Net Fishery Research Articles

Are Cloth Tarpaulin Mounted Nets Effective for Discard Reduction in Trammel Nets?

Discarding is a significant problem due to net damage and labour loss in trammel net fisheries. In this study, the effects of 15, 25, and 35 cm high cloth tarpaulin rigged between the lead line and the net were investigated in reducing the discard amount of trammel nets for red mullet (Mullus barbatus) in the south-eastern Black Sea. During the study, twenty fishing trips were carried out on-board a commercial vessel between May 11 and June 20, 2018. Results showed that there were no significant differences in the amount of discards between the commercial and experimental nets (P>0.05) However, cloth tarpaulin mounted nets (CTMN) were found to be significantly successful to reduce the amount of shore crab (Liocarcinus depurator) and the veined rapa whelk (Rapana venosa) (P<0.05). Although it is insignificant, a decline of capture was also observed in the amount of target species in CTMN compared to the commercial net (CN). Finally, the advantages and concerns of this gear modification, and potential reasons for the reduction of target and discard species are discussed.

A multidecadal Bayesian trend analysis of harbor porpoise (Phocoena phocoena) populations off California relative to past fishery bycatch

AbstractHarbor porpoises, Phocoena phocoena, off California, comprise four recognized population stocks: Morro Bay (MOR), Monterey Bay (MRY), San Francisco‐Russian River (SFRR), and Northern California‐Southern Oregon (NCSO). The three southernmost stocks experienced substantial bycatch in gill net fisheries during the 1970s and 1980s. While the SFRR stock received full protection from gill nets in 1989, the MOR and MRY stocks continued to experience at least some bycatch through 2001–2002. We examined long‐term population trends for these four harbor porpoise stocks, based on two sets of systematic, aerial line‐transect surveys conducted off California during summer/fall of 1986–2017. We applied a Bayesian hierarchical framework to specify a process model of population density and an observation model of porpoise counts during line‐transect surveys. Growth rates were estimated for periods with and without bycatch. Posterior distributions indicate the MOR, MRY, and SFRR stocks, respectively, grew at 9.6%, 5.8%, and 6.1% per year after gill nets were largely or fully eliminated for each stock. Abundance off northern California appears stable or slightly increasing. This study provides a first empirical estimate of maximum net reproductive rate for harbor porpoise (at least 9.6%), and demonstrates that porpoise populations can recover from substantial gill net impacts if bycatch is eliminated.

Utilization of Light Emitting Diode (LED) lamp with difference color as attractor for fixed lift net as small scale fisheries in Makassar Strait, Indonesia

Use of light for the some types of fisheries has been one of the most advance and successful methods to control fish to capture process. Several fishing technology operated in Indonesia waters, used of light as attractor for catching of the small pelagic fish. A lot of typed of lamps used by the fisherman, like incandescent lamp, florescent lamp, mercury lamp and metal haline lamp. In the development of technology, now the some company, was introduce new lamp typed with environmentally friendly technology called Light Emitting Diode (LED) lamp. Research about utilization of Light Emitting Diode (LED) lamp with different color and color combination of fixed lift net was conducted in Makassar Strait during the May- November 2018 and March – September 2019. The research aimed was to determine the best effectively color of LED can use as attractor for pelagic fish in fixed lift net in Makassar Strait. Experimental fishing was conducted in one unit commercial fixed lift net with bamboo platform size 15 m x 15m in Pangkep regency Makassar Strait. Data were obtained at every fishing operation by examining the catch species, total catch, by-catch and discard species every hauling time. In 2018 there are three color LED namely white, yellow and blue color. Experimental fishing for 30 hauling time for each color of LED in 2018 and 35 time for each LED in 2019 with color combination. Data were collected two time a week during. Fixed lift net did not operated during the full month (one week a month). Total lighting power of 374 W, with 16 total unit LED lamps was setting under the lift net flatform. The result showed that Light Emitting Diode (LED) is effective as attractor in fixed lift net fisheries to utilization of small pelagic species in coastal area. There are 25 species captured of the fixed lift net during the experimental fishing in Makassar. There are five dominant and commercial species, there called main species are Anchovies (Stolephorus sp), Sardine (Sardinella sp), Pony fish (Equulites sp), squids (Loligo sp), and Big eye scad (Selaroides sp). White color and combination of white-blue – yellow color is preference color for small pelagic species.

