Gillnet Catches Research Articles

Detailed Insight into Gillnet Catches: Fish Directivity and Micro Distribution

Gillnets are widely used in research and commercial fishery activities. As passive gear, gillnets can be selective and dependent on the diel migration of fish. In areas with limited littoral extent, inshore–offshore migration may cause bias in the gillnet catch. Our hypothesis was that some factors, such as gillnet saturation, fish depletion, or chemical cues, could be the cause of the bias. We used a total of 66 CEN gillnets deployed at Římov Reservoir parallel to the shore at different positions of littoral-pelagic gradient. Individual fish direction was recorded from inshore, offshore, or unknown direction (i.e., entangled fish). A total of 5791 fishes from nine different species were caught. For most fish, it was possible to determine their directivity, and most fish were captured in littoral or first pelagic gillnets. Shallower and deeper benthic gillnets differed in their bleak (Alburnus alburnus) catch. No significant differences were found between fish directions. At the species level, only asp (Leuciscus aspius) and ruffe (Gymnocephalus cernua) showed differences between the captured directions in one case. The results support the assumption that gillnet capture is a random process that to a great extent is connected to random local movements. This is good news for fish monitoring projects. Sampling catch is likely to reflect true changes in the fish community, and not the effects of the deployment of the sampling gear. The experiment also showed that fish directivity statistics can be used for investigation of fish behavior and gear performance.

Mercury exposure in ringed seals (Pusa hispida saimensis) in Lake Saimaa, Finland, and the placenta as a possible non-invasive biomonitoring tool

The Saimaa ringed seal (Pusa hispida saimensis) is a subspecies of ringed seal, landlocked in Lake Saimaa, Finland. The small population of less than 500 seals is facing many human-induced threats, including chemical contaminants. Mercury, in particular, has previously been suggested to be one of the chemicals affecting the viability of this endangered population. We analysed mercury concentrations from placentas and lanugo pup tissues (blubber, brain, kidney, liver, and muscle) to determine current prenatal exposure levels. These pups were found dead in or near birth lairs and were less than 3 months old. Additionally, we used threshold values available in the literature to estimate the potential mercury toxicity to the Saimaa ringed seal. We also determined selenium concentrations for its potential to alleviate the adverse effects of mercury. We further supplemented our study with brain samples collected from various seal age classes. These seals were found dead by either natural causes or by being caught in gillnets. The analysed chemicals were present in all tissues. For lanugo pups, mercury concentrations were the highest in the kidney and liver, whereas the highest selenium to mercury molar ratio was observed in placentas. The toxicity evaluation suggested that, in severe cases, mercury may cause adverse effects in lanugo and older pups. In these cases, the selenium concentrations were low and selenium to mercury ratio was below 1:1 threshold ratio and thus unlikely to provide adequate protection from the adverse effects of mercury. Furthermore, adverse effects are more likely to occur in adult seals, as mercury bioaccumulates, leading to higher concentrations in older individuals. Placental mercury concentrations correlated to those in the livers and muscle tissues of lanugo pups. This, together with the fact that placentas can be collected non-invasively and in good condition, provides a potential novel method for biomonitoring mercury exposure in Saimaa ringed seals.

Vertical distribution of Lake Superior cisco (Coregonus artedi) spawning aggregations and implications for population monitoring

Cisco (Coregonus artedi) support an evolving commercial roe fishery in Wisconsin waters of Lake Superior. To monitor trends in spawning cisco abundance, fishery managers recently began estimating adult biomass and exploitation using fall hydroacoustic surveys, which were combined with gill net surveys to inform apportionments of acoustic data. The gill net survey design consisted of paired top-suspended and bottom-set gill nets, but only the sex ratios from top nets are currently used with the hydroacoustic surveys due to an assumption that cisco in Lake Superior are pelagic spawners. However, the vertical sex distribution of cisco during spawning aggregations has been described as dynamic, with males becoming more bottom-oriented throughout the spawning season. We used multilevel aggregated binomial regressions to: 1) determine if there is bias between top and bottom gill net catches of cisco for either sex and if it changes throughout the spawning season, 2) evaluate how the vertical distribution of males and females may create bias in sex ratios used to estimate exploitation, and 3) explore the effect that maturity (i.e., gonadal development) has on vertical distribution during spawning aggregations. We identified sex-specific bias in vertical catch location that has the potential to bias estimates of sex ratio, and the source of this bias may be attributable to maturity driven changes in behavior. These findings highlight a need for caution when relying on gill nets to apportion cisco sex ratios during spawning aggregations and provide support for a non-pelagic alternative hypothesis of spawning behavior.

