Multifilament Gillnets Research Articles

Length-Weight Relationship and Condition Factor of Synodontis schall (Bloch & Schneider, 1801), from Roseires Reservoir, Sudan

This study was carried out to investigate the length-weight relationship and condition factor of the Mochokid catfish S. schall, a commercially important fish species in the Roseires reservoir on the Blue Nile, Sudan. A total of 643 specimens were collected using the multi-filament gillnets of mesh sizes (4.0, 8.0, 10.0, and 12.0 cm) and twine (No. 2 and 12) during the period from November 2015 to October 2016; Samples were collected from four sites namely: Awal Bab, Elregiba, Kirma, and Wad El Mahi.; The length and weight of sampled fish were measured and recorded on the sampling sites and used to determine a length-weight relationship. The growth coefficient (b) ranged from 1.196 to 2.649, with moderate to high correlations (r) between 0.437 and 0.798. Values of (b) were less than 3 indicating a negative allometric growth pattern, whereas weight increased at a lower rate than length. The condition factor (K) ranged from 1.966 ± 0.696 to 3.856 ± 3.856, suggesting the fish were in good health condition throughout the sampling sites. The findings of this study provide valuable insights into the biological aspects of S. schall, which can form the basis of sustainable management and conservation policy for the fishery resource of this economically important fish species in the Roseires reservoir.

The catch amount of Mediterranean horse mackerel Trachurus mediterraneus (Steindachner, 1868) gillnets in the Sea of Marmara

The small-scale fishermen in the coastal area of the Marmara Sea between April and June caught the Mediterranean horse mackerel Trachurus mediterraneus (Steindachner, 1868) with gillnets. This target species, T.mediterraneus and significant amounts of non-target species are caught in these nets. So, the technical and structural characteristics of the gillnets for a commercial fishermen were determined and the target and non-target species were evaluated in catching operations. The multifilament gillnet mesh size of 18 milimeters polyamid, twine thickness of 210d/2, hanging ratio of 0.33 and the total length of approximately 200 meters. Also, guarding nets were added to gillnets. The total amount was determined as 397.8 kilograms (kg) and 9204 individuals (ind). The weight of T.mediterraneus was constituted 39.3% of the total weight. The in of T.mediterraneus was constituted 43.4% of the total ind. While the catch per unit effort (CPUE) for T.mediterraneus was calculated at 0.026 kg/m.operation-1 and 0.7 ind/m.operation-1, the CPUE for the total amount was calculated at 0.066 kg/m.operation-1 and 1.5 ind/m.operation-1. The total economic value was calculated at 15814.4 Turkish Liras (TL), which 9390 TL from T.mediterraneus and 6424.4 TL from non-target species. This study is important in terms of revealing for the first time the catch efficiency of gillnets used by commercial fishermen to catch T.mediterraneus in the coastal area of the Marmara Sea, which is an important fishing area. These results will contribute to the creation of management plans and fisheries management for species-specific fishing gear used in a region.

Effect of mesh size in monofilament and multifilament gillnets on catch efficiency in the Black Sea whiting (Merlangius merlangus) fishery

Gillnets are widely used fishing gear for targeting various fish species. Gillnet fisheries use different gear configurations such as different mesh sizes and number of netting twines (mono- or multifilament) depending on the species targeted. Gillnet fishery targeting whiting (Merlangius merlangus) is one of the economically important year-round fisheries in the Black Sea. However, large bycatch of whiting below minimum landing size (MLS) has led to a stock decrease, questioning sustainability of this fishery. This study evaluated how netting twine construction and mesh size can affect the capture probability of whiting. The results showed that changes in gillnet mesh size significantly affect the capture probability with increased mesh size reducing the average capture probability of undersized whiting from around 60%–5%. The results showed no significant differences in the average catch efficiency between monofilament and multifilament gillnets of the same mesh sizes; however, monofilament gillnets showed an increased catch efficiency for some length classes of whiting > MLS. Based on these results, use of 32 or 34 mm mesh size monofilament gillnets is advisable for sustainable whiting fisheries management in the Black Sea.

