Effect of mesh size on catch performance of driftnets fishing in Lake Kainji

Item Type conference_item

Authors Ahmed, Y.B.; Tagago, T.A.

Publisher FISON

Download date 02/10/2021 01:37:32

Link to Item http://hdl.handle.net/1834/39067 Effect of mesh size on catch performance of driftnets fishing in Lake Kainji

Ahmed, Y. B. / Tagago, T.A.

Abstract \ The studies on effect of mesh size on catchperformance of driftnetsfishing in Lake Kainji was experimented using 38.1mm, 63.5mm and 88.9mm stretched mesh size for 21 consecutivefishing days. The drijinets were operated by twofishing canoe the operation was done between 14.30 hours - 16.00 hours daily in the afternoon. Twenty twofish species belonging to tenfish families were caught. Thefish Species Diversity Index (SDI) revealed that 38.Imm stretched mesh size drijinet recorded the highest index ofO. 77 next by 63.5mm mesh size with 0.45 and the least index of 0.36 was obtained in 88.9mm stretched mesh size drijinet. A total of 372fish was caught, 54.30% of this was caught by 38.1mm mesh sizefollowed by 68.9mm mesh size (26.34%) and lowest (19.35%) was recorded by 63.5mm mesh size drijinet. The seven abundant fish species in the driftnets catches were S. galilaeus,D. rostratus, A. baremoze, S. membranaceus, T: zilli, L. senegalensis and H. fasciatus. The total biomass of 25,314g (25.3kg) was obtained, 45.51% of this weight was captured by 88.9mm mesh size while the least 24.24% was obtained in 63.5mm mesh size drijinet. S. galilaeus contributed the greatest proportion of weight 49.5%followed by D. rostratus 13.2% and L. senegalensis 10.3%. Recommendation was madefor further studies in this aspect; • policies should also be directed to provide social amenities to the communities around the Lake.

Introduction he term "driftnet fishing" means a fish-harvesting method in which a driftnet is placed in water and allowed to drift with curvets and winds for the purpose of entangling fish in the webbing. The driftnet fishing techniques involves the Tdeployment offlat nets made offine mono or multi-filament nylon mesh lying in straight lines to hang vertically in the water like curtains (Rafiqul Islam, 2013). The operation is controlled through adjustment of the buoyancy of the nets with its floats on the surface and its bottom weights under the water. It is passive fishing gear, but operated in active form. It can be left to drift with wind and current overnight or operated by two canoes. In a recent study of inland fisheries of Lake Kainji, northwest shows, there are 4, I00 fishers, 314 fishing locali• ties with about 1,224 fish landing sites located all along 874km length of shoreline of the Lake (Abiodun and Niworu, 2004). The authors reported the economic value of fish yield by fishing gear type showed that the gillnet fishing contributed 51% to the total catch value, followed by driftnet and longline fishery, which contributed 17 and 16% respectively. According to Abiodun and Niworu (2004) showed that 37% of gillnets 75% driftnets, 100%of beach seine nets and 20% of castnets were illegal according to the and Kebbi States Fisheries Edict of 1997. The mesh size is defined as the length of the stretched whole mesh (Sparre and Venema, 1992). Mesh size is the most important factor affecting selectivity of fishing gear (Ahmed and Jpinjolu, 2008). Many factors influence the efficiency and the selecting of the gear directly or via interaction with other factors. The efficiency (catcbability) of fishing gears defined by Machiels et al. (1994) Ahmed and Jponijolu (2008) as the proportion of total population of a certain size-class, which is caught and retained by a unit-operation of the gear, while selectivity is the relative efficiency per size-class. Objectives of the study: The study was carried out in order to: a. Compare the efficiency (catchabiJity) of three different mesh sizes of driftnets in Lake Kainji. b. Determine the selection range and size selection offish caught by the nets, and c. Make appropriate recommendation on the driftnet mesh size that willsuit catching offish in the Jake. PROCEEDINGS OF 28TH FISON ANNUAL CONFERENCE, NOV. 25-30, 2013

