Codend Mesh Size Research Articles

The challenge of harvesting common sole (Solea solea) in highly selective trawl fisheries

Common sole (Solea solea) is an economically important species in several European trawl fisheries, yet little is known about the size selective properties of codends used in bottom trawl fisheries targeting sole. This study presents results from a sea trial conducted in the inner Danish waters where common sole is fished in a seasonal trawl fishery using a 90 mm diamond mesh codend with a mandatory large mesh escape panel. To improve understanding of the selectivity in this gear, we in addition tested a plain 90 mm diamond mesh codend without an escape panel. This combination of codend mesh size and large mesh escape panel is part of an ambitious management plan aimed at eliminating bycatch of cod (Gadus morhua) in trawl fisheries in the inner Danish waters. In the fishery for common sole, we found a severe mismatch between gear regulations and minimum conservation reference size of the target species. The outcome is a highly inefficient fishery in which only 22 % (CI: 18–27 %) by weight of the marketable sole is retained in the 90 mm diamond mesh codend. Further, we estimated that 25 % (CI: 16–35 %) of the sole entering the codend would contact the mandatory escape panel and escape, resulting in a total loss of 83 % (CI: 79–87 %) of marketable sole through the mandatory gear. The inefficiency in this fishery demonstrates the need for other means than gear specifications to regulate this type of fishery.

Length-Weight Relationship of Four Species of Deep-Sea Congrid Eel (Congridae) from the Southwest Coast of India, Arabian Sea

Length-weight relationship was estimated for the deep-sea congrid eel species collected from the trawler landings at Kalamukku, of Kochi, Kerala and Colachel, of Kanyakumari, Tamil Nadu, Arabian Sea, southern India, between February 2021 and August 2022. The samples were obtained from the deep-sea trawlers, operated along the Exclusive Economic Zone of India, Arabian Sea with a cod end mesh size of 35 mm at 200–250 m depth. The estimated b values range from 2.80 to 3.19. Novelty of the study is providing length-weight relationship for two newly described eel species viz. Ariosoma indicum and A. maurostigma will help in the conservation and management of these species in the future.

Effect of Codend Design and Mesh Size on the Size Selectivity and Exploitation Pattern of Three Commercial Fish in Stow Net Fishery of the Yellow Sea, China

To address the issue of minimum mesh size regulations of the stow net fishery for croaker species, we tested and compared the size selectivity and exploitation pattern for diamond- and square-mesh codends with mesh sizes 35, 45 and 55 mm for little yellow croaker (Larimichthys polyactis), silver croaker (Pennahia argentata), and flower croaker (Nibea albiflora) in the Yellow Sea, China. Our results showed that the legal codend (35 mm diamond-mesh) was inadequate to protect the juvenile croaker species because more than 75% of undersized individuals were retained, and the discard ratios were as high as approximately 60%. Irrespective of mesh shape, increasing the codend mesh sizes could significantly improve the size selectivity and exploitation pattern of croaker species. Between codends with the same mesh size, the square-mesh codends had higher size selectivity than diamond-mesh codends. Based on results, the 55 mm square-mesh codend was recommended for rational exploitation of croaker stocks. This study can provide feasibility and insight for the enforcement and reform of management strategies for sustainable fishing in Chinese stow net fisheries.

The capability of square-meshes and fixed-shape meshes to control codend size selection

Trawl codends are commonly made of diamond-mesh netting. However, diamond-mesh codends vary in mesh geometry along its length and during fishing due to catch build up. This introduces variability in the size selection process. This phenomenon compromises the rationality of regulating exploitation patterns in trawl fisheries through adjustments in codend mesh size. One technical solution often applied to achieve more well-defined size selection is turning the codend netting 45 degrees (square-mesh). However, there is a lack of evidence that square-mesh codends result in more constant size selectivity. Therefore, we aimed at quantifying the variability in size selection in square-mesh codends. We tested the size selectivity of three codends; a standard square-mesh codend, and two rigid codends where mesh geometries were fixed in diamond shape with an opening angle of 60° and square shape, respectively. The two rigid codends were used to establish baselines with limited variability in size selection. The size selectivity of these codends was compared to results - previously obtained for a standard diamond-mesh codend. Using Atlantic cod (Gadus morhua) as a case study, we demonstrated that the standard square-mesh codend had significantly larger variability in size selection compared to the fixed diamond-mesh codend. Moreover, we found no evidence that the standard square-mesh codend had lower variability in size selection than a standard diamond-mesh codend with same mesh size. These results demonstrate that the use of standard square-mesh codends is not sufficient to reduce variability in codend size selection. Additionally, we demonstrate that the sizes of fish retained is strongly dependent on mesh shape and openness. We conclude that a profound re-thinking over codend designs is required in order to achieve better control of size selection in trawl fisheries.

