Bottom Gillnet Research Articles

Bycatch and discard rates assessment of the gillnet fishery in the southern Brazil

The fisheries discard patterns are an important element to be considered in stock assessment, fisheries management, and conservation measures. Using data collected by scientific observers on board, we analysed the bycatch and discard rates of the pelagic and bottom gillnet fishing in southern Brazil. Bottom gillnet was responsible for discarding from 77 taxa; 35 % of the discarded biomass was composed of teleost fishes, 33 % of elasmobranchs, and 22 % of other taxa. Pelagic gillnet, targeting the Pomatomus saltatrix, resulted in the discard of 13 species and taxa not identified at the species level, such as Cnidaria and Malacostraca. The most discarded fish species was Brevoortia pectinata, constituting 94.8 % of the total discarded biomass. The discard rate of bottom gillnets targeting Micropogonias furnieri was higher (20 %) than that of those targeting the demersal species (6 %), such as Cynoscion guatucupa (formely Cynoscion striatus) and Umbrina canosai. The high biomass proportion and numerous discarded species emphasize the need for effective management through temporal and spatial fishing restrictions. Our findings suggest potential measures, including the closure of fishing areas in coastal waters.

Catch Composition and Catch Per Unit Effort of Small-scale Fisheries on the Coasts of the Bodrum Region (Güllük Bay, South-eastern Aegean Sea)

This study presents the species composition of fish caught using gill/trammel nets in the Bodrum and surrounding areas on the coasts of the southern Aegean Sea, along with the fish catch per unit effort (CPUE) values by fishing area and seasonality. Five types of set nets were examined: gillnets for the bogue (Boops boops) fishing, trammel nets for the common sole (Solea solea) fishing, bottom trammel nets, bottom gillnets, and trammel nets for the red mullet (Mullus barbatus) fishing. Among these, gillnets used for bogue fishing are primarily deployed near fish cages. The study revealed that the highest average CPUE values of gill nets were 50.3±8.3 kg.1000 m-1 in spring and 64.5±24.9 kg.1000 m-1 around the sea cages, attributed to the increased presence of bogue, particularly during the spring season.

KOMPARASI JUMLAH HASIL TANGKAPAN JARING INSANG DASAR PADA DAERAH KARANG DAN LAMUN DI DESA LEBETAWI, KOTA TUAL

Bottom gillnet is a fishing gear which is operated in the morning, afternoon, and evening in the waters around Lebetawi Village. However, there is limited information about the specific composition of catch, especially the differences of catch between coral and seagrass areas. The aim of this study is to compare the number of catches from coral and seagrass areas and how the fish were first caught. The research was conducted for two months, from December 2023 to January 2024, in the waters of Lebetawi Village, Tual City, Southeast Maluku Regency. Data was collected from precisely observation on bottom gillnet aperated at seagrass and coral habitatss. The catches consisted of 18 species, with total 220 individuals fish and weight 34,161.18 grams. Throughout the fishing operations at both habitats, all demersal and pelagic fish were captured by way of gilled and wedged.

Catch composition of fishes by different types of fishing gears in the Andaman sea, Thailand

The Andaman Sea is a rich ecosystem providing significant ecosystem goods and services for people in coastal areas and these areas have fisheries activities using different fishing gears appropriate for different species and habitats. We assessed catch composition and size distribution of economically important finfish captured by a range of fishing gears employed by commercial and artisanal fishers in three provinces adjacent to the central Andaman Sea of Thailand over a 2-year period. Between January 2019 and December 2021, fishers employed 7 main capture gears: surface gillnet, bottom gillnet, fish trap, handline and hook, trawl, purse seines and light-luring anchovy falling net. Trawling captured the highest diversity of target species (35 species) followed by surrounding net (32 species), fish trap (16 species) hook and line (15 species), surface and bottom gillnet (15 species) and the last one of anchovy falling net (2 species). When comparing size at the first maturation of both target species and bycatch, it was found that the percentage of mature fish caught from artisanal fishing gears was higher than of commercial fishing gear because artisanal gears had better selection of catch, especially fish trap and hook and line. Understanding the operation of fishing gears, catch composition and the size frequencies of target species could be particularly important for stock assessment because gear may influence catch composition.

