Nylon Gillnets Research Articles

Length‐Weight and Length‐Length Relations of 14 Freshwater Fish Species from the Qiantang River, China

The Qiantang River, located in Zhejiang Province, China, is a crucial water resource with significant ecological and economic importance. This study aimed to evaluate fishery resources in the Qiantang River Basin by analyzing the length‐weight relationships (LWRs) and length‐length relationships (LLRs) of 14 fish species. Fish samples were collected between July 2021 and November 2023 using multipanel nylon gillnets and cage nets. Each specimen was measured for total length (TL) and standard length (SL), as well as weighed. Linear regression models were employed to estimate LWRs and LLRs, with statistical tests revealing significant relationships (P < 0.05) and high R2 values above 0.91. The study contributed new LWRs for two species and LLRs for three, deepening our understanding of their biology. These findings enriched FishBase and offered valuable data for fish stock assessments and management strategies in the Qiantang River Basin. Future research can utilize this foundation to explore population dynamics and promote sustainable management practices.

Status, ecology and conservation of Irrawaddy dolphins (Orcaella brevirostris) in Malampaya Sound, Palawan, Philippines

A geographically isolated population of Irrawaddy dolphins was recently discovered in Malampaya Sound, Palawan, Philippines. Line-transect surveys conducted in April-November 2001 covered 884km of trackline in the entire Sound and resulted in a total population estimate of 77 individuals (CV = 27.4%), confined to the inner portion (133.7km2 ). For all Irrawaddy dolphin sightings, where ecological data were collected (n = 48), the mean temperature was 30.2°C, depth 6.5m, salinity 28.3ppt and turbidity 2.2NTUs. Significantly higher turbidity, lower salinity and shallower depth were recorded in the inner Sound compared to adjacent waters. Bottlenose dolphins Tursiops sp. (probably truncatus) were observed in waters just outside of where Irrawaddy dolphins were recorded. During the study, at least two Irrawaddy dolphins were accidentally killed in bottom-set nylon gillnets used to catch crabs, locally called matang quatro. Reports from local fishermen also indicated that as many as three additional animals may have been killed in these nets during the same period. These findings strongly suggest that the Irrawaddy dolphin population in Malampaya Sound is in immediate danger of extirpation due to low numbers, limited range and high mortality. This is the only known population of the species in the Philippines and the nearest known other population is in northern Borneo, some 550km to the south. Recommendations for conserving the population include that: (1) socioeconomic alternatives be developed to promote the conservation goal of reducing the incidence of dolphin entanglement in matang quatro gillnets; (2) gillnet free zones be established in core areas of dolphin distribution; (3) Irrawaddy dolphins be promoted as a flagship species of environmental health in the Sound; (4) a long-term programme be established to monitor the dolphin population; and (5) additional investigations be conducted to determine if Irrawaddy dolphins occur in other areas of the Philippines.

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

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

Length–weight and length–length relations of 16 freshwater fish species (Actinopterygii) caught in Jiaxing section of the Beijing–Hangzhou Grand Canal, China

The length–weight (LWRs) and length–length (LLRs) relations were estimated for 16 fish species obtained from Jiaxing section of the Beijing–Hangzhou Grand Canal, China. One species represented Engraulidae: Coilia nasus Temminck et Schlegel, 1846; 11 species Cyprinidae: Hypophthalmichthys molitrix (Valenciennes, 1844); Hypophthalmichthys nobilis (Richardson, 1845); Chanodichthys erythropterus (Basilewsky, 1855); Chanodichthys mongolicus (Basilewsky, 1855); Culter alburnus Basilewsky, 1855; Chanodichthys dabryi (Bleeker, 1871); Pseudobrama simoni (Bleeker, 1864); Hemiculter leucisculus (Basilewsky, 1855); Megalobrama terminalis (Richardson, 1846); Carassius auratus (Linnaeus, 1758); Cyprinus carpio Linnaeus, 1758; one species Bagridae: Tachysurus fulvidraco (Richardson, 1846); two species Odontobutidae: Odontobutis potamophilus (Günther, 1861); Micropercops swinhonis (Günther, 1873); and one species Osphronemidae: Macropodus ocellatus Cantor, 1842. Fishes were collected using multipanel nylon gillnets with mesh sizes of 1–8 cm from November 2020 through August 2021. All fishes were measured for length (total length, TL; standard length, SL) to the nearest 0.1 cm and weight (W) to the nearest 0.1 g. The coefficients of determination R2 of LWRs and LLRs were all over 0.950, and the 16 values of LWR parameter b were estimated from 2.505 to 3.364. Our study provides new information on LWRs for 2 species and LLRs for 7 species, as well as a new maximum total length recorded for 3 species for FishBase. This study would allow for the convenience of the conversion of TL–W and SL–TL in fish stock assessment and is expected to provide a useful baseline for further studies of population parameters to improve management decisions.

