Size Selectivity Of Gill Nets Research Articles

Gillnet size selectivity of shark and ray species from Queensland, Australia

AbstractGillnets are size‐selective fishing gears commonly used by industrial and small‐scale fishers, so understanding selectivity can aid fisheries management by identifying suitable mesh sizes to optimize catches of target species while reducing bycatch. Few size selectivity parameters have been estimated for sharks, with even fewer for rays. Size selection parameters were estimated for seven species of sharks and two species of rays from the Queensland East Coast Inshore Finfish Fishery (ECIFF). Size frequency data from a fishery observer program on ECIFF vessels was used to fit a standard size selection model. Mesh size independent parameters, θ1 and θ2, were estimated for each species to define selectivity curves for different mesh sizes for each species. Parameter values were compared with previous studies that used the same method. Estimates of θ1 were similar among species within the same genus, such as Carcharhinus, Rhizoprionodon, and Sphyrna. Anoxypristis cuspidata had the largest θ1 and θ2 values, likely because of its toothed rostrum that affected catchability in gillnets. Our findings can be used for the ECIFF and other gillnet fisheries to aid in mesh size recommendations and risk mitigation.

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 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.

Density and temperature dependent growth of pikeperch (Sander lucioperca) in the Archipelago Sea

In the Archipelago Sea, pikeperch (Sander lucioperca) is an important species in both commercial and recreational fisheries. Pikeperch is caught mainly with small mesh size gillnets, and annual fishing mortality is high. The possible effects of such fisheries, as well as temperature or density on pikeperch growth have not been studied earlier. The first hypothesis of this study was that the effect of temperature on growth is positive and that of density is negative. The second hypothesis was that size-selectivity of gillnets causes the fast-growing individuals to be caught at younger ages than the slow-growing ones. The results showed that temperature had a significant positive effect on growth, and this was greater than the negative effect of year-class density, which was also significant. The gillnet selectivity caused a difference of up to 60 mm in back-calculated lengths in the fully recruited age groups within the same year class, between pikeperch caught at age 6+ and age 9+. Thus, the Rosa Lee phenomenon caused by gillnet size-selectivity led to the removal of faster growing specimens from the population at younger ages. This can potentially cause underestimation of real growth, and thus, poor fishery management.

Selectivity parameters of European hake gillnets for target and by-catch species with a perspective on small-scale fisheries management in the Sea of Marmara, Turkey

This study aims to describe the selectivity features of European hake gillnet for Merluccius merluccius (European hake, target species) and Solea solea (common sole, by-catch species) in the southern Sea of Marmara in terms of small-scale fisheries. For this purpose, the size selectivity of gillnets for European hake and the common sole was studied in the Sea of Marmara. Experimental fishing operations were carried out by using gillnets with a mesh size of 28, 30 and 32 mm. A total of 523 specimens of European hake and 418 specimens of common sole were caught. Total lengths ranging from 23.5 to 41 cm were recorded for European hake and from 18.5 to 35.5 cm for the common sole. The experimental data estimated by applying the SELECT method showed that the bi-modal and log normal models gave the best fit for European hake and the common sole selectivity, respectively. Estimated modal lengths were found to be 30.61; 32.80; 34.99 cm for European hake and 19.94; 21.37; 22.79 cm for common sole for each mesh size studied. The present study is the first report on the selectivity of these species using the SELECT method for European hake gillnets in Turkey. The results obtained from the present study show 30 mm mesh size which is used currently by fishermen is highly selective and very suitable for sustainable fisheries both European hake and common sole. These findings will help to improve the management and conservation of small-scale fishery, especially, in this region.

Fish species composition and size structure exploited by gill net fishery in The New Calabar River, Nigeria

The purpose of this study was to investigate the species composition and size selectivity of gillnets commonly used by the artisanal fishers in the New Calabar River, Rivers State, Nigeria. The data was collected during February-July 2018 from 3 sampling stations: SI Choba, S2 Ogbogoro, and S3 Iwofe all along the stretch of the river. Twenty-eight fish species were found belonging to 15 families. The prevalent families were Cichlidae, Mugilidae and Clupeidae representing 32.22%, 30.36% and 10.23% of the total catch, respectively. The most dominant species in terms of number were Liza falcipinnis (12.58%) and Mugil cephalous (12.26%) while in terms of biomass, the most abundance species were Xenomystus nigri (24.12%) and Lutjanus agennes (12.50 %). The girth and total lengths of the fishes ranged from 5.20±0.20 to 21.00±0.00 cm and 8.85±0.15 to 28.19±1.13 cm respectively. The length at first capture (L50%) for the most abundant species (Liza falcipinnis) was calculated to be 14.13 cm while that of L25% and L75% were 12.70cm and 15.25cm respectively. It was concluded that the gill nets used in the New Calabar River exploit fish species of small sizes and few medium sized specimens relative to species potential maximum size. It is therefore recommended that for an improved and sustainable exploitation fish stock of the New Calabar River, the use of gillnets of less than 25 mm-mesh sizes and “other gears” should be prohibited.Keywords: gill nets; species composition; mesh size; selectivity; New Calabar River