ABUNDANCE AND SPECIES COMPOSITION OF THE FISHES IN BLUE NILE RIVER BELOW THE TISS ISSAT FALL, ETHIOPIA

In the present study we evaluate the relative abundance and species composition of fishes in Blue Nile River below the fall during the wet season (September-October 2010) and dry season (March-April 2011). Fish samples were collected by using monofilaments gillnets (5-55 mm) and multifilament gillnets, having mesh sizes of six, eight, ten, twelve and fourteen centimeter stretched bar mesh, having a length of twenty five meter and depth of one and half meter, on three sampling sites of the Blue Nile River below Tisisat Fall. Eight hundred fifty seven fish specimens that belong to a single class, Actinopeterygii (ray-finned fishes), four orders, and five families and 6 genera were collected. The most dominant species were Labeobarbus intermedius, Labeo forskalii and Mormyrus kannume. The site harbors large flock of L. intermedius population. Sefiana site had the higher diversity (average H'=3.02). Labeobarbus intermedius was the most dominant (39.67% by number) followed by Labeo forskalii (27.77%) and M. kannume (11.67%). The other species, L. nedgia, B. docmak, L. crassibarbis, C. gariepinus and O. niloticus were found in 9.57%, 5.13%, 3.50%, 1.98% and 0.70%, respectively. All fish species except C. gariepinus and O. niloticus were found in all sites. All the fish species except L. crassibarbis, B. docmak and C. gariepinus showed significant differences in abundance between seasons with overall catch composition of 39.67%, 27.77%, 9.57%, and 11.67% for L. intermedius, L .forskalii, L. nedgia and M. kannume, respectively. L. intermedius, L. forskalii, L. nedgia and M. kannume were the most important species in both seasons and in most of the sampling sites. The studied habitats are in danger being eroded and therefore catchment rehabilitation should be considered and the massive seasonal fishing by the local communities should be reduced

Protection of fish breeding areas in Lake Baringo and the potential for sustainable resource management

AbstractLake Baringo (located in Kenya, East Africa) fishery is currently under perturbation with diverse annual fluctuations in the catch landings. In an attempt to remedy the declining fishery, Kenya Marine and Fisheries Research Institute, Fisheries Department and Beach Management Units, identified and demarcated three fish breeding areas for protection. To assess the effectiveness of these protected fish breeding areas, three fleets of multifilament gillnets (mesh sizes; 25.4 to 203.2 mm) were set between February and December 2018. One fleet was set inside the breeding area, whereas the other two fleets were set 200m and 400m outsides. Fish species abundance, size structure and maturity stages were analyzed from the catch. Fish species abundance was higher within fish breeding areas (67.8%) than outside (32.2%). Labeobarbus intermedius was the most abundant (55.3 %), followed by Oreochromis niloticus baringoensis (29.9%), Labeo cylindricus (13.2%) and Clarias gariepinus (1.7%). Even though larger fish sizes were recorded outside than inside fish breeding areas, they were not statistically different irrespective of seasons (P˃0.05). Majority of the fish (approx. 70%) both inside and outside the breeding areas were in gonad stages 1 and 2. The results indicate that the three areas have great potential to increase fish productivity through fish recruitment and subsequent spillover into fishing grounds. It is recommended that stakeholders, especially Beach Management Units and County Government Department of Fisheries, focus on actualizing the protection of fish breeding areas through enhanced monitoring and surveillance. Fishers should also be sensitized on protected areas concept, coupled with the need to use proper mesh sizes and fishing effort. Beach Management Units should be strengthened as co-management units to guarantee sustainable fisheries resource utilization in Lake Baringo.