Visual Health Assessment and evaluation of Anthropogenic threats to Arabian Sea Humpback Whales in Oman

The sub-population of humpback whales inhabiting the Arabian Sea is a small and genetically distinct population that remains in low latitudes year round. Designated as Endangered on the IUCN Red list of Threatened Species, the population faces a number of threats throughout its range, including entanglement in fishing gear, ship strikes, and habitat degradation. Research conducted primarily off the coast of Oman over the past 20 years has contributed to understanding the population’s distribution, abundance, and conservation status. However information on the population’s health and specific threats is limited. This study examines all available images of Arabian Sea humpback whales obtained between 2000 and 2018 for evidence of disease, predation, epizoites and human-induced scarring or injury to individuals. Tattoo-like skin disease was detected in 43.4% of 83 adult whales, with a roughly equal distribution between males and females. Prevalence of the disease was significantly higher in 2012-2018 (51.7%) than in 2000-2011 (24.1%). Killer whale tooth rakes were detected on the ventral surface of the tail flukes of 12% (95% CI 4.5-18%) of 77 individuals. Roughly two thirds (66.6%: 95% CI 52-80%) of the 42 individuals represented by good quality photos of the caudal peduncle region at the fluke insertion bore scarring patterns consistent with entanglement in fishing gear. Four individuals had injuries consistent with vessel strikes and at least two other individuals showed severe injuries and deformations likely caused by interactions with fishing gear. Documented entanglement events from Oman and Pakistan involved large-mesh nylon gillnets, known to be used extensively throughout the Arabian Sea. These findings indicate an urgent need to design effective management and mitigation of threats, and to continue monitoring Arabian Sea humpback whales, with an emphasis on methods that allow continued and expanded assessment of health, body condition, and anthropogenic interactions.

Documentation of gill net operation and major fish landings at Andaman Islands, India, during 2014 - 2018

Three decades before, the gillnet was the major gear in Andaman and Nicobar Islands(ANI), India, because of the less expensive and simple method of operation with non-motorised small dinghies or without craft. Earlier, the gillnet landing was 39% of the total landings and a further report said 27%, which indicated the decrease in gillnet landings. The present study was carried out from 2014 to 2018 at four main fish landing centers (FLCs) Junglighat, Dignabad, Guptapara and Wandoor of ANI to investigate the present status of major gillnet landings. Altogether 1097 visits were carried out at all FLCs and 63.1% of visits occurred at Junglighat. The total landings of all FLCs were 3880.6 tons, of which 98.6% were recorded at Junglighat. The total gillnet landings were 330.4tons, of which Driftnet covered 82.1%, followed by bottom plastic(9.8%) and bottom nylon(8%) gillnets. Significant landings (P<0.0001) of Scombridae family were recorded through Drift gillnet (182.47tons) compared to other families. The family of Carangidae(7.71tons) and Clupeidae(16.54tons) were recorded dominantly through bottom plastic and bottom nylon gillnets, respectively. The gillnetters explored 31 fishing grounds in the South, Middle, North and Little Andamans sectors. The significant (P<0.0001) fish catch was recorded from the South Andaman sector. A total of 17 validation experiments carried out in each Potential Fishing Zone (PFZ) and Non-PFZ by using PFZ advisories indicated a significant(P<0.0001) catch from PFZ(3.5:1). There was a decline of 18.5% in the landings of gillnet than earlier studies. It is suggested that the fishermen may follow the PFZ forecast for a better catch. The gillnet fishing to be promoted to under-exploited pelagic fishes of these islands will benefit the gillnetters.

The fate of conventional and potentially degradable gillnets in a seawater-sediment system

Abandoned gillnets in the marine environment represent a global environmental risk due to the ghost fishing caused by the nets. Degradation of conventional nylon gillnets was compared to that of nets made of polybutylene succinate co-adipate-co-terephthalate (PBSAT) that are designed to degrade more readily in the environment. Gillnet filaments were incubated in microcosms of natural seawater (SW) and marine sediments at 20 °C over a period of 36 months. Tensile strength tests and scanning electron microscopy analyses showed weakening and degradation of the PBSAT filaments over time, while nylon filaments remained unchanged. Pyrolysis-gas chromatography/mass spectrometry revealed potential PBSAT degradation products associated with the filament surfaces, while nylon degradation products were not detected by these analyses. Microbial communities differed significantly between the biofilms on the nylon and PBSAT filaments. The slow deterioration of the PBSAT gillnet filaments shown here may be beneficial and reduce the ghost fishing periods of these gillnets.