Freshwater turtle bycatch research supports science‐based fisheries management

AbstractAlthough it is sometimes difficult for researchers to ensure that their work is used by resource managers to make informed decisions, an example where this knowledge–action gap has been breached is in research published inAquatic Conservation: Marine and Freshwater Ecosystems(AQC) – among other journals – that has assisted fisheries managers in identifying strategies for reducing freshwater turtle bycatch in commercial hoop net fisheries in Ontario, Canada.Research published in AQC has provided evidence towards a simple and effective method for preventing turtle bycatch mortality in hoop nets, which could be adopted by the fishers. Other research published in AQC evaluated the effect of bycatch mortality on the probability of persistence of turtle populations with population viability analyses, and outlined the need to minimize bycatch mortality to prevent local extirpation. Nine other papers have been published on freshwater turtle bycatch in Ontario, furthering our knowledge on this issue including seasonality and temperature effects on catches, other net modifications, post‐release effects and assisted recovery, and the perspectives of fishers.The research results were presented to local resource managers with further discussions involving industry and stakeholders to minimize turtle bycatch mortality. Over several years, researchers have provided information to resource managers; however, when an incident of high turtle mortality caught the public eye, the research was readily available and changes in regulations were quick to occur.Reasonably good communication among researchers, resource managers, industry, stakeholders, and the broader public allowed the rapid implementation of regulations to mitigate freshwater turtle bycatch mortality and bridged the knowledge–action gap between researchers and resource managers.Both articles published in AQC had practical conservation impacts and were influential in providing local resource managers with feasible solutions, and the impetus to change regulations. These impacts extended to other jurisdictions and their monitoring programmes, where methods to reduce turtle bycatch mortality were also implemented.

An economic feasibility analysis of the reduction of accident at fishing operation in stow net fishery

An economic feasibility analysis of the reduction of accident at fishing operation in stow net fishery

Identification and characterization of trammel net métiers: A case study from the southwestern Sicily (Central Mediterranean)

The high variability of trammel fisheries, due to a marked seasonality in target species and fishing activities needs to be investigated with high spatial and temporal resolution. The present study focuses on trammel net fishery in southwestern Sicily (central Mediterranean Sea) identifying and characterizing the main métiers in relation to some key aspects of the fishery such as the target species, composition of landings, main fishing grounds and time of the year. For this purpose, a multivariate statistical approach based on landings and effort data of the Mazara del Vallo southwestern Sicily, Italy) trammel fleet in the period 2009–2013 was applied. A total of 153 different landed species and four different trammel net métiers were identified. These métiers showed differences in target species (i.e. Sepia officinalis, Palinurus elephas, Mullus surmuletus and a mix of species), fishing season, fishing grounds and dimension of fishing vessels. The métiers identified were significantly different in terms of total average landing per unit of effort (LPUE) with métier 1 targeting M. surmuletus, showing the highest average LPUE (2047 (192 s.e.) g*(h)−1*103 m net) and métier 2 targeting S. officinalis, exhibiting the lowest value (1175 (119 s.e.) g*(h)−1*103 m net).The study provides new knowledge on the dynamics of trammel fisheries in southwestern Sicily also showing that the complex nature of this peculiar fishery should be taken into account in any future sampling program aimed at the monitoring and management of artisanal fisheries in this area and more in general in the Mediterranean Sea.

Estimating protected species bycatch from limited observer coverage: A case study of seal bycatch in static net fisheries

Fisheries bycatch represents a major anthropogenic threat to marine megafauna worldwide. To identify populations at risk, it is essential to estimate the total number of individuals removed from a population as bycatch. However, estimating total bycatch remains challenging due to the often-limited scope of monitoring programmes. In this study, we aimed to maximise the value of limited bycatch data collected by scientific observers and self-reported by fishers to provide estimates of total seal bycatch for static net fisheries operating in Irish waters. We constructed a model of bycatch rate as a function of known predictors of seal bycatch, and used this to predict bycatch rates throughout the Irish Exclusive Economic Zone. Annual estimates of seal bycatch, from 2011 to 2016, ranged between 202 (90% CI: 2-433) and 349 (90% CI: 6-833) seals per annum. Estimated bycatch exceeded the precautionary threshold of Potential Biological Removal (PBR = 165-218; Fr=0.5) for the national grey seal population but was below less conservative threshold values (PBR = 330-437; Fr=1.0), with confidence intervals spanning both. Further research on the population structure of grey seals in the Northeast Atlantic is needed to set appropriate bycatch thresholds. Nonetheless, this study shows that by utilising predictive models to maximise the value of limited bycatch observer effort, we can produce informative estimates of protected species bycatch and highlight areas of high bycatch risk. We present this as a case study for maritime nations with comparatively limited bycatch data to fill key data gaps in protected species bycatch worldwide.

