Experimental Gill Nets Research Articles

Evaluating Growth Rates of Two Newly Introduced Populations of Blue Catfish in Kansas

Blue Catfish Ictalurus furcatus have been introduced into many of Kansas reservoirs since 1972. They ranked sixth in terms of favorite fish to catch and target among licensed Kansas anglers in 2013 despite limited management. Blue Catfish were sampled and aged from two reservoirs located on the northern and western periphery of their current distribution.Fish were sampled using experimental gill nets, low frequency electrofishing, and float lines. Ages were assigned to a subset of captured fish by a panel of three independent readers examining a thin section cut from the articulating surface of a pectoral spine. Rapid growth was observed in Lovewell Reservoir with Blue Catfish reaching 659-mm by age 6. Growth of Blue Catfish was slower in Wilson Reservoir (552-mm by age 6) but comparable to other populations in the United States. Recruitment of stocked fish was variable but more consistent in Lovewell Reservoir. Year classes established by stockings that contained larger individuals at greater densities were more prevalent in both populations. These results demonstrate inconsistent recruitment patterns of Blue Catfish population development when stocked in large reservoirs.

Length‐weight relationships of 6 fish species caught in a Mediterranean lake (Trichonis‐NW Greece)

In the present study the length–weight relationships (LWRs) of 6 fish species which are endemic to Western Greece, caught in the natural Lake Trichonis by experimental gillnets and electrofishing were estimated. Benthic (mesh size 5–55 mm; height 1.5 m; length 30 m) and pelagic (mesh size 6.25–55 mm; height 6 m; length 27.5 m) Nordic type multimesh gillnets were used seasonally, between February 2019 and November 2019, at different depth zones (0-57m). Electrofishing (80 Hz) conducted in the littoral zone of the lake during four samplings (2018, 2019). All the estimated LWRs were highly significant (p < .05) with high correlation coefficient (r2 ≥ 0.962). The estimated b values ranged from 3.058 to 3.344. For five of the studied species (Trichonis spined loach (Cobitis trichonica Stephanidis 1974), Trichonis blenny (Salaria economidisi Kottelat 2004), Trichonis rudd (Scardinius acarnanicus Economidis 1991), Acheloos roach (Leucos panosi (Bogutskaya & Iliadou 2006)) , Hellenic minnowroach (Tropidophoxinellus hellenicus (Stephanidis 1971)) new maximum total body lengths (TL) were recorded, while for two species (T. hellenicus and L. panosi) LWRs are presented for the first time.

Fish community structure in Sermo Reservoir, Yogyakarta, Indonesia: Initial study on invasive fish species

Invasive species are becoming issues in freshwater ecosystems throughout the world including Indonesia. Sermo Reservoir is located in Yogyakarta, Centra Java, was indicated to have invasive species identified as Cichlidae family. The study aimed to assess fish communities’ structure and identified invasive fish in Sermo Reservoir. The research was conducted in Sermo Reservoirs, Yogyakarta, Indonesia on March-October 2019. In total, about 3,084 individuals of 10 fish species belonging to 3 families and 8 genera were captured using a experimental gillnets (mesh size 0.75; 1; 1.5; 2; 2.5; 3 inch) at five stations. The fish community in Sermo Reservoir was dominated by Cichlid fish (98.66%). Red devil (Amphilophus labiatus) and Midas cichlid (A. citrinellus) were dominant species founded in Sermo Reservoir (58.82% and 37.00%, respectively). Another species of cichlid that caught consist of nile tilapia (Oreochromis niloticus), mozambique tilapia (O. mossambicus), and jaguar cichlid (Parachromis managuensis). The study showed that Amphilophus spp. have high dispersal (One-way ANOSIM revealed Amphilophus spp. was not significantly different for spatio-temporal (p>0.05)). SIMPER analysis (p < 0.05) showed that A. citrinellus and A. labiatus had spread throughout the waters and were concentrated in Tegiri station which had more littoral zones.

