fish yield by gears and water level …ntu.edu.vn/portals/66/tap chi khcnts/so 3.2016 stephanie,...

92 • NHA TRANG UNIVERSITY

Journal of Fisheries science and Technology No.3 - 2016

FISH YIELD BY GEARS AND WATER LEVEL FLUCTUATIONS IN NUI COC RESERVOIR

Stéphanie Kamondo12*, Aloys Musoni12, Anh Bui The3

Received: 20/6/2016; Revised: 09/9/2016; Accepted: 26/9/2016

ABSTRACTA part of being an important source of animal protein and employment opportunities for people living

in its vicinity, Nui Coc Reservoir supplies water used to control fl ooding and irrigate agriculture land and industrial zone. With the purpose of fi nding out whether seasonal water level fl uctuations could affect fi sh production in the latter, monthly fi sheries catch data by fi shing gear were collected and analyzed taking into consideration the water level changes. Two main fi shing seasons (March - July and September - November) were observed using gill net and cover net gear; trammel net was used almost the all year except in winter whereas fi shing with purse seine were done during the two main fi shing seasons but in addition some activities were also done in winter. High levels of fi sh production in this water body were related to the drawdown and impounding processes. Some management activities are recommended to improve the benefi ts of utilizing the reservoir.

Keywords: water level fl uctuations, fi shing gears, fi shing seasons

1 Rwanda Agriculture Board (RAB) – Kigali in Rwanda 2 Faculty of Aquaculture, Nha Trang University, Vietnam 3 Ministry of Agriculture and Fisheries, Hanoi, Vietnam *author for correspondence, email: [email protected] and P.O. Box 5016 Kigali

I. INTRODUCTION A lot of people depend directly or

indirectly on fi shery and aquaculture for their livelihoods and in addition to that fi sh plays a signifi cant role in nutrition and good health of many people around the world.

In recent years, the number of reservoirs has been steadily growing all over the world in order to provide water for irrigation, hydro-electric power generation, fl ood control, public water supply, recreation and navigation (Bhukaswan, 1980; De Silva, 2001) but they are never impounded for fi shery development per se. Reservoir construction in Vietnam is continuing, as response to the growing demand for energy, water for crops and these water areas can usually be used secondarily for fi sheries (Phan and Sollows, 2001). Nui Coc Reservoir was impounding by damming Cong River of the Ba Vi Mountain range

from 1976 to 1978 with the main purposes of controlling fl ood and irrigate about 11,500 ha of agriculture land and industrial zone.

Due to natural variations in the affl uent fl ow into a reservoir and variations in user water demand, coupled with the need in many cases to accommodate fl ood water, it is virtually impossible to operate a dam so as to produce a year round constant water level in the reservoir (Bernacseck, 1984). The water level changes in Nui Coc Reservoir when water is stored or discharged and the change in water level may infl uence positively or negatively the fi sh production. It is in this framework that the objectives of this study were to collate information about fi shing gear, seasonal harvesting, catch data and evaluate the effect of water level fl uctuations on fi sh production for 2001-2003 and 2006-2008 periods.

NHA TRANG UNIVERSITY • 93


II. MATERIAL AND METHOD

1. Study siteNui Coc Reservoir (21o33’ - 21o37’N,

105o40’ - 105o44’E) is located at 15 km west from the capital city of Thai Nguyen Province, Northern Vietnam. This is an artifi cial water body which was constructed from 1976 to 1978 for fl ood control and irrigation purpose of 11,500 ha of agriculture land and industrial zone. This reservoir was impounding by damming Cong River of the Ba Vi Mountain range and it has an average area of 25,000 ha, expanding to 2,800 at high level of water and receding to 1,800 ha at the lowest water level. Forty percent of the water surface covers the

shallows in the upstream region and the rest is deep water. The water level varies depending on the season and it normally reaches the lowest level of around 32.5m in summer (April - May) and its highest level of around 45 m in autumn (October) (Figure 1). The air temperature in this area decreases up to 10oC during winter (October - January) and can reach 39oC - 40oC in the fall summer. Whereas the water temperature ranges between 34oC to about 18oC corresponding to summer and winter respectively. The iron content of about 0.5 mg/l and pH value of 7.4 with undetectable level of ammonia and all these parameters make the reservoir suitable for aquaculture(Nguyen, 1999).