Population Size Structure and Length–Weight Relationships of Selected Pelagic Fishes From The Gambian Waters (West Africa)

The population size structure and length–weight relationships (LWRs) are fundamental tools in fishery science, providing valuable insights into the health, dynamics, and management of fish populations and contributing to the sustainable use of aquatic resources. The data used in this study were estimates from the main small pelagic fishes exploited in the Gambia. They were collected using surface and bottom gillnets between November 2020 and October 2021 during scientific fishing operations. The main small pelagic fish size composition showed a modal class of 20 cm for Ethmalosa fimbriata, 21 cm for Sardinella aurita, 22 cm for Sardinella maderensis, and 30 cm for Trachurus trecae. The parameter b value of these fish species ranged from 1.6831 to 2.9461, and the correlation coefficient ranged from 0.81 to 0.95. Statistical LWRs for all species were very significant. Information obtained is essential in reviewing and establishing basic management measures for depleted shared pelagic stocks in the Gambian fisheries and the sub‐region. In the context of poor data fisheries, such results also encourage the Gambian government and intergovernmental subregional organizations to support data collection in the long term.

Monitoring and management of abandoned, lost and discarded fishing gear (ALDFG) in Penghu Islands, Taiwan

This study investigated the conditions of abandoned, lost, discarded fishing gear (ALDFG) in natural and artificial reef zones and removed it afterward in Penghu Islands. Various feasible suggestions for improving ALDFG management were proposed for the county government to manage and reduce the generation of ALDFG in the future and maintain the marine ecosystem. This study divided the ocean areas of Penghu into five sub-areas for carrying out research and surveys. 165 boat trips of ALDFG investigation and removal were conducted from July 2018 to October 2019. The results show the ALDFG in natural reef areas is mostly large-mesh gillnets (26 %). The rest are single-layer bottom gillnets (21 %) and multi-layer bottom gillnets (20 %). In line with the recent efforts of the Penghu County Government to address ALDFG, it is recommended that the participation of citizen scientists and the promotion of ocean education can be utilized for fishery co-management in Penghu.

Using a visual deterrent to reduce seabird interactions with gillnets

Bycatch is one of the main threats to seabird conservation. In Portugal, there are alarming estimates of seabirds bycaught per year in bottom gillnet fisheries, which get entangled during fishing operations, when the gear is close to the surface. In this study, a visual deterrent (scarybird) was tested in a fishing vessel operating bottom gillnets near and within Berlengas Islands SPA (Special Protection Area). Trials were conducted between 2019 and 2020, with 18 control and experimental fishing trips monitored by a trained observer. The scarybird proved to be an effective bird deterrent measure, affecting both the numbers and distribution of seabirds and keeping a large portion of birds away from the vessel during fishing operations, making them potentially less vulnerable to bycatch. The deterrent device was more effective in the closest area to the vessel (0–20 m) where there was a significant reduction in the number of gulls (Larus michahellis/fuscus, −56 %) and northern gannets (Morus bassanus, −72 %) close to the vessel, by comparison to control fishing trips. The use of this aerial deterrent device had no impact on the fishery's target catches and revenue, which contributed to a good acceptance by fishermen. This simple and “easy to implement” deterrent device has potential to be further tested as a bycatch mitigation measure in bottom gillnets but also in other gears, whenever interactions with birds occur mainly close to the surface.