Food habits, ecomorphological patterns and niche breadth of the squeaker, Synodontis schall (Pisces: Siluriformes: Mochokidae) from Niger River in Northern Benin

The squeaker, Synodontis schall dominates the Mochokid fish sub-community in Niger River in Northern Benin and shows a great economic and commercial importance. The diet of S. schall has been analysed to evaluate the food habit and resource utilization in this regional River. Fish samplings were made monthly from February 2015 to July 2016 using unbaited longlines and traps, seines and experimental gillnets. The results indicated that S. schall is an omnivore foraging in benthic and pelagic habitats with diet dominated by aquatic insects (34.32%), sand particles (18.768%), macrophytes (13.415%), seeds (8.549%), roots (8.319%), detritus (5.344%), mollusks (1.204%) and phytoplankton (0.6255%). The omnivore food habit depicted was also shown by the ecomorphological analysis mainly the relative gut length (GL/SL) varying between 0.8 and 5. The species showed high diet flexibility with high niche breadth ranging between 1.86 and 5.74. Synodontis schall exhibited an ontogenetic diet shift that was also confirmed by Pianka’s diet overlap indexes ranging between O jk =0.54-0.93. The conservation and the sustainable fisheries exploitation of S. schall require the reinforcement of fishing regulation, habitat protection and ecosystem follow-up.

Water quality and fish diversity of Federal University of Agriculture Abeokuta reservoir

Federal University of Agriculture reservoir is one of the recently constructed in Abeokuta, Ogun state, Nigeria, therefore the need to assess the water quality, fish diversity and catch assessment of this new water body. Data on fish species were collected on a forthnight basis using multi-stage gillnet sampling techniques for four months (September- December, 2011). Three sampling stations were randomly selected from the entire reservoir. A variety of sampling methods were used at each site in order to reach every fish species. At the river channel and the floodplain sites, traps, cast nets (2.55cm mesh), seine nets (2.55 x 2 cm mesh), monofilament nylon gillnets (15.55 cm mesh), and hook and line were employed. Efforts were made in order to catch fish species in large abundance. Some sampled fish (dead) were collected and placed in cool boxes and examined within 18 hours of capture. Others were preserved in 15% formalin and stored for later examination. A total of 863 fish specimens were caught during the study period. These were identified and classified into 5 species belonging to 3 families. The percentage species composition of the harvest by numbers and weight for all fish species that contributed more than 1% in all the stations combined, were computed. Study of the physico-chemical parameter such as dissolved oxygen ranged from 5.03 to 7.19mg/l; 26 to 280C temperature; 64.8 to 148ppm alkaline; pH 6.67-6.90; 32.5 to 53.5m transparent; 8.86 to 13.72mg/l nitrate; 0.58 to 0.64mg/l phosphate; 0.024 to 0.069 o/oo saline; 103-270cm deep. pH and water temperature serve as variables since the fluctuation of one affects the values of others. The water quality parameters were favourable for fish production. The gillnet fisheries indicated that different mesh sizes of experimental gillnets were sensitive to different fish species. 67.2mm, 78.4mm and 112mm, mesh sizes were efficient in catching Clarias gariepinus, Barbus occidentalis and the Cichlids respectively. The study has shown that middle water was the most suitable habitat for fish in the reservoir. Water level and temperature were observed to guarantee high fish yield in the reservoir.

