Net Mesh Size Research Articles

Length-weight relationships of four indigenous fish species from Brahmaputra River, Assam, India

The present study was undertaken with the objective to estimate the length-weight Relationships (LWRs) for four species collected from the Brahmaputra River, Assam, India. The fish samples were collected quarterly from different sampling sites using gill net (mesh size ranges 1–1.5 cm, locally called Mola lungi jal), cast net (mesh size ranges 1.0–2.0 cm, locally called Kevalijal) and triangular dip nets (mesh size ranges 0.75–1.25 cm locally called khorajal) during the time period between May, 2016 to April, 2018 (2 years). The b value of the LWR ranged from 3.028 (for Parambasis lala) to 3.196 (for Psilorynchus balitora). In this study the relationship between length-weight were highly correlated (p < 0.05).

Bio-economic studies on the catch of Bardawil Lagoon, North Sinai, Egypt

The paper aims to give a comprehensive descriptive survey on the production of Lake Bardawil from 1985 to 2015. The average production in this period was 2970 tons. Monthly samples were collected for 12 species of fish during fishing season 2015. The results showed that the Length at first capture (Lc) of different species in Bardawil Lagoon was less than the length at first maturity (Lm); Lm of Mugil cephalus, Sparus aurata and Dicentrarchus labrax was 31.1, 24.5 and 31.0 cm, meanwhile, Lc was 29.0, 18.5 and 27.8 cm respectively. The percentage of small fish with less than the Length at first maturity (Lm) constitutes 67.3% for inexpensive species and 77.05% for expensive species. The loss of biomass in the inexpensive species was estimated at 3268 tons and the loss in income was 199 million Egyptian pounds (LE). The loss of biomass of expensive species was calculated at 1455 tons and the loss of income was 175 million LE. The total loss of biomass was 4723 tons and 374 million LE due to fishing violations and the use of illegal nets in only one fishing season. For proper management, the Length at first capture (Lc) must be increased by widening the nets mesh size. Legal fishing methods and the development of appropriate non-traditional methods for the management of Bardawil Lagoon must be applied.

Length-weight relationships of nine freshwater fishes from six rivers of the Western Ghats of India

Length–weight relationships (LWRs) were estimated for nine freshwater fish species collected three times using a scoop net (mesh size 0.3–0.5 cm), cast net (mesh size 1–1.5 cm) and gillnet (mesh size 2.5–4.5 cm) from six rivers of the Western Ghats of India during August 2017–October 2018. The b values for LWRs varied from 2.862 to 3.656 (R2 > 0.916 and p < 0.0001 for all species).

Length–weight relationships for 15 fish species from the Three Gorges Reservoir

The length–weight relationships (LWRs) for 15 fish species from the Three Gorges Reservoir (TGR) were described in this paper. Specimens were collected using gill nets (mesh size: 6, 8, 10, 12 cm), cage net (mesh size: 1 cm), benthic fyke net (mesh size: 1 cm), hook longlines (80 m long, 3 barbless hooks per meter line) and electrofishing (power: 1,500 w; distance of electrodes: 1–2 m; water depth: 0.2–1.0 m; water area: 1–2 m²; catch by dip net [mesh size: 0.4 cm]) at four sections of the TGR, monthly in June–August and October–November in 2017 and 2018. The first LWR reference for Zacco acutipinnis (Bleeker, 1871), Discogobio brachyphysallidos Huang, 1989, Squalidus nitens (Gunther, 1873), Leptobotia pellegrini Fang, 1936, Sinibotia reevesae (Chang, 1944), Pseudobagrus tenuifurcatus (Nichols, 1931), Pseudobagrus medianalis (Regan, 1904), Liobagrus marginatoides (Wu, 1930), Glyptothorax fokiensis (Rendahl, 1925), and Ctenogobius szechuanensis (Liu, 1940) and new maximum total length for 12 species are provided.