Fish Species Composition of Bottom Gillnet Catches by Japanese Fishing Vessels Operated in Russian Zone of Kunashir Strait in 1998–2014

Fish Species Composition of Bottom Gillnet Catches by Japanese Fishing Vessels Operated in Russian Zone of Kunashir Strait in 1998–2014

Fish Species Composition of Bottom Gillnet Catches by Japanese Fishing Vessels Operated in Russian Zone of Kunashir Strait in 1998–2014

Overall, 85 fish species assigned to 56 genera, 27 families, and 13 orders were observed in the bottom net catches from the Kunashir Strait in 1998–2014. The highest number of species (18) represented the family Pleuronectidae, while the family Cottidae involved the lower number of species (14). Thus, 35 species were found in the Nemuro Strait (including the Kunashir Strait) for the first time. Considering the information in the literature, the total number of fish species in the strait separating the Southern Kuril Islands from the Hokkaido Island increased to 173.

The The Effect of Using Led Lights (Light Emitting Diode) in the Operation of Bottom Gillnets on Catches In Pangandaran Waters, West Java

The objectives of the study were to analyse the response of dominant fish to different light colours that reflect the wavelength of light and to analyse the species composition of the gillnet catch to determine the fish that are positively phototaxis to LED light. Data collection was conducted using the experimental method. The experimental design used 1 unit of bottom gillnet gear with a mesh size of 4 inches, and used LED (Light Emitting Diode) lights. Trials using green LED lights and white LED lights were operated simultaneously between the control gillnet (without LED lights) and the experimental gillnet (with LED lights). The results of statistical analysis of gillnet catches with green LED light aids with white LED light aids and control nets have a significant effect on the number of gillnet catches. The results were: (1) The number of fish caught at a distance of < 1 m and at a distance of 1-2 m, this proves that many fish are attracted to light (positive phototaxis); (2) Proven by gill net fishing gear using green LED light aids obtained fish weighing up to 77.7 kg. (3) It is proven that the distance of the lamp with the position of the fish caught on the net sheet can produce the highest weight of fish caught, on green LED lights at a distance of <1 m the weight of the fish reached 30.89 kg.

Assessment of the bycatch level for the Black Sea harbour porpoise in the light of new data on population abundance

Incidental catch in fishing gear (often known as bycatch) is a major mortality factor for the Black Sea harbour porpoise (Phocoena phocoena relicta), an endemic subspecies listed as Endangered in the IUCN Red List. The primary gear, responsible for porpoise bycatch in the Black Sea are bottom gillnets and trammel nets targeting turbot (Scophthalmus spp.), the most valuable commercial fish species in the Black Sea. From 2019 to 2021, a study was conducted in Bulgaria, Romania, Türkiye and Ukraine, to estimate the bycatch level in light of new information on porpoise distribution and abundance obtained from aerial surveys (CeNoBS) undertaken in 2019 as part of ACCOBAMS Survey Initiative (ASI). Bycatch data were collected by independent observers onboard turbot fishing boats (Bulgaria and Romania), complemented by questionnaire surveys and examination of stranded carcasses (in all countries). Some 48 monitoring trips took place (63 hauls by 11 different vessels). Cetaceans were caught on just over half of the trips (55%): 182 harbour porpoises, 4 bottlenose dolphins and 3 common dolphins. The median number of porpoises bycaught per trip was 1 (maximum 41) and the number of porpoises per km of net varied between 0 and 3.66 (median 0.1). Bycatch rates showed seasonal variation with marked increase in summer, compared to spring. The total annual bycatch of harbour porpoises in the Black Sea was roughly estimated as between 11 826 and 16 200 individuals. These numbers were the product of median values for effort (days/trips and vessels) and bycatch rate. Given the new estimates of porpoise abundance based on the CeNoBS survey of 2019 and reconciling abundance and bycatch estimates, harbour porpoise bycatch in the Black Sea represents between 4.6% - 17.2% of the estimated total population, depending on assumptions used. Even the most conservative estimate is among the highest worldwide and far exceeds the probable sustainable levels of around 1.0-1.7%. This study confirms that bycatch poses the most serious threat to the Black Sea harbour porpoises and that all riparian countries engaged in turbot fisheries must implement urgent measures to reduce it immediately, if the population is to survive in the long-term.

