Gillnet Selectivity Research Articles

Gillnet Selectivity for the Coromandel Flying Fish, Hirundichthys coromandelensis (Hornell, 1923), along the Nagapattinam Coast, Southeast Coast of India

Gillnet Selectivity for the Coromandel Flying Fish, Hirundichthys coromandelensis (Hornell, 1923), along the Nagapattinam Coast, Southeast Coast of India

Selectivity of gillnets for the capture of Selene peruviana and Peprilus medius in the Ecuadorian Pacific

In the Ecuadorian Pacific, Selene peruviana and Peprilus medius are target species for artisanal fishing caught with gillnets that constitute an important fishery resource for local consumption, given that they are highly valued species due to their low cost and their contribution of high biological value protein. However, no studies have determined selectivity in capturing these species. This study evaluates the selectivity of monofilament surface gillnets with mesh sizes of 3" (7.62 cm) and 3 ½" (8.89 cm), mostly used by artisanal fishers. Data were obtained from several fishing operations within the coastal zone of 8 nautical miles (nm) in Manabí, Ecuador, in 2017, between 6:00 pm and 6:00 am. Selectivity parameters and curves were evaluated through multi-model analysis using the SELEC method. The lognormal model showed the best fit with modal lengths of 24.23 and 21.96 cm for S. peruviana and P. medius, respectively, and selection factors of 3.23 and 3.11. The optimal mesh sizes were calculated at 7.20 and 6.91 cm, respectively, which are smaller than those commonly used by most local artisanal fishers. Therefore, it can be inferred that the size distribution of the captured species follows a lognormal distribution, suggesting that gillnets have a higher probability of capturing larger fish.

Catch Composition and Selectivity Drift Gillnet in Pambang Pesisir Village Bantan Subdistrict Bengkalis Regency

Gill nets are placed perpendicular to the water to block the swimming direction of the fish. Fish are caught by being entangled in the meshes or entangled (spun) in the body of the net. This research was conducted in Pambang Pesisir Village, Bantan District, Bengkalis Regency, to know the composition of the catch and the selectivity of drift gill nets, comparing the composition of the number, type, weight, and size of the catch from different mesh sizes, and knowing how to catch fish (entangled, gilled, snagged, wedged) on the same mesh used. This research was carried out in December 2020 using the experimental fishing method, which is a research method that uses samples of research objects caught on fishing gear for observation. The research results of drift gill nets are species-selective fishing gear. Moreover, drift gill nets with a mesh size of 7.62 cm are more selective than nets of 5.72 cm because they have a catch ratio value closer to 1 and catch more large fish (worth catching). How to catch fish with a mesh size of 5.72 cm, many fish were caught by snagged; namely, 65 fish (30%), wedged 61 fish (28%), gilled 59 fish (27%), and 33 fish entangled (15%). Meanwhile, for the mesh size of 7.62 cm, 30 fish (31%) were caught wedged, 27 fish (29%) snagged, 27 fish (29%) gilled, and ten fish entangled (11%).

A Machine Learning Technique for Deriving the Optimal Mesh Size of a Gizzard Shad (Konosirus punctatus) Gillnet

Gizzard shads are facing a continual decline in population, necessitating the implementation of selective gear design for effective resource management. This study aims to prevent the bycatch of young gizzard shads, a non-target fish species, and to derive mesh sizes appropriate for fishery management. Experimental fishing (n = 11) was conducted by manufacturing gillnet fishing gear with different mesh sizes (50.5, 55.1, 60.6, and 67.3 mm) in the coastal waters of the southern Gyeongsang Province. Two methods were employed to estimate the appropriate mesh size of the shad gillnet as follows: firstly, by analyzing the selectivity curve based on body length data; secondly, by developing a complex machine learning model considering biological and economic factors. Model 1 was constructed using mesh variables to classify the score groups. As a result of this study, the total length with a 0.5 gillnet selection ratio. which was estimated to be 179.3, 195.6, 215.1, and 238.9 mm for the 50.5, 55.1, 60.6, and 67.3 mm mesh sizes, respectively. In Model 1, a mesh size of 57.85 mm or less was determined as the most appropriate mesh size. Therefore, considering both biological and economic aspects, shad gillnets should have a mesh size in the 50.5 to 55.1 mm range.