Distribution and sources of macrolitter on the seafloor in Belgian fisheries areas

Marine litter is recognized as a global environmental concern. Seafloor litter can provide important information to help assess the status of the marine ecosystem and is relatively easy to collect on a regular basis. The Belgian fisheries area covers different parts of the OSPAR Greater North Sea region and the Celtic Seas. In these regions, seafloor litter data were gathered by quantifying the litter items caught in the trawl net during two different fisheries surveys to investigate litter distribution on both regional and local scales. In the international beam trawl survey (BTS), covering essentially the OSPAR Greater North Sea and Celtic Seas, an average of 2.2 ± 0.05 items.ha-1 were caught with a median of 1.4 items.ha-1. In the environmental monitoring survey (EMS) only the Belgian part of the North Sea was covered and a smaller cod-end mesh size was used, resulting in 12.7 ± 1.7 litter items.ha-1 in the coastal zone (< 12 nm) and 2.8 ± 0.2 items.ha-1 in the more offshore zone (> 12 nm). In both surveys plastic items were predominant, representing up to 88% of the collected litter in the Belgian part of the North Sea. The impact of human activities at sea such as fisheries, sand extraction, wind farms and dredge disposal was investigated. A significant correlation was found between fishing activities and the amount of litter registered in the Belgian part of the North Sea, but not for the OSPAR Greater North Sea and Celtic Seas.

Fish Catch Rate and Fish Composition of Commercially Operated by Multi-Day Trawling off Sindhudurg Coast of Maharashtra, India

The commercial-operated multi-day trawlers from Sindhudurg coast carried out fishing operations at Malvan landing center, South Konkan region, Maharashtra, India in the mean depth range of 18–31 m in September, 2016 to May, 2018 to assess the changing trends in the fish catch composition, catch and discards rate by multi-day trawlers operating along the Sindhudurg coast of Maharashtra state. The average catch rate was observed 25.03 kg h-1 and 31.72 kg h-1 with average discards 5.07 kg h-1 and 7.81 kg h-1 by multi-day trawler during 2016–17 and 2017–18 respectively. During two fishing seasons, the average catch rate was 28.37 kg h-1, with average discards of 6.44 kg h-1 by multi-day trawlers. Major catch composition of multiday trawlers comprised Arius maculatus, Parastromateus niger, Lactarius lactarius, Otolithes cuvieri, Lepturacanthus savala, Rastrelliger kanagurta, Scomberomorus guttatus, Cynoglossus macrostormus, Uroteuthis duvaucelii, and Penaeid prawns. Discards comprised juveniles of commercial species and adults of low market value fishes. Cod end mesh size of trawl net varied from 15–35 mm depending on the fishery resources harvested. Duration of fishing trips by multi-day trawlers varied from 2–4 days, peak fishing activities were observed during October to December followed by February in terms landing. The study clearly indicated an increase in the average catch rate h-1 trawler-1 during the year 2017–18 compared to the previous year 2016–17 along the Sindhudurg coast. The t-Test performed on fish catch and discard of multi-day trawlers showed a statistically significant difference (p<0.05) in a fish catch (kg h-1) and fish discards between two fishing seasons, i.e., 2016–17 and 2017–18.