Saros Körfezi Ağ Dalyan Balıkçılığı Üzerine Bir İnceleme

Çalışma Saros Körfezinde bulunan ağ dalyanların av verimleri, tür boy kompozisyonları ve ağ planlarının incelenmesi amacıyla Nisan 2019 – Eylül 2019 tarihleri arasında gerçekleştirilmiştir. Dalyanlara karadan ulaşım olmadığı için, dalyanların lojistik ihtiyaçları beşyol köyü sınırları içinde yer alan Ece Limanından yapılmaktadır. Çalışmada Ece limanına gidilerek dalyan sahipleri ile görüşmeler ve dalyanlardan gelen balıkların boy ölçümleri yapılmıştır. Sezon başlamadan önce dalyanda kullanılan ağların teknik planları incelenerek Türkiye’de ilk defa planlarının çizimi yapılmıştır. Çalışmada, 2019 balıkçılık sezonunda Saros Körfezi'nde incelenen 3 adet ağ dalyanda 9 familyaya ait 12 türün yakalandığı belirlenmiştir. İncelenen Ağ dalyanların av verimleri Arifağa taşları mevkii için 53,9 kg/gün, Bozburun mevkii için 52,6 kg/gün ve Mersinlik bölgesi için 43,2 kg/gün olarak hesaplanmıştır. Araştırma sonucunda, Saros Körfezi'nde dalyanların yaptığı avcılığın yasal boy altı balıkları önemli derecede yakalamadığı görülmüştür. Ek olarak, sonuçlar Saros Körfezi'ndeki dalyanlarının ağ yapılarının modernize edilmesi gerektiğini ortaya koymuştur. * Bu çalışma İsmail ÇALIŞKAN’ın yüksek lisans tezinden üretilmiştir.

定置網漁業を核とした六次産業化:沖縄県国頭漁協・読谷村漁協の事例

定置網漁業を核とした六次産業化:沖縄県国頭漁協・読谷村漁協の事例

On-board study of gas embolism in marine turtles caught in bottom trawl fisheries in the Atlantic Ocean

Decompression sickness (DCS) was first diagnosed in marine turtles in 2014. After capture in net fisheries, animals typically start showing clinical evidence of DCS hours after being hauled on-board, often dying if untreated. These turtles are normally immediately released without any understanding of subsequent clinical problems or outcome. The objectives of this study were to describe early occurrence and severity of gaseous embolism (GE) and DCS in marine turtles after incidental capture in trawl gear, and to provide estimates of on-board and post-release mortality. Twenty-eight marine turtles were examined on-board fishing vessels. All 20 turtles assessed by ultrasound and/or post-mortem examination developed GE, independent of season, depth and duration of trawl and ascent speed. Gas emboli were obvious by ultrasound within 15 minutes after surfacing and worsened over the course of 2 hours. Blood data were consistent with extreme lactic acidosis, reduced glomerular filtration, and stress. Twelve of 28 (43%) animals died on-board, and 3 of 15 (20%) active turtles released with satellite tags died within 6 days. This is the first empirically-based estimate of on-board and post-release mortality of bycaught marine turtles that has until now been unaccounted for in trawl fisheries not equipped with turtle excluder devices.

Short-term changes in demersal fish assemblages exploited by an artisanal set gill net fishery in the Caribbean Sea (Colombia)

A basic input for implementing ecosystem-based management measures is the knowledge on fish assemblages exploited by multispecies fisheries, such as the set gill net artisanal fishery in the Gulf of Salamanca (GoS), Caribbean Sea (Colombia), which catches a large number of high-value demersal species. Assemblages of this type were identified in this study, and significant differences (P < 0.01) between sampling periods (2008 and 2013) and seasons were found by means of a two-way permutational multivariate analysis of variance. These results were consistent with those obtained with the principal coordinates analysis, indicating the occurrence of short-term structural changes in these assemblages. Interannual and seasonal variations in discriminant and typifying species were also identified using similarity percentages, and a decreasing trend in landing per unit effort was established by the bootstrap method. On the other hand, both the geographic location of the fishing grounds and the characterization of historical changes in the set gill nets used in the GoS were determined using the traditional ecological knowledge of local fishermen, who reported a decrease in mesh sizes. In conclusion, temporal variations could be related to changes in the gill nets, the fishing trip schedules, and the spatial distribution of fishing effort, all which occurred in response to the decrease in catch rates in traditional fishing grounds.

