A final year project on “Effectiveness and specie selectivity of wire gauze trap” submitted by Obafemi Abiola Bidemi (from the University of Lagos) to extrudesign.com.
A study on the selectivity and efficiency of galvanized wire gauze trap in Abule Agege and Abule Eledu Creeks was carried out between March and August 2019. Processed cassava (Fufu) and coconut were used as baits all twenty galvanized wire gauze trap between March – August 2019; all traps were set day and night twice a month for the six months period. The swimming crab (Callinectes amnicola) from the Portunidae family was the most abundant from both creeks of Lagos lagoon and Sarotherodon melanotheron from the Cichlidae family was the most fin fish caught in abundance. . The highest catch was recorded in the month of July in Abule Eledu creek where 9specimens were caught per trap. The catch recorded using galvanized wire gauze trap is relatively low which makes it not very efficient (considering the number of the trap 20 to the total catch of 125 specimens) in catching fish in the Abule Agege and Abule Eledu creeks. There was slight difference in the physico-chemical parameters of the two sampling stations throughout the sampling period except for the salinity of the stations which varies greatly from 0.384%o in July to 0.93%o in August and TSS which varies 104.0 – 140.0 in July and August respectively.
Fishing is one of the oldest ways by which people have fed themselves and their families which also involves the gathering of shellfish by hand and spearing of fish (Von Brandt, 1996). In early times, flowing water caused by tidal movement and changes in river and lake levels were probably used to trap fish behind rudimentary barriers, often made from sticks and stones. The heavy materials used for fishing materials in primitive times are developed as time moves on to lighter materials, more readily available such as tree branches, brushes, nets (Slack-Smith, 2001). Traps are simple, passive fishing gear that when fish enter to and then made it hard for them to escape which is achieved by putting chambers in the trap or pot that can be closed once the fish enters, having a funnel that makes it difficult for the fish to escape (FAO, 2001). Traps can vary, from simple structures such as rock corrals which are able to hold various fish species passing by, to highly specialized equipment such as lobster pots (Emmanuel, 2008). The widely different habits and habitats of the vast variety of West African freshwater and brackish water fishes, the striking seasonal variations in their environment, and the ingenuity of local fishermen have all contributed to the development throughout the region of a bewildering array of traditional fish-catching devices (Holden and Reed, 1991; Emmanuel, 2004; Emmanuel and Kusemiju, 2005). It is well recognized that estuaries, lagoon, and enclosed embayment are important spawning habitats and nursery areas for inshore fishes (Potter et al., 1990; Emmanuel and Kusemiju, 2005). The frames used in making the traps are made from strong materials that prevent the traps and pots from losing their shape during fishing and storing (Aitken, 1997).Trap frames can be made from steel rods, timber, some sticks, etc. The modern traditional traps are covered with wire netting, nylon mesh, plastic-covered steel, welded steel mesh, etc. The trap consists of funnels that lead from the outside to the inner chamber of the trap (Emmanuel, 2008). The river fishery in Nigeria is still predominantly employing canoes and traditional gears and the catch composition of these traditional fishing gears often depends on the experience and skills of the fishers. It also varies among gears, habitats, species, and even sizes of the same species. This means that all fishing gears are only able to catch a certain part of the total (multispecies) fish community present. However, the indiscriminate use of different traditional fishing gears and occasional use of harmful techniques threatens the fish biodiversity in the rivers in Nigeria because of huge participation and it is open. It is very important to study the nature of gears commonly used that may lead to selective fishing, thus minimizing the stress on a particular size group of fishes (Srivastava and Srivastava, 2002). A traditional dugout canoe between 3-18 meters long is used for artisanal fishing. Artisanal fishers used gears that include cast nets, hand lines, basket traps, longlines, set gillnets, etc. The coastal artisanal fisheries are divided into two major sectors which are the brackish water fisheries with fishing activities in creeks and estuaries where the freshwater flowing down the rivers mixes with the saltwater moving up with the high tide and the artisanal fisheries with fishermen operating in waters of less than 40m depth(Ssentongo et al., 1983). The creek and lagoons of South-Western Nigeria, apart from their ecological and economic significance, serve as a link for the disposal of an increasing array of waste types (Onyema, 2007). Tidal creeks are known to be fertile coastal environments used as feeding and nursery grounds by a large number of fishes and aquatic crustaceans (Kusemiju, 1991). The creeks are dominated by many influences such as industrial and municipal waste discharges, fertilizers, and pesticides from agricultural soils, chemical leakages from landfills/ waste disposals pits, leaching animal and human wastes. Human activities such as fishing, transportation, dredging, sand mining and mangrove cutting all which affects the physical and chemical characteristics of the water body which directly and indirectly affect the distribution and production of fish and another aquatic organism (Obot et al., 2016). A creek refers to a small waterway that contains mixed water origin. It is the part of a stream that is affected by ocean tides. A tidal creek is also called a tidal channel and has variable electrical conductivity and salinity, during low tides, the creeks may dry up forming a muddy channel while on the other hand, during high tides, they have large amounts of water (Omondi, 2018).Creeks are found along rivers, coasts, and estuaries, which floods and drains by the tidal movement of the adjacent estuary, sea, and ocean. There are numerous creeks associated with the Nigerian coastal environment. They are of two types the tidal freshwater/brackish creeks which are surrounded partly by mangrove and partly by freshwater swamps from points beyond the reach of tidal influence, while the non-tidal creeks are surrounded by freshwater and are infested by aquatic macrophytesall year-round (Adesalu and Nwankwo, 2008).
