Mesh Size Regulation Research Articles

Demographics and reproductive characteristics of threatened Malabar pufferfish (Carinotetraodon travancoricus) from Western Ghats hotspot, India

Context Carinotetraodon travancoricus is a threatened ornamental aquarium fish endemic to Western Ghats (WG) biodiversity hotspot of India and indiscriminate collection of this species resulted in a severe population decline. Aims To understand the impacts of wild collection of C. travancoricus for aquarium-fish trade, information on their population status and reproductive characteristics is required. Methods Specimens for the present study were collected from the Chalakudy River of WG and growth, mortality, exploitation and reproductive characteristics of C. travancoricus were investigated. Key results The natural mortality of the species was higher than the fishing mortality. The peak spawning period of the species was from May to September. Length at first maturity (L50) for males and females was estimated to be 18.4 and 18.1 mm respectively. Conclusions The stock of C. travancoricus in the Chalakudy River may be in near full exploitation under current harvesting strategy. The lower value of length of first capture than size at first maturity indicated that C. travancoricus is likely to be captured before it matures and breeds, subsequently contributing to declining recruitment. Implications A combination of different strategies (closed fishing seasons, mesh-size regulation and no-fishing areas) will improve sustainable management and conservation of species.

Time-series ARIMA modelling of the Labeobarbus spp (Cyprinidae) fishery in water hyacinth-infested and non-infested sites in Lake Tana, Ethiopia

Ethiopia’s largest freshwater lake, Lake Tana, is home to 21 endemic fish species, the majority of which are cyprinids in the genus Labeobarbus. The lake is undergoing numerous ecological changes, including an invasion of water hyacinth (Eichhornia crassipes (Mart.) Solms (WH). The aim of this study was to predict the future fish productivity in Lake Tana by considering the increasing water hyacinth infestation. This was accomplished by analyzing a 12-year fishery-independent time-series data set of Labeobarbus, collected from sites infested and not infested by water hyacinth. The stationarity of the data was investigated using the Augmented Dickey-Fuller (ADF) unit root test. First-order data differencing was applied to solve the non-stationarity data to stationarity. With the same standardized fishing gillnet and the same sites, the CPUE during the dry season decreased from 3,502 grams (3.5 kg/day) in 2010 to 360 grams (0.36 kg) in 2020 at the water hyacinth-infested sites, demonstrating a 90% decrease in the daily catch. A reduction in catch per unit effort (CPUE) is evident at the WH sites in all seasons, and the rate of fall in there was faster than at the non-infested site. Box Jenkin’s auto-regressive integrated moving average models (ARIMA) modelling predicted that Labeobarbus CPUE will decline by a threefold % by 2032 compared to the current catch. Based on these results, the most suitable model for all the seasons and areas was confirmed to be ARIMA (0, 1, 0) using the lowest value of Akaike Information Criteria (AIC’s). The fish production declines with expanding WH infestation will necessitate integrated water hyacinth reduction strategies, closed area and closed spawning seasons, and mesh size regulations to conserve and utilize the resource sustainably. As Labeobarbus is the only examined species in this study, forecasts should be made for other commercially significant fish species in the Lake, such as Oreochromis niloticus and Clarias gariepinus.

Length based-stock assessment and Spawning Potential Ratio (LB-SPR) of exploited tilapia species (Coptodon zillii, Gervais, 1848) in Lake Volta, Ghana

Length based stock assessment parameters and LBSR of C. zillii in Lake Volta were investigated for the purpose of sustainable management. The lengths of 517 individuals were measured from the lake from January to December 2020 and analyzed using TropFishR. The von Bertalanffy parameters including asymptotic length (L∞), growth rate (K), and growth performance index (Φ) were estimated as 30.4 cm, 0.38 per year, and 2.73 respectively. Total mortality rate (Z), natural mortality rate (M) and fishing mortality rate (F) were 4.58 per year, 0.89 per year and 3.96 per year respectively. The exploitation rate (E) was highly above the exploitation rate at the maximum sustainable yield (Emax) which shows that the fishery of the stock is facing high unsustainable fishing pressure. Based on the findings of the study, it is recommended that fishing pressure be reduced and, mesh size regulation be strictly enforced to ensure sustainability of the stock.