Stable isotopes reveal trophic ontogeny in Cisco (Coregonus artedi).

Cisco (Coregonus artedi) are a widespread, cold-water zooplanktivore native to North America. Although Cisco are generally referred to as an "obligate zooplanktivore," there is some evidence that the species exhibits considerable variability in trophic niche. Here, we assessed how Cisco body size relates to trophic position, that is, trophic ontogeny. We analysed 13C and 15N isotopes from Cisco ranging from 127 to 271 mm in body length (n = 66) from Trout Lake, Vilas County, Wisconsin, USA. 15N isotopes showed smaller Cisco had a trophic position of ~3, which steadily increased to ~3.5 for larger Cisco. Further, 13C isotope signatures showed Cisco transitioned to be more pelagically reliant (lower 13C signatures). Using gillnet catch data, we found that larger Cisco were using deeper habitats than smaller Cisco. Our results support that Cisco have significant variability in trophic niche even though they are traditionally thought of as an obligate planktivore. Overall, we emphasize that researchers should be cautious when generalizing Cisco trophic function, particularly when considering the broader food web.

Fish predation on newly stocked juvenile predatory fish in a biomanipulated reservoir

Jůza T, Blabolil P, Čech M, Draštík V, Kubečka J, Muškaa M, Prchalováa M, Sajdlováa Z, Tušera M, Vašeka M, Vejříka L, Peterkaa J. 2024. Fish predation on newly stocked juvenile predatory fish in a biomanipulated reservoir. Lake Reserv Manag. 40:325–337. Juveniles of pikeperch, asp, and northern pike were stocked into the Římov Reservoir. Subsequently, potential fish predators were monitored by gillnets at the stocking sites and their diet was analyzed for presence of stocked fish. Asp and European perch were predominant predators, while pikeperch and northern pike were less abundant in gillnet catches. Digestive tract analysis revealed the highest percentage of ingested fish in northern pike, followed by pikeperch, asp, and European perch. The amount of stocked fish did not correlate with the number of predatory fish caught in gillnets. When asp was stocked, this species was strongly preferred by northern pike and partly by pikeperch and 0.3 individual of stocked asp was eaten per 1 kg of predatory fish captured by gillnets. During the northern pike stocking, this species was mainly preyed upon by asp and occasionally by northern pike, and 0.8 individual of stocked northern pike was eaten per 1 kg of predatory fish. When pikeperch was stocked, it was strongly preferred by pikeperch, northern pike, and European perch, it was almost absent in the diet of asp, and 1.1 individual of stocked pikeperch was eaten per 1 kg of predators. Our results indicate that pikeperch juveniles had the highest mortality rate due to predation after stocking, mainly due to sedentary behavior and the high proportion of cannibalism. In northern pike, cannibalism was found in only one case, and was never found in asp, which was under the lowest predation pressure.

UTILIZATION OF GILLNET CATCHES FISHERMEN OF MATANG RAYEUK VILLAGE, NUSANTARA FISHERY PORT, EAST ACEH

The purpose of this community service is to determine the composition of the main and by-catch of gill nets and the size of the catch. This community service was carried out during April 2023 at PPN Idi Rayeuk, Matang Rayeuk Pedawa Puntong Village, East Aceh Regency. The data collection method used was obtained from primary data (surveys and interviews) which included the type, quantity, size, and weight of the gill net catch and secondary data can be obtained from scientific references books, journals, theses and dissertations). The data analysis used was the analysis of the composition of the catch and the analysis of the size of the catch. The results of the community service showed that the composition of the main catch of the gill net at a mesh size of 1¼ inches was tembang fish, at a mesh size of 2 inches was ribbon fish and at a mesh size of 3 inches was kapasan/kerot-kerot and kwee fish. By-catch with a net size of 1¼ inches is jackfruit seed fish (upeneus moluccensis), kurisi (nempiterus hexodon), petek (leiognathus equulus), yellow trevally (Atule mate), saurida (Saurida undosquamis), swanggi (Priacanthus hamrur), next (Psettodes erumei), parang-parang (chirocentrus dorab), tetengkek (megalaspis cordyla). ) and layur (trichiurus Sp.A). Next, at a mesh size of 2 inches, namely talang fish (scomberoides tala), diles (johnius carouna), petek (leiognathus equulus), moon (Megalops cyprinoides), machete (chirocentrus dorab), jackfruit (upeneus moluccensis), kurisi (nempiterus hexodon), kwee (carangoides armatus), tetengkek (megalaspis cordyla), gerot-gerot ( Pomadasys kaakan), kerong-kerong (Terapon Jarbua), and alu-alu (Sphyraena genie). Then at the 3 inch mesh size, namely the kapasan/kerot-kerot fish (Pomadasys argenteus), talang (scomberoides tala), petek (leiognathus equulus), kuro (Polydacctylus microstoma), diles (johnius carouna), parang-parang (chirocentrus dorab), mackerel (Scomberomorus Commerson), kapas (Gerres filamentosus), and tetengkek (megalaspis cordyla). The catch at the 1¼ and 2 inch mesh sizes is said to be not yet suitable for catching, while the 3 inch mesh size is said to be suitable for catching.