Figure 1. Fluctuation in water level of Nui Coc Reservoir

Table 1. Some physical and chemical features of Nui Coc Reservoir [6]No Physical and chemical features Value

1 River basin Red River

2 Location 21o33’ N and 105o 40’ E

3 Maximum length 10 km4 Mean depth 15 m5 Area 2,5006 Volume (million m3) at msl 220 million m3

7 Temperature ± 28.1 oC8 Dissolved oxygen ± 6.8 mg/l9 pH ± 7.2

Apart of being a source of water supply, Nui Coc Reservoir plays an important role in providing good quality of fi sh at affordable prices and in maintaining the level employment

and enhance incomes of about 10,000 people including 50 - 60% of ethnic minorities who were displaced during the impoundment period and re-settled around the reservoir.



Fifty fi ve fi sh species belonging to fi ve orders and 13 families were found in Nui Coc Reservoir. Cyprinid dominates the reservoir fi sh fauna with 34 species and contributed 62% of the total fi sh species. There are 23 species mainly caught in this water body with Cyprinidae species being dominant (17) and Gobiidae being the second most important with three species (Bui, 2006).

2. Catch data collectionSecondary data collection was done

through which data for years prior 2006 were collected from the scientifi c publications, documents from local and central governmental organizations.

By means of primary data collection, information from logbooks of 2006 up to 2008, which supplied fi shery center in charge of the reservoir during that period were collected, coded and digitized.

Field trips as Participatory Rapid Appraisal were organized to walk around for direct observation and interview some fi shers and local authorities to get information on fi shing gear and fi shing seasons.

3. Data analysisTo carry out the study, time series information

(2001 - 2003 and 2006 - 2008) was digitized

and analyzed using MS EXCEL. Data were classifi ed by gear type and month then both numerical and graphical methods of descriptive statistics were taken into consideration.

III. RESULTS AND DISCUSSION

1. Fishing gearsFisheries are artisanal and use different

gears in tropical water bodies. In Vietnam, gillnet, trammel, and Cover net and seines are the main fi shing gears. However there are also other types such long and hooks; lift net, long lines, shrimp traps, etc.

Gill net is the traditional gear of the fi shers in reservoirs in Vietnam. This type usually uses to catch fi sh in shallow areas or the upstream.

Trammel net, a common gear used in Chinese reservoirs, has been introduced in Vietnam. It has rapidly and widely developed. Traditionally, this net was made by hemp thread but now made of nylon and this rapidly developed to be the most effective gear. The net is spread in a large area of water surface and is sunk down to catch fi sh at the bottom of the water bodies. It has been introduced in to Vietnam since 1990 and has one to three layers of nylon mesh panels. It mostly catches bigger sized fi sh such as common carp, yellow cheek (Elopichthys bambusa) and bighead carp.

Table 2. Summary of the features of the main types of gear used and the species of fi sh caught in Nui Coc Reservoir

Gear Description Species caught*

Gill net Commonest: 200 x 1.2 m; mesh size = 17-110 mm; mainly used at night; fl oating technique used ss, xn, ce, hm

Trammel net Three layers of nylon mesh panels; mesh size = 80-100 mm; depth = 4-10 m; length = 300-400 m gc, imc, sc, cc, ce

Cover net

A rectangular net with about 1000 - 2000 m2; mesh size = 80 mm; the net is turned over from a bamboo fl oat and pulled over to opposite direction by boats, then dropped down to catch the bold fi shes.

cc, imc, sa, cn

Purse seine netVery small mesh size = 10-12 mm; catch aquatic animals near the shoreline; » 200 m of length; there are cod ends in the bottom of the net.

ss, ce, hm and small aquatic animals

(gc) grass carp; (xn) Xenocypris spp.; (imc) indian major carp; (sc) silver carp; (cc) common carp; (ss) small shrimp; (hm) Hemiculter leucisculus; (ce) Culter erythropterus; (sa) Silurus asotus; (cn) Canassiscides cantonensis (* information extracted from Bui; 2001)



However considering this study, the measures of gill net, trammel net, covert net and seine net are 100m length-1m width; 120m length-6m width; 100m length-15m width and 300m length-4m width, respectively.

In Nui Coc Reservoir, there are about over 1000 fi shers. Seventy per cent of the fi shers have daily or monthly licenses to fi sh. There are fi ve main fi shing gears used in Nui Coc Reservoir, such as gill net, trammel net, cover net, seine net and shrimp traps. In 2001, 37% of the fi shers used shrimp traps and 22% gill nets and trammel nets contributed 20%. Only about 1% of fi shers used cover and seine nets. Nineteen per cent of fi sher used other type of fi shing gear such as long line hooks, cast nets, fi shing baskets and shimmy nets (Bui, 2006).