Effect of Codend Design and Mesh Size on the Size Selectivity and Exploitation Pattern of Three Commercial Fish in Stow Net Fishery of the Yellow Sea, China

To address the issue of minimum mesh size regulations of the stow net fishery for croaker species, we tested and compared the size selectivity and exploitation pattern for diamond- and square-mesh codends with mesh sizes 35, 45 and 55 mm for little yellow croaker (Larimichthys polyactis), silver croaker (Pennahia argentata), and flower croaker (Nibea albiflora) in the Yellow Sea, China. Our results showed that the legal codend (35 mm diamond-mesh) was inadequate to protect the juvenile croaker species because more than 75% of undersized individuals were retained, and the discard ratios were as high as approximately 60%. Irrespective of mesh shape, increasing the codend mesh sizes could significantly improve the size selectivity and exploitation pattern of croaker species. Between codends with the same mesh size, the square-mesh codends had higher size selectivity than diamond-mesh codends. Based on results, the 55 mm square-mesh codend was recommended for rational exploitation of croaker stocks. This study can provide feasibility and insight for the enforcement and reform of management strategies for sustainable fishing in Chinese stow net fisheries.

Assessing the pomfret stock for setting catch limits in the northern Bay of Bengal, Bangladesh

Pampus argenteus and Pampus chinensis form the high-value demersal Pomfret fishery of Bangladesh. But, due to a monotonic decline in catches over the last five years, it is essential to explore the current stock status concerning the removal rate to ensure the sustainability of this fishery. Therefore, given the reliability and minimal data requirements, this study employed an extended Bayesian State-Space Surplus Production Model, JABBA (Just Another Bayesian Biomass Assessment), to assess the stock rigorously. The results revealed that the stock biomass of the Pomfret fishery in the final year of the time series is significantly lower than BMSY, the biomass required to produce MSY. Consequently, this study recommends a yearly catch limit (TAC) of 10,000 metric tons to prevent further depletion of the stock biomass. Furthermore, to avoid growth overfishing by allowing all immature fishes to reproduce at least once before being caught, this study also calculated the optimum length (Lopt) for catch for both species at which biologically maximum yield and revenue can be obtained. The estimated Lopt is 25 cm for P. argenteus and 30 cm for P. chinensis, and not to capture fishes with lengths lower than these limits, this study further calculated the minimum mesh size limits for gill and set bag nets is 7.5 cm. Though the mesh size regulation was estimated using length-based reference points derived from an empirical equation, this regulation can be used as an associate reference point when TAC is applied to assure the sustainability of this fishery.

Growth, mortality and stock status of three commercially important catfishes from the River Ganga, India

A study was undertaken to determine population parameters and stock status of three commercially important catfishes viz. Eutropiicthys vacha (Hamilton, 1822), Clupisoma garua (Hamilton, 1822) and Ailia coila (Hamilton, 1822) from middle and lower stretch of the River Ganga. Monthly length and weight data of three species from Patna, Buxar and Bhagalpur was collected for determining population parameters and stock status using standard procedures. The von Bertalanffy growth parameters (VBGF) parameters including the total mortaliy (Z), natural mortality (M) and fishing mortality (F) rates for all three catfishes were analysed and compared with past studies. The calculated E value of the three catfishes was above the level of optimum exploitation (0.5) but was below 0.7 indicating that caution need to be excercised in order to avoid overexploitaton of the fish stocks. Management measures such as reduction of fishing pressure either by limiting number of boats or fishing hours, imposing mesh size regulation to avoid growth overfishing, minimum legal size, declaring closed season or closed area throughout the breeding season of the catfish can be suggested for revival of the fish stocks. Further, studies on the reproductive biology, identification of spawning season and spawning grounds is suggested which will play apivotal role in the management of stocks of these fishes in the River Ganga. Keywords: Exploitation rate, FiSAT II, Length frequency, Population dynamics (Hamilton, 1822)