Artisanal elasmobranch fisheries of northwestern Baja California, Mexico

Elasmobranch species composition and spatiotemporal variability can often be characterized from landing surveys of local fisheries, with important management implications. In the present study, we describe the elasmobranch landing composition of 4 major artisanal fishing ports in northwestern Baja California, Mexico. Sampling was conducted opportunistically between 1995 and 2010 and included an effort of 684 fishing days. Species composition was gear-dependent and varied with the fishing area, with thresher sharks (Alopias vulpinus) and spiny dogfish (Squalus suckleyi) dominating the catches landed by coastal gill net fisheries, and blue sharks (Prionace glauca) and shortfin mako sharks (Isurus oxyrhinchus) dominating the catches landed by the offshore longline fishery. Size-structure analysis indicated that catches were composed primarily of juveniles for most species, although the catch of mature soupfin sharks (Galeorhinus galeus) increased in longline fisheries during the winter. The results indicate that minor regional differences in elasmobranch species composition occur along the Pacific coast of Baja California and are most likely related to regional oceanographic or habitat differences. The results of this study may form the basis for future efforts to monitor species composition changes over time, to more completely assess elasmobranch populations.

Procedures for managing the quota of set net fisheries for the stock of Pacific bluefin tuna

Procedures for managing the quota of set net fisheries for the stock of Pacific bluefin tuna

Minimum drift times infer trajectories of ghost nets found in the Maldives

This study explores methods to estimate minimum drift times of ghost nets found in the Maldives with the aim of identifying a putative origin. We highlight that percentage cover of biofouling organisms and capitulum length of Lepas anatifera are two methods that provide these estimates. Eight ghost nets were collected in the Maldives and estimated drift times ranged between 7.5 and 101 days. Additionally, Lagrangian simulations identified drift trajectories of 326 historical ghost nets records. Purse seine fisheries (associated with Korea, Mauritius, the Philippines, Spain, France and Seychelles) and gill nets from Sri Lanka were identified as 'high risk' fisheries with regard to likley origins of ghost nets drifting into the Maldives. These fisheries are active in areas where dense particle clusters occured (drift trajectories between 30 and 120 days). Interestingly, ghost nets drifting less than 30 days however, remained inside the exclusive economic zone of the Maldivian archipelago highlighting potential illegal, unreported and unregulated fishing activity is occuring in this area. This study therefore points to the urgent need for gear loss reporting to be undertaken, especially by purse seine and gill net fisheries in order to ascertain the source of this major threat to marine life. This should also be coupled with an improvment in the data focused on spatial distribution of the abandoned, lost or discarded fishing gear originating from both large- and small-scale fisheries.

Modifying selectivity to reduce unwanted catches in an English trammel net and gill net common sole fishery

Modifying the design and selectivity of commercial fishing gears can reduce unwanted catches. Most gear selectivity research focusses on trawl gears, and there are relatively few examples of modified static nets, such as gill and trammel nets, which are used all over the world. Fishers operating in the southeast England’s common sole (Solea solea) static net fishery wanted to explore methods to try to reduce the unwanted catches of thornback ray (Raja clavata). In 2017, the fishery had common sole landings of 343 tonnes making it an important local fishery. The largest port, the beach launch port of Hastings, is the home port for 65 vessels. Here we describe the performance of a modified trammel net with reduced mesh size in the two outer walls, intended to reduce catches of thornback rays without reducing the landings of the target species of common sole. There no published studies on modifying the outer meshes of a trammel net. The fieldwork was undertaken onboard a vessel from Hastings, fishing over ten days. The catches from a standard gill net, a standard trammel net and a modified trammel net were compared. Six fleets of nets were fished, each made up of five different net sections. The three net designs were placed into the fleets in a random set design. All of the net designs had a minimum (inner) mesh size of 90 mm. There was no statistically significant difference in the number of thornback ray caught between the nets but the number of common sole was estimated at 87 % higher by value in the modified trammel net compared to the other nets. Therefore, when using the modified trammel net, considerably less fishing effort was required to catch the same quota of common sole, but with no increase in the rate of thornback ray catches. If this design were to be applied more widely in this fishery, it could reduce overall catches of thornback ray. The study shows the difference in selectivity towards common sole, plaice (Pleuronectes platessa), whiting (Merlangius merlangus) and thornback rays between a gill net and two trammel net designs.