ANALYSIS OF PRODUCTION FACTORS FOR GILLNET FISHING GEAR AT THE TECHNICAL IMPLEMENTATION UNIT (UPT) OF THE FISHERY PORT OF RIAU PROVINCE

Dumai City relies entirely on marine waters for its fisheries production, with gillnets being a predominant fishing gear among local fishermen. Gillnets, characterized by their rectangular shape with varying mesh sizes, utilize floats and weights. This study aimed to identify the factors influencing gillnet catches in Dumai City. Results from simultaneous testing revealed that all production factors significantly impact catch quantities. Through multiple linear regression analysis, it was determined which factors exerted positive and negative effects. The regression equation, Y = 0.108 – 0.183 X1 – 0.411 X2 – 0.345 X3 + 0.173 X4 + 0.116 X5 + 0.451 X6 + 0.181 X7 – 0.106 X8 + 0.223 X9, elucidated these relationships. The cumulative effect of production factors on catches amounted to 64.20%. This study provides valuable insights into optimizing gillnet fishing practices in Dumai City's marine environment.

Composition of gillnet catches based on network size at UPT Fishery Port of Riau Province

Gill net catches are one of fishermen's dominant fishing gear at UPT Dumai City Fishing Port. Gill net catches are easy to operate, have a low price, and are durable. This research was conducted in July-August at UPT Port of Fisheries, Riau Province. This study aimed to determine differences in gill net catches based on different mesh sizes. The method used is the survey method. The catch of gill nets by type with a mesh size of 2 inches is 25 fish species. Based on the weight and number of individual fish, it was dominated by lomek (Harpodon sp), namely 1,359.5 kg or 21.5% and 16,314 individuals or 27.18%. The catch in the 3-inch mesh size was 23 species of fish. The percentage of catches based on weight dominated by senangin (Eleutheronema tetradactylum) was 30.38% (1,353.5 kg), and based on the number of individuals dominated by pomfret of 18.72% (4,534 individuals). The main catches in gill nets at UPT Dumai are lomek (Harpodon sp), senangin (Polynemus sp), pomfret (Bramidae sp) and machete (Chirocentrus sp). The primary and bycatch yields for the 2-inch mesh were 51.58% and 42.42%, while the 3-inch mesh sizes were 57.99% and 42.01%.

Struggles beneath the waves: Unveiling the incidental capture of sea turtles by artisanal fisheries in Angolan waters

The modernization and intensification of fishing practices have raised the threat to sea turtles, with escalating unintentional captures endangering turtles of all life stages. In this study, we examined the impact of artisanal fishing on sea turtles in two coastal regions of Angola, southern Africa. Between August 2015 - March 2016, through participatory monitoring (n = 8) and interviews with fishers (n= 41), we documented unintentional turtle captures occurring year-round during fishing activities. A total of 405 turtles, 403 olive ridley (Lepidochelys olivacea) and 2 green (Chelonia mydas), were caught in gillnets by fishers engaged in participatory monitoring. Net characteristics, including length and proximity to the shoreline, as reported by the interviewed fishers, correlated with those used by the monitoring group. We estimated approximately 1219 turtles captured by the 41 interviewed fishers over the 8-month study period. Most captures occurred within 100 m from the shoreline. The likelihood of accidental turtle captures increased significantly with proximity to the beach, larger mesh sizes, and greater net lengths and number of hauls. We calculated a survival rate of 41%, and a mortality rate of 59% for captured turtles. Number of turtles caught as bycatch varied throughout the year, with the highest Catch Per Unit Effort (CPUE) reported for Oct. – Dec. Since this period aligns with the nesting season, most captured turtles are likely to be females. The high mortality rate reported in this study emphasizes the immediate threat posed by accidental captures to sea turtle populations, underscoring the critical importance of conservation efforts, particularly in artisanal gillnet fisheries.