Materials and Methods • Study area: The fishing trial was conducted in Lake Kainji in Yuna Village about 6.5km from the Federal Col• lege of Freshwater fisheries Technology, New Bussa (Ahmed, 2012). Lake Kainji is situated between latitudes 9° 50'-10°57' North and longitudes 4°25' - 4°45'. The lake was impounded in August, 1968 and it 134km in length and 24.lkm in width. It is surface area has been variously quoted as approximately 1,270km2 (du Feu and Abio• dun, 1998). ..."tI • Nets construction: Three nets were constructed in the fishing gear shed ofFCFFT Yuna-adopted village. The nets = of 38.1, 63.5 and 88.9mm stretched mesh size (210d/3) polyamide (PA) were constructed; the length and depth of t!2 the three nets were 60m and 48m respectively. They were all hung at 50% hanging ratio. ~ t!2 • Nets operation: The driftnets were operated by two canoes, with the full length of the driftnets stretched across CIJ the water body and the two of the head ropes held by two fishermen each in the canoe. The nets were powered and ~ hauled by the canoe movement serving as alternative to wind and current drifts on the net. After the hauling, the Z net were raised from the water surface gently, fish caught were removed and placed in respective labelled container. .G')> The hauling was repeated 3 times a day with each net for 21 consecutive fishing days, this fishing operation was ~ carried out between 2:30 p.m. to 4:00 p.m. in the afternoon. t!2 Z • Fish identification and measurement: The fish caught were identified using the monograph of Olaosebikan and ~ Raji (2004). However, they were sorted into their respective species and these measurement were taken; total length (TL), standard length (SL), girth length (GL) in centimeter and total weight (TW) in gram. •Data analysis: The data collected was compiled and computed statistically using means and percentages. The spe• cies diversity index (SD) and length frequency distribution was computed based on Ahmed and Ipinjolu (2008). SDI = No. of fish caught in a net Total No. of fish caught in all nets. Results and Discussion Table1: Types of fish species caught by driftnets in lake Kainji. Mesh sizes (mm) Families Species 38.1 63.5 88.9 Centropomidae Lates ni/oticus + + Characidae --- A/estes baremoze Brycinus /euciscus Cich/idae Chromidotillapia guntheri guntheri Hemichromis fasciatus Ti/apia zilli Oreochromis ni/oticus Sarotherodon galilaeus Citharinidae Citharinus citharus C/aroteidae C/arotes /aticeps Chrysichthys auratus Chrysichthys nigrodigitatus Auchenog/anis occidentalis Cyprinidae Labeo coubie Labeo senega/ensis Distichodontidae Distichodus fOstratus budgetti Synodontis c/arias Synodontis membranaceus Mormyridae Mormyrus rume Schilbeidae Schi/be isidori Schi/be intermidius Number of species caught Species Diversity Index (SOl)

The types of fish caught comprised of twenty two species belonging to ten families (Table I). Table 2 contains the numberand percentage offish caught by driftnets in Lake Kainji with respect to the different mesh sizes.The study showed that22 different fish species were caught during the experimental fishing trial. The species caught were similar to those re• oorted for the artisanal driftnets in the Lake Kainji (du Feu and Abiodun, 1999) and in VoltaLake Ghana (Braimah, 1995).The seven dominant species (S, galilaesus, D. rostratus,A. baremoze, Hifasciatus, T zilli, L. senegaleusis and S. membranaceus)

327 PROCEEDINGS OF 28TH ANNUAL CONFERENCE, NOV. 25-30, 2013

also followed the same trend in which Synodontis sp, Citharinus sp, Distichodus sp and Tilapines were reported to dominate the artisanal driftnets catches of the lake, though with slight variations in order of abundance.

Table 2: Number and percentages of fish caught by driftnets in Lake Kainji . 0\ Mesh sizes (mm) ...."r:I 38.1 6.5 88.9 Total :z:(J) Species % No. % No. % No. % tr1 Lates niloticus 1 1.4 4 1.1 ~ .... A. baremoze 33 8.9 tr1 (J) Brycinus leuciscus 7 1.9 ~ C. guntheri guntheri 1 0.3 > H. fasciatus 5.1 Z > Tilapia zilli 5.1 6.7 o o.niioticus tr1 ~ S. galilaeus tr1 C. citharus 0.8 Z ..., Clarotes laticeps 13 3.5 C. auratus 4 1.3 C. nirodigitatus 1 0.5 A.occidentalis 1.3 Labeo coubie 0.3 L. senegalensis \' 21 D. rostratus 31 15.4 15 Synodontis budgetti 3 1.5 S. clarias 1 0.5 S. membranaceus 3 4.2 Mormyrus rume 1.4 Schilbe isidori 5.5 S.intermidius 3.0 Total number of fish caught 100 72 100 372 100 Relative percentage 19.35