Effect of codend mesh sizes on the size selectivity and exploitation pattern of cocktail shrimp (Trachypenaeus curvirostris) in shrimp trawl fishery of the South China Sea

This study aims at improving fishery management by testing and comparing the size selectivity and exploitation pattern of diamond-mesh codends, with mesh sizes ranging from 25 to 54 mm, for cocktail shrimp (Trachypenaeus curvirostris) in the South China Sea (SCS). Beginning from 25 mm, the minimum mesh size regulated by the shrimp trawl fishery industry, we investigated how the mesh sizes of the codends would affect the size selectivity and exploitation pattern in reference to the minimum conservation reference size (MCRS, 7.0 cm total length) of cocktail shrimp in the SCS. According to our results, the selective properties of the codend mesh sized at 25 mm in line with the regulation failed to protect the undersized individuals of cocktail shrimp because of its 50% retention length of 5.85 cm (confidence interval, CI: 5.16–6.18 cm), far less than the MCRS of cocktail shrimp. As the retention probability of a shrimp with a MCRS length was as high as 97.45 % (CI: 86.86–100.00%), more than 40% of the undersized shrimp was retained. It was proved that increasing the codend mesh size did not significantly improve the size selectivity and exploitation pattern which might be improved by other gear modifications.

Some Growth Properties and Length at First Maturity of Big Scale Sand Smelt (Atherina boyeri Risso, 1810) in İznik Lake, Turkey

In this study, the length at first maturity and growth characteristics of the big scale sand smelt (Atherina boyeri Risso 1810) were investigated in İznik Lake. Catching trials were conducted on a monthly basis at 4 different stations of the lake between March 2014 and February 2015 and beach seine net with 6 mm of codend mesh size was used in the samplings. The overall sex ratio of the subsample was founded as 1:1.46 (F:M; 1180 females, 1729 males). The fork length range were 3.3-11.2 cm for females and 2.9-9.7 cm for males. The growth equations were found as TW=0.005FL3.160 and TW=0.006FL3.067 for female and male respectively. Allometric (+) growth has been shown in both sex groups. According to the logistic regression model results, length at first maturity (L50) was estimated as 4.62 and 4.25 cm fork length for female and male respectively. While the growth properties of the species shown similarity with other habitats of populations, the values of length at first maturity (L50) shown some differences.

Design and General Characteristics of ‘Disco Dol’ (Two Seam Trawl) Operated along Ratnagiri, Maharashtra

The present investigation was taken to know the variations with respect to design, net specification, mesh size of Disco dol trawl net operated along the Ratnagiri coast. A total of 42 trawl net was sampled physically by using measurement tape and scale. The data were collected by structured schedule consisting of two major sections. The first section was for vessel details and second for the specifications of trawl nets. The study revealed that, two seam locally known ‘Disco dol’, operated from Ratnagiri was observed with eight belly sections of overall length ranges from 41 to 52m. Wings of the net were triangular in shape with a mesh size variation between 120-440 mm. The dimensions such as breadth, number of meshes along breadth and mesh size were decreasing from first to last belly section, but average number of meshes per metre were increasing from first to last belly. Wide reduction of 400-40 mm was observed in mesh sizes of belly section for Disco dol from first to last belly. Cod end mesh size of trawl operated from Jaigad, Kasarveli, Mirkarwada and Purnagad landing centres was recorded as 20 mm. In Ratnagiri, two seam trawl net was used mainly to catch fishes.

Morphological and meristic features of Vulnerable Tenualosa toli (Valenciennes, 1847) from Narmada estuary, Gujarat, India

A clupeid group (Hilsa) in the Indian sub-continent is represented by three species viz ., Tenualosa toli , T. ilisha and Hilsa kelee , which has great economic significance for the fishers. Tenualosa toil is observed to have narrow distribution in the Indian sub-continent, along with vulnerability status. The present study describes the morphological and meristic features of T. toli collected from the Narmada estuary, Gujarat, India. A single specimen was collected from the bag net catches (10 mm cod-end mesh size) - from Bhadbhut fishing site in December 2019. The size of specimen with a total length of 298 mm, standard length of 224 mm, and weight of 214 g. The morphometric and meristic characters were assessed and compared with other published literature. The present investigation of T. toli suggested that immediate measures should be adopted to rejuvenate the species in the aquatic habitats.