Condition Factor, Length-Weight Relationship and Sexual Maturity Stages of Labeobarbus tanensis in River Kathita of the Upper Tana River Basin of MT. Kenya

Information on health of fish populations and sexual maturity is useful in formulating fisheries management regulations. There is little such information on fish species of upper Tana River basin of Mt. Kenya. Therefore, a study was conducted to estimate condition factor, length-weight relationship, sexual maturity and length at 50% maturity of Labeobarbus tanensis during March - August 2020. Fish were caught in River Kathita and in adjacent four dams on upper Tana River using electrofishing equipment and gillnets respectively. Specimen of L. tanensis were sorted from the catch and lengths measured to the nearest 0.1 cm TL using a measuring board and weights to the nearest gram using a weighing balance. Specimens were dissected to reveal gonads which were further dissected to evaluate the sexual maturity stages of eggs on a 1 to 6 scale (Witte & Vandensen, 1995). Estimated condition factor was greater than 1 indicating that the fish populations were healthy. Smallest mature male and female were 12.0 and 12.89 cm TL respectively. Length at 50% maturity for males and females were 13.9 and 14.9 cm TL respectively. Over 90% of mature fish were caught in Kathita River and few in dams. Length-weight relationship for both sexes are as follows: Females: Log W = 3.154 log TL - 2.104; R2 = 0.958. Males: log W = 3.184 log TL - 2.125; R2=0.960. Information obtained will be useful in formulating mesh-size regulations for sustainable exploitation of the fish.

Bet-hedging strategies determine daily choices in effort allocation for Nile perch fishers of Lake Victoria

Small scale fishers experience high variability in daily catches within a resource space limited in extent by operational constraints, and biophysical factors affect daily choices in spatial effort allocation. We focus on the management consequences of the extent of the individual fisher’s resource space and his options to handle risk arising from daily catch variability through a portfolio of sizes and species from within that resource space. Gillnet and longline Nile perch fishers in south-eastern Lake Victoria, Tanzania were provided with a GPS and recorded their position together with their daily catch and operations. Three different gillnet and longline fishing strategies could be discerned. All had bet-hedging characteristics, differing in the size of their resource space of on average 120 – 141 km2, distance from the shore fished and emphasis on the mix of sizes of Nile perch and other species caught. Daily choice of fishing locations did not relate to previous days’ catch success. Still, fishers used the general inshore to offshore distributional patterns of small and large Nile perch in their daily choices of mesh and hook sizes. The mix of sizes and species reduced day-to-day catch variability due to a portfolio effect. Current mesh and landing size regulations based on classical arguments around growth-overfishing interfere with these strategies and force individual fishers to specialise in size, species, and area. They must accept higher uncertainties by either choosing their fishing locations further offshore or accepting a more variable lower catch, leading to higher personal and occupational risk or ongoing management conflicts when disregarding regulations. Portfolio management of fished resources by compromising on mesh size regulations would make sense by allowing fishers to utilise a certain proportion of smaller mesh or hook sizes that are now illegal as part of their fishing strategies.

Impact of closed fishing season on supply, catch, price and the fisheries market chain