F igure 2. Fishing gear utilisation in Nui Coc Reservoir (based on data from Tran, 1996;

Nguyen, 1999; Bui, 2006)The forma earnings from capture fi sh to Nui

coc fi shery station is approximately about 12% to the total income (personal communication to the Unit Head of Nui Coc fi shery station).

However, the fi shery exploitation program will continue to enable local people to participate, but it must be added in a long-term program of the aquaculture and fi shery development of Thai Nguyen province.

To improve its current management, from October 2012, this unit has joined as a member of Thai Nguyen Irrigation Management Co. Ltd. (TNIMC), under the management of People’s Committee of Thai Nguyen Province and the latter is in charge of promoting aquaculture development on the reservoir as well as creating better conditions for the surrounding habitants to exploit the reservoir resources.

2. Fishing seasonsThe two main fi shing seasons observed

using gill net and covert net gears in P1 and P2 were from March to July and from September to November (Figure 3, 4, 5 and 6). And there was no big difference of fi sh yield during the two periods (2001 - 2003 and 2006 - 2008). Fishing activities with trammel net were done almost all the year except during winter season as shown in Figures 7 and 8. Purse seine net was used during the same fi shing season as gill and covert nets but in addition some activities were also done during winter (Figures 9 and 10). It is noticed that the fi sh yield increases to a high level during these main fi shing seasons and decreases over other months of the year. Accordingly these results were also fi gured out in previous studies done in Nui Coc Reservoir (Bui, 2001; Nguyen, 2004; Bui, 2006).

Figure 3. Monthly changes in fi sh yield using gill net during the period P1 (2001-2003)

Figure 4. Monthly changes in fi sh yield using gill net during the period P2 (2006-2008)



There are usually relative changes between fi sh yield to the reservoir feature such as water level fl uctuation. In addition to that changes in fi sh catch may be linked to the fact that water level fl uctuation infl uences the fi shing areas and fi shing activities. Monthly fi sh yield changes and main fi shing seasons in Nui Coc Reservoir during which fi shing activities and fi sh yield are of high level may be related

to the water level fl uctuations particularly as in many medium-sized reservoirs build for irrigation purposes as well as the type of fi shing gears and methods used in the water body.

Beam (1983), Sreeviasan (1986), De Silva (1987) detected in their studies that there was a signifi cant but negative impact on the fi shery system due to the fl uctuations in water level which are detrimental to fi sh reproduction,

Figure 5. Monthly changes in fi sh yield using covert net during the period P1 (2001-2003)

Figure 6. Monthly changes in fi sh yield using covert net during the period P2 (2006-2008)

Figure 7. Monthly changes in fi sh yield using trammel net during the period P1 (2001-2003)

Figure 8. Monthly changes in fi sh yield using trammel net during the period P2 (2006-2008)

Figure 9. Monthly changes in fi sh yield using seine net during the period P1 (2001-2003)

Figure 10. Monthly changes in fi sh yield using seine net during the period P2 (2006-2008)



survival of young juveniles; submerged plants and bottoms animals are exposed to desiccation; and fi nally reduction of the foods supply and refuges of many fi sh particularly herbivorous fi sh species are observed.

However fl uctuations in reservoir water level are unavoidable and indeed from fi shery perspective are desirable. During drawdown, more terrestrial species such grasses and sedges die and decompose resulting in large release of nutrients into the water, the biomass of benthic invertebrate increases greatly and species diversity. Gradually sloping drawdown areas can become in effect tilapia nurseries. The expansion reservoir surface area can be considerable and this probably acts to reduce juvenile mortality by predation and increase stock recruitment. Furthermore, the presence of submerged macrophytes increases substantially the abundance and species diversity which in turn supports increased production of some fi sh species when the water level rises (Figure 10) (Bernacsek, 1984; Bui, 2006).

Considering the fact that fi shing gear and techniques used in Nui Coc Reservoir are described as both passive and active, the low water level observed usually from February to June may bring advantage to the fi sh catch. Bernacsek (1984) explained that the simplest possible effect of water level fl uctuations on the ichthyomass of a reservoir is a change in population density due to change in reservoir volume and area. This concentration effect should be theoretically results in higher fi sh catches during drawdown because the fi sh become more crowded together and thus easier to catch. Logically, the greater the drawdown in a particular reservoir the more important is the concentration effect and the greater the increase in low water catch relative to the high water catch. Evidence is available from several reservoirs supporting this concentration effort such as Mwadingsha (Goorts et al., 1961); Kainji (Blake, 1977; Ita, 1978); Volta (Coppola and Agadzi, 1977) and Nasser/ Nubia (El Tahir Ali; Latif) reservoirs.