Comparing size selectivity and exploitation pattern of diamond-mesh codends for Southern velvet shrimp (Metapenaeopsis palmensis) in shrimp trawl fishery of the South China Sea.

In this study, size selectivity and exploitation pattern of six diamond-mesh codends with different mesh sizes, ranging from 25 to 54 mm, for Southern velvet shrimp (Metapenaeopsis palmensis) were tested and compared in a shrimp trawl fishery of the South China Sea (SCS). We used a codend with a mesh size of 25 mm (D25) as a starting point, which is the minimum mesh size (MMS) currently regulated in the studied area. Four different fishing population scenarios were applied to quantify and compare how mesh sizes of codends used would impact the size selectivity and exploitation pattern for the target shrimp species. The results demonstrated that the D25 codend was not proper for protecting juvenile shrimp at the studied area. By applying this legal codend, L50 (50% retention length) of the target shrimp species was below its minimum conservation reference size (MCRS, 7.0 cm total length), the retention probability of shrimp with a length of MCRS was above 95% CI [91–99] and more than 43% of undersized shrimp was retained. To mitigate the bycatch issue of undersized shrimp, increasing the mesh size in the diamond mesh codend is a simple and effective option. However, the loss of catch efficiency for marketable shrimp is a major concern while increasing the mesh size. A good compromise between releasing undersized shrimp and maintaining the legal individuals is manifested by using the codend with 35 mm mesh size (D35). Our study will be beneficial for the management of shrimp trawl fisheries in the SCS.

Length‐weight relationship of five species of Nemipteridae family along the Gulf of Mannar, Eastern Indian Ocean

The parameters 'a' and 'b' of the length-weight relationship of five Nemipteridae species viz., Nemipterus bipunctatus (Valenciennes, 1830), Nemipterus randalli Russell, 1986, Scolopsis bimaculata Ruppell, 1828, Scolopsis xenochrous Gunther, 1872 and Scolopsis vosmeri (Bloch, 1792) are reported from the Gulf of Mannar, Eastern Indian Ocean. The fish samples were collected fortnightly from the trawlers of Thoothukudi Fishing Harbour between September 2020 and June 2021. The trawlers operate at a depth of 40–150 m with a 2–2.30 hours hauling period. These are operating bottom trawl nets and have a total length of 40 m with a cod-end mesh size of 35 mm. The total length of the fish was measured to the nearest 0.1 cm and weight to the nearest 0.01 g, respectively. The descriptive statistics and estimated length-weight relationships (LWRs) parameters were detailed in the paper.

Identification of three cephalopods from the Iranian waters of the Gulf of Oman (Continental shelf area)

This study aimed to find new species of cephalopods in the Iranian waters of the Gulf of Oman. Two species of Oegopsida (Abralia steindachneri Weindl, 1912 and Joubiniteuthis portieri (Joubin, 1916)) and also one species of Sepiida (Sepia omani Adam & Rees, 1966) were identified. Samples were collected in March and April 2019, using a Myctophidae trawler. To capture A. steindachneri a two-panel bottom trawl (codend mesh size (A) equal to 60 mm) was used, while for J. portieri and S. omani a four-panel midwater rope trawl (codend mesh size (A) equal to 90 mm) was applied. Taxonomic studied on these rare cephalopods, in this region, would be helpful for protecting their stocks as well as safely exploitation them.

New Distributional Record of Triacanthus nieuhofii Bleeker, 1852 (Tetraodontiformes: Triacanthidae) from Maharashtra, North West Coast of India

Background: Fishes of the family triacanthidae are highly diversified throughout the world, but studies on these fishes were very limited in India. Now a day’s catch of species belongs to this family increasing and showing new geographical distributions due to overfishing of top predators. Methods: Experimental fishing method was conducted by using the M.F.V Narmada-IV vessel of ICAR- Central Institute of Fisheries Education, Mumbai. The vessel operated with a demersal trawl net with a cod-end mesh size of 30 mm. Spatial distribution map of the family Triacanthidae was generated from previous literature using the IDW interpolation method in Arc GIS 10.4.Result: New distributional record of silver tripodfish, Triacanthus nieuhofii Bleeker, 1852 was recorded for the first time from the Mumbai waters, northwest coast of India. Spatial map showing that the species of the family Triacanthidae were highly diversified along the east coast than the west coast of India.