Productivity Analysis of Gillnet Fishermen Business at the Fishing Port of Archipelago Pemangkat

Pemangkat Archipelago Fisheries Port (PPN) has a very strategic role in the development of capture fisheries business, namely as a center or center for marine fisheries activities, especially those in the Sambas Regency, West Kalimantan Province. The purpose of this study was to determine the productivity level of gillnet fishing gear and to determine the factors that affect gillnet catches. The method used in this research is descriptive method. Based on the results of the analysis using the Cobb Douglas model, the production factor that affects the catch using gillnet fishing gear is the distance traveled with a value of Tcount 2,168 < Ttable 2,048. The highest productivity of catch units on gillnet fishing gear, which is 8 tons/trip, is found on the Sri Ayu Bahari vessel with a 29 GT vessel size, while the lowest is 1,3 tons/trip on the Sumber Abadi – 3 vessel with a 30 GT vessel size. Considering that the gillnet catching business is still profitable, the Pemangkat Fisheries Port can still develop its business with this tool, but it is necessary to control the PPN so that the catches obtained by gillnet fishermen remain optimal.

Fisheries characteristics and biology of Indo-Pacific King Mackerel in Tarakan Waters, North Kalimantan

The Indo-Pacific king mackerel (Scomberomorus gutatus) is one of the catches of drift gill nets in the waters of Tarakan, north Kalimantan, and makes an important contribution to fisheries production in the region. In order for its use to be sustainable, it is necessary to make efforts to manage fish resources based on studies of fisheries and their biology. Monthly data for the period January to November 2021 were obtained from tangkahan based on tarakan with the aim of obtaining information and analyzing the dimensions of fishing gear, fishing grounds, catch composition, frequency of fish size, and fishing effort (cpue). Furthermore, fish biology data were analyzed by the analytical method. the results showed that there was a change in the dimensions of the longer fishing gear; the abundance of fish caught by drift gill nets was dominated by indo-pacific king mackerel (Scomberomorus gutatus) (49.3%), dorab wolf-herring (Chirocentrus dorab) (12.8%), fourfinger threadfin (Eleutheronema tetradactylum) (8.5%), silver grunt (Pomadasys argenteus) (4.7%), narrowbar spanish mackerel (Scomberomorus commerson) (4.3%), barramundi (Lates calcarifer) (2.3%), goldstripe sardinella (Sardinella gibbosa) (2.2%), common pike conger (Muraenesox bagio) (2.2%), daggertooth pike conger (Muraenesox cinereus) (1.9%), needleskin queenfish (Scomberoides tol) 1.7%, great barracuda (Sphyraena barracuda) 1.3%, and other fish (11.1%). The distribution of fishing grounds is dominated by grid 6005 by 46.5%, grid 6004 by 7.08%, and grid 5760 by 6.7%. The length at first capture (lc) of mackerel was 38.06 cmfl. The yield per unit effort (cpue) of drift gill nets in Tarakan is an average of 44.3 kg/day.

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

Effect of artificial lights on catch efficiency and capture patterns in Asian paddle crab (Charybdis japonica) gillnet fishery

The gillnet fishery targeting Asian paddle crab (Charybdis japonica) is an important commercial fishery in the Yellow Sea of China. However, low catch rates represent a challenge, and solutions for improving the catch efficiency are crucial for economical sustainability in this fishery. Therefore, we tested whether the use of artificial fishing lights could improve gillnet catch performance. Specifically, we investigated the effect of using different colored light-emitting diodes (LED) on gillnet catch efficiency and capture patterns. The results showed that attaching white and blue LED lights to gillnets did not significantly affect the catch efficiency of C. japonica, compared to the conventional gillnets without LED lights attached. However, green LED lights significantly improved catch efficiency of legal-sized C. japonica by an average of 57%. Furthermore, a significant reduction (∼35%) in the catch efficiency of undersized crabs was observed for gillnets equipped with red LEDs; however, without any significant effect on catches of legal-sized C. japonica. Moreover, significant differences were observed for the catch composition of species between gillnets with and without LED lights. The findings of this study can provide insight into potential improvements of the fishing strategies in the C. japonica gillnet fishery.