Uzatma ağlarında ip kalınlığının Marmara Gölü’ndeki sazan (Cyprinus carpio Linnaeus, 1758) avcılığında av verimi ve seçicilik üzerine etkisi

The effects of multifilament gillnet twine thickness on selectivity and catching efficiency for the common carp fishery were investigated in this study. Sampling was carried out with multifilament gillnets of two different twine thicknesses (with 210d/2 and 210d/3) on 140, 150, 160, 180, 200 mm mesh sizes between June 2015 and December 2016 in Marmara Lake, located in Western Turkey. Higher modal lengths and lower catch per unit effort (CPUE) values and lower sub-minimum landing size (MLS) individuals rate (excluding 180 and 200 mm mesh sizes) were obtained in the thick multifilament material (210d/3) with the same mesh size compared to thin material (210d/2). All mesh sizes in both twine thickness provided modal lengths above the MLS. However, the thin twine material had a higher nominal percentage of undersized fish (8%), greater than the 5% accepted limit for total catches when all mesh sizes are considered together. As a result, the modal lengths and spread values increased and the selectivity and catching efficiency decreased with the thicker twine material.

Aspects of the biology and population structure of Oreochromis niloticus, Coptodon zillii and Oreochromis leucostictus tilapia in Lake Naivasha, Kenya

AbstractThe Nile tilapia (Oreochromis niloticus), Redbelly tilapia (Coptodon zillii) and Blue spotted tilapia (Oreochromis leucostictus) were introduced into Lake Naivasha in the 1950s to diversify and boost the lake fisheries. These species have since been exploited in the commercial gillnet fishery. The fish stocks, however, are currently facing problems of pollution, wetland degradation and intense fishing pressures. Accordingly, the present study investigated some aspects of the biology and population structure of the three tilapiine species in light of changing lake conditions. Fish samples were collected from January to December 2019 using multifilament gillnets of 2.0‐to‐6.0‐inch mesh sizes. Immediately after their capture, the fish specimens were transported to the lab for morphometric measurements and analysis of maturity. The highest and lowest mean (±SD) total length (TL) were exhibited by O. niloticus (22.9 ± 5.2 cm) and C. zillii (14.5 ± 2.1 cm), respectively. Similarly, O. niloticus exhibited a higher mean weight (268.4 ± 18.0 g) and body depth (7.6 ± 2.5 cm), compared to the other species. O. niloticus exhibited an isometric growth pattern, while C. zillii and O. leucostictus exhibited negative allometric growth. The fish species were in good condition, with mean condition factors of 1.59 ± 0.07, 1.51 ± 0.06 and 1.23 ± 0.03 for C. zillii, O. leucostictus and O. niloticus, respectively. Furthermore, the condition factors for O. leucostictus and O. niloticus varied by size class, exhibiting a decreasing trend with increased fish size. The male:female sex ratio revealed significantly more males than females for O. niloticus (2.30:1.0) and O. leucostictus (2.36:1.0), although not for C. zillii (1.15:1.0). O. niloticus (28.0–29.0 cm TL) matured at a larger size, followed by O. leucostictus (21.0–26.0 cm TL), and C. zillii (15.0–17.0 cm TL). In comparison, values of length‐weight parameters, condition factor, sex ratio and size at first maturity of the studied fishes varied in Lake Naivasha, Victoria, Albert and George. The gillnet mesh ≤3.0″ mainly targeted small‐sized immature fish, while mesh ≥4″ targeted mature fish, particularly O. niloticus. It was concluded that gillnets with ≥4.0″ mesh could safely be applied for this fishery in Lake Naivasha, whereas the use of smaller mesh should be controlled to protect the juveniles as a means of maintaining sustainable fisheries. Furthermore, the present study also provided useful information, including size at maturity that is vital for setting mesh size for managing the lake fishery.