Length-weight relationship and condition factor of endemic fish Bilih (Mystacoleucus padangensis Blkr.) in Lake Singkarak, West Sumatra, Indonesia

Bilih (Mystacoleucus padangensis) is an endemic species of Lake Singkarak and has important economic value. Overfishing of Bilih fish using non-selective fishing gear has led to a decline in its population. High demand, resulting in decreased production and size of Bilih fish. This research aims to determine this endemic fish's length-weight relationship and condition factor as basic data to the effort conservation. The fish was captured with experimental gillnet mesh sized 5/8, ¾, and 1 inch in Sumani, Batu Taba, Paninggahan, and PLTA intake stations. The total length and the weight of Bilih fish ranged from 40 – 95 mm and 10 – 74 mg, respectively. The highest length and weight of Bilih were 80.3 mm, and 45.0 mg were found at the Sumani station. The growth pattern of male and female fish was a negative allometric characteristic. The length-weight relationship of male and female fish was W = 0.00137 L2.368 and W = 0.00179 L2.312, respectively. Condition factors of males and females are 1.02 and 1.004, respectively. The result of condition factor value for males is higher than the female. The water quality values are within the normal range that supports fish life.

Ecosystem Integrity of the Upper Victoria Nile in East Africa based on Habitat and Fish Species Biotic Indices

Riverine ecosystems are continuously been compromised by human activities resulting in threatening their integrity. In this study, integrity of Upper Victoria Nile River was assessed using habitat quality and fish biotic indices. Experimental gillnetting was done bi-annually in 9 stations along the river from 2008 to 2018. Nine habitat metrics were used to estimate habitat quality index at every sampling station. Fish sampled, were sorted, identified to species level, and weighed. Counts of introduced and indigenous as well as tolerant and intolerant species were recorded to generate species richness. A total of 10.642 fish, 65 species belonging to nine families were recorded. Dominant species were Lates niloticus 62.79%, Oreochromis niloticus 23.51%, Mormyrus kannume 13.64%; other species were ≤0.06%. Tolerance and trophic guild showed carnivores (61.5%), omnivores (21.5%) and detrivores (16.9%).Mean habitat quality index, total fish catch and fish-based index of biotic integrity varied among stations with highest record of 26.6±6.9, 289.2±51.8 and 30.6±7.9 at sampling station (ST4) respectively. The lowest was 19.4±7.3, 93.1±13.2 and 26.7±6.8 at sampling station (ST2) respectively. On a spatial basis, indices recorded significant differences among stations (p &lt; 0.05). Results indicated a fair fisheries biodiversity that need better conservation management of habitat type of the upper Nile.

Some reproductive biology aspects of bonylip barb (Osteochilus vittatus Valenciennes, 1842) in the waters of Benanga Reservoir, East Kalimantan

Bonylip barb (Osteochilus vittatus Valenciennes, 1842) that belongs to the Cyprinidae family is one of the native freshwater fishes in Indonesian waters. Currently, status of this species in Benanga Reservoir, East Kalimantan is in over-exploited. Fish resources management, therefore, is needed to maintained fish stock in the reservoir based on fish reproductive biology aspects. The purpose of this study was to analyze some aspects of the reproductive biology including sex-ratio, gonad maturity, length at first gonad maturity, spawning season, fecundity, and spawning patterns as basic information for its management. Fish collection was carried out monthly on the third week from January to May 2019 at three stations. The fish samples were captured by using experimental gill nets with mesh size of 1; 1.5; 2; and 3 inches. A total of 278 bonylip barb was caught, consist of 92 males and 186 females. Sex ratio of male and female in the gonad mature stage was 1: 2.4. The average length at first gonad maturity in male and female were 136.08 mm and 137.38 mm, respectively. Peak of spawning occurs during the rainy season in May, with more than 90% of fish in mature stage with GSI in male and female were 6.88%, 13.16% respectively. Total fecundity ranged from 7312-22923 eggs individual-1 and egg diameter ranged from 0.6-1.94 mm. According to distribution of egg diameter, bonylip barb was categoried as a total spawner. Some management strategies that can be carried out are using fishing gears with mesh size above 2 inches, limiting fishing activities in the peak of the spawning season, prohibiting fishing gear using electric shocker and protection the reservoir from erosion.