The Cost of Fishing on Juveniles of Finfish and Shellfish: Assessment of Economic Impacts of Trawl Juvenile by-Catch along the Coast of North Andhra Pradesh, India

A study was carried out to assess the economic value of juveniles of commercially important species of finfish and shellfish caught as by-catch by multiday commercial trawlers operated off the coast of Visakhapatnam, north Andhra Pradesh from January 2014 to December 2015. Juveniles of twenty species (four species of cephalopods and sixteen species of finfish) were found to dominate the trawl by-catch. The landed juveniles of these 20 species formed 12,757.16 t and 286.86 million numbers per year and their contribution to the total landings of these species in trawl by-catch were 55.30% by weight and 57.03% by numbers. The highest percentage of quantities of juveniles (biomass) was found in trawl by-catch in the months of August and July in, 2014 and 2015 respectively. Among the juveniles, ribbonfish (Trichiurus lepturus) and goatfish (Upeneus vittatus) dominated, contributing together, on an average 11.60% by weight and 33.68% by numbers respectively. Using the bio-economic model, it was estimated that if the juveniles were allowed to grow up to length at first maturity; total annual economic gain would have been Rs. 273.21 crores (42.03 million USD) with biomass gain of 44,493.02 t per annum. The estimated total annual biomass would have increased 3.46 times with an increase in revenue by 4.20 times. Annual average loss due to fishing of juveniles was estimated to be Rs. 209.62 crores (32.25 million USD). The results of the present study suggested that sustainable harvest of these resources would have yielded maximum economic return to the fishers. With the help of stakeholders using a participatory approach, management measures such as increase of cod end mesh size of trawl to 40 mm from the present mesh size of 10–12 mm, use of square mesh for trawl cod ends, fishing effort restriction and awareness campaign on the detrimental impacts of catching juveniles needs to be implemented at the earliest for avoiding growth overfishing.

Population Dynamics, Fishery, and Exploitation Status of Norway Lobster (Nephrops norvegicus) in Eastern Mediterranean

Norway lobster (Nephrops norvegicus) is one of the most valuable shellfish resources in the Mediterranean and the northeast Atlantic. Sustainable management of its fishery require long-term scientific monitoring of its stocks. Population dynamics, fishery, and exploitation status of the Norway lobster were studied over a long time series (between 2008 and 2014) in a semi enclosed gulf in Easter Mediterranean (Pagasitikos Gulf). Sampling was carried out using a commercial bottom trawl with a codend mesh size of 28 mm in three different regions within the Gulf. Sex was identified macroscopically and all individuals were measured and weighed. Growth and Age groups were investigated by analysis of length–frequency distributions of the Carapace length (CL) for both sexes. Fishing, Natural and Total Mortality, along with Exploitation rate of the total stock were estimated by the FiSAT software package. Females were further examined and classified based on their maturity stage and the size at onset of sexual maturity was estimated by Probit analysis. Temporal differences in mean CL were detected for both sexes, with a tendency of lower values each year, along with a respective increase in Fishing Mortality and Exploitation Rate, indicating the effects of fishing pressure over the population. Size at onset of sexual maturity was estimated at 32.6 mm, higher than the official mesh sizes for creels (28 mm) and gillnets (26 mm). According to the analyses, the local Norway lobster stock is over-exploited, which should be taken under consideration by the regional policy makers.

Length-Weight Relationships of Four Demersal Fish Species from Chendering, Terengganu, Malaysia

The length-weight relationships (LWRs) of four demersal fish species were estimated using fishes collected over a seven-year period (2012–2019) from the commercial fish landing jetty of Chendering, Terengganu, Malaysia. These fishes had been caught in every fourth quarter of the year from the Terengganu water of South China Sea using trawl net (local name: pukat tunda) with 38 mm cod end mesh size at the depths ranging from 26 to 38 m. The value of exponent b ranged from 2.756 (Nemipterus nemurus) to 3.186 (Synodus tectus) while regression parameters r2 was between 0.964 and 0.979. The present study provides a new maximum length data for all four species: 19.5 cm for Upeneus guttatus (Day 1868), 25.5 cm for Nemipterus hexodon (Quoy and Gaimard 1824), 22.5 cm for Nemipterus nemurus (Bleeker 1857), and 21.6 cm for Synodus tectus Cressey 1981.