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.

Evaluating the suitability of fyke nets for small-scale fisheries in the Free State Province of South Africa

South Africa is under increasing pressure to develop small-scale fisheries in inland waters. To inform appropriate development of this sector in the Free State Province, the catch rate of double-ended fyke nets was evaluated using survey data from 20 impoundments sampled during the 2013/2014 summer season. Fyke nets were set over night and the total sample effort was 114 fyke net nights. Overall catch per unit effort (CPUE) was 16.8 ± 28.3 kg·net-1·night-1 and catch composition was dependent on impoundment, but generally comprised of a mixture of common carp Cyprinus carpio, African sharptooth catfish Clarias gariepinus, smallmouth yellowfish Labeobarbus aeneus, Orange River mudfish Labeo capensis and moggel Labeo umbratus. The influence of temperature and the potential benefits of baiting the nets were subsequently evaluated through monthly sampling in the hyper-eutrophic Krugersdrift Dam and at the oligotrophic Gariep Dam. Baiting did not significantly influence CPUE, which was significantly higher at Krugersdrift Dam (19.97 ± 23.22 kg·net-1·night-1) than at Gariep Dam (5.02 ± 6.05 kg·net-1·night-1). Increasing temperature had a positive effect on CPUE at Krugersdrift Dam but not at Gariep Dam. Species composition also differed between impoundments and, as a result, we conclude that seasonal catch rates and species compositions will need to be evaluated prior to implementation of fyke net fisheries in specific localities.

Study on a Fixed Net Fishing Vessel (19 GT Type)

The fixed net fishery is essential, because the quantity of catch is the second in Japan. And it is said that this fishery consumes very little oil and is friendly to the ocean environment. But researching fixed net fishing vessels has not been done at all for a long time. Under these backgrounds, study on a fixed net fishing vessel is carried out. Subjects on a vessel are cleared through field survey, so that hull form, hull construction, the difference of loading conditions and sea speed at between departing from the port and the fixed net and so on. Improving hull form is tried to 19 gross ton type, and the performance is evaluated through a model resistance test in a circulating water channel (cwc). The hull form design for fore body is improved by the use of wave making resistance theory, and one for aft body is enhanced by the use of the Eulerian scheme with the Lagrangian particles. The fixed net fishing vessel is defined as low fuel consumption. But the level of hull resistance is not very good, so the fact is cleared of that improving of hull form and decrease speed is necessary for saving energy and for getting up profit. Through present study, the truth is cleared that the cwc experiments are very useful for inducing the projects on developing hull form and there is the difference of view point to cwc experiments on between general merchant ships and special small ships including fishing vessels.

Relationship between damage to set net fisheries caused by Kyucho and vertical structure of current speed at fishery grounds on the coast of the Tango Peninsula

Relationship between damage to set net fisheries caused by Kyucho and vertical structure of current speed at fishery grounds on the coast of the Tango Peninsula

Structural variability and composition of fish communities in the northern continental shelf of the Bay of Bengal, Bangladesh

The structural variability and composition of fish communities in the northern continental shelf of the Bay of Bengal, Bangladesh were assessed from monsoon 2014 to pre-monsoon 2015. A total of 73 species belonging to 43 orders, comprising 61 species of finfishes and 12 species of shellfishes were identified from estuarine set bag net (ESBN) fisheries. Of these, sixty species were commonly found throughout the study period and while nine species were dominant with higher contribution to the total communities. Community parameters and abundance were higher in monsoon and lower in winter. Multivariate analysis revealed a clear structural and compositional variation in fish communities. Furthermore, RELATE (coefficient of correlation between the fisheries communities and environmental parameters) and BIOENV/BEST (Biotaenvironment best matching) analyses showed that these variations were driven by both single (transparency) and multistressors [transparency in combination with associated factors such as salinity, total dissolved solids (TDS), total suspended solids (TSS), phosphate-phosphorus (PO4-P) and nitrite-nitrogen (NO2-N)]. Community parameters showed significant positive correlation with transparency, salinity and PO4-P which indicated that structure of fish communities is shaped by ecological conditions in this coastal habitat.