benthic fish found in ordinaryrivers. Surveys of the living environment, including the wintering environment, ofbenthic fish in swift current rivers with gravel beds, were carried out to examine howchanges in the physical habitat were reflected in quantitative measurements such as fishpopulations.

INTRODUCTIONTo maintain and restore the river environment, it is imperative to quantitatively evaluatehow the river ecosystem is affected by human activities including river improvement anderosion control work, and to study more effective measures for maintenance andrestoration. From 1998 to 1999, the environment of the Makomanai River, which is atributary of the Toyohira in the Ishikari river system, was monitored by sampling thepopulation of “Cottus Nozawae” (hereafter: sculpin). This fish is usually only distributedin the upstream tributaries of the Ishikari river system. It was revealed that the populationdensity of sculpin was lower in an artificially, reinforced section of the river, (a projectcompleted 20 years ago) to be known as the channel section, than in two sectionsdownstream: a 30-year-old bank-protected section and a natural section. The artificially,reinforced, channel section had provided the river with a gentler, longitudinal gradientand a greater width. Reinforcing the channel section had resulted in a decrease in flowvelocity as well as a reduction in the average size of riverbed grain materials. In addition,river channels with such reinforced bottoms are known to have less variation in bed formand this can lead to fewer riffles and pools. The factors contributing to the low populationdensity of the sculpin in the channel section were clarified in this paper.

1 Civil Engineering Research Institute of Hokkaido, Hiragishi 1-3, Toyohira-ku, Sapporo, 062-8602,Japan. E-mail: nogami@ceri.go.jp

2 Hokkaido University, Sapporo, Japan3 Foundation for Riverfront Improvement and Restoration, Tokyo, Japan4 Hokkaido Engineering Consultant Co., Ltd., Sapporo, Japan

Field experiments, conducted in 2000, were designed to determine how to improve thesculpin’s habitat and clarify the environmental conditions conducive to populationenhancement. According to the results of surveys conducted after renovation of channelsection, the population density of sculpin and its population per channel length increasedin the loose stone area. The density became closer to that of the natural andbank-protected sections.

Whereas game fish such as salmon and trout, due to their commercial as well asrecreational popularity, have been the subject of previous research (Kobayashi, 1999), toofew studies have focused on benthic fish. Migratory fish tend to seek a wintering habitatthat has limited light-transmittance, low water current speed and has vegetation present.In an effort to shed some light on the wintering habits of benthic fish an investigation wascarried out in the natural section of the Makomanai river in mid-winter and the results areshown. It was revealed that the habitat could be studied in detail and as a result it waspossible to determine the features of the hibernation environment of the sculpin. Thesefeatures included flow velocity, depth of water and river bottom quality.

MONITORING FISH HABITATION IN THE MAKOMANAI RIVERHabitats of sculpin in the Ishikari river systemIn contrast to the widely distributed loach (Namacheilus barbatulus toni, hereafter: loach),the sculpin are caught only in mid-sized and small tributaries in the Ishikari River basin.Thus it may be assumed that their habitats are limited to specific locations, as far as theIshikari river system is concerned. This section examines ways to improve the sculpin’shabitat. As landlocked, freshwater benthic fish, they are confined to the river all theirlives and mainly live under gravel at riffles (Goto, 1989).

Outline of monitoringThe Makomanai River, a tributary of the Toyohira River, is a fast-flowing river with achannel length of 20.8 km, a drainage area of 37.1 km2, and an average bed slope of 1/19.It joins the Toyohira River upstream of KP 21.0. Sediment disasters occurred there in1975 and August 1981, after which erosion and sediment support were built into theriver’s sides and bottom. Today, eight check dams stand at the upper reaches, and in themiddle portion, the man-made, reinforced channel section has been put in place.

The monitoring section was between 3.6 km and 10.4 km upstream from the Makomanairiver’s confluence with the Toyohira. 15 monitoring sites were established in this section.Each observation unit measured 4 to 21 m in width and 7 to 44 m in length; with thelengths varying in order to ensure the inclusion of at least two riffles and pools. The fishspecies and details of their habitat (flow velocity, water depth, bed materials, etc.) wereinvestigated.

The monitoring section was divided into three parts: a man-made graded bottom channelsection; a natural section and a bank-protected section from upstream to downstream.The channel section (2 km) built nearly 20 years ago, had bed-stabilization supportequipped with 17 fish ladders. The river channel in the natural section was largelyuntouched, and was characterized by a steep natural riverbank. The bank-protectedsection, where river improvement work was implemented nearly 30 years ago, includedfive bed-stabilization support sections partially installed with revetments and fish ladders.Riverbank vegetation had recovered considerably more in this section than in the channel

section.