Selectivity of gillnets on the main fish species caught in the floodplains of the Madeira River (Rondônia, Brazil)

Small-scale fishing in the floodplains of the Amazon basin has intensified, with gillnets being one of the main types of tackle used. In this study, we evaluated the length structure of fish species in a floodplain lake of the Madeira River basin, emphasizing the selectivity of the nets in the main species caught. The fisheries were collected in periods of high water and low water, with nets of mesh sizes of 40, 60, 80, 100, 120 and 160 mm. Tests between the periods and also comparing the meshes were performed and the parameters of the selectivity curves estimated with the SELECT calculation code. Records of 17 new maximum lengths are presented. Of the 12 most abundant species, the selectivity of the nets in the modal lengths for Anchovia surinamensis were 13.3, 19.9, 26.6 and 33.2 cm in the nets with mesh sizes of 40, 60, 80 and 100 mm, respectively. In the three smallest mesh sizes, the values for Potamorhina altamazonica were 12.7, 19.0 and 25.3 cm and for Pellona flavipinnis values were 15.4, 23.2 and 30.9 cm. In the two smallest mesh sizes, the following values were presented for the species Potamorhina latior (12.9 and 19.4 cm), Potamorhina rutiloides (11.3 and 16.9 cm), Triportheus elongatus (19.7 and 29.5 cm), Triportheus flavus (14.1 and 21.1 cm) and Pimelodus blochii (15.5 and 23.0 cm). The estimates of selectivity of the nets, in addition to being basic information for fishery sciences, are also fundamental for the management of Amazonian fish stocks.

Investigating the Mesh Size Selectivity of Olive Flounder (Paralichthys olivaceus) Gillnets for Fisheries Resource Management in the East Sea

This study aimed to evaluate the mesh selectivity of gillnets used in olive flounder (Paralichthys olivaceus) fishing by examining the distribution of total length (TL) across various mesh sizes. A marine fishing experiment was conducted at Gajin Harbor in Goseong County, Gangwon Province, employing experimental gear with four different mesh sizes: 90, 105, 135, and 150 mm. Mesh selectivity analysis involved a comparative assessment of selectivity curve methods through normal, log-normal, and bi-normal functions. Among these, the bi-normal function demonstrated the best fit for estimating the mesh selectivity curve within the SELECT model. The critical finding was the net size at which 50% of the minimum landing size (35 cm in TL) of olive flounder was selected, ranging from 108.7 to 121.1 mm. According to the bi-normal function curve, this size was estimated as 114.0 mm. Our findings indicate that using a mesh size larger than the theoretically estimated size in mesh selectivity analysis can further decrease the catch of immature individuals. These findings provide essential data for devising strategies to efficiently utilize and manage olive flounder resources.

Evaluation of the influence of correcting for gillnet selectivity on the estimation of population parameters.

Gill nets are a common sampling technique in inland and marine fisheries. However, gill nets are size selective and may result in bias estimates of population parameters. As such, selectivity is commonly assessed using indirect estimation techniques. Indirect estimates of gillnet selectivity have been suggested to improve estimates of important populations metrics (e.g., total annual mortality), but this assertion has not been assessed. In the current study, we simulated hypothetical populations of channel catfish Ictalurus punctatus, lake trout Salvelinus namaycush, walleye Sander vitreus, and white crappie Pomoxis annularis and sampled the populations based on published gillnet encounter and retention probabilities. Total annual mortality and von Bertalanffy parameters were then estimated using unadjusted (not "correcting" for selectivity processes) and adjusted ("correcting" for selectivity processes) age and(or) length data to evaluate the value of accounting for gillnet selectivity when estimating these metrics. Our results indicate that adjusting for retention and encounter probabilities rarely leads to improved estimates of total annual mortality, K, and L∞. For instance, estimates of annual mortality of lake trout based on age data adjusted for retention probability resulted in an overestimate of A by 14.4%. As such, we suggest that analysis of gillnet selectivity only be used when specific questions are being addressed (e.g., catch-at-age models) or in situation when all processes contributing to gillnet selectivity (e.g., contact probability, size-specific availability) are known.