Adaptation Strategies to a Changing Resource Base: Case of the Gillnet Nile Perch Fishery on Lake Victoria in Uganda

Sustainable management of fisheries has proven to be a daunting exercise for Lake Victoria. Exploitation patterns in the fishery are driven by fishers who adopt different strategies as a response to changing economic, management, socio-economic, and resource conditions. Fisheries managers, however, seldom consider these changes in management policies. The aim of the study, therefore, was to evaluate the adaptation strategies of the Nile perch gillnet fishers on Lake Victoria in Uganda using 8-year catch and effort data collected in the period from 2005 to 2015. Trends of the selected effort and catch variables in the study period identified two adaptive fishing strategies by gillnet fishers on the lake. The first group, the paddled fishermen whose gillnet use varied in the first half of the study, diverted to harvesting juvenile Nile perch by using smaller, mesh sizes, monofilament nets and gillnets of less depth in the second half of the study. Motorized fishers, on the other hand, maintained their mesh size, using multifilament gillnets, however, they increased the depth of their nets in the second half of the study period to maintain their targeted fish size. Fishers on Lake Victoria adapted strategies to cope with their constraints and opportunities based on the Nile perch population structure and their economic needs. It is important for fishery managers to consider that the fishers are an integral part of the fisheries ecosystems, and considering their behavior in management decisions will aid in devising adaptive policies for sustainable resource use and sustainable livelihood development of the fishers’ communities.

Baseline Survey on the Fisheries of Tekeze Reservoir, Ethiopia

This baseline survey was aimed to: (Amare, A et al, 2014) assess the role of fisheries of Tekeze in improving fisher’s livelihood; (Andersson J., et al 1998) assess household and individual involvement in fisheries and their inputs used; (Asmare, E., 2015) recommend means of interventions for sustainable use of the fishery resource of Tekeze. Data was collected from September to October 2017 by preparing structured questionnaire and checklists. In addition, mixtures of purposive and random sampling methods were employed to collect the data from 302 sampled households. Finally, the collected data were analyzed by using both descriptive and inferential statistics. Fishing in the study area is the main source of immediate cash income for the household next to crop production. Because of this, 50.33% of the respondents involve in a part time basis and the remaining 32.78% and 16.89% involves in a full time and seasonal basis of fishing respectively. Fishing in the study area is practiced by using both monofilament and multifilament gill nets, hooks, and hook and lines. In addition, the fishing boat, which mostly used are steel boat and planked boat. Mostly, fishers actively participate in fishing starting from October to May and some fishers involves even up to June. A highly significant difference in fishing input ownership were also observed between zones (t = 12.5). Even though highly significant difference in total annual gain from fishing is observed between zones and regions (t = 8.8), fishing plays a considerably important role for fishers (80941.46 ETB per a year on average) including part-time seasonal fishers and crop producer. On the other hand, fishing in the study area is highly gender-biased activity, which makes women’s participation negligible. However, destructive way of fishing by using 4cm stretched mesh sized monofilament gillnets; resource equity problem; poor infrastructure such as; road; and market competition problem are among the main problems in Tekeze fishery.

Setting the net lower: A potential low‐cost mitigation method to reduce cetacean bycatch in drift gillnet fisheries

Abstract Bycatch is the most significant threat to marine megafauna (sea turtles, marine mammals, elasmobranchs, seabirds) worldwide, and the leading cause of the decline of several cetacean species. The bycatch issue in the Indian Ocean is poorly understood, but high bycatch levels in gillnet fisheries have been documented for the past two decades, in both small‐scale and semi‐industrial fisheries. Unfortunately, methods to reduce bycatch are often unavailable, financially non‐viable or socially unacceptable to fishermen. Using a network of trained boat captains in the tuna drift gillnet fishery in the Arabian Sea, targeted catch and bycatch data were collected from 2013 to 2017 off the coast of Pakistan (northern Indian Ocean). Two fishing methods using multifilament gillnets were used: surface deployment and subsurface deployment (i.e. headline of net set below 2 m depth). Predicted catch rates for targeted species did not differ significantly between the two fishing practices, although a drop in tuna (6.2%) and tuna‐like (10.9%) species captures was recorded in subsurface sets. The probability of cetacean bycatch, however, was 78.5% lower in subsurface than in surface sets. Cetacean bycatch in tuna drift gillnet fisheries has the potential to be significantly reduced at a relatively low cost for fishers. However, further research with an appropriate sampling design and a large sample size is required to confirm the efficacy of the proposed mitigation method. The acceptability and adoption of subsurface setting by fishers also needs to be further investigated. Despite some limitations, this preliminary study also highlights the importance of crew‐based observer data as an alternative source of data when observers cannot be deployed on fishing vessels.