Catch dynamics of set net fisheries in Israel

Artisanal fisheries are globally common, providing almost 50% of total world landings. However, due to overfishing, they are worldwide on the verge of collapse. Fisheries in the eastern Mediterranean Levantine Basin must additionally cope with extreme thermal conditions, meaning that fish are typically smaller relative to other regions. In Israel, mesh size restriction has been suggested as a means to rebuild stocks, but data on artisanal fishing landings across mesh size are extremely sparse. The aim of this study was to quantify set net catches across different mesh sizes in order to identify fishing methods that can benefit both fish populations and fishers. We hope to identify which mesh size provide the highest ratio of commercial to non-commercial fished biomass, the lowest variance in fisher’s revenues and benefits the reproductive potential of the resource by targeting mature individuals. We found that across the range of mesh sizes examined, smaller mesh sizes (i.e. 25, 28, 30) did not catch a larger proportion of individuals below reproductive size but, rather, smaller species. The 43 mm mesh, caught larger individuals with lower total biomass but of larger species, with similar proportions of individuals below reproductive size to smaller mesh sizes. Net mesh size was not associated with fisher revenue. Trammel nets were found to be the least selective in relation to non-commercial by-catch, although the proportion of mature individuals in the catch was larger than for the other nets examined. These findings suggest that mesh size restrictions, across the range of mesh sizes examined, will not result in a decrease in catch of individuals below reproductive size but rather shift the species composition of the catch towards large-bodied, often high trophic level, species. Thus, mesh size restrictions are unlikely to rebuild fish stocks of high-value commercial species nor increase fisher revenue. We suggest that artisanal fisheries management in the Levantine Basin should evaluate new management measures and consider reducing overall fishing pressure along with implementing ecosystem-based fisheries management, such as the closure of fish reproduction and recruitment areas and establishment of marine protected areas.

PENERAPAN PERUBAHAN UKURAN MATA JARING DALAM PENANGKAPAN IKAN TERBANG SECARA BERKELANJUTAN DI KECAMATAN SENDANA KABUPATEN MAJENE

Catching flying fish in Sendana Majene Subdistrict is carried out continuously with gill nets 1-1.5 inches. The catch of flying fish is mostly still young fish (not yet worth catching). The demand for flying fish is quite high due to the existence of special stalls of smoke fly fish around fishing settlements. Apart from smoke flying fish, dried flying fish are also sold as souvenirs. Therefore, fishermen will continue to increase production. Various results of research and field observations show that gill net is able to catch flying fish well but the size of fish caught is dominated by young fish. The effort to increase the net mesh size to 1.5 inches resulted in the diminishing number of young flying fish. Catching flying fish in Majene waters is generally carried out with drifting gill nets with mesh sizes of 1 and 1.25 inches which are very intensive every fishing season while L50 (11.92 cm) and Lm (13.59 cm) for 1 inch more net mesh size were smaller compared to the length of the first gonad maturity, in this case most of the catch is still classified as young fish (Palo, 2009). Partners are a group of flying fish fishermen. Partner problems, flying fish production is getting smaller, group capacity is not strong and group management is still weak. Partners have not been able to obtain assistance facilities from various community empowerment programs carried out by the government. The approach to be used in this service includes: identification, observation, counseling, demonstration, construction, application, assistance, field observation and evaluation monitoring. Indicators of the success of activities are measured based on the results of the application of technology compared to the results of fishing gear commonly used by fishermen. Implementation of service includes counseling, construction of fishing gear, fishing operations and assistance has been going well. The size of 1.5-inch mesh is only able to catch flying fish in a limited amount, while the size of the 1.25-inch mesh can catch flying fish in relatively large numbers. Flying fish caught with 1.25-inch mesh size has passed the size of the first gonad mature so that it supports sustainable fisheries.