This study assessed how the closed fishing season policy that was implemented in Davao Gulf through the joint administrative order (JAO-2014 series 02) of the Department of Agriculture (DA) and the Department of Interior and Local Government (DILG) impacted fish supply, catch, and price and described the roles of actors involved in the fisheries supply chain. Data collection included semi-structured questionnaires (N = 150) and validated using in-depth interviews (N = 80) in Tagum, Panabo, and Davao public markets. Secondary data were used to compare the catch, value of production, and consumer price index. Results showed that most of the actors in the chain were trained by family members, worked in the market because of better income (Php 5001–20,000; U$100–400) and majority of them approved the closed fishing season because of perceived fish stocks recovery (>90%). Analysis of catch data for the municipal fisheries showed an increase from 223 tons to 317 tons while the catch of commercial fisheries showed decline from 238 tons to 92 tons (t (286) = 11.57, P < 0.001). Similarly, the value of production also increased for the municipal fisheries (up to Php 34 million) and a decline of value for the commercial fisheries (down to Php 9 million) (t (286) = 10.76, P < 0.001). An increase in the consumer price index (CPI) was also recorded after the implementation of the closed fishing season e.g. Php 102 vs Php 113 (t(382) = 6.52, P < 0.001). Our results strongly recommend the retention of closed fishing season complemented by other effort control measures such as boat and gear registration, mesh size regulation, establishment of marine sanctuaries, and livelihood provisions for affected fishers.

Length-Based Stock Assessment for the Data-Poor Bombay Duck Fishery from the Northern Bay of Bengal Coast, Bangladesh

The Bombay duck (Harpadon nehereus) forms the second-largest single-species marine fishery in Bangladesh and therefore has a significant impact on the local economy, providing employment, food, and nutrition to thousands of people. Despite the immense importance, this fishery has never been a priority for the relevant regulatory authorities. To enhance the sustainability of this fishery, an effective management policy based on the scientific evaluation of the current stock’s status is urgently required. Therefore, this study used three methodological approaches (traditional size structure-based stock assessment to reveal current exploitation status; the length-based spawning potential ratio (LB-SPR) to evaluate the stock’s spawning biomass; and Froese’s sustainability indicators for sustainable fishing) to conduct a thorough assessment of the Bombay duck stock to establish basic standards for the sustainable management of this fishery. The results revealed that this fishery is presently suffering from overexploitation and the stock’s spawning biomass (SPR = 8%) is below the limit reference point because of the juvenile-oriented fishing behavior of the fishery. Based on the outputs, this study recommended the mesh size regulation of the set bag nets (SBNs) (5 cm mesh size for the codend) to ensure not to catch immature fishes with a length equal to or smaller than 17.95 cm; and reduce the existing number of SBNs by half to reduce fishing pressure on the stock to ensure the sustainability of this fishery.

Spatio-temporal changes in ecology and fisheries in a tropical large Indian reservoir: insights from a long-term data series for sustainable development.

The geographic information systems (GIS) play an important role in all geospatial aspects of assessment, monitoring, and management of inland open water resources for strategic development in the fisheries sector. In India, reservoir fisheries development is one of the flagship programme and several initiatives have been taken up towards enhancement and sustainable development. The present study investigates spatio-temporal changes in ecology and fisheries in Hirakud reservoir, Odisha, build across river Mahanadi which features one of the largest dams in South Asia during 2016-17 to 2018-19. The reservoir is mainly utilized for electricity generation, irrigation and offers tremendous scope to support fisheries and livelihood. The mean water spread area during 2016-17 to 2018-19 was at the minimum (42721 ha) during premonsoon period and was at the maximum (62059 ha) during monsoon. Most of the water quality parameters including nitrate, BOD, and alkalinity during 2016-17 to 2018-19 were higher in the premonsoon period and overall, the parameters were under favorable range for fisheries. The present investigation from the fish landing sites of the reservoir, recorded merely 40 fish species, indicating loss of fish diversity as compared to the historical reports. The IUCN conservation status showed that among the 40 species only one species, Wallago attu is under the VU category and 4 species Chitala chitala, Ompok bimaculatus, Ailia colia, and Bagarius bagarius are under the NT category. The fish production in the reservoir was 8200 t during 2018-19. The analysis of time series annual fish catch data using the ARIMA model forecasted the increasing trend of fish production. The water quality parameters were presented in the GIS platform for a better understanding of the spatial variations over time. Habitat protection of fish breeding grounds, closed seasons, mesh size regulations, scientific management, and community participation are recommended as the measures for conservation of fish diversity and sustainable enhancement of fish production in the reservoir.