Güneydoğu Karadeniz’in Fatsa kıyılarında kullanılan dip uzatma ağlarıyla yakalanan avın miktarı üzerine derinlik ve mevsimin etkileri

The study was conducted along the Fatsa coasts of the South-eastern Black Sea, to investigate the effects of depth and season on catch volume of the bottom gillnet fishery. During the study, fishing was carried out using multifilament gillnets with mesh sizes of 32, 34, 36 and 38 mm in each of the four different depth strata (0-14 m, 15-29 m, 30-49 m and ≥50 m) three times per month between March 2013 and February 2014 (except for July and August), with a total of 30 gillnet hauls performed. The results of the study revealed that in all seasons whiting (Merlangius merlangus) was caught most in the 30 m and deeper water layers. However, whiting catch increased with increasing water depth. Most red mullets (Mullus barbatus) were caught in the 0-14 m depth waters during spring, winter and autumn periods, while its catch was the greatest in the 15-29 m during the summer period. Catch of this species decreased gradually with increasing water depth. Another fish species was pontic shad (Alosa immaculata) which was caught least in the shallow waters. However, during all seasons its catch increased gradually with increasing water depth up to the 30-49 m depth strata. Nevertheless, it was determined that catch volume for this species decreased in the ≥50 m level again. On the other hand, Mediterranean horse mackerel (Trachurus mediterraneus) was mostly caught in the shallow waters (0-14 m and 15-29 m) during all seasons. Especially in the ≥50 m waters, no Mediterranean horse mackerel was sampled during the study. This study presents that amounts of catch for the fish species sampled were affected especially by water depth and seasons.

Evaluation of Alligator Gar Broodfish Collections in the Lower Mobile–Tensaw Delta, Alabama

AbstractIn Alabama, Alligator Gar Atractosteus spatula populations have experienced a decline in abundance and due to their limited distribution are classified as a nongame species of moderate conservation concern. Conservation management plans have included creel limits and stocking to augment a diminished population within the lower Alabama River. Our objective was to evaluate gill‐net efficacy on catch and the environmental variables associated with improving broodfish capture rates for hatchery propagation. Broodfish collections were initiated and completed over 75 sample dates between March 2005 and April 2015. Collectors utilized multifilament gill nets consisting of three mesh sizes (101.6, 127.0, and 152.4 mm) and three net lengths (22.9, 30.5, and 61.0 m). Gill nets (n = 569) expended 2,173 h of soak time, resulting in the capture of 101 individuals (TL range = 1,020–2,210 mm). Catch was highest for the smallest mesh size, but net panel length did not influence catch rates. Median fish lengths increased with larger mesh sizes. Catch declined more than sevenfold for net soaks of 1 h or more, and the proportion of successful gill nets declined threefold for longer soak times. Examination of environmental conditions during and prior to the setting of gill nets demonstrated that fish capture success was in part influenced by various aspects of tidal current and water temperature. Catch success was 68% when nets were set at water temperatures of at least 20°C and when at least 50% of net soak time occurred during rising tides. However, success was lower when nets were set at temperatures less than 20°C, capturing Alligator Gar in 44% of all soaks and 37% for those on falling or slack tides. Agencies involved in hatchery propagation programs should continually evaluate field sampling methods, use of collection gear, and environmental conditions to increase broodfish catch rates and improve staff efficacy.