Seasonal variations of plankton structure as bioindicators in Zayandehrud Dam Lake, Iran

Abstract Zayandehrud Dam Lake located in Isfahan province is the largest lake in central Iran. In this study, the plankton communities including phytoplankton and zooplankton were studied as bioindicator organisms for assessment of water quality in the Zayandehrud Dam Lake. The water and phytoplankton organisms were collected from four stations at different seasons during 2014 by using a Nansen bottle sampler. The zooplankton samples were collected with a plankton net (mesh size = 50 µm). The phytoplankton community was composed of Bacillariophyceae, Cyanophyceae, Euglenophyceae, Dinophyceae and Chrysophyceae. The zooplankton community viz; Cladocera, Rotifera and Copepoda were found to have a density range of 13–155, 21–141 and 11–93 (ind. m−3), respectively. In general, phytoplankton and zooplankton communities, especially the presence of genera such as Cyclotella, Dynobrion, Bosmina and Daphnia (as indices of oligotrophic lakes) and also absence of Microsystis, Brachionus and Lecane are seen as important indices of eutrophic lakes. It could be concluded that the Zayandehrud Dam Lake can be classified as a healthy water body.

Diversity of phytoplankton species in Cheonjin Lake, northeastern South Korea

BackgroundSeveral investigations carried out from large brackish lagoons in South Korea. However, no studies have yet examined phytoplankton in lagoons that changed to freshwater, such as Cheonjin Lake. The present study examined the algae from Cheonjin Lake.MethodsSamples were collected at monthly inetrvals from May 2017 to April 2018, from the surface layer using a plankton net (mesh size 20 μm), and sequeezing submerged macrophytes. Microscopic examinations were conducted at a magnification of 200 to 1000x using a Zeiss microscope (Axio Imager. A2), and photographs were taken with an AxioCam HRC camera. Silica-scaled samples of Chrysophyta for SEM were placed on coverglass, air dried, coated with gold, and then examined with a Hitachi SV8220 SEM.ResultsA total of 376 taxa from six major algal groups (Chlorophyta, Chrysophyta, Euglenophyta, Cyanophyta, Dinophyta, and Cryptophyta) were identified. Among these algae, 28 taxa of desmids, 9 taxa of Euglenophyceae, 4 taxa of Chlorophyceae, 2 taxa of Chrysophyceae, and 1 taxon of Xanthophyceae are reported for the first time in Korea. A new species, Cosmarium hexagonum sp. nov was described. The phytoplankton communities were characterized by an abundance of Desmids (within Charophyceae) accounted for 148 taxa from 22 genera. Species richness were particularly high in the Autumn.ConclusionIn this study, a total 376 taxa of 148 desmids (Charophyceae), Chlorophyceae (103 taxa), Chrysophyceae (53 taxa), Euglenophyta (49 taxa), Dinophyta (8 taxa), and Cryptophyta (2 taxa) were identified from Cheonjin Lake. Twenty-eight taxa of desmids including a new species (Cosmarium hexagonum sp. nov.), 9 taxa of Euglenophyceae, 4 taxa of Chlorophyceae, 2 taxa of Chrysophyceae, and 1 taxon of Xanthophyceae were newly recorded in Korea.

Length-weight relationships of two fish species from the South China Sea

The length–weight relationships were determined for two fish species: Kumococius rodericensis (Cuvier, 1829) and Inegocia japonica (Cuvier, 1829). Samples were collected at seasonal surveys in the South China Sea using bottom trawl nets (mesh size 4.0 cm, at a towing speed about three knots) from September 2014 to October 2017. The estimated growth coefficient (b) of these two species ranged from 3.2963–3.2980.

Length-weight relationships of four endemic snakeheads [Channa andrao Britz, 2013, Channa aurantimaculata Musikasinthorn, 2000, Channa bleheri Vierke, 1991, and Channa stewartii (Playfair, 1876)] from the Brahmaputra drainage, northeast India

The paper provides the Length–weight relationships (LWRs) for four endemic snakehead fish species namely Channa andrao Britz, 2013, Channa bleheri Vierke, 1991, Channa aurantimaculata Musikasinthorn, 2000 and Channa stewartii (Playfair, 1876), based on seasonal catches along the Brahmaputra river drainage from October 2016 to May 2018, using cast net (mesh size: 10–20 mm), scoop net (mesh size: 05–10 mm) and bamboo traps. Total lengths (TL) (nearest to 0.1 cm) and body weights (nearest to 0.1 g) were taken respectively. The b values in the LWRs were 3.26 for C. andrao, 2.74 for C. bleheri, 3.04 for C. aurantimaculata, and for 2.78 C. stewartii respectively. For C. aurantimaculata (=36.2 cm), C. bleheri (=14.4 cm) and C. stewartii (=29.7 cm) each, a new maximum total length (TL) was recorded.