Biological aspects, exploitation rates, and spawning potential ratio of scalloped hammerhead shark (Sphyrna lewini Griffith & Smith, 1834) in Lampung Bay waters, Indonesia

The scalloped hammerhead shark is an endangered species that is listed in CITES Appendix II. Information on the biological aspects, exploitation rate, and spawning potential ratio of scalloped hammerhead sharks are very limited, especially in Lampung Bay waters. These data were important to find solutions and the best management to sustain the scalloped hammerhead sharks in Indonesia, especially in Lampung Bay waters. The aim of this study is to investigate the biological aspects, exploitation rates, and spawning potential ratios of scalloped hammerhead sharks in Lampung water. Scalloped hammerhead shark samples were collected from the catch of bottom gillnet in Kalianda Fish Landing Place, Lampung Province. Enumerators collected biometric data (length and weight) of 332 scalloped hammerhead sharks from July to November 2020. Biological aspects include distribution of length, length-weight (L-W) relationships, length at first capture, and length at first maturity. The utilization rate was calculated using the exploitation rate (E) and the estimated SPR based on length data. The results show that the length of scalloped hammerhead sharks ranged from 37.5 to 173.0 cm FL. Most of the samples fish had not spawned yet or were immature (Lc =47.1 cm FL; Lm =89.4 cm FL). The growth pattern of scalloped hammerhead sharks was allometrically negative. Scalloped hammerhead sharks have natural mortality of 0.18/year, while fishing mortality was 1.08/year. The fishing status of scalloped hammerhead sharks in Lampung Bay was fully exploited (E=0.85), and the stocks were in a recruitment overfishing condition. These findings indicate that effective management is required to ensure the sustainability of scalloped hammerhead sharks in Lampung Bay waters, such as adjusting mesh size, fishing season, and avoiding capture in the nursery area.

Fisherman productivity of bottom gill net and drift gill net during covid-19 in Napabalano Sub- District Napabalano District Muna Regency

This study aims to determine the productivity of fisherman who use bottom gill nets and drift gill nets during the Covid-19 period. This research was conducted in Napabalano Village, Napabalano District, Muna Regency from April to May 2022. The sampling method used was the census method with the number of respondents being 8 bottom gill net fisherman and 8 drift gill net fisherman. Data was collected trough interviews, observation and documentation. Analysis of the data used is the productivity Analysis. The results of the study showed that the productivity obtained by bottom gill net fisherman averaged 2.42, meanwhile, the productivity obtained by drift gill net fisherman is 3.01 on average. Thus, the two fishing gears are declared productive because the average productivity value is >1.

UKURAN KEPADATAN DAN POTENSI IKAN BARONANG TOMPEL (Siganus guttatus Bloch 1787) DI TELUK KOTANIA SERAM BAGIAN BARAT

Spotted rabbitfish (Siganus guttatus Bloch 1787) are valuable commercial fish species. Research on the fish species has been carried out in the waters of Kotania Bay, aiming to obtain information about size, density and potential of the fish species. Data are collected about total length (TL), weight and number of individual fish at four observation stations using 120m length of bottom gillnet with mesh size of 2.0, 2.5, 3.0 dan 3.5 inches. The bottom gillnet is operated in a circle that starting two hours before the low tide then the spotted rabbitfish caught are collected at the low tide. The results showed that the total length of the spotted rabbitfish is in the range of 11,3 – 33,9 cm which has dominated by fish with sizes of 18, 24 and 26 cm. Mean density of the fish is 209 individual/ha, so the abundance the fish in the area of seagrass beds 823.62 ha was estimated as 172.486 of fish individual, it’s 72,51% or 125.070 individuals are those fishes that has spawned for the first time. The mean weight of the spotted rabbitfish at this size is 533,51 grams, so calculated biomass is 66,73 tons and MSY value is 33,365 tons in wet season.