Effects of fisheries policy implementation strategies on regulatory compliance in the small-scale fisheries sector in Lake Victoria: A case study of Busia County, Kenya

Lake Victoria is an integral part of Kenya's food production system. Fisheries policies and regulations have been formulated and implemented for sustainable management of the lake's resources, but the lake's ecological health continues to deteriorate. This study investigated the effect of fisheries policy implementation strategies on regulatory compliance in the small-scale fisheries sector in Lake Victoria, in Busia County, Kenya. A descriptive and explanatory research design was applied to a cross-section of randomly selected 324 respondents. Findings from the study show that legitimacy was not significant in compliance on closed seasons and mesh size regulations (p˃0.05). Examining the fishery's specific conditions is required to debate the importance of non-recognized regulations, why this happens, and how to strengthen the procedures to make them legal. The study further indicated that fishermen with consistent income do not violate the regulations (p˂0.05). Government commitment is thus required to implement long-term alternative livelihood strategies to increase compliance with fisheries regulations.

Stock assessment of Scomberomorus commerson (Kingfish) fishery of Oman: Perspectives of sustainability

Scomberomorus commerson (here after ‘Kingfish’) is the choicest table fish of the Gulf Cooperation Council (GCC) region and the most valuable finfish of Oman. Catch-effort data from 2000 to 2019 of Oman’s Kingfish fishery was fit to Schaefer model (log-normal assumption) for estimating maximum sustainable yield (MSY) and biological reference points (BRPs). Carrying capacity (K), catchability coefficient (q), population growth rate (r) and MSY of Kingfish were 36,745 tonnes, 0.0000161, 0.382 and 3,507 tonnes, respectively. At present, fishing effort (ENOW) (i.e. number of boats) is 18,982, which is beyond the sustainable limit i.e. EMSY= 11,846 and if the number of boats reaches to 23,692 then Kingfish stock may collapse. All the BRPs are higher than their sustainable limits, which indicate Kingfish stock is overfished. Stock Reduction Analysis suggests that the stock was in the safe zone between 2005 and 2007, it was in the overfishing zone from 2008 to 2012 and 2013 onwards the stock is in the overfished zone. A complete ban on Kingfish fishing in Oman may allow the stock to rebuild to Biomass at Maximum Sustainable Yield in three years or limiting the annual catch at 1,500 tonnes/year till 2026 may yield the same result. A transboundary management of Kingfish fishery is suggested for the GCC region. Forming a joint scientific council for monitoring and facilitating data availability, similar ban periods, mesh size regulations and a ‘payment for ecosystem services’ scheme may lead Kingfish fishery of the GCC region towards sustainability.

Length-Based Stock Assessment of Smith's Barb, Puntioplites proctozystron (Bleeker, 1865) (Cyprinidae) and Asian Redtail Catfish, Hemibagrus nemurus, (Valenciennes, 1840), (Bagridae) in a Multipurpose Reservoir in Thailand

Catches from inland fisheries in Thailand are about 200,000 tonnes annually and plays an important role in food security and subsidiary income. However, fish stocks are seldom assessed because of the lack of catch and effort data. In this study, two fish stock assessment models, viz., relative yield per recruit and length-based spawning potential ratio, were used to evaluate the status of two species as well as to highlight their applications to datalimited situation in Thailand. The study was conducted at Kangkrajan Reservoir, Thailand, for two targeted species, viz., Smith's barb, Puntioplites proctozystron (Bleeker, 1865) and Asian redtail catfish, Hemibagrus nemurus (Valenciennes, 1840) using length frequency data. The data were collected throughout 2019. Both species showed isometric growth. Von Bertalanffy growth parameters were estimated. Asymptotic length, curvature parameter and theoretical age at length zero were 36.2 cm TL, 0.39 yr-1 and -0.28 yr for P. proctozystron, respectively, and 63.2 cm TL, 0.37 yr-1 and -0.32 yr for H. nemurus. The exploitation rates reveal that both species are slightly overfished. Sizes at 50 % maturity and 50 % selectivities were 17.8 and 23.5 cm TL for P. proctozystron, respectively, and 15.6 and 20.8 cm TL for H. nemurus. Considering both parameters, the size at first capture to sustain the fisheries of P. proctozystron and H. nemurus should be &gt;18 cm and &gt;30 cm, respectively, which can be achieved by mesh-size regulations.