2. Materials and Methods for Wire Gauze Trap
2.1 Description of the study areas
Abule Eledu is a shallow creek situated between 6°31.30’North and 3°23.15’East latitude of the Lagos lagoon. It is a brackish shallow creek with a depth of fewer than 1m during low tides and dry seasons. It is one of the numerous sluggish creeks that empty into the Lagos lagoon. It is tidal with depth that decreases inland and located in the wet tropic where the alternation of the dry and wet seasons is phenomenal. Abule Agege is an isolated freshwater swamp that is part of a creek that empties into the Lagos lagoon. It is located between the coordinates of 6° 30°.45’North and 3° 24.0’East. It falls within the rain forest belt and receives a creek with an average depth of (≤1m).
2.2 Design Study and Description of Wire Gauze Trap
The wire gauze trap is constructed using wire mesh (36mm), cane stick, and thread on both sides. The trap had a single funneled entrance known as the valve of no-return. The mesh was curved to make a bag-like shape. The diameter of the trap is 50cm and the length of the trap was 55cm, the traps were threaded at the sides so as to allow the retrieval of the catch from the trap the mesh size of the trap is 36mm.
2.2.1 Sampling Procedures and Identification
Sampling was done twice a month for a period of 6months between March and August 2019 in two different creeks. A total of 20 wire gauze traps with a mesh size of 36mm (measured with a meter rule) were used throughout the duration of the study. The traps were divided into 10 at each location; the 10 traps were baited in equal numbers with the two baits (coconut and processed cassava) at each station. Fish caught were identified with aid of literatures (Schneider, 1990; Holden and Reed, 1991; Emmanuel 2009). The measurement of the catch was taken by placing the fish on the measuring board and the measurement of the carapace width for shellfishes and the total length (tip of the mouth to tip of the tail) for the fin fishes were taken using a meter rule the recordings were recorded in nearest centimeter. The specimens were also weighed on a sartorius weighing balance to the nearest gram.
A total of 64 finfish and shellfish specimens of weight range 10-106.6g and length range of 4cm – 25cm were caught at the Abule Agege Creek during the sampling period (Table 1 ). The family Portunidae was represented by Callinectes aminicola which was the most abundant of the species caught during the sampling period, Cichlidae represented by Sarotherodon melanotheron, Sarotherodon melanopleura, Hemichromis fasciatus,Claridae represented by Clarias gariepinus,Lutjanidae represented Lutjanus goreensis and Family Gecarcinidae represented by Cardiosoma armatum. The family Portunidae was represented by Callinectes amnicola has 73% occurrence, Family Cichlidae was represented by Sarotherodon melanotheron with 14.06%, Hemichromis fasciatus with 3.12%, Sarotherodon melanopleura with1.5%, Family Clarridae represented by Clarias gariepinus has 3.12% occurrence, Family Lutjanidae represented by Lutjanus goreensis has 3.12% occurrence and Family Gecarcinidae represented by Cardiosoma armatum has 1.5% while at Abule Agege a total of 61 fin fish and shell fish specimen of weight range 8 – 80.9g and length of 8 – 52cm was caught. The species caught are from the families of Portunidae represented by Callinectes amnicola which is the most abundant of the species caught during the sampling period, Family Cichlidae represented by Sarotherodon melanopleura, Sarotherodon melanotheron and Family Gecarcinidae represented by Cardiosoma armatum. Family Portunidae was represented by Callinectes amnicola has 72.14% occurrence, Cichlidae was represented by Sarotherodon melanopleura has 8.19% occurrence, Sarotherodon melanotheron has 18.03% has a combined occurrence of 26.22% and Gecarcinidae represented by Cardiosoma armatum has 1.63% occurrence.