PROPORTION OF LEGALLY SIZE BLUE SWIMMING CRABS CAUGHT BY FISHERMEN IN BETAHWALANG VILLAGE

Blue swimming crab is a fishery product with high economic value in Indonesia. Betahwalang Village, Demak, is one of the crab fisheries locations in the province of Central Java. High selling prices and processing industry demand encourages fishing activities. One issue brought on by increased fishing activity is the smaller crab size. It will impact the crab fishing industry in Betahwalang. The majority of the fisherman in Betahwalang Village catch crabs using arad nets, simple gill nets, and traps. This study aims to evaluate the size of crab catch results on fishing gear used by fishermen and recommend proper fishing gear for catching crabs. This research was conducted in April 2019. The catch size of crab was the primary data collected for this study, also with data on fishing grounds, methods, and characteristics of fishing gear. Data were collected by observation, interviews, and measurements of fishing gear and the carapace width of the crab. The results of data collection and processing were analyzed descriptively. The results showed that the highest proportion of legal size crabs (carapace width ≥10 cm) was caught in traps, while the proportion of unlegal size crabs caught was mostly in bottom gillnets and mini trawl.

Dampak Pandemi Covid-19 pada Kelayakan Usaha Perikanan Rajungan di Teluk Banten

The Archipelagic Fishing Port of Karangantu located in Banten Bay is one of the blue swimming crab fishing centers in the Java Sea. Covid-19 pandemic had significant effect on blue swimming crab fisheries in Karangantu, especially on the increasing of fishing operational cost, decreasing of price, and limited acces for market distribution. This study aims to analyse the feasibility of blue swimming crab fisheries activity using bottom gillnet in Banten Bay after Covid-19 pandemic. The research was conducted in May-June 2021 in Karangmulya Village, Kasemen District, Serang City with a total of 22 respondents. The data were collected using deep interview with each respondent who was selected purposively. The analysis of business feasibility was conducted based on the parameters of the ratio between income and costs (R/C), payback period (PP), and net present value (NPV). The results show the Covid-19 induced the decreasing of R/C ratio value from 2.08 before to 1.81 after Covid-19 pandemic, respectively. The value of PP also increased from 0.65 years to 0.68 years. Moreover, the potential profit of blue swimming crab fishing also decreased from IDR 55 million before Covid-19 to IDR 52 million after Covid-19 pandemic. However, due to the positive NPN value, the blue swimming crabs fishing actvity using bottom gill nets in Banten Bay is still feasible to be developed. Keywords: blue swimming crab, Covid-19, impact, fisheries

Length‐weight relationships and condition factors of 28 fish species belonging to Leuciscidae (Cypriniformes) from Turkey

Length-weight relationships (LWRs) were estimated for 28 freshwater fish species belonging to the family Leuciscidae. Length-weight relationships (LWRs) were estimated for 28 freshwater fish species belonging to the family Leuciscidae. Surveys were undertaken during the spring, summer, and autumn of 2014 and 2015, as well as from 2017 to 2019. Fish were sampled in 13 different water basins using a backpack electroshoker as a standard sampling method. The water depth varied between 2 and 40 cm depending on the habitat. Sampling was done by using bottom gill nets, which were designed to be 30 m in length and reach 1.5 m in depth, consisting of 12 different mesh panels (each panel is 2.5 m in length with 5, 6.25, 8, 10, 12.5, 15.5, 19.5, 24, 29, 35, 43, and 55 mm). The nets were settled-up at the end of the day and collected in the morning after being left in the water overnight for at least 12 h. The estimated values of parameter b ranged from 2.683 (Squalius berak) to 3.349 (Alburnus carianorum). R2 values varied from 0.888 to 0.998, indicating a high degree of the positive relationship between length and weight. The maximum total lengths of seven of the studied species are new records and have not yet been reported in any database.