Gillnets selectivity and effectivity for controlling invasive fish species in Lake Matano, South Sulawesi

Lake Matano is one of the ancient lakes in East Luwu Regency, South Sulawesi, which has uniqueness and high endemicity for freshwater fishes. The presence of invasive alien fishes there can threaten the existence of endemic fishes. This study aimed to investigate the selectivity and effectiveness of the use of gillnets on several mesh sizes for controlling the population of invasive alien fishes in Lake Matano, South Sulawesi. Sampling was conducted in May, October, November 2015 and February, July, November 2016 using monofilament experimental gillnets with various mesh sizes (0.75, 1.0, 1.5, 2.0, 2.5, 3.0 inches) and yarn thickness (D = 0.15, 0.20, 0.25 mm). The mesh size of 1.5, 2.0, and 2.5 inches could catch flowerhorn cichlid as the dominant and invasive alien fish with little chance to catch native fishes in Lake Matano. The selectivity factor (SF) for the mesh size of 1.5, 2.0, and 2.5 inches was 3.02. The average catch size of flowerhorn cichlid captured by the mesh size of 1.5. 2.0, and 2.5 inches were 11.5, 15.3, and 19.2 cm, respectively. The yarn diameter did not significantly affect flowerhorn cichlid capture (P <0.05). However, the mesh size of 1.5 inches was significantly different (P>0.05) to other mesh sizes. For effectiveness, gillnet was better to operate in littoral areas of lakes, especially in the location associated with the sand substrate with macrophytes. The operation of the gillnet in Lake Matano needs to be regulated in terms of location and setting time to minimize the capture of fish species other than flowerhorn cichlid.

ANALISA ASPEK REPRODUKSI IKAN TOMAN (Channa micropeltes) DI SUNGAI BELIDA KABUPATEN MUARA ENIM

Management of snakehead fish resources in swamp waters need to be done to anticipate a decline in stock in the waters. At this time the area where snakehead fish still have an abundant population is in southern sumatera, precisely in the Belida River, Muara Enim Regency. Until now there has been no information regarding the reproductive aspects of snakehead fish, their location and spawning season. The purpose of this study was to obtain information about the reproductive aspect of snakehead fish which includes sex ratio, gonad maturity level. Gonad maturity index and egg fecundity. The research was conducted in September-December 2019. The location was determined based on the natural conditions of the Belida River and human activities. Fish sampels were caught using experimental gill nets with ½ mash net size. Sampling of fish is done every 4 months with a time interval of once a month. The resuls of study in the male and female fish ratio 1,6:1. This ratio consisted of 109 fish (62,3%) and 66 female fish (37,7%). Gonadal maturity indeks for male snakehead fish ranged from 0,21 to 0,86, while female snakehead fish ranged from 1,18 to 2,30. snakehead fish egg fecundity were 24.786 eggs with a diameter of 2,20 – 2,51

Length-weight relationships and ponderal index of three reef fish (Teleostei: Labridae) off the Tanjung Tiram coast, Southeast Sulawesi, Indonesia

Abstract. Asriyana A, Irawati N, Halili H. 2020. Length-weight relationships and ponderal index of three reef fish (Teleostei: Labridae) off the Tanjung Tiram coast, Southeast Sulawesi, Indonesia. Biodiversitas 21: 1279-1286. Parameters of length-weight relationship and ponderal index were estimated for first time for three reef fish (Labridae), Cheilinus trilobatus, Cheilinus chlorourus, and Choerodon anchorago, off the Tanjung Tiram coast, Indonesia. A total of 292 specimens (C. trilobatus 146 specimens; C. chlorourus 100 specimens; C. anchorago 46 specimens) were collected monthly in experimental gillnets in coral reefs and seagrass beds from January to June 2018. The length-weight relationship and ponderal index were calculated for each species. C. trilobatus showed total length and weight of 9.0-17.2 cm and 12.33-78.79 g, respectively, while C. chlorourus was 8.5-17.5 cm and 10.41-100.21 g, and C. anchorago 9.0-27.0 cm and 18.51-414.00 g. C. trilobatus showed negative allometric growth, while C. chlorourus and C. anchorago had isometric growth. The length-weight relationship of C. trilobatus followed the linear equation of W=0.10TL2.35, while C. chlorourus and C. anchorago fit to W=0.03TL2.83; W=0.03TL2.91 respectively. The highest ponderal index occurred in May for C. trilobatus and in June for C. chlorourus and C. anchorago indicating a peak of the spawning season. The study results could be used as baseline information for future fisheries management of the area.