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.

Comparison of the efficiency and modes of capture of biodegradable versus nylon gillnets in the Northeast Atlantic cod (Gadus morhua) fishery

Modern gillnets are usually made of nylon with high breaking strength, suitable elasticity and durability making them an efficient fishing gear. Lost, abandoned, or discarded gillnets at sea cause plastic pollution and can continue capturing marine animals over long periods of time. Biodegradable materials are being developed to replace nylon in gillnets. However, biodegradable gillnets have shown reduced catch efficiency compared to the nylon gillnets which challenges their acceptance by the fishing sector. This study investigated catch efficiency and modes of capture between biodegradable and nylon gillnets in commercial cod (Gadus morhua) fishery. On average, new biodegradable gillnets caught 25% fewer cod compared to new nylon gillnets. The main capture modes were by the gills and by the body in used and new biodegradable gillnets, respectively. Differences in catch efficiency are related to specific modes of capture that may be related to differences in material properties.

A new method for estimating length-dependent capture modes in gillnets: a case study in the Danish cod (Gadus morhua) fishery

Abstract Gillnets are used world-wide for harvesting groundfish and pelagic species at sea and in freshwater. Little consideration has been given to how fish are caught in gillnets, even though the capture mode provides valuable information for understanding gear catchability. This paper describes a new method of estimating the length-dependent fish capture modes in gillnets. Using this method, we investigated the length-dependent capture modes for cod (Gadus morhua) in commercial monofilament nylon gillnets. Cod is a target species for several fisheries in the Northern Atlantic. This is the first time the capture mode was formally related to fish size with a direct representation of the experimental observations. The results demonstrated that gillnets are clearly designed for gilling. However, capture modes were size dependent, with small fish being caught by the mouth and larger fish by the maxillary. The application of the method is relevant when used by gear technologists to evaluate different gear characteristics to improve size or species selectivity. Changing the hanging ratio, for instance, or replacing nylon twine by thicker biodegradable material may considerably change the capture modes and their effect on gear efficiency.

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.

The effect of long-term use on the catch efficiency of biodegradable gillnets

The effect of long-term use on the catch efficiency of biodegradable gillnets was investigated during commercial fishing trials and in controlled lab aging tests. The relative catch efficiency between biodegradable and nylon gillnets was evaluated over three consecutive fishing seasons for Atlantic cod (Gadus morhua) in Norway. The biodegradable gillnets progressively lost catch efficiency over time, as they caught 18.4%, 40.2%, and 47.4% fewer fish than the nylon gillnets during the first, second, and third season, respectively. A 1000-hour aging test revealed that both materials began to degrade after just 200 h and that biodegradable gillnets degraded faster than the nylon gillnets. Infrared spectroscopy revealed that the chemical structure of the biodegradable polymer changed more than the nylon. Although less catch efficient than nylon gillnets, biodegradable gillnets have great potential for reducing both capture in lost fishing gear and plastic pollution at sea, which are major problems in fisheries worldwide.

Governance implications for the implementation of biodegradable gillnets in Norway

Gillnets are among the most widely used fishing gear in global fisheries because of their simplicity, high operability, catch efficiency and low entrance cost for fishermen. In Norway, the Northeast Atlantic (NEA) cod (Gadus morhua) fishing industry represents the most important economic single species fishery and the gillnet fishery accounts for 24% of the national total allowable catch (TAC) of NEA cod. Despite the importance of the gillnet fishery in Norway, significant amounts of gillnets are lost at sea each year. As gillnets are made of synthetic materials (i.e. nylon) with high breaking strength and durability, lost, abandoned and/or discarded fishing gear (LADFG) continues catching target and non-target species for years. This phenomenon, known as "ghost fishing", cause negative impact on the benthic marine environment and to the fisheries management. Over the last years, the development of biodegradable gillnets to replace traditional nylon gillnets has become particularly sought after in fisheries worldwide. However, biodegradable gillnets are less efficient and more expensive than traditional nylon gillnets. As the urgency to eliminate the negative environmental impacts of LADFG increases, a crucial question remains how to successfully implement biodegradable gillnets to replace the more efficient nylon gillnets currently used in commercial fisheries. In this article we investigate how central elements of fisheries management may be used to implement biodegradable gillnets and how this may challenge the current resource allocation policy among different gear- and vessel groups.