Mono- vs multifilament gillnets: effects on selectivity of narrow-barred Spanish mackerel Scomberomorus commerson in the Persian Gulf

AbstractIranian coastal fishers targeting narrow-barred Spanish mackerel (Scomberomorus commerson) recently replaced their historical multifilament gillnets with those made from monofilament, evoking management concerns over potential increases in catch-per-unit-of-effort. During 20 fishing days, we compared catches from replicate surface-set gillnets that were identical in terms of mesh size (140 mm stretched opening), length (180 m), depth (30 m), hanging ratio (0.56) and spatio-temporal deployment, but had different materials: multifilament (1.8-mm diameter twisted twine) vs monofilament (0.8-mm diameter twine). Compared with the multifilament gillnet, there was a trend of greater catches (up to 1.3×) of S. commerson and another retained species, mackerel tuna (Euthnus affinis), along with one discarded species, giant catfish (Netuma thalassina) by the monofilament gillnet. However, statistical significance was restricted to E. affinis catches and a bias towards smaller S. commerson. These differences were attributed to species-specific catching mechanisms within gillnet material, with larger S. commerson retained by their teeth in the multifilament and all E. affinis more securely retained by their deeper bodies in the monofilament. Gillnet materials require regulation to preclude excessive effort on fully exploited stocks of species such as S. commerson.

Increased Probability and Efficiency of Gar Capture Using Multi- vs. Monofilament Gill Nets

Abstract Monofilament gill nets have increased in popularity in recent decades and are often considered to be superior to multifilament gill nets; however, this claim is still contested by many researchers. Target species, habitat characteristics, and mesh characteristics can all affect the efficacy and selectivity of these nets. Increased angling interest and declining home ranges have led to increased management efforts for gars (Lepisosteidae) among state and federal agencies. However, the sampling of gar species is notoriously difficult and has hindered subsequent management actions in some cases. This study aimed to compare probability and incidence rate of gar capture between net constructions (multi- vs. monofilament), net length (75 vs. 46 m length), sampling habitat (run vs. bend), and deployment orientation (parallel vs. perpendicular vs. diagonal in relation to river channel). We also assessed mode of capture investigate the effects of small mesh sizes (50.8 mm) on capture and potential retention of gars captured in gill nets. Results showed that the use of multifilament gill nets were three times more likely to capture at least one gar (1.3–6.3, 95% CI) than monofilament nets. Multifilament gill nets also averaged approximately twice as many gars per net than monofilament gill nets. Increasing water temperature also significantly increased the probability of gar capture, particularly above 15°C. In addition to mesh type and water temperature, habitat and gill net orientation also had significant effects on the incidence rate of gar capture. We primarily captured gars captured in the gill nets by entanglement (63%), which may have allowed for the wide range of length frequencies sampled in this study. Our study highlights the importance of considering multiple gill net constructions, deployments, and habitats when designing a research project or management plan for gar species. The use of multifilament gill nets can help resource managers to sample gar populations more effectively, resulting in better management strategies and practices.

Population Characteristics and the Potential Suppression of Common Carp in Lake Spokane, Washington

Abstract Common Carp Cyprinus carpio is a nonnative species that often has deleterious effects on aquatic systems. As such, there is interest in suppressing nonnative Common Carp populations in areas where humans have introduced them. The objectives of this study were to 1) provide insight on efficient techniques for capturing Common Carp, 2) describe their population demographics and dynamics, 3) evaluate whether temperature and water elevation were related to growth and recruitment, and 4) develop an age-structured population model for evaluating different management scenarios of Common Carp removal in Lake Spokane, Washington. Catch rates of Common Carp varied among sampling gears with slightly higher catch rates in monofilament (mean ± SD; 15.5 ± 9.8 fish/net night) vs. multifilament (12.7 ± 7.3 fish/net night) gill nets. Catch rates of Common Carp with nighttime electrofishing (0.3 ± 0.4 fish/min) were higher than daytime electrofishing (0.1 ± 0.2 fish/min). Common Carp in Lake Spokane exhibited variable recruitment, rapid growth, large-length structure, high longevity (i.e., age 18 y), and low total annual mortality (17.0%). Air temperature was positively associated with annual growth increments (R2 ≤ 0.25). Neither air temperature nor water elevation was highly correlated (R2 ≤ 0.20) to recruitment of Common Carp. A Beverton–Holt yield-per-recruit model suggested that yield declined with increasing exploitation. Recruitment overfishing would occur at exploitation rates of 20–40% for all targeted minimum length categories (i.e., 150, 300, 450 mm) except 600 mm. Results from this study provide important information on the ecology of Common Carp that can be used to guide management efforts (e.g., suppression) in western systems.