Van Gölü İnci Kefali (Alburnus tarichi (Güldenstädt,1814)) avcılığında kullanılan farklı ağ göz açıklığına sahip monofilament sade uzatma ağlarının seçiciliği

This study was carried out between September 2020 and March 2021 to determine the selectivity of monofilament gillnets used in pearl mullet, Alburnus tarichi (Güldenstädt, 1814), fishing in Lake Van. The SELECT method was applied to determine the selectivity. The best model for the selectivity of monofilament gillnets used in pearl mullet fishing was determined as the log-normal model. The optimum catch lengths of monofilament gillnets with 20, 22 and 24 mm mesh sizes were calculated as 21.69 cm, 23.84 cm and 26.01 cm, respectively. Catch per unit effort was determined as 10.03 kg/90 m/day at 20 mm, 15.91 kg/90 m/day at 22 mm and 12.99 kg/90 m/day at 24 mm. The average catch per unit effort was determined as 151 unit/90 m/day at 20 mm, 151 unit/90 m/day at 22 mm, and 110 unit/90 m/day at 24 mm. According to the results of optimum catch length and daily average catch per unit effort, using monofilament gillnets with 22 mm mesh size was more convenient for sustainable pearl mullet fishing in Lake Van.

Simulating Mesh-size and Selection Pattern Impacts on the Lake Turkana Fisheries Sustainability in Kenya

The study compared impacts of different gear mesh sizes and landing sizes (Lcap) through gillnet and knife-edge selection patterns on Tilapia and Nile perch of Lake Turkana. The results will help contribute to the debate on whether to capture large and protect small fish or vice versa. R simulation employing the 1934 Thompson and Bell's model for data-deficient stocks was used to simulate fish cohorts using secondary input data for the two species. Gillnet selection pattern with recommended mesh size (127 mm) produced an 80% increase in Tilapia YPR while ESS and SPR ratios reduced by 12.5%. and 14.3% respectively when fishing mortality (F) was tripled to 3.0. Nile perch's YPR increased by 90% while ESS and SPR dropped by 70 and 75% each when F increased to 0.8. Tilapia YPR maximized by reducing mesh size to 101.6 mm at F=2, and maintained ESS and SPR at 20% each, while the Nile perch YPR dropped by 20% and 66.7% respectively at F=1.0. Small mesh-sized (<40 mm) gears had no effect on Tilapia’s ESS and SPR but produced the lowest YPR ratios. The 152.4 mm mesh for Nile perch produced a 25% YPR increase and maintained optimal ESS and SPR at F=0.5. Knife-edge selection pattern utilizing 127 mm, 20 cm Lcap and F=1.5, produced 50% YPR, ESS, and SPR for Tilapia, and maintained at F=3.0. Large-sized Nile perch using 152.4 mm gear resulted in about 40% YPR of the stock. Reduction of Lcap using 127 mm gear, produced a 75% increase in YPR. ESS and SPR depicted Nile perch collapse at F>0.65. Mesh size and selection pattern impacts are dependent on F. Small mesh gillnets are not damaging if F is controlled and caution should be taken with them in a knife-edge selection. This study recommends 101.6 mm and 152.4 mm mesh sizes for Tilapia and Nile perch respectively in Lake Turkana

Gillnet Selectivity Estimating for Sustainable Stock Management of Endemik Tarek (Alburnus tarichi Güldenstädt, 1814) Population in Lake Van (Eastern, Turkey)

This study was carried out to estimate the selectivity properties of gillnets for Tarek (Alburnus tarichi Güldenstädt, 1814) in Lake Van, Turkey. The Tarek is the most fished freshwater fish species in Turkey. The study was carried in 2021 fishing season at seven different sampling locations in the lake. Gillnet selectivity estimated was based on eight different gillnet mesh sizes (i.e. 1.25, 1.6, 2.0, 2.5, 3.1, 3.9, 4.4, 4.8 cm). The SELECT method was used to determine the selectivity parameters. According to the gamma model, optimum modal lengths for 1.25, 1.6, 2.0, 2.5, 3.1, 3.9, 4.4 and 4.8 cm mesh sizes were estimated as 6.61, 8.46, 10.58, 13.22, 16.39, 20.62, 23.27 and 25.38 cm respectively. When considering the minimum landing size, the findings of the study showed that use of gillnets which have less than 3.9 cm mesh size should be prohibited for the fishing of A. tarichi in Lake Van.