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Figure1: Outline of monitoring on the river

Problems in the channel sectionTable 1 has detailed information about the Makomanai River and the average values ofmeasurement data for each section. As for the longitudinal distribution of species, thetable indicates dominance of loach in the channel section and sculpin at the lower sections(natural and improved). These fish are both benthic species inhabiting chiefly the gapsbetween bed materials, and their population density was higher in the riffle with a lotloose stone. The channel section, because of the existence of the graded support on thesides and bottom, had a gentle bed slope of 1/100 and the area ratio of pool to riffle was aslow as 1/7, compared with 1/1.5 to 1/1.6 in the other sections. In addition, 60 %cumulative grain size distribution in the riffle was less than half the size of those in theother sections and the proportion of loose stone was lower.

Figure 2 shows the relationship between the proportion of loose stone and the populationdensity of sculpin, by using 60 data units from the monitoring survey conducted in May,July and September in the natural and bank protected sections. Generally, gaps betweenbed materials are considered to be an important habitat for benthic fish. In this diagram,the data collected in December, when the population density was low, and that collectedin the channel section where the environment, (riverbed) had been reinforced, wereomitted.

As in Figure 2, Figure 3 shows the relationship between Froude number (Fr) and theproportion of loose stone, by using 60 data units from the monitoring survey conducted inMay, July and September in the natural and bank protected sections. The correlationcoefficient was relatively high (0.62).

Table 1: Details on monitoring section ofthe Makomanai River

Channel-worksection

Naturalsection

Bankprotectedsection

Bed slope 1/100 1/72 1/61

Section length 2.0 km� 2.2 km 2.6 km

Drainage area�(downstream end)

29.7 km2 31.7km2 33.7 km2

Area ratio of pool /riffle 1/7 1/1.5 1/1.6

Riffle 136 250 24960% cumulativegrain size (mm)

Pool 173 159 128

Riffle 0.23 0.60 0.57Proportion of loosestone

Pool 0.29 0.27 0.33

Riffle 0.34 0.47 0.50Average flowvelocity (m/sec)

Pool 0.23 0.27 0.25

Riffle 16.3 10.9 8.2Surface width (m)

Pool 13.5 8.2 10.0

Riffle 18.4 60.2 89.4Population densityof sculpin(N/100m2) Pool 18.0 28.4 32.4

Riffle 31.2 28.2 37.7Population densityof loach (N/100m2)

Pool 27.9 15.1 14.5

Figure 2: Proportion of loose stoneand population density of sculpin

Figure 3: Proportion of loose stoneand Froude number

INSTALLATION OF A TEST WATER CHANNEL AND ITS CONSEQUENCESAn experimental section (L = 40 m) and the control section (L = 30 m) were establishedin the form of a test water channel situated about halfway along the channel section(2.6 km long × 20 m wide). Tests were conducted to reveal the change in sculpindistribution by narrowing the width of ordinary flow (Fig. 4), creating an artificial riffle,and increasing the number of loose stones in the experimental section. On this occasion,to clarify the difference in the populations between the experimental section and thecontrol section, each section was stocked with 140 sculpin, nearly twice the number offish collected in the monitoring prior to the installation. The facility was installed in July2000, a pre-installation examination was conducted in July 2000 and a post-installationexamination was conducted in July 2001 (Fig. 5 and Fig. 6).

Table 2 shows the number of sculpin and the average hydraulic values for both theexperimental section and the control section before and after installation. While thepopulation density of sculpin doubled in the experimental section from 12/100 m2 beforeinstallation to 25/100 m2 after installation, that in the control section decreased from19/100 m2 to 12/100 m2. Furthemore, the proportion of loose stone was also improved inthe experimental section to 0.2, it remained the same in the control section.

Figure 4: Installation of test water channel

Table 2: Comparison of test water channels before and after installation

July 2000 July 2001

Experimentalsection

Controlsection

TOTAL Experimentalsection

Controlsection

TOTAL

Sample number (N) 77 86 163 162 55 217

Population density(N/100m2)

12 19 16 25 12 19

Proportion of loose stone 0.09 0.06 0.08 0.20 0.07 0.13

Average water depth (m) 0.22 0.31 0.27 0.24 0.26 0.25

Average flow velocity(m/sec)

0.19 0.12 0.16 0.27 0.20 0.24

Figure 5: Before installation. Figure 6: After installation.

SURVEY OF THE WINTERING ENVIRONMENTA fish population survey was conducted during the coldest period of winter, because thewintering environment is crucial for fish in rivers in cold, snowy regions. The survey wasmade in the natural section in early February 2002. The water temperature was 1.2 C°,which was higher than average. In a 20-m section, meshe, 1m by 1m were established tocollect physical environment data and catch sculpin. The average width of the section was7.3 m, and measurements were taken at 146 units of mesh. The number of sculpin wasgreater in meshes along the centerline of stream areas where the water was deep than inmeshes along the riverside. The water was covered with ice at some places along theshore.