The Hydrological Cycle of the Lower Amazon in Brazil Determines the Variation in Local Fishing Patterns

Fishery catches on the Lower Amazon River were analyzed in relation to the hydrological cycle, temporal shifts in fishing effort, and the use of nets or lines in lakes and rivers. The study was based on a temporal series of catch data collected between January 1993 and June 2011. The variables analyzed were the total catch, use of gillnets or lines, the environment targeted (lakes or rivers), and fishing effort. Temporal trends in the data series were analyzed using the Mann–Kendall test. An Analysis of Covariance (ANCOVA) was used to evaluate whether gillnet and line catches had independent effects on the catch data. Duncan’s test was applied to identify the groups (months) of means that were significantly different from each other. The majority of the catch landings were taken with gillnets (98.65%) in a lake environment (64.98%). The temporal series showed a significant decline over time in the gillnet catches from both lakes and rivers, as well as in fishing effort. The influence of the annual flood cycle was reflected in the catches and the flood pulse regulated fishing productivity patterns in the region. The fishers who adapt their activities to this flood pulse have good traditional knowledge of the environment. The results of the study also indicated that any changes in this dynamic system may impact traditional local fisheries and affect the economic wellbeing of local fisher populations.

Gill net catchability of walleye (Sander vitreus): Are provincial standards suitable for estimating adult density outside the region?

Standard gill netting protocols are increasingly used to assess freshwater fish populations. Understanding the catchability (q) of fish following these protocols enables direct estimation of density, which has advantages over relative abundance from analytical and applied research perspectives. However, catchability is complex. The application of q estimated in one region may be inappropriate for another if physical and biological processes driving catchability differ. Cross-region assessments of q are needed to assess the applicability of estimates over a broader geographic and environmental range. In this study, we evaluated whether the global estimate of q (1.044 ha/gang; variance = 0.2268) derived by Giacomini et al. (2020) for walleye Sander vitreus ≥ 350 mm total length (TL) was suitable for application in two Colorado, USA reservoirs supporting recreational fisheries and wild spawn operations. We followed provincial standards in Ontario and Quebec, Canada (i.e., Fall Walleye Index Netting) combined with other corrections for size-dependent catchability to estimate the density of mature, adult walleye ≥ 470 mm TL for comparison to independent estimates from mark-recapture analyses. Following similar methodologies, we found that the global estimate of q combined with size-dependent gill net retention coefficients underestimated the density of adults by nearly 80%, but uncertainty in point estimates can be high. Results highlighted the need to better understand sources of uncertainty, including factors influencing size-dependence in gill net encounter when extending estimates of q to other size classes of fish, systems, and regions. Estimates of catchability for large-bodied adult walleye in our systems were consistent, but relatively low, ranging from 0.203 ha/gang (95% confidence limits = 0.133–0.298) to 0.227 ha/gang (0.091–0.556). We expand the geographic and environmental range of paired mark-recapture and gill net Catch Per Unit Effort information and discuss potential factors contributing variability to estimates of catchability for adult walleye.

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.