Assessment of catch composition and economic analysis of monofilament and multifilament under-meshed gears (Ngongongo) at Likoma Island, Lake Malawi

The study was conducted to assess catch composition and economic analysis of monofilament and multifilament under-meshed gillnets (Ngongongo) from March to April 2018 at Likoma Island, Lake Malawi. Catch efficiency for targeted fish species in monofilament gillnets showed that catch per unit effort (CPUE) was three times higher than that of multifilament gillnets for Copadichromis spp. (402.2 Kg, 43.3%), Opsaridium microcephulus (315.47 Kg, 34.6%), Rhamphocromis spp. (26.2 Kg, 2.8%), Bagrus meridionalis (21.6 Kg, 2.3%), Oreochromis karongae (40.7 Kg, 4.4%), Bathyclarias spp. (23.2 Kg, 2.5%), Dimidiochromis kiwinge ( 14.4Kg, 1.6%) among others. Catches for Copadichromis spp. comprised of 43% for both gillnet material type combined indicating the importance of this species in gillnet fishery in the district. Monofilament gillnet caught the highest number of fish (7569) while multifilament gillnet caught the least (5427). Again monofilament gillnet has the highest weight of fish (692.87kg) while multifilament has the least (238.22kg). T-test analysis showed that the weight of fish caught by monofilament and multifilament gillnets were significantly different from one another (p=0.000).The profitability performance non-motorized monofilament and multifilament gillnets canoe fisheries in Lake Malawi (Likoma) recorded profit margins at the end of the first year of operation with the minimum Return on Investment (ROI) of 58.9% and 34.4% respectively. On the other hand, the motorised monofilament and multifilament Gillnets canoe fisheries recorded loss 51.1% and 74.4% ROI. The study results point out to recommend for management interventions be put in place to manage the Lake Malawi fishery by imposing restrictions on effort, gear type and mesh sizes and access to illegal material.

Age, growth and reproduction of non-native largemouth bassMicropterus salmoides(Lacépède, 1802) populations in two temperate African impoundments

Summary This study aims to improve the understanding of the establishment success of Micropterus salmoides by assessing growth, maturity and reproductive seasonality of two populations from the temperate region in South Africa. Results are compared to those from other populations to test previously proposed hypotheses that the (i) extent of the spawning season, (ii) longevity, and (iii) growth performance are environmentally temperature dependent. Micropterus salmoides were sampled monthly between March 2010 and March 2012 from Wriggleswade and Mankazana impoundments using either angling or multi-meshed (35, 45, 47, 57, 65, 73, 77, 93, 106, 118, 150 and 153 mm) multifilament gillnet fleets, and a 1 m seine net. The assessed populations in South Africa performed as expected compared to other introduced populations. Age at maturity (1.3–2 years) and length at maturity (232–254 mm FL) were similar to other temperate populations. A well-defined, spring spawning season conformed to findings in other temperate populations. Using sectioned sagittal otoliths it was shown that fish were long-lived (14 years). Growth rates differed significantly between the two assessed populations but both were slower growing than tropical and subtropical introduced populations. Growth performance (Φ′: 2.77–2.99) was similar to other temperate populations. These results indicate that the biology of introduced M. salmoides populations in South Africa is comparable to those of other temperate populations and supports the environmental temperature-dependent hypothesis.