Komposisi By-catch Perikanan Lele Laut (Famili Plotosidae) di Perairan Teluk Kolono, Sulawesi Tenggara

The by-catch on the gill net fisheries is the current global fisheries problems and issues. This study aimed to analyze by-catch composition of fishery eel catfish (Plotosidae) in Kolono Bay, Southeast Sulawesi. Sampling was done monthly from April to July 2019, with bottom experimental gillnets of ¾, 1¼, 1½, 1 ¾, and 2 inches mesh sizes. The highest proportion of catches was found in by-catch (62.72%) than the main target, the family Plotosidae (37.28%). The by-catch includes 23 families consisting of two groups namely the useable by-catch 55.57% (19 families) and discarded by-catch 7.15% (4 families). Out of these 23 families, 44 species belong to the Least Concern (LC) and 24 species Not Evaluated (NE) categories on the IUCN red list 2019. The results showed that the use of bottom gillnets in eel catfish fisheries has a low selectivity which is characterized by high diversity and low dominance of by-catch.

The Effect of Seasons on Gill Net Selectivity

In this study, the aim was to investigate the seasonal variations in the selectivity of striped red mullet (Mullus surmuletus L., 1758) captured by gill nets during the year in the north Aegean Sea. Fisheries’ operations were carried out between August 2008 and August 2009. Gill nets with 18, 20, and 22 mm mesh sizes were used in the trials. These nets are widely used in the region. Gill nets were deployed three hours before sunset and were removed from the sea at sunset. Similarly, the nets were set up two hours before sunrise and hauled from the sea an hour after sunrise. The SELECT method was used to determine the selectivity of gill nets. The deviances from the SELECT method revealed that lognormal models gave the best fits for all seasons. As a result of the calculations made according to the lognormal model, the modal lengths of the gill nets were calculated as the shortest in the spring season and the longest in the summer. The spread values of the selectivity curves of the experimental gill nets were determined the lowest in the winter season and the highest in the summer season. As a result of selectivity analysis, the differences between the spring and summer season modal lengths of the nets were calculated as 1.5 cm, 1.65 cm, and 1.82 cm for the nets with 18 mm, 20 mm, and 22 mm mesh sizes, respectively. The study results showed that the fishing season was important in gill nets selectivity.

Cumulative Effects of Thermal and Fisheries Stressors Reveal Sex-Specific Effects on Infection Development and Early Mortality of Adult Coho Salmon (Oncorhynchus kisutch).

Multiple stressors are commonly encountered by wild animals, but their cumulative effects are poorly understood, especially regarding infection development. We conducted a holding study with repeated gill and blood sampling to characterize the effects of cumulative stressors on infection development in adult coho salmon. Treatments included chronic thermal stress (15°C vs. 10°C) and acute gill net entanglement with an air exposure (simulating fisheries bycatch release). The potential loadings of 35 infectious agents and the expression of 17 host immune genes were quantified using high-throughput quantitative polymerase chain reaction, while host physiology was characterized with chemical analysis of blood. Temporal increases in infectious agent richness and loads were concurrent with decreased expression of immune genes in fish sampled in the river. In the laboratory, mortality was minimal in cool water regardless of fishery treatment (<15%). Elevated water temperature under laboratory conditions increased mortality of males and females (8% and 28% mortality, respectively, delayed by >1 wk) and enhanced mortality associated with handling and biopsy (∼40% both sexes). Experimental gillnetting at high temperature further enhanced female mortality (73%). Fish held at high temperature demonstrated heavier infectious agent loads, osmoregulatory impairment, suppressed female maturation, and upregulation of inflammatory and extracellular immune genes. At high temperature, heavy Parvicapsula minibicornis loads were associated with premature mortality. Females exhibited physiological impairment from both stressors after 1 wk, and infection burdens correlated poorly with immune gene regulation compared with males. Cumulative effects of multiple stressors on female mortality are likely a function of physiological impairment and enhanced infections at high temperature.