Перспективи промислового використання карася Київського водосховища

Purpose. Establishing modern parameters of Prussian carp population as a promising object for increasing commercial fish productivity of the Kyiv Reservoir. Methodology. The work is based on field materials obtained during the period 2019-2021 on the Kyiv Reservoir. Data collection and processing was carried out in accordance with generally accepted methods. Ichthyological material was collected from catches of the survey gill nets with mesh sizes of 30-120 mm and commercial gill nets with mesh sizes of 38-50 and 75-100 mm. A total of 1215 net-days of surevy and commercial nets were analyzed during the study period, of which 2372 specimens of Prussian carp were analyzed. Statistical data processing was carried out using MS Excel. Findings. The main parameters that characterize the commercial stock of Prussian carp of the Kyiv Reservoir in the context of optimizing the commercial fishing pressure on this species have been determined. It was found that the state of recruitment of the commercial stock of this species was satisfactory and the dynamics of its size-age structure indicated a low commercial fishing pressure, especially on the right wing of the variation series — the average annual fishing mortality in 2019-21 was φM=0.13. The majority of the commercial stock is steadily composed of age-6 to age-10 fish, the share of older age groups was consistently high, which led to fluctuations in the weighted average age in catches within 6.7...8.5 years. It was shown that the intensification of Prussian carp harvest (due to specialized fishing with nets with mesh size of 50 mm) would allow increasing catches in the Kyiv Reservoir by 52...65%. Originality. For the first time, a detailed description of Prussian carp of the Kyiv Reservoir is presented as an adventive species that quickly assimilates free econiches and requires scientifically based measures to localize its abundance. Practical value. Based on the processing of information on the state of stocks of Prussian carp as part of the source of commercial fishery of the Kyiv Reservoir, the procedure of intensification of its commercial exploitation was determined, taking into account both fishery and environmental aspects. Proposals regarding the quantitative characteristics of specialized fishery with nets with mesh sizes of 50-60 mm are included in the new edition of the Rules for commercial fishery in inland fisheries water bodies (parts thereof). Key words: Kyiv Reservoir, Prussian carp, size-age structure of the catch, commercial stock, specialized fishing.

Calibration of fish biomass estimates from gillnets: Step towards broader application of gillnet data

Fish are an important component of aquatic ecosystems, thus representative and reliable assessments of their population variables are essential for a variety of ecological applications, management and conservation. Determining Fish Density per actual Spatial Unit (volume or area, FDSU) as a measure of absolute fish quantity is of particular interest. Gillnets are undoubtedly one of the most common and important methods for assessing fish populations in large lentic waters. However, direct calculating of FDSU from gillnet catches is impossible because of the passive nature of this method, and to date there is no reliable model for calculating FDSU from gillnet catches. This weakness largely limits the use of gillnet data for applications requiring FDSU estimates.The aim of this study was to calibrate gillnet catches using FDSU obtained by active methods (beach seine nets and hydroacoustics) to develop a tool for assessing FDSU from gillnet catches. To achieve this goal, we compared gillnet biomass to fish biomass estimated from the active methods, both of which cover similar spatiotemporal niches. This comparison was performed using a statistical approach based on the recognition of non-negligible random measurement error in both the explanatory (active methods) and response (gillnets) variables.We found a strong positive linear relationship between fish biomasses sampled with gillnets and with active methods. The slope of the fitted linear model was similar when comparing gillnets with the two active methods. The statistical method used allowed for the inclusion of error in the biomass estimates with gillnets and active methods, refining the credible intervals of the estimated relationship. The effect of gillnet effort on model accuracy was simulated to show how increased effort narrows the credible interval. Finally, comparison with previously published relationships revealed a large but explainable discrepancy between our model and previous models.Our study showed that conversion of gillnet biomass to biomass per actual spatial unit is possible. The effective sampling area of one square meter of gillnet was determined to be 8 m2 of waterbody surface area when European standard 12 mesh-sizes gillnets are used, and 5 m2 when four larger meshes are added to the European standard gillnets. Our model further stressed the impact of increased sampling effort on reducing estimation variability and shows that the model may be dependent on the fish community.

Paired passive acoustic and gillnet sampling reveal the utility of bioacoustics for monitoring fish populations in a turbid estuary

Abstract Estuaries worldwide provide critical habitat to many ecologically and socioeconomically important fish species. However, the high turbidity and strong environmental gradients inherent to many estuaries make the monitoring of fish populations a challenging task. To assess the health and diversity of local fish populations, resource managers often employ fisheries-independent sampling methods, which result in valuable population assessments, but suffer from low-temporal resolution and high rates of mortality. Passive acoustic monitoring (PAM) provides a near-continuous, non-invasive means for monitoring soniferous fish activity over extended periods, but its utility for quantifying entire fish communities is largely untested, especially in turbid estuaries. Here, we use synchronized acoustic and gillnet sampling at 51 locations in the Mission-Aransas Estuary (TX), across two sampling seasons to test correlations between acoustic indices and gillnet catch. Positive correlations were observed between gillnet catch and sound pressure levels in both broadband (50–22050 Hz) and low-frequency (50–2500 Hz) bands. Additionally, sciaenid calling activity was positively correlated with sciaenid catch during the spring, when most spawning activity occurs. Our results indicate that PAM can be used to monitor the relative abundances of fish in Gulf of Mexico estuaries and beyond, although this is subject to species identity and seasonal dynamics.

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.