Length-weight and length-length relationships of four fish species from rivers in the Tibetan Plateau, China

Length-weight (LWRs) and length–length relationships (LLRs) were estimated for three native and one non-endemic fish species, representating three families and four genera from four sites in the Tibetan Plateau, China. Specimens were caught by a gill net (mesh size: 1-inch), cast net (mesh size 1–2 cm; depth: 1–2 m) and a traditional shrimp coop during July 2006, and from July 2013 to August 2014. The LWRs b-values of all fish species ranged from 2.63 to 3.29. All correlation coefficient values were higher than 0.95. Their LLRs were highly correlated.

Length and weight relationships of five different fish species from northern areas of Pakistan

In present study five different species were studied from three different rivers from northern Pakistan. Specimens were collected in the period of January to December 2017 using cast nets (10–12 mm mesh size) for Barilius, Glyptothorax and Schistura species while cast nets (mesh size 1.25 × 1.25 cm) used for Schizothorax species. Total length (TL) and fork length (FL) to the nearest 0.1 cm and body weight (BW) to the nearest 0.1 g were recorded for each individual.

POPULATION DYNAMIC AND EXPLOITATION RATE OF THE BLUE SWIMMING CRAB (Portunus pelagicus) IN THE KENDARI BAY WATERS

Kendari Bay waters consitute a potential blue swimming crab (BSC) fishing ground in WPP NRI 714 (the Banda Sea). The intensive fishing activities have been increasing from year to year that raised concern to the fishing that will disturb resource sustainability. Therefore, an alternative sustainable management is advisable. The purpose of this research was to examine the population dynamics and exploitation rate of BSC in the Kendari Bay waters conducted between January and November 2016. The results show the isometric of BSC growth pattern and balance of male and female ratio. The length at first capture (L c ) of BSC was 116.65 mm (carapace width),smaller than the length at first maturity (L m ) at 119.7 mm (carapace width). The von Bertalanffy growth equation for the blue swimming crab was L(t) = 182.0[1-e -0.91 (t - 0) ] and the fishing mortality rate (F) was higher than the natural mortality rate (M). The blue swimming crab exploitation rate calculated BSC from Kendari Bay has exceeded the optimum rate of 0.73 per year and is indicating a category “overfishing”. Therefore, to maintain the BSC stock sustainability, a management measure is needed to reduce the current fishing effort of approximately 46 % from the current effort and regulation of net mesh size.

Catch Trend and Stock Assessment of Hilsa Tenualosa ilisha Using Digital Image Measured Length‐Frequency Data

AbstractThe annual global average catch shares of the anadromous Hilsa Tenualosa ilisha of Bangladesh increased rapidly from 74.5% all through 1984–2013 to 86.7% during the 2010–2015 periods. With a few exceptions, an increasing trend of Hilsa production over the last three decades was found in Bangladesh. Initially three options incorporating digital image measurements were compared to determine the best method for obtaining accurate length data. The length‐frequency data measured from digital images showed that Hilsa have a moderate growth rate (K = 0.90 year−1) of up to 58.70 cm (L) TL. High fishing mortality (F = 2.83 year−1) and exploitation level (E = 0.67) suggest a slight overexploitation of the Hilsa fishery; the maximum sustainable yield (MSY) was estimated at 526,000 metric tons/year if the recommended TL at first capture (Lc) of 27 cm is adhered to. The present annual Hilsa catch is about 496,417 metric tons, which indicates the potential benefit of achieving MSY through sustainable fisheries management by regulating mesh size of nets and protecting brood fish. Size distribution of Hilsa within sanctuaries revealed a remarkable presence of juvenile fish during February–March in some areas, which suggests a need to readjust the fishing ban period from March–April to February–March. More fisheries management is necessary to reduce the exploitation level of Hilsa by 17% and at the same time increase the allowable Lc to potentially increase the MSY and CPUE.