In Abule Agege processed cassava (fufu) bait caught a total of 19 species Callinectes amnicola (12), Sarotherodon melanotheron (3), Hemichromis fasciatus(1)Clarias gariepinus(1),Lutjanus goreensis(2) during the day while coconut bait caught 11 species Callinectes amnicola (19), Sarotherodon melanotheron (1),Cardiosoma armatum(1) during the day also. A total of 26 species Callinectes amnicola (21),Sarotherodon melanotheron (2),Sarotherodon melanopleura(1),Hemichromis fasciatus(1), Clarias gariepinus(1) species was caught in the day using processed cassava (fufu) as the bait while a total of 8 species Callinectes amnicola (5),Sarotherodon melanotheron (3) was caught in the night using coconut as the bait (Table 4). A total of 61 fin fish and shell fish were caught in Abule Eledu (Table 2) processed cassava (fufu) as the bait caught 19 species Callinectes amnicola (14), Sarotherodon melanotheron (3), Sarotherodon melanopleura(2) while using coconut as the bait caught 18 species Callinectes amnicola (14), Sarotherodon melanotheron (2), Sarotherodon melanopleura(2) all catch were recorded during the day. 11 species was caught in the night using processed cassava (fufu) as the bait Callinectes amnicola (10), Cardiosoma armatum(1) and 13 species Callinectes amnicola (6)Sarotherodon melanotheron (6),Sarotherodon melanopleura(1) was caught using coconut as the bait in the night (Table 5).
3.1 Physico Chemical Characteristics Of The Creeks
The salinity of the Abule Agege creek ranges between (0.384 – 2.14%o) with standard deviation of 0.702. The recorded values of Dissolved oxygen varied by2.0ppm with maximum value of 5.5ppm and a minimum value of 3.5ppm. PH of the Abule Agege creek ranged 6.4 – 8.2 and a mean of 7.5 was recorded. BOD declined in August to 10ppm in the creek while the highest value of 60ppm was recorded in the month of May. Turbidity varies slightly all through the six months; the highest value 109.1 was recorded in April. The salinity has standard deviation of 0.072 and ranged between 0.345-0.584%o with a mean value of 0.487, the highest value of Dissolved oxygen was recorded to be 6ppm in the month of July. The PH values were relatively constant all through the sampling period. Recorded values of Turbidity ranged between 7.0 – 7.8 with a standard deviation of 0.279. Also, BOD highest value was recorded in the April, June and July. Turbidity lowest value was recorded in May to be 101.6 but peaked in August to 105.0. TSS ranged between 115.9-135.0 with a standard deviation of 6.30 and the highest Temperature value was recorded in March with the lowest value recorded in July (Table 3).