Size Selectivity of Sampling Gears Used to Sample Kokanee

AbstractKokanee Oncorhynchus nerka provide valued recreational fisheries and also serve as a prey resource for economically, socially, and ecologically important fishes. As such, management of kokanee is a major focus of natural resource agencies. Kokanee are typically monitored using midwater trawls, but the interpretation of data collected using midwater trawls is difficult due to the unknown size selectivity of the gear. We sought to assess the length selectivity of midwater trawls by comparing estimates obtained from midwater trawls with estimates obtained from gill nets adjusted for size selectivity. Experimental curtain gill nets and midwater trawls were used in conjunction to sample kokanee in seven lentic systems in Idaho. The size selectivity of gill nets was estimated by accounting for the probability of encounter and the probability of retention. Estimates of size selectivity were then used to adjust the length distribution of fish sampled in gill nets. The adjusted length distribution of fish sampled in gill nets was compared with estimates obtained from midwater trawls to identify potential size selectivity of midwater trawls. A pattern of size selectivity was apparent for both sampling techniques. The average length of kokanee sampled with midwater trawls was 111 mm; whereas, kokanee sampled with gill nets had a mean length of 235 mm. Our results suggest experimental gill nets are useful for common sampling of kokanee (e.g., trend monitoring) because the gear is less size selective than midwater trawls and is adjustable for size selectivity. However, midwater trawls are likely the best gear for addressing questions associated with early life history. Overall, our results provide a better understanding of gill‐net and midwater trawl selectivity and ultimately improve the ability to sample and manage the species.

Natural resource modelling: accounting for gillnet size selectivity in dynamic deterrence model

Natural resource modelling: accounting for gillnet size selectivity in dynamic deterrence model

Estimating the Size Selectivity of Trap Nets using a Gill‐Net Selectivity Experiment: Method Development and Application to Lake Whitefish in Lake Huron

AbstractFisheries management requires information about the size selectivity of the fishing gears, but often the experimental data to estimate size selectivity are absent. We developed a two‐stage method to use data from an experimental survey for one type of gear (gill nets) to estimate the size selectivity of another type of gear (trap nets) based on the commercial catch data from both gear types, and we applied this method to Lake Whitefish Coregonus clupeaformis in Lake Huron. In stage I, an information‐theoretic approach (Akaike's information criterion) was used to select among five candidate models for the size selectivity of experimental gill nets. A double logistic function (a dome‐shaped curve skewed to the right) was chosen as the best model to describe the size selectivity of gill nets targeting Lake Whitefish. In stage II, we estimated the size selectivity of trap nets by applying the model of size selectivity from experimental gill nets to commercial catch data from trap‐net and gill‐net fisheries operating in a similar region and temporal period. Trap‐net selectivity was fitted by using a symmetric logistic equation. This two‐stage method predicted that 513‐mm FL Lake Whitefish are fully selected by gill nets with a mesh size of 114 mm, whereas ≥615‐mm FL fish are fully selected by commercial trap nets.Received April 12, 2017; accepted September 8, 2017 Published online November 9, 2017

Seasonal variability of gillnet selectivity in Chilean hakeMerluccius gayi gayi(Guichenot, 1848)

This study examines the seasonal variability in gillnet size selectivity for the main Chilean hake (Merluccius gayi gayi) fishery off the coast of central Chile. Selectivity estimates were based on five gillnet mesh sizes (50, 60, 70, 80, 90 mm) in four traditional fishing areas, and during periods of low and high reproductive activity. Average fish length caught in the earlier period (low reproductive activity) was 30.8 cm LT (±4.17), and significantly longer (p < .05) at 35.9 cm TL (±6.15) in the latter period (high reproductive activity). For males, the selectivity factor was similar in both periods, thus the estimated modal lengths did not differ seasonally (p > .05). For females, however, both the selectivity factor and the estimated modal lengths changed significantly depending on the time of year (p < .05). A significant increment was estimated in the girth/perimeter ratio and condition factor during the period of higher reproductive activity. This change in the fish girth of females during spawning helps explain the significant reduction in their selectivity factor estimates in August–October.