Population structure of <i>Paralonchurus brasiliensis</i> (Steindachner, 1875) (Perciformes: Sciaenidae) in the coast of Sergipe, northeastern Brazil

Paralonchurus brasiliensis is one of the most common fish species found in the bycatch of shrimp trawling in Sergipe. We analyzed its population structure through four sampling programs, two using hired shrimp trawlers (2013-2014 and 2017-2018) and two from the commercial shrimp fleet (2015-2016 and 2018-2019). The codend mesh size varied among programs (18, 20, and 21 mm). All specimens of P. brasiliensis were identified and had their standard and total lengths (SL and TL; cm) and their total weight (TW; g) measured. A total of 1509 specimens were collected measuring 4.7-22.9 cm TL and 0.4-114.8 g. About 67% of all specimens were below the length at first maturity (14.7 cm). The length-length and weight-length relationships estimated were TL=1.141+1.176×SL and TW=0.00270×TL3.391, respectively. The recruitment probably occurs in September-October and May. This species appeared to be more abundant at 15 m, and larger individuals were found at 5 m. Although P. brasiliensis is frequently caught in shrimp fisheries, it is not reported in catch statistics. Here, for the first time, we have documented its presence in Aracaju’s market under the categories ‘miunça’ and ‘pescadinha’ (97% adults), with the largest specimens landed and commercialized as ‘pescadinha’ together with other species. Smaller individuals are probably discarded by commercial fishers. The low selectivity of the fishing gear used leads to the capture of many juveniles, which may impact the population dynamics of this species as well as other species found in the same fishing ground.

Small steps high leaps: Bio-economical effects of changing codend mesh size in the North Sea Brown shrimp fishery

Small mesh codends applied in the brown shrimp (Crangon crangon L.) fishery in the North Sea cause large bycatch of fish, invertebrates and undersized shrimp. We investigated the most obvious and enforceable mitigation measure: the increase of mesh size beyond 20 mm, which was the medium mesh size of the fleet before 2016. The predicted selectivity from different codend designs was applied in a yield-per-recruit model able to reproduce the seasonal pattern of landings and biomass by sex, size, and age. The model enables assessment and quantifying population responses to possible management actions, also considering other influential variables such as natural mortality, which vastly decreased during the 1990s to the contemporary low level due to the decrease of cod in the Southern North Sea. Model results show that the selectivity of 20 mm codends leads to the poorest fishery and population indexes. Any increase in mesh size within the range considered and in the present low-predator situation would lead to a larger shrimp stock and higher catches. Increasing mesh size reduces catches of undersized and small commercial-sized shrimps entering the fishery mainly in summer time, thus leading to surplus catches in autumn and spring. Model results reveal that an increase of mesh size diminishes growth overfishing and allows the formation of a larger stock that may better cope a fluctuating natural mortality and the steadily upwards creeping fishing intensity.

Length‐weight relationships of three Clupeiformes species from the Southeast coast of India, Bay of Bengal, Eastern Indian Ocean

This study deals with the length-weight relationships (LWRs) of three commercially important marine fishes belonging to the family Clupeidae from the major landing centers in Tuticorin, Mandapam, Thondi, Nagapattinam and Chennai in southeast coast of India. Monthly sampling were done at the respected landing centers from June, 2018 to April, 2019 from the commercial trawlers (with cod-end mesh size of 25–35 mm) and gill netters (with different mesh size vary from 20 to 170 mm). The estimated ‘b’ values ranged from 3.1215 (Sardinella albella) to 3.1819 (Amblygaster clupeoides) and ‘a’ values varied from 0.0059 (A. clupeoides) to 0.0074 (S. albella). The study also provides a new maximum total length (TLmax) for two species A. clupeoides and Sardinella fimbriata.