KOMPOSISI HASIL TANGKAPAN RARAPE (BOTTOM GILLNET) DI DESA KULU KECAMATAN LIPKUPANG, KABUPATEN MINAHASA UTARA

The aim of this research was to determine the species composition (Kj) and the weight composition (Kb) of the catch using a bottom gillnet whom operated by fishermen the village of Kulu. The research was conducted from October to December 2020. The research method was experimental fishing using gillnets with a 3 inch mesh size. The fishing operation took place over 15 trips and the fishing area was around the waters of the village of Kulu. The results showed that the catch was 117 fish including 15 kinds of fish and one type crustacean. The composition based on the dominant fish species is Naso hexacanthus (29.06%), whereas the composition based on the dominant weight is Portunus pelagicus (33.6%). Keywords : bottom gillnet, composition, kulu village

Economic Conditions for New Entrants in Coastal Fishing in Miyazaki Prefecture, Japan

A significant decrease in the number of fishery workers is be-coming a problem in Japan. For new entrants to become estab-lished in the region, they must be profitable as fishing busi-nesses. Using the case of Miyazaki prefecture in Japan, this paper identifies the economic conditions required to make longline fishing and bottom gillnet fishing profitable by ap-plying the net present value (NPV) method. When operating on 200 days, which is the guideline for new entrants in longline fishing, if the value of investment is less than 44.1% of the minimum required, the investment will not provide positive returns. However, the study also finds that new entrants using both longline and bottom gillnet fishing can easily generate the revenue required to cover investments and can, therefore, be profitable. For 226 operating days, which is the guideline for new entrants in longline and bottom gillnet fishing, investment will offer positive returns when it exceeds ¥ 5.698 million. Moreover, increasing the number of operating days by 13.3% to 256 raises the return on investment by 14.0%. Therefore, the value of investment is proportional to an increase in operating days. If the price of half-smooth golden pufferfish, the main catch in longline fishing, increases by 5% to ¥ 624.1 per kilo-gram, the number of operating days can be reduced by up to 8.9%. If local initiatives raise the value of half-smooth golden pufferfish, new entrants can significantly reduce their number of operating days, thereby promoting fisheries management and reducing their labor burden.

Gillnet fisheries around Polaku and Koroama communities in the lower Taylor creek, Bayelsa state, Nigeria

The study examined Gillnet Fisheries around Polaku and Koroama Communities in the Lower Taylor Creek, Bayelsa State, Nigeria. The instrument of the study was a structured questionnaire. A total of 100 gillnet fishers were randomly selected from the study area. Fishes caught were identified to species level using a field identification guide. Data collected were analyzed using simple percentages, frequency count and Mean (X). The results show a dominance of males (95.0%) over females (5.0%) in gillnet fisheries in the study area. Majority (43.0%) of fishers fell within the agile and economically active age brackets of 30-39 years. More than half (62.0%) of the fishers are married, 25.0% are single, 6.0% are divorced and 7.0% are widowed. The majority of fishers (44.0%) had primary education, while none had tertiary education. Eighty percent of fishers are from Polaku and 20.0% from Koroama. Thirty-nine percent of fishers use bottom gillnets, 35.0% drift gillnets and 26.0% surface gillnets in the study area. The mesh size of nets ranged from 2” to 5”. Species from the family Alestidae was the most abundant (15.7%) and the family Notopteridae was the least abundant (0.8%). Between 10 to 20 hours are spent by the fishers in fishing and the daily catch quantity ranges between 20 to 40 kg. Generated weekly income ranged below N35, 000 to N63, 000. The challenges encountered by the fishers include lack of storage facilities and destruction of fishing gears by maritime vessels operating in the area. It was thus recommended that government should provide storage facilities and regulate maritime vessel operation in the area.