Size selectivity of gill-nets and growth of roachRutilus rutilus(Linnaeus, 1758) an alien species in Piediluco lake (Italy)

The analysis of catch selectivity of fishing equipment is a crucial step for the management of alien species in freshwater ecosystems. Roach Rutilus rutilus was introduced in many waterways in Italy often becoming the dominant species of the fish community and it is now considered potential pest. In Piediluco lake the species was first found in 2004 and its abundance has increased at a level that creates concern for the other fish species present in the lake. The growth of R. rutilus and the selectivity of gill-nets on its population were examined in Piediluco lake by analysing the selectivity of gill-nets of different mesh size. Sampling was conducted from January 2011 to October 2012 by means of gill-nets of different-sized mesh (8, 10, 12.5, 15.5, 19.5, 24, 28, 35, 45 and 55 mm). The results showed that R. rutilus in Piediluco lake had a growth faster and higher than in many other lake environments. The results of gill-nets selectivity gave important information to design a plan to control this species and confirmed that the use of suitable fishing techniques could be useful to manage the population of this alien species in Piediluco lake as well as in other similar environments.

Relationship between opercular girth, maximum girth and total length of fishes caught in gillnets in the estuarine and lower river sections of Shatt al-Arab River (Basrah Province, Iraq)

Summary In fisheries, the two morphological parameters of opercular and maximum girth are related to the effectivity of capture methods in gilled and wedged fish, respectively. The present work investigates the relationship between opercular (Gope) and maximum girths (Gmax) to total length (Lt) for 10 fish species captured from Shatt al-Arab River, Basrah, Iraq. Data were collected October 2005 to December 2006. Cyprinids were the best represented family with six species; engraulids, silurids, heteropneustids and mugilids were each represented by one species. Gope and Gmax were found to increase linearly with total length of all species, all r2 values being greater than 0.73 and statistically significant (P < 0.01). When Gope and Gmax for all species were plotted against total length, two groups were identified (G1, G2), corresponding to general girth-length relationships: (a) G1 = −0.252 + 0.424 Lt and G2 = −0.262 + 0.600 Lt for opercular girth and, (b) G1 = 1.538 + 0.419 Lt and G2 = 1.538 + 0.696 Lt for maximum girth. These groups correspond to different body shapes of fishes: G1-round and G2-compressed. These relationships have implications when using length data and mesh size to determine size selectivity of gill nets.

강원 영안 겨울 도루묵(Arctoscopus japonicus) 수컷의 자망에 대한 어획선택성

We describe a catch experiment and the size selectivity of gill nets for male Japanese sandfish (Arctoscopus japonicus) caught near Gosung, Korea. The experiment, which was conducted between October and December 2007, examined six different mesh sizes: 36.4, 39.4, 45.5, 51.5, 53.0, and 57.6 mm. The catch was mostly Japanese sandfish (91.3%) and some others (8.7%). More male Japanese sandfish were caught with smaller mesh sizes and more females with larger mesh sizes. Relationships between the weight and fork length of the male and female Japanese sandfish were obtained. The relationship between the catch (Y) and mesh size of the gill net (X) was <TEX>$Y=0.1773X^3-5.3753X^2+40.042X+26.846$</TEX> (<TEX>$R^2=0.99$</TEX>). The selection curve for male Japanese sandfish caught in the experiment was fit, via Kitahara's method, to a polynomial equation, which was <TEX>$s(R={\exp}\{(-2.1391\;R^3+24.294\;R^2-88.289\;R+105.5)-5.180\}$</TEX>, where R=l/m, and l and m are the fork length and mesh size, respectively.

Effect of thin twine on gill net size-selectivity analyzed with the direct estimation method

: To analyze the effect of thin twine on gill net size selectivity, a series of fishing experiments using gill nets of two twine thicknesses (no. 0.8 of 0.16 mm diameter and no. 3 of 0.28 mm diameter) and three nominal mesh sizes (41 mm, 46 mm and 51 mm) was conducted in outdoor water tanks containing a rainbow trout (Oncorhynchus mykiss) population of known size frequency. For nets of the same nominal mesh size, mesh openings of the no. 0.8 twine nets were approximately 2 mm larger than those of the no. 3 twine nets. The effects of both mesh opening and twine thickness are combined in the conventional analysis with the selectivity curve against fish length. Selectivity against the ratio of fish girth to mesh perimeter was calculated to avoid the direct effect of changes in mesh openings due to twine diameter at the same nominal mesh size. Results demonstrated that the thinner twine gill net was more likely to capture rainbow trout of smaller girth than the mesh perimeter. Fish with girths smaller than the mesh perimeter were often retained by the net with its body tangled by the thinner twine, possibly due to the increased flexibility of the thinner twine.