Quantification of catch composition in fisheries: A methodology and its application to compare biodegradable and nylon gillnets

When evaluating fishing gear catches, the focus is often on a few species as opposed to the entire catch. In some fisheries this can lead to ignoring major part of catch composition. Thus, there is a need for a more holistic approach when evaluating the ecological impact of using a specific fishing gear and when comparing two or more gears. In this context, it is relevant to have a method that describes the total catch and quantifies proportions of the catch being wanted and unwanted. In this study, we outline such a method and demonstrate its applicability to catch data from a small-scale coastal gillnet fishery targeting European plaice (Pleuronectes platessa, Linnaeus, 1758) by comparing catch composition when using nylon and biodegradable gillnets. The results showed no significant differences in catch composition between gillnets made of the two materials. Therefore, the catch composition obtained using the more environmentally friendly biodegradable materials does not represent a barrier in this specific gillnet fishery. However, species selectivity of gillnets is still of concern as the primary target species constituted only half of the total catch composition in numbers while the rest was unwanted catch. The presented approach for quantifying and inferring the differences in catch composition can be further applied for assessing the performance of different fishing gears and their modifications.

Population Characteristics of Brook Trout in Idaho Streams and Alpine Lakes

In western North America, nonnative brook trout (Salvelinus fontinalis) frequently threaten native salmonids via competition and hybridization, so fisheries managers often implement eradication programs for conservation purposes. In conjunction with such programs, managers often construct population models to evaluate the effects of different management strategies designed to control the undesirable population, but such models require demographic data (e.g., age, growth, sex ratios, and survival), which are lacking for western brook trout populations. Brook trout were sampled from 12 alpine lakes and two streams in Idaho, with total length varying from 80 to 380 mm and age varying from 1 to 11 yrs. Across all waters, the von Bertalanffy growth parameters L∞ varied from 231 to 490 mm (mean = 345 mm) and K varied from 0.15 to 0.76 (mean = 0.37). Survival estimates, constructed from age-length keys, were corrected for streams with mark-recapture data; for alpine lakes, corrections were made via gill net selectivity data. Survival varied from 0.30 to 0.56 (mean = 0.45), and except for one waterbody, estimates were minimally affected by correcting for capture efficiency. The proportion of the population that was male varied from 0.34 to 0.75 (mean = 0.53). Our results indicate that brook trout population vital rates in Idaho were similar to those observed in their native range, and were surprisingly similar between alpine lake and stream environments.

Gill Net Selectivity for Fifteen Fish Species of the Upper San Francisco Estuary

Gill-net size selectivity for fifteen fish species occurring in the upper San Francisco Estuary was estimated from a data set compiled from multiple studies which together contained 7,096 individual fish observations from 882 gill net sets. The gill nets considered in this study closely resembled the American Fisheries Society’s recommended standardized experimental gill nets for sampling inland waters. Relationships between gill-net mesh sizes and the sizes for each fish species retained in them were estimated indirectly using generalized linear modeling and maximum likelihood. Selectivity curves are provided for each species to inform researchers about population characteristics of fishes sampled with similar gill nets.