Variation over Time of Length–Weight Relationships and Condition Factors for Four Exotic Fish Species from a Restored Shallow Lake in NE Iberian Peninsula

Length–weight relationships (LWRs), condition factors, and their variation over time were analyzed for four exotic freshwater fish (bleak, common carp, pikeperch, and roach) in the Estany d’Ivars i Vila-sana shallow lake in Catalonia, Northern Spain. Fish samples were collected twice a year (early summer and autumn), between 2008 and 2016, by using between three and five multi-mesh nylon gillnets. This study provides novel information about four common exotic fishes outside of their natural range and within the context of a restored shallow lake, where the ichthyologic community is evolving in concordance with the ecosystem conditions and the fish community dynamics.

Comparison of fishing efficiency between biodegradable gillnets and conventional nylon gillnets

Gillnets made of a new biodegradable resin (polybutylene succinate co-adipate-co-terephthalate (PBSAT) were tested under commercial fishing conditions to compare their fishing performance with that of conventional nylon (PA) nets. The relative catch efficiency between the two gillnet types was evaluated over the entirewinter fishing season for cod (Gadus morhua) in northern Norway. The nylon gillnets caught 21% more fish (in numbers) than the biodegradable gillnets throughout the fishing season and generally showed better catch rates for most length classes, except for sizes between 82 and 90 cm. The difference in elasticity and breaking strength could explain the major difference in the size structure of fish caught by each type of gillnets, especially for larger fish. The number of times that the gillnets were deployed affected the relative catch efficiency of the gillnets with the biodegradable continuously loosing efficiency compared to the nylon. Although less catch efficient than nylon gillnets, biodegradable gillnets still show great potential for reduction of ghost fishing and plastic pollution at sea caused by this fishery.

Fishing efficiency of biodegradable PBSAT gillnets and conventional nylon gillnets used in Norwegian cod (Gadus morhua) and saithe (Pollachius virens) fisheries

Abstract Fishing trials were carried out to compare the relative fishing efficiency of gillnets made of a new biodegradable resin (polybutylene succinate co-adipate-co-terephthalate, PBSAT) with conventional (nylon) nets. The fishing trials covered two consecutive fishing seasons (2016 and 2017) for cod (Gadus morhua) and saithe (Pollachius virens) in northern Norway. Results generally showed better catch rates for the nylon gillnets. The biodegradable PBSAT gillnets caught 50.0% and 26.6% fewer cod, and 41.0% and 22.5% fewer saithe than the nylon gillnets in 2016 and 2017, respectively. Even though the relative catch efficiency of the biodegradable gillnets was slightly better in 2017 than in 2016, the difference with respect to the catch efficiency of nylon gillnets may be too large for biodegradable gillnets to be accepted by fishermen if they were available commercially. Tensile strength measurements of the nylon and biodegradable PBSAT gillnets carried out before and after the fishing trials showed that the both types of gillnets had significant reductions in tensile strength and elongation at break, especially in 2017. Although less catch efficient than nylon gillnets, biodegradable PBSAT gillnets show great potential for reducing ghost fishing and plastic pollution at sea, which are major problems in these fisheries.

Genetic diversity of upper Lake Constance whitefish Coregonus spp. under the influence of fisheries: a DNA study based on archived scale samples from 1932, 1975 and 2006.

This investigation examined changes in the genetic diversity of pelagic upper Lake Constance (ULC) whitefish Coregonus wartmanni population before and after the alteration of fishery methods and management from 1932 to 2006. The study spans a period of pronounced changes in trophic status of the lake and transitions from traditional relatively unselective pelagic seine (Klusgarn) fishing to highly size-selective nylon gillnet techniques. In addition, supportive breeding and stocking became most popular during the phase of eutrophication in the 1970s. The main hypothesis is that size-selective fisheries and breeding lead to an overall decrease in genetic variability over time. A total of 215 archived C. wartmanni scale samples from 1932, 1975 and 2006 were analysed by genotyping 11 microsatellite loci. A comparison of population genetic parameters, including allelic richness, observed and expected heterozygosities, and estimates of effective population sizes, suggests that the genetic diversity of C. wartmanni population has not decreased. The appearance of new alleles in the gene pool in 1975 and 2006 may be indicative of admixture with other forms in the lake or with stocked allochthonous forms. Overall, the fisheries management practice in ULC, including the effects of size-selective fisheries, supportive breeding and stocking, have not significantly altered the genetic diversity of Coregonus spp. over an 80 year period.