Table 3: Population density of sculpin andproportion of loose stone

Population density(N/100���

Proportion of loosestone

�Downstream

riffle (a)Upstreampool(b) a/b

Downstream riffle

Upstreampool

May2000

101 26 3.9 0.81 0.16

July2000

35 19 1.8 0.81 0.38

Sep.1999

76 20 3.8 0.42 0.20

Dec.1999

27 24 1.1 0.72 0.41

Feb.2002

37 25 1.5 0.43 0.15

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Figure 7: Cumulative number ofsculpin caught vs. water depth

Table 3 compares the results of the surveys performed at the same site in 1999 and 2000,including population density and proportion of loose stone. There was a 69-m2 poolupstream of the survey site and a 65-m2 riffle downstream of that site. In each surveyperiod, the proportion of loose stone and population density were higher on thedownstream side than on the upstream side. Population density ratios of upstream todownstream were large at: 1.8–3.8, in May, July, and September, but were small, at1.1–1.5, in December and February.

Next, mesh 1 m by 1 m of the February 2002 data were analyzed. Mesh with a lot of loosestone accounted for 29 % of all mesh. The 76 % of all sculpin caught were snared in thesemesh. Based on the mesh collection data, Figure 7 shows the cumulative number ofsculpin caught versus water depth. The graph shows that 72 % of all the sculpin caughtwere caught in the mesh of water depth 0.5 m or greater; mesh which accounted for onlyabout 30 % of the survey area. Table 4 depicts hydrological quantities and populationdensity by water depth range: smaller than 0.3 m (I), 0.3 m to 0.5 m (II), and 0.5 m orgreater (III). The population density was 4 individuals per 100 m2 for depth I as against69 per 100 m2 for depth III. At depth III the flow velocity was high and there was a largeamount of loose stone.

The 1-m-mesh-based analysis of the sculpin wintering environment revealed that thepopulation density tended to be high along the centerline of the stream in areas where thewater was deep and there was a lot of loose stone. The comparative analysis of the poolupstream and the riffle downstream found the population density to be greater in the riffle,

in the seasons other than winter, and almost equal, upstream and downstream, in winter.The winter and summer habitat of migratory fish, such as trout and salmon, differ greatly.Especially in winter, these fish prefer a habitat near the river’s shore where the flowvelocity is high. The sculpin, a benthic fish, can thrive in the same habitat the year round;one with riffles in its center and a river bottom-lined with loose gravel.

Table 4: Averages of hydrologicalquantities and population densities

Water depth range I II III

Water depth (m) Shallow Medium Deep

Population density(N/100 m2)

4 21 69

Flow velocity(m/s)

0.14 0.26 0.32

Proportion of loosestone

0.39 0.62 0.82

Ratio of frozenwater surface area

0.39 0.06 0

Froude number 0.12 0.13 0.13 Figure 8: Survey site in theColdest winter period.

CONCLUSIONSToward improving the river environment and fish habitat, a correlation between numberof sculpin, the main subject of this study, and several hydraulic factors such as channelwidth, flow velocity and grain size of river bed material were examined in an artificially,reinforced channel section of the Makomanai River, where the population density ofsculpin was low. It was concluded that measures to increase flow velocity and grain sizewere necessary to help increase the fish population in the channel section.

A comparison of the population density of sculpin before and after installation of the testwater channel revealed that it decreased from 19/100 m2 to 12/100 m2 in the controlsection, while it doubled from 12/100 m2 to 25/100 m2 in the experimental section. Also,in areas with a proportion of loose stone of 0.4 or higher, the population density andpopulation per channel length were improved to exceed the average in the natural andbank protected sections.

Whereas migratory fish, in winter, tend to choose a habitat with reduced flow velocitynear the river shore, the sculpin, a benthic fish, prefers one with riffles in the central partsof streams and a lot of loose stone on the river bottom, regardless of the season.

REFERENCESKobayashi, M., Nogami, T. and Nakatsugawa, M. Creation of the winter rearing habitat

of juvenile masu salmon,Oncorhynchus masou (in Japanese), CERI of Hokkaido(2001)

Goto, A. Freshwater Fish in Japan, Yamato-Keikokusha (in Japanese) (1989) 662p.Watanabe, K., Nakamura, F., Kamura, K., Yamada, H., Watanabe, Y. and Tsuchiya, S.

Influence of stream alteration on the abundance and distribution of benthic fish (inJapanese), Ecology and Civil Engineering Society 4(2): 133–146 (2002).