Size selectivity and catch efficiency of diamond-mesh codends in demersal trawl fishery for conger pike (Muraenesox cinereus) of the South China Sea

Size selectivity and catch efficiency of six diamond-mesh codends with different mesh sizes, 25–54 mm (termed as D25-D54), for conger pike (Muraenesox cinereus) were tested and compared using the covered codend method in the South China Sea (SCS). In order to address the present minimum mesh size (MMS) regulations of the trawl fishery for conger pike in the SCS, we quantified the selective properties of two legal codends, D25 and D40, which followed the MMS regulations in the studied area, and used them as baseline to compare with other codends. Our results demonstrated that the catch efficiency decreased with the increment of mesh sizes in codends. The D25 codend was insufficient to protect juvenile conger pike. For this legal codend, 54.31% of conger pike below the Market Reference Size (MRS, 22.4 cm) was retained, and more than 93% of conger pike retained would have to be discarded. Applying the other legal codend, D40, the problem of capturing juvenile fish was significantly mitigated. In this codend, only 9.61% of conger pike below the MRS was retained. However, the loss of commercial-sized fish was considerable, as about 50% fish above the MRS would escape from it. Our study will be beneficial to the enforcement and reform of the MMS regulations in China's fisheries management.

Evaluating Kenya’s coastal gillnet fishery: trade-offs in recommended mesh-size regulations

Evaluating Kenya’s coastal gillnet fishery: trade-offs in recommended mesh-size regulations

Habitat based fish assemblage and distribution pattern in a large reservoir of peninsular India

The pattern of a fish assemblage of a large reservoir, Stanley (also called as Mettur) in Peninsular India was studied to derive various management protocols, specifically fish enhancement. The investigation was carried out in the spatial and temporal scale of the reservoir during 2017–2019. A total of 52 species belonging to 35 genera were recorded indicating high species richness. Simpson (0.17), Shannon (0.17), dominance (0.104), and evenness (0.52) indices did not show significant differences among zones whereas there was a significant difference during different seasons. On a temporal scale, maximum species were recorded in monsoon (47) followed by post-monsoon (43) and pre-monsoon season (33). On a spatial scale, it represented that riverine (47) and transitional zone (37) showed more species richness compared to lacustrine zone (30). Based on the catch structure of this reservoir, it is evident that exotic fishes play a major role in the recent past. One species under critically endangered and endangered, three species under near threatened, and two under vulnerable species were observed in the catch during this study period. The trophic guild of fishes showed the dominancy of planktivores. Abiotic factors such as temperature, pH, and chlorophyll were found directly influencing the species abundance. The study suggested management measures, including observation of closed fishing season, protection of breeding grounds, use of fish aggregating devices, mesh size regulation, and fish seed stocking in the reservoir.

Growth, Mortality and Exploitation Rates of African Moonfish (Selene dorsalis, Gill 1863) Encountered in the Coast of Ghana (West Africa)

Growth, mortality and exploitation rate of Selene dorsalis (Gill, 1863) from the continental shelf of Ghana (West Africa) were examined between July 2018 and June 2019. The study provided results on fishery dynamics parameters needed to estimate the stock status and characteristics of S. dorsalis in the coast of Ghana. Monthly length-frequency data were collected from 629 samples and analysed using fisheries models fitted in TropFishR package in R software. The von Bertalanffy growth parameters were utilised to analyse the population dynamics of the species using ELEFAN Simulating Annealing. Based on the estimates, the asymptotic total length (L∞) was 22.2 cm, the coefficient of growth (K) was 0.76 year-1, and the calculated growth performance index (phi) was 2.58 with Rn value of 0.55. The total mortality rate (Z) was 3.32 year-1 with a natural mortality rate (M) of 1.21 year-1 and fishing mortality rate (F) of 2.11 year-1. The exploitation rate (E) estimated for the species was above the optimum level of 0.5, which indicates that S. dorsalis is overexploited in the coast of Ghana. It can be concluded that the exploitation rate of S. dorsalis has exceeded the optimum limit, hence the need for enforcement and improvement of fisheries management measures such as mesh size regulations, capping of canoes, closed fishing seasons and compliance with fisheries policies.