Figure 11. Effect of reservoir water fl uctuations on fi sh yield



Water level fl uctuation (drawdown and impounding) affect the fi sheries in Nui Coc Reservoir where they appear to enhance fi sh production during Summer and Autumn. In order to predict and manage water level, timing and magnitudes of infl ows of the reservoir need to be known approximately. This will also help to implement some management fi sheries activities to optimize fi sh production such as cage culture, stock enhancement depending on the level of water.

IV. CONCLUSION AND RECOMMENDATIONSGillnet, trammel net, cover net and purse

seine net are the types of gears used in Nui Coc Reservoir which caught grass carp, Xenocypris, indian major carp, silver carp, common carp, small shrimp, Hemiculter leucisculus, Culter erythropterus, Silurus asotus, Canassiscides cantonensis.

March to July and September to November are the two main fi shing seasons which were observed and during which the fi sh yield increases to a high level.

REFERENCES

1. Beam J. H., 1983. The effect of annual water level management on population trends of white crappie in Elk City Reservoir, Kansas. North American Journal of Fisheries Management 3: 34-40.

2. Bernacsek G. M., 1984. Guidelines for dam design and operation to optimize fi sh production in impounded river basins (based on a review of the ecological effects of large dams in Africa). CIFA Tech. Pap.(11):pp 98.

3. Bhukaswan T., 1980. Management of Asian Reservoir Fisheries. Fisheries Technical Paper No.207. FAO. Rome, Italy: pp 69.

4. Blake B. F., 1977. Lake Kainji, Nigeria: a summary of the changes within the fi sh population since the impoundment of the Niger in 1968. Hydrobiologia, 53(2): 131-7.

5. Bui T. A., 2001. Preliminary results of the fi shery in Nui Coc Reservoir, Thai Nguyen Province. Thesis submitted for the degree of Master of Science., University of Fisheries.

6. Bui T. A., 2006. Fish and Fisheries in Large and Medium-sized reservoir in Vietnam. Doctor of Philosophy degree thesis (Aquactic Science), Deakin University.

7. Coppola S. R.,and Agadzi K., 1977. Evolution of the fi shing industry over time at Volta Lake 1970–1976. Rome, FAO, Volta Lake Research and Development Project, GHA/71/533. Statistical Studies, (6): pp 41 .

8. De Silva S.S., 2001. Reservoir Fisheries: Broad Strategies for Enhancing Yields. In: Reservoir and Culture-Based Fisheries: Biology and Management. Proceedings of an International Workshop. Bangkok, Thailand, Australian Centre for International Agricultural Research.

9. De Silva S. S., 1987. The reservoir fi sheries of Asia. In Reservoir Fisheries Management and Development in Asia. Proceedings Workshop, Kathmandu, Nepal.

10. El Tahir Ali, M. Lake Nubia (Sudan). CIFA Tech.Pap./Doc.Tech.CPCA (10) (in press).11. Goorts P. N., Magisand J. W., 1961. Les aspects biologiques, humains et économiques de de la pêche dans le lac

de barrage de la Lufi ra (Katanga). Liège, Editions FULREAC, Université de Liège.12. Ita E. O., 1978. An analysis of fi sh distribution in kainji Lake, Nigeria. Hydrobiologia, 58(3): 233–44.13. Nguyen S.H., 1999. Aquaculture status in Thai Nguyen Province. In conference on reservoir fi sheries

management: Research Institute for Aquaculture No3. p. 15.14. Nguyen L. V., 2004. Statistical data of fi sh production in Nui Coc Reservoir. 15. Nguyen S. H., 1999. Aquaculture status in Thai Nguyen province. Paper presented in Reservoir Fisheries

Management Seminar. Research Institute for Aquaculture No.3, Nha Trang, Vietnam (in Vietnamese).16. Phan P. D., and Sollows J. D., 2001. Status and Potential of Reservoir Fisheries in Dak Lak Province,

Vietnam. In: Reservoir and Culture-Based Fisheries: Biology and Management. Proceedings of an International Workshop, Bangkok, Thailand, Australian Centre for International Agricultural Research.

17. Sreeviasan A., 1986. Changes in the fi sh population of Lewis and Clark Lake, 1956-1974, and their relation to water management and the environment. Research Report 79. U.S. Fish and Wildfi fe Service.

18. Tran T. L., 1996. Survey on reservoir fi sheries/Aquaculture in Vietnam. In: A document of MRC project for the management of reservoir fi sheries in the Mekong basin, p.85. MRC, Vientiane, Lao PDR, Bangkok, Thailand.

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