A review of sawfishes (Pristidae) in the Arabian region: diversity, distribution, and functional extinction of large and historically abundant marine vertebrates

Abstract Sawfishes (Pristidae) are large shark‐like batoids (rays) that are among the most threatened of all marine fishes. While there is a broad consensus of severe sawfish declines globally, detailed status assessments for most of their vast circumtropical distribution do not exist. This paper reviews sawfishes of waters adjacent to the Arabian Peninsula, focusing on the Gulf. Until around the 1960s, sawfishes were abundant and widespread in the region, but since around the 1980s, they have been rarely recorded. Sawfishes can now be considered extinct as a functional component of coastal ecosystems, and may be close to being regionally extinct. This assessment is based on the overwhelming weight of evidence from diverse sources such as archaeological data, historical accounts, grey literature, personal communications and extensive fish surveys. Based on 176 individual records, Pristis zijsron was the most frequently recorded species, occurring in all regional seas. Anoxypristis cuspidata records were limited to the coasts of Iran, Pakistan, and Masirah Island (Oman). The first substantiated Pristis pristis records from the Arabian Peninsula are provided, and two records not identifiable to species do not exclude the possibility that Pristis clavata occurs in the region. Humans have used sawfishes as a food, oil, trade, and cultural resource for several thousands of years. Fins have been highly valued since at least the mid‐19th century. Based on recent and historical records, known biology, and marine conservation programmes for other species or habitats, priority areas for sawfish research and recovery programmes are the central southern Gulf; significant mangrove areas in Iran and the UAE; the Musandam Peninsula; and Masirah Island (Oman). Historical regional declines coincide with the widespread availability of nylon gillnets, to which sawfishes are disproportionately vulnerable. Any attempt at sawfish recovery must enforce strict controls on gillnetting, which could have significant benefits for other marine species of commercial and conservation interest. Copyright © 2014 John Wiley & Sons, Ltd.

그물실의 물성에 따른 동해안 가자미 자망어업의 어획 특성

Physical characteristics of net filament were investigated to test the fishing capacity of gill nets due to the flexibility difference between nylon and biodegradable nets (PBS 95%+PBAT 5% and PBS 80%+PBAT 20%). In addition, a total of 16 fishing experiments were conducted in the coastal waters of Jeongja, Ulsan, from August 10 to October 20, 2011 and from September 11 to November 3, 2012. The test results showed that nylon net filament exhibited more flexibility than biodegradable net filament when they were wet. Accordingly, the longer submerged time, the more fishing capacity the nylon gill nets demonstrated in comparison with the biodegradable gill nets. A total of 16 species were caught in 2011 with the nylon gill nets (1,323 fishes, weighing 342,885g) and the biodegradable gill nets (958 fishes, weighing 236,857g). 15 species were caught in 2012 with the nylon gill nets (1,582 fishes, weighing 448,360g) and the biodegradable gill nets (1,431 fishes, weighing 406,590g). Thus catch weights and the number of fish caught produced by the nylon nets were 1.45 times and 1.38 times higher than those of the biodegradable nets produced in 2011, and 1.1 times and 1.11 times higher in 2012. A test on the target species, pointhead flounder (Cleisthenes pinetorum) has similar results. The flexibility of a net was proved to be related to the fishing capacity, and as a result, it is concluded that the higher flexibility, the higher fishing capacity.

Gillnet selectivity in the Ebro Delta coastal lagoons and its implication for the fishery management of the sand smelt, Atherina boyeri (Actinopterygii: Atherinidae)

Multimesh nylon gillnets were set in three Ebro Delta (North-East of Spain) lagoons to determine mesh selectivity for the inhabiting fish community. Each gillnet consisted on a series of twelve panels of different mesh size (ranging from 5.0 to 55.0 mm bar length) randomly distributed. The SELECT method (Share Each Length’s Catch Total) was used to estimate retention curves through five models: normal location, normal scale, gamma, lognormal and inverse Gaussian. Each model was fitted twice, under the assumptions of equal and proportional to mesh size fishing effort, but no differences were found between approaches. A possible situation of overfishing in the lagoons, where artisanal fisheries are carried out with a low surveillance effort, was assessed using a vulnerable species inhabiting these brackish waters as case study: the sand smelt, Atherina boyeri. The minimum size for its fishery has not been established, thus remaining under an uncontrolled exploitation situation. Therefore, a Minimum Landing Size (MLS) is proposed based on sexual maturity data. The importance of establishing an adequate MLS and regulate mesh sizes in order to respect natural maturation length is discussed, as well as, the proposal of other measures to improve A. boyeri fishery management.