Gill net selectivity for four fish species ( Mullus barbatus, Pagellus erythrinus, Pagellus acarne and Spicara flexuosa) in Greek waters

In the present study, the size selectivity of gill nets for Mullus barbatus, Pagellus erythrinus, Pagellus acarne and Spicara flexuosa was estimated from samples collected with nets of 17, 19, 21 and 23 mm mesh sizes (nominal bar length). Sampling was conducted at 15 stations in the South Euboikos Gulf (western Aegean Sea) in 1992 and 1993. The individual selection factors ranged from 6.15 to 9.01 and the optimum selection lengths increased from 10.7 to 14.4 cm fork length (FL) for P. erythrinus, from 11.0 to 14.9 cm FL for P. acarne, from 13.3 to 17.9 cm FL for M. barbatus, and from 13.0 to 17.6 cm FL for S. flexuosa for the 17 and 23 mm gill nets, respectively. Comparisons between the estimated optimum selection lengths and the minimum legal landing sizes and sizes at 50% maturation as well as comparisons between the length frequency distributions of the above mentioned species in gill net catches with those in trawl catches are also presented and discussed.

刺し網のサイズ選択性の計算法とその水槽実験による検証

A method to assess size-selectivity of gillnets on the basis of variation of fish body forms was considered. Size-selectivity of a gillnet was defined as the probability both if a girth at anterior (around operculum) section of fish does not exceed a mesh perimetre and if the girth at the maximum body section exceeds it. In the present method, the probability distribution at each section against fish lengths were calculated according to normal distributions of the girth approximated with its means and standard deviations linearly correlated with lengths. Size-selectivity was derived from multiplication of the respective probability distributions. A series of tank experiments were conducted to obtain cartch ratios by tested gillnets for various sizes of tilapia, carp and rainbow trout. Selectivity curves of the tested gillnets for the species were calculated on measurements of body forms of the tested fish individuals, which were compared to the catch ratios. Regarding the wedged capture, the calculated selectivity curves were well supported by the catch ratios. It was concluded that the present method assesses e%-selectivity lengths of gillnets with errors less than 4% for species and size ranges caught by mainly the wedging function of gillnets.

Indirect and Direct Estimates of Gill-Net Size Selectivity for Northern Pike

Size biases in gill-net sampling of populations of northern pike Esox lucius were described with indirect and direct estimates of gill-net selectivity. In deriving indirect estimates of selectivity, length distributions of northern pike retained in gill nets of five different mesh sizes were compared, and swimming performance relative to body length was used as a measure of the rate at which northern pike encounter gill nets. Selectivity was estimated directly by trapping and marking fish, and then recapturing the fish by gill netting. Indirect estimates showed that gill nets were most effective for retaining northern pike when fish length/mesh perimeter ratio was between 3.5 and 3.7. A generalized gamma function was used to model retention in the gill nets. The length structure of the northern pike population in a small lake was closely predicted when our indirect measure of selectivity was used to correct gill-net catches. Direct estimates of selectivity for all five meshes combined showed increasing selectivity with increasing fish length. Both direct and indirect methods projected increases in efficiency for catching northern pike up to 500 mm in total length. However, the indirect method tended to project higher efficiencies for catching small fish. Results from this study should be useful for interpreting northern pike catches in relation to size selection by gill nets.

Direct estimation of gill-net selectivity for roach ( Rutilus rutilus (L.)) in a small lake

Gill-net size selectivity for roach ( Rutilus rutilus (L.)) was estimated directly in a small eutrophic lake by fishing with littoral and pelagic gill nets. The number of roach in the population was estimated by a mark-recapture method. The estimated height of the selectivity curves increased with increasing mesh size, i.e. a pronounced size selectivity. In explaining the observed differences in catch efficiencies, the encounter probability may be less important than the probability of capture and retention. In assessment of length-frequency distribution of roach populations by gill-net sampling, the numbers of large roach will be considerably overestimated relative to small roach if the catch data are not corrected for size selectivity.

Gillnet selectivity to pikeperch, Stizostedion lucioperca (L.), and perch, Percafluviatilis L., caught mainly wedged

Abstract. The size selectivity of gillnets to pikeperch, Stizosiedion lucioperca (L.), and perch, Perca fluviatilis L., caught mainly wedged, was estimated by the selective use of the deterministic model of Holt (1963). The selectivity characteristics for pikeperch based on samples in gillnets with 48-65-mm bar mesh were: k= 0·903 and σ= 4·93cm (fork length). When a higher efficiency of large-meshed nets is accounted for, the estimated selectivity curve shifts to the right. The condition of the pikeperch had a major influence on the position and shape o(the selectivity curve. The selectivity to perch was established with 25–35-mm gillnets in a year with a poor food supply: k= 0·723 and σ= 2·59cm (fork length). Estimates based on literature data from an exploited perch population showed a much lower k= 0σ639 (total length) (σ= 2·69cm).