Table 3: Weight and percentages of fish caught by driftnets in Lake Kainji. Mesh sizes (mm) 38.1 63.5 88.9 Total Species No. No. % No. % No. % 135 50 0.8 185 0.7

L. senegalensis D. rostratus ---~-~~ S. budgetti 'S.-c/a'ria__s ~ ~ __ ~~ __ k

1.2 S.intermldlUs 0.5 Total weight of fish caught (g) 6135 100 100 Relative percentage 24.24

328 PROCEEDINGSOF 28TH FISON ANNUAL CONFERENCE, NOV. 25-30, 2013

Table 4: Summary of length and weight of fish caught by 38.1mm mesh size driftnet in Lake Kainji. Length (cm) Weight (g) Species Min. Min. Max. L. niloticus 11 30 70 12 60

S.intermidius 10 14.5 21 22

Table 5: Summary of length and weight of fish caught by 63.5 mesh size driftnet in Lake Kainji. Length (cm) Weight (g) Species Min. Min. Max. T. zilli 11 40 60 S. ga/i/aeus 30 150 L. senega/eusis 80 175 D. rostratus 50 130 S. membranaceus 60 150 A. occidentalis 14 70 130

Table6: Summary of length and weight of fish caught by 88.9 mesh size driftnet in Lake Kainji. Length (cm) Weight (g) Species Min. Max. Min. Max. T. zilli 12 15.5 60 S. galilaeus 10 18 40 C. citharus 21 22 250 S. membranaceus 12 19.5 40

'able 7: Length distribution analysis for the seven abundant fish species in the driftnets catches.

Length Midpoint Species/mesh sizes (mm) I Number of fish class (mm) length class T. zilli (mm) 38.1 60-69 65 70-79 30-89 30-99 00-109 4 4 2 3 11 30-139 8 40-149 50-159

48 23 64 18 18 21 23

329 PROCEEDINGS OF 28TH ANNUAL CONFERENCE, NOV. 25-30, 2013

There was wide difference between species diversity of the species caught by 38.1,63.5 and 88.9mm stretched mesh size driftnets (0.77, 0.45 and 0.36 SDI respectively) showed that both nets had different species selection process. This was in line with Ahmed (2005) and Oyatoye (2012) observations in Lake Kainji, North West Nigeria. It was found that there was significant variation in the number and weight of fish caught in each net type. The 38.1mm stretched mesh size driftnetwhich caught more fish than the two other mesh sizes (63.5 and 88.9mm mesh size) driftnets. The weight and percentage of fish caught by driftnets in Lake Kainji are presented in Table 3. While in terms of weight 88.9mm stretched mesh size driftnet re• corded the greatest proportion of biomass followed by 38.1mm mesh size driftnet and least was obtained in 64.5mm stretched mesh size. The length (ern) and weights (g) of the different fish species caught are summarised in tables 4--{). Length distri• bution analysis for the seven abundant fish species in the driftnets catches are presented in table 7. This indicated the ability for the larger mesh size net to retain large size fish. Ita (1998), du Feu and Abiodun (1999), Ahmed and Ipinjolu (2008) and - ~ Allison et at. (2009) observed a trend in which the larger th; mesh size of net, the bigger the size of fish caught: since bigger >- fish of same species could be assumed to attain a more matured stage, concentration of fishing effort on small mesh sizes of ~ driftnets would result to stock depletion .due to overfishing.The banning of small mesh sizes for the lake's driftnet fishery ~ was justifiable. The use of 63.5mm and above as the recommended mesh size for driftnet fishery on the lake would therefore ~ result to several species left unexploited. trJ Z >-l Conclusion and Recommendations The study has revealed that driftnets of38.1 mm stretched mesh size are most efficient in catchability in terms of number than that of63.5 and 88.9mm stretched mesh size driftnets in Lake Kainji. Whereas, in terms ofweight 88.9mm mesh size obtained more weight than 38.1 and 63.5mm mesh size. Further studies need to be done on the catch efficiency of the nets over a lon• ger period (for at least 2 seasons). As an additional step toward raising the standards of living of driftnet fishermen, policies should also be directed to provide better infrastructure such as efficient marketing system and road network.

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