Gillnet selectivity for non‐targeted shark species in temperate Australia

AbstractThe use of size‐selective fishing gear has been fundamental for the successful management of shark populations. For the main Australian shark fisheries, available data sets on gillnet selectivity experiments conducted since the 1990s were used to estimate gillnet selectivity parameters for nine commonly caught non‐target species: broadnose, draughtboard, Port Jackson and school sharks, common and southern sawsharks, smooth hammerhead and spikey and whitespotted dogfish. Size at selection increased with mesh size, but it varied with species, with some species having broader selectivity curves due to their particular morphological features. In particular, smooth hammerhead had much broader selectivity curves and larger length at maximum selection than other species of comparable size such as the broadnose shark. The selectivity curves derived in this study will allow a more accurate interpretation of catch size composition and model‐based assessments of stock status of these species

Gillnet Selectivity for Three Freshwater Alien Invasive Fish Species in a Long-Term Monitoring Scenario

Gillnet selectivity is poorly understood for most freshwater fish species, particularly for invasive alien species. However, their use to determine mesh selectivity could be essential for establishing management measures, such as the selective removal of exotic invasive species. This study aims to the assess size selectivity of exotic invasive species in a restored lentic freshwater ecosystem. Therefore, we analysed gillnet size selectivity based on experimental fishing trials performed by using multimesh gillnets. Twice a year, for 8 years, multimesh nylon gillnets were set up in the Estany d’Ivars i Vila-sana, a restored shallow lake in Catalonia (NE Iberian Peninsula). We caught 4105 individuals belonging to three widely distributed freshwater fish species—3583 pikeperches (Sander lucioperca (Linnaeus, 1758)), 115 common roaches (Rutilus rutilus (Linnaeus, 1758)) and 407 common carps (Cyprinus carpio, Linnaeus, 1758). The SELECT method was applied to fit six different gillnet selectivity uni- and bimodal models. As a result, bi-lognormal provides the best fit for the three species. This is in line with previous studies that found size–frequency data skewed to the right or to multimodal models when high numbers of fish are captured. These results provide the essential information required for fish community management with the presence of these invasive alien species.

Gillnet Selectivity on the Narrow-barred Spanish Mackerel (Scomberomorus commerson) Fishery in Pangandaran Waters

Analyzing the selectivity of gillnet fishing gear using two different mesh sizes, namely 3.5 and 4 inches. Gillnets of these mesh sizes are commonly used by fishermen in Fish Landing Base (PPI) Cikidang, Pangandaran Regency, West Jawa. A total of 8 fishing trips were conducted at the coastal waters around PPI Cikidang, Pangandaran Regency, West Java from August 2018 to January 2019 using gillnet fishing gear As for each trip, 2-3 times the operation of the tool is carried out. The operation of the fishing gear is carried out with the help of vessels measuring 2-3 Gross Tonnage (GT). The catch obtained was differentiated based on the main catch and bycatch and the amount is calculated for analysis of the proportion of the catch. Mackerel (Scomberomorus commerson) is caught as the main catch, the fork length was measured for analysis of the length frequency distribution and selectivity curves. The operation of gillnets with a mesh size of 3.5 inches obtained a higher proportion of bycatch compared to gillnets with a mesh size of 4 inches. In addition, the length distribution of mackerel caught by gillnets with a mesh size of 3,5 inches is smaller (27-49 cm FL) compared to a mesh size of 4 inches (40-55 cm FL). Based on the distribution of length distribution, gillnets with a mesh size of 3.5 inches are more dominant in catching mackerel in a smaller size class interval than gillnets with a mesh size of 4 inches. Meanwhile, based on the selectivity curve for the length of mackerel with a 50% chance of being caught, it shows that gillnets with a mesh size of 3.5 or 4 inches are selective in catching mackerel, this is because the chances of catching fish at more than L50 are high.

Catch composition of drift gillnets in a multi‐species fishery with an emphasis on kingfish (Scomberomorus commerson) in Northern Persian Gulf

Gillnets are the primary fishing gear used in tropical multi-species fisheries along the Iranian southern coastal waters. Therefore, it is necessary to investigate the catch composition and performance of fishing gear for the possible negative effects on the stocks. Catch data and length frequency distribution (just for Kingfish, S. commerson) were examined for three kinds of drift gillnets: 1) small-meshed nets, 2) medium-meshed nets, and 3) nets with a single mesh size of 165 mm. This study was conducted in the northern part of the Persian Gulf from 2014 to 2015. Overall, 60 species of 32 families from four fish groups (i.e., Pelagic, Demersal, Benthopelagic, and Reef-associated) were recorded. Each net-type was used to target more than one species, with most species being considered as bycatch. Commercial fish species were caught the most, accounting for around 83% of the total catches. S. commerson is targeted by all kinds of nets, with medium-meshed nets being most efficient. The majority of S. commerson caught by the nets were immature. Overall, the total ban of gillnets with small mesh sizes is recommended to protect young S. commerson and prevent the possible risk of growth overfishing. Studies on gillnet selectivity are needed to set minimum mesh regulations for S. commerson and other commercial species if the potential impacts of gillnet are known.