Ecology, fish and fishery of Lake Liambezi, a recently refilled floodplain lake in the Zambezi Region, Namibia

Lake Liambezi (300 km2) refilled in 2009 after a prolonged 22-year dry period. Its aquatic macrophyte populations, fish fauna and fishery shortly after refilling are described. The emergent aquatic macrophyte Phragmites australis formed dense stands covering large parts of the lake, while extensive beds of submerged Lagarosiphon ilicifolius and Najas horrida occurred in shallower areas. Twenty-nine fish species were recorded in experimental gillnets. Catches were dominated by Brycinus lateralis and Schilbe intermedius, contributing 39.5% and 38.5% by weight, respectively. Large-meshed (3–4.5 inch) monofilament and multifilament gillnets emulating those used in the commercial fishery caught mostly Oreochromis andersonii (42.7% by weight) and Serranochromis macrocephalus (28.3% by weight), respectively. Commercial gillnet catch per unit effort (CPUE) averaged 7.0 kg 100-m net−1 night−1, and the annual yield for 2011/2012 was estimated at 2 700 tonnes. Aquatic macrophytes and fishes quickly recolonised the lake and, just two years after refilling, the lake supported a thriving fishery that yielded 4.5 times more than the 600 tonnes recorded in 1974.

Spawning migration of <i>Labeobarbus</i> species to some tributary rivers of Lake Tana, Ethiopia

Spawning migration of Labeobarbus species was studied from August to December 2013 in some tributary rivers (Qimon, Guanta, Shini, and Chibirna) of Lake Tana. Fish specimens and physico-chemical parameters were measured bimonthly in August and September but monthly from October to December. Adult fish specimens were caught using 6 and 8 cm stretched mesh size monofilament gillnets and 6, 8, 10 and 12 cm mesh size multifilament gillnets. A total of 933 adult Labeobarbus specimens were collected during the study period. Labeobarbus intermedius was the most abundant species followed by L. brevicephalus . The peak spawning season of L. intermedius was from fourth week of August to end of September and for L. brevicephalus it was from fourth week of August to beginning of October. Both species were found to spawn in all sampling rivers. However L. truttiformis spawned only at Guanta and Qimon Rivers during August while L. nedgia in Shini and Chibirna Rivers at the end of September. This implies the presence of micro-spatial segregation among species. Pair-wise comparison of Labeobarbus species showed temporal segregation in all sampling months, except L. brevicephalus and L. nedgia . The present findings showed that small tributary rivers and streams are the main spawning grounds for Labeobarbus species of Lake Tana. Therefore, main spawning grounds or routes should be protected from the deleterious effects of anthropogenic activities like illegal fishing, irrigation and sand mining for wise use of the fish resources. Keywords: Fecundity, Fish, Migration, River, Spawning

Monofilament gill net and trammel net selectivity for the silver crucian carp (Carassius gibelio Bloch, 1782) in the Eğirdir Lake, Isparta-Turkey

The aim of this study was determine the selectivity of gillnet and trammel net with different mesh sizes for C. gibelio in Egirdir Lake. Gillnets with mesh sizes of 32, 40, 50, 60, 70, 80 and 90 mm; and trammel nets with of 100, 110, 120, 130 and 140 mm were tested for catching of C. gibelio. Fieldwork was carried out in two different station of Egirdir Lake, in a monthly period from December 2009 to April 2010 and with a total of 10 catching trials. The SELECT method was used to determine the selectivity parameters. Number of 592 C. gibelio species were caught in the experiments which the lengths ranged between 7.3 - 34.8 cm. According to the Bi-modal model which gave the lowest deviation for multifilament gillnets, the optimum lengths were determined as 8.74, 10.92, 13.65, 16.38, 19.11, 21.84 and 24.57 cm for 32, 40, 50, 60, 70, 80 and 90 mm mesh sizes respectively. According to the Normal scale model which gave the lowest deviation for trammel nets, optimum lengths were determined as 27.20, 29.92, 32.64, 35.36 and 38.08 cm for 100, 110, 120, 130 and 140 mm mesh sizes in trammel net respectively.