Length-weight relationships of three species in northern China

Length-weight relationships were estimated for three species (Triplophysa microphysa, Triplophysa zamegacephala and Gobio coriparoides) belonging to two families and two genera from northern China. Specimens were collected using trap nets (mesh size 1 cm) in May, June and December 2017, and March 2018. Total length (TL) for each individual was determined to the nearest 0.1 cm by digital slide caliper and each body weight (BW) to an accuracy of 0.1 g using digital balance. The b-values for LWRs varied from 2.583 to 2.876 (r2 > 0.979). This biometric data and their relationships are relevant to the management and conservation for local fishes and fisheries.

Effect of drift sampler exposure time and net mesh size on invertebrate drift density in the Njoro River, Kenya

Although invertebrate drift is an important ecological process in lotic ecosystems, very little is known about it in Kenyan rivers. The primary aim of this study was to investigate the effect of driftnet mesh size and exposure duration on drift density in 2017. Drift samples were dominated by Chironomidae, Baetidae, Simuliidae, Caenidae and Culicidae. The 100 µm mesh driftnet had the highest mean invertebrate density, followed by the 250 µm and 500 µm nets. Invertebrate drift densities decreased with increased exposure time. This study demonstrates that sampler mesh size and exposure time should be taken into account when characterising invertebrate drift in streams. Future studies should consider sampling different biotopes and during different seasons.

Length-weight relationships of three fishes from the Nujiang River, China

The length-weight relationships (LWR) for three fish species collected from the Nujiang River, China, were determined. Fishes were caught quarterly by drift gill net (stretched mesh size: 4 cm, depth: 2–4 m) and cast net (mesh size 1 cm; depth: 1–2 m) from May 2016 to July 2017. The values of parameter b in the LWR equations were estimated as 2.69 for Balitora nujiangensis Zhang & Zheng, 1983, 2.80 for Glyptothorax deqinensis Mo & Chu, 1986 and 2.94 for Pseudexostoma brachysoma Chu, 1979, respectively.

New Record of the Big-Scale Sand Smelt Atherina boyeri Risso, 1810 (Atherinidae) in the Seyhan Dam Reservoir (Seyhan River basin, Turkey)

Fifteen specimens of the big-scale sand smelt, Atherina boyeri were caught by a single trawl haul with a net mesh size of 3 mm on February 2017 from the Seyhan Dam Reservoir (South Anatolia, Adana/Turkey). In this study the big-scale sand smelt, A. boyeri, was recorded for the first time in the Seyhan Dam Reservoir. In addition, some morphometric and meristic measurements of A. boyeri were given and these values were compared to populations in two different lakes. Furthermore, the possible ecological effects of A. boyeri on Seyhan Dam Reservoir were briefly discussed.

Length-weight relationships of four fish species from the Beibu Gulf, South China Sea

The length–weight relationships of four fish species: Lophiomus setigerus (Vahl, 1797), Uranoscopus oligolepis Bleeker, 1878, Cynoglossus oligolepis (Bleeker, 1855), and Cynoglossus arel (Bloch & Schneider, 1801) were determined. Specimens were collected from the Beibu Gulf in the South China Sea by using bottom trawl nets (mesh size 4.0 cm, at a towing speed about 3 knots) in the seasonal investigations from August 2010 to May 2011. The values of parameter b of these four species ranged from 2.982–3.489 and remained within the normal range of 2.5–3.5.

Length-weight relationships of 4 fish species from a seagrass Zostera marina bed in Koje Bay, Korea

Length-weight relationships of 4 fish species collected from a seagrass Zostera marina bed in Koje Bay on the southern coast of Korea were analyzed. The fish samples were captured using a seine net (mesh size 6 mm) at water depth of approximately 1.5 meters during low tide. Fishes were collected 8 times from summer 2016 to spring 2017. The regression parameter b varied between 2.47 for Favonigobius gymnauchen and 3.03 for Ditrema temminckii temminckii.