Mesh Codend Research Articles

Size selectivity and catch efficiency of bottom trawl with a double sorting grid and diamond mesh codend in the North-east Atlantic gadoid fishery

This study investigated the size selectivity and catch efficiency in the North-east Atlantic demersal trawl fishery targeting cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). The use of a sorting grid followed by a size selective codend is compulsory in this fishery. Experimental fishing was conducted with a commercially rigged trawl, flexigrid section, and diamond-mesh codend. The flexigrid section is a dual sorting system and all fish that escaped from the two grids in the flexigrid system and the codend were retained in separate covers. This allowed us to estimate the combined size selectivity of the system, as well as the separate contributions from the first grid, second grid, and codend. The catch efficiencies for cod and haddock below and above the minimum reference length (MRL) were quantified by estimating the values for a set of exploitation pattern indicators. The results showed that most fish escaped from the flexigrid section. Only a few fish below the MRL entered the codend and nearly all of them subsequently escaped through the codend meshes. The probability of retaining undersized cod and haddock was low with the combined system. Furthermore, the results showed that the probability of escape was high through the second grid in the system for fish above the MRL, and this finding was supported by the exploitation pattern indicators. In particular, the estimated exploitation pattern indicators showed that using the current MRL and the fish size distributions encountered during the trials, no haddock and only 2.3 % of cod below the MRL were retained by the gear. However, 77.4 % of the haddock and 16.0 % of the cod above the MRL were found to escape, thereby indicating poor catch efficiency, especially for haddock. These results demonstrate the importance of supplementing size selectivity research with estimates of