Table 1: Finfish and Shell fish caught in Abule Agege Creek
|Family/Species||Number||Weight range(g)||Total length(cm)||% occurrence|
|Portunidae Callinectes amnicola||47||10-69.0||4-20||73|
|Cichlidae Sarotherodon melanopleura||1||27.0||9.00||1.5|
|Claridae Clarias gariepinus||2||78.5-83.1||24-25.0||3.12|
|Lutjanidae Lutjanus goreensis||2||39.5-106.6||14-20.0||3.12|
|Gecarcinidae Cardiosoma armatum||1||41.0||15.0||1.5|
Table2: Finfish and shell fish caught in the Abule Eledu Creek
|Family/Species||No of catch||Length range(cm)||Weight range(g)||%Occurrence|
|Portunidae Callinectes amnicola||44||8-16||8-80.9||72.13|
|Cichlidae Sarotherdon melanopleura||5||9-12||20-27.7||8.19|
|Gecarcinidae Cardiosoma armatum||1||16||72,0||1.63|
TABLE 3: PHYSICO CHEMICAL CHARACTERISTICSOF ABULE ELEDU CREEK
S D : Standard Deviation
Table 4: DAY AND NIGHT VARIATION, BAIT PREFERENCE IN ABULE AGEGE SAMPLING STATION
|Day catch||Night Catch|
|Portunidae Callinectes amnicola||12||63.15||9||81.81||21||80.76||5||62.5|
|Cichlidae Sarotherdon melanotheron||3||15.78||1||9.0||2||7.69||3||37.5|
|Cichlidae Hemichromis fasciatus||1||5.26||–||–||1||3.84||–||–|
|Cichlidae Sarotherdon melanopleura||–||–||–||–||1||3.84||–||–|
|Claridae Clarias gariepinus||1||5.26||–||–||1||3.84||–||–|
|Gecarcinidae Cardiosoma armatum||–||–||1||9.0||–||–||–||–|
|Lutjanidae Lutjanus goreensis||2||10.52||–||–||–||–||–||–|
Table 5: DAY AND VARIATION, BAIT PREFERENCE IN ABULE ELEDU SAMPLING STATION
|Day Catch||Night Catch|
|Portunidae Callinectes amnicola||14||73.68||14||77.77||10||99.90||6||46.15|
|Cichlidae Sarotherdon melanotheron||3||15.78||2||11.11||–||–||6||46.15|
|Cichlidae Sarotherdon melanopleura||2||10.52||2||11.11||–||–||1||7.69|
|Gecarcinidae Cardiosoma armatum||–||–||–||–||1||9.09||–||–|
One hundred and twenty-five fish belonging to five families and seven species were caught in both creeks during this study, all the species agreed to the work reported by Fagade and Olaniyan (1974) of the Lagos Lagoon species diversity and this is because Lagos Lagoon has great influence on the species diversity, salinity and physico-chemistry of the creeks. Most of the species caught are juvenile and this is because the creeks serve as a nursery ground which shows the importance of creeks where mangrove prop-roots create a special underwater habitat, especially during the breeding and juvenile stages as reported by Bennett (1989). It can also be suggested that the creeks are stressed ecosystem due to unregulated fishing activities in the water bodies which results in the low species diversity that occurred in the study as noted by Emmanuel and Onyema (2007). The most abundant of the species caught during the study is the Portunidae family represented by Callinectes amnicola also reported by Emmanuel and Olojede (2011).This may have occurred due to the soak time of the trap that has allowed the crab to use the finfishes in the traps as bait and also some of the decayed fishes smell and this also attracted the crab to the trap as noted by Emmanuel (2008). Galvanized wire gauze trap baited with processed cassava (fufu) performed better and had more catches than the trap baited with coconut and this happens because processed cassava (fufu) attracts fish by releasing the strong smell into the water which makes the fish perceive the stimuli faster and stronger compare to coconut bait (Lokkeborg, 2014). The chemical stimulus released by processed cassava (fufu) is dispersed over a long distance in the water by the continuous movement of water current, it can be therefore agreed that processed cassava release strong and lasting chemical stimulus compared to coconut when used as bait in fishing gear. The occurrence of Sarotherodon melanotheron, Hemichromis fasciatus and Callinectes amnicola in both sampling stations indicated that these species can tolerate a wide range of salinity, and that they migrate at a stage in their life cycle for the purpose spawning, breeding, feeding etc. A similar finding has been reported by Albaret and Lac (2003) and Emmanuel (2008) for the Ebrie lagoon (West Africa) and Abule Agege creek (Lagos) respectively. The slight variation in the water temperature in the creeks can be linked with the shallowness of the creeks and regular tidal motions of water into the creeks which ensured the complete mixing of the water this observation agrees with Ajao, (1990). Since the optimum PH range for sustainable aquatic life is PH range of 6.5 – 8.2 (Murdock et al., 2001), the PH of the creeks is within optimum range all through the sampling period. The low level is attributed D.O to high level of organic pollution which resulted in biodegradation by biotic microorganisms (Nkwoji et al., 2010). The continuous rise and fall in the salinity level of the creeks can be attributed to the inconsistent flow sea incursion, reduced flood, water inflow from associated river, creeks and freshwater lagoons (Emmanuel and Onyema, 2007).
Keywords: Wire gauze trap, Baited Wire Gauze Trap
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Credit: This project work was completed by Dr B.E Emmanuel, Obafemi, Abiola Bidemi Department of Marine Sciences University of Lagos.