Evaluating Kenya’s coastal gillnet fishery: trade-offs in recommended mesh-size regulations

Gillnets are a widely used fishing gear in Kenya’s artisanal fisheries, yet their mesh sizes are inadequately monitored or regulated. This study evaluated the impacts of gillnets of seven stretched-mesh sizes, through comparative analysis of species-related metrics and catch per unit effort (CPUE), to inform Kenya’s small-scale fisheries regulations. Data were collected from June 2014 to May 2015. Three mesh-size groups were identified from catch composition data using non-metric multidimensional scaling and comprised small (1.3, 5.1 and 7.6 cm), medium (10.2 and 15.2 cm) and large (20.3 and 25.4 cm) mesh. The dominant species (and their mean lengths) that were caught in the small, medium and large mesh sizes, respectively, were whitespotted rabbitfish Siganus sutor (21.7 cm [SD 5.3]), mackerel tuna Euthynnus affinis (40.8 cm [SD 9.1]) and honeycomb stingray Himantura uarnak (87.3 cm [SD 37.4]). Values of length at first capture (L 50) for S. sutor and E. affinis caught with the small and medium mesh sizes were below length at maturity (L m). Catches of juveniles were proportionately high in the small meshes (61.3–74.2%) and lower in the medium (38.3–50.9%) and large (9.1–36.2%) mesh sizes. Catches with small mesh tended to be species categorised as Least Concern on the IUCN Red List, in contrast to catches with large mesh which tended to be Near Threatened or Vulnerable species. Biomass CPUE differed between mesh-size groups, with the small sizes recording low CPUE. The medium sizes caught mid- to high-trophic-level species with high-income returns, displayed moderate CPUE, and had the lowest juvenile retention and capture of threatened species. Medium mesh sizes are therefore recommended for artisanal fisheries, given low trade-offs between ecological impact and fishery returns.

Stock Assessment of &amp;lt;i&amp;gt;Oreochromis niloticus&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;Clarias gariepinus&amp;lt;/i&amp;gt; from River Hadejia, Jigawa State

The study aimed at assessing the fisheries potentials of Hadejia River. Data on the captured of the fishes were collected over a period of five weeks using gill nets of various mesh sizes, with the assistance of the fishermen. A total of twenty five different fish species belonging to 14 families were identified. The family Cichlidae dominated the fish fauna with 54%. The families Claridae constituted 20%, while the others were the least with only 26%. The fish caught per day was about 1,308 from six landing sites, with 14 fishermen operating averagely from each site. The study also revealed that the river was partially over-fished. Fish samples were collected weekly for five weeks period, from the sampling station using fishing gears of various mesh sizes (3, 4, 5, 6, 7, 8 centimeters), with the assistance of the fishermen. Fish samples were identify and weighed fresh, at landing sites to the nearest gram. Standard and total lengths were taken using a measuring board and also the diversity of fish recorded in this study indicates that the River has relatively high fish diversity. The number and biomass of fish caught during the study is considered high, when compared to other Nigerian Rivers. The sizes of fish recorded also indicate that the River is been over fished. It is therefore recommended that the government and other donor agencies should provide support for research and studies to collect analyze and synthesize information and harmonize existing policies, edicts and byelaws that conform to Integrated Water Resources Management (IWRM) principles, including establishing criteria for water use. The artisanal fishermen should also be encouraged to maintain the use of mesh size regulation.