Utility of gillnets for selectively targeting penaeids off Iran

In response to concerns over the mortality of discards and other negative environmental impacts of otter trawling for penaeids, the utility of bottom-set gillnets deployed by artisanal vessels to target Penaeus monodon, Metapenaeus affinis and other retained species by-product was assessed in the Sea of Oman. Two gillnets (each comprising several 80-m panels for total lengths of up to 1.3 km) were diurnally fished at two locations (off Beris and Govater, eastern Iran) within established penaeid fishing grounds. During 30 days, the total catch was 2721 kg, comprising penaeids (981 kg), eight retained by-product species (598 kg and mostly Otolithes ruber, Cynoglossus bilinearus and Carangoides talamparoides) and 19 discarded species (1142 kg). The catch-per-unit-of-effort (CPUE, kg/gillnet-panel · hour-fished) of targeted penaeids and by-product varied significantly between areas (0.5–1.0 kg), but nevertheless reached economically viable levels. The CPUEs of total bycatch were similar at both sites (<0.5 kg) and no marine turtles were caught. The concomitant ratios of retained-catches-to-bycatch were considerably less than those for regional penaeid-trawl fisheries. Nevertheless, while gillnet selectivity was satisfactory for M. affinis, most of the P. monodon were smaller than their carapace length at maturity at both fished sites. The results support using gillnets to target penaeids and by-product species as an alternative to otter trawling in the Sea of Oman; albeit with ongoing assessments of modifications to maximise selectivity.

Long-term changes in body condition and gillnet selectivity in Lake Constance pelagic spawning whitefish (Coregonus wartmanni)

The body condition of Lake Constance pelagic spawning whitefish (Coregonus wartmanni) has changed substantially during the past century and altered the length-based selectivity of gillnets. Linked hierarchical models using Bayesian inference and error propagation were used to estimate the monthly body condition of whitefish from 1932 to 2018 and condition-dependent gillnet selectivity from 1964 to 2018. As expected, body condition followed past trends in nutrient dynamics and was highest in summer months. Body condition was clearly linked to gillnet selectivity, with a weight increase of a 300 mm whitefish from 205 to 260 g predicted to reduce the mean (from 374 to 330 mm) and standard deviation (from 30.8 to 25.1 mm) of lengths selected by a 38 mm mesh gillnet. Simulations demonstrate that such changes can reduce the mean age in harvest by over 1 year and greatly bias population age distribution estimates if selectivity changes are ignored. Similar variation in gillnet selectivity is expected where trophic conditions or other factors cause body condition differences, and accounting for these changes could reduce biases to inform fishery management.

Design Characteristics and Specifications of Gill Net Operated Along the Lower Stretches of Vembanad Wetlands, Kerala, India

Gill net (Locally called odakku vala) design variation, operational techniques, catch composition and selectivity analysis in Vembanad wetland, Kerala was examined between January 2020 to June 2021. Netting materials used for gill net construction in Vembanad Lake were monofilament, multifilament Nylon (polyamide). The Gill net length was 25-55 m with a hung depth of 2-3 m. Gill net was highly species specific and showed selectivity for shallow water species. Its durability ranged from 3.5 months to 2 years depending on the netting material and the environmental conditions where it is being operated. Gill net fishery is one of the main types of artisanal fishery practiced occupationally by the fishermen community of Kerala. The region so far is untouched with the introduction of mechanized fishing apart from small traditionalized improvements. The Gill net was used to catch the fishes of marketable size, small fingerlings which were either used as bait or dried. Instead of using lead or aluminium needles as sinkers many of them were used to carry normal electric wire without copper string inside which reduce their cost of purchase.