ANCAMAN JENIS IKAN ASING LOUHAN TERHADAP IKAN ENDEMIK DI DANAU MATANO, SULAWESI SELATAN

Lake Matano is one of the ancient lakes in Sulawesi where some endemic fish species of Telmatherina, Mugilogobius, Oryziasand Glossogobius matanensis lived. The presence of alien species can be on threat for the loss of biodiversity in fresh waters, including endemic fish in Lake Matano. The research aim to review the threat of louhan fish as alien species to endemic fish in Lake Matano. The study was conducted in Lake Matano at five stations in April and August 2015 namely Lawa, Nuha, Petea, Pantai Impian, and Pantai Kupu-kupu. Sam-ples were collected using experimental gillnet with mesh size of ¾; 1; 1¼; 1⅟2; 2; 2,5; and 3 inches. Fouteen species were found consist of 10 endemic species and red list.These were three of genus Glossogobius, seven species of Telmatherina, and four alien species of the carp (Cyprinus carpio), louhan, gourami (Trichopodus trichopterus), and tilapia (Oreochromis niloticus). The most common species of endemic fish is T. antoniae. Louhan is the result of a hybrid species Amphilopus citrinellus x Cichlasoma trimaculatum. The abundance of louhan is 64 in April and 40 fishes in August, respectively at a time caught. The percentage ratio of louhan to endemic fish was of 8.6% and 18.3%. This indicated that the louhan fish tend to be invasive and certainly threatened endemic fish survival in this lake. The maturity of gonads of louhan is in the level of I - IV that enables the fish to reproduce quickly.

Gillnet catchability of brown trout Salmo trutta is highly dependent on fish size and capture site

Use of experimental gillnet fleets is common both in scientific studies of fish populations and in fishsampling for management purposes. Fish catchability may vary considerably with fish and gillnet meshsize, and catches obtained by gillnet fleets composed of nets with different mesh sizes may give lengthand age distributions that deviate considerably from the length and age structure of the population.We have estimated the absolute catchability of allopatric brown trout (Salmo trutta) in the littoral andpelagic habitat of a small lake based on a mark-recapture experiment. The brown trout catchabilityvaried considerably both with fish size and habitat type, probably due to a size-related variation inswimming distance per time unit and a size-related use of the different lentic habitats. The samplingbias in experimental gillnet fishing may be reduced by operating the gillnet fleets in all possible lentichabitats and most fundamentally, by use of catchability data obtained from populations with ‘known’length and age structures. By reducing this sampling bias, more realistic estimations of the age andlength distribution for a given population will be possible.

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.

Biodiversity of fishes of Tagwai reservoir, Minna, Niger state, Nigeria

The biodiversity of the fishes of Tagwai Reservoir, Minna, Niger State, Nigeria was conducted for a duration of four months (January-April 2018). A set of experimental gill nets comprising nine mul...

Depredation in gillnets operated along the south-west coast of India

Experimental gillnet (polyamide, 210 d×9×3 with 140 mm mesh size) fishing was conducted onboard FV Sagar Harita (LOA19.5 m) during September, 2016. Out of six sets deployed, three incidents of depredation, possibly by puffer fish were observed, when 41.5, 33.7 and 40% of the catch was lost. Depredation could be prevented effectively by frequent monitoring of the deployed gillnets at shorter intervals. Studies on depredation with special reference to soaking time, hauling speed, seasonal variation and location of fishing grounds are needed in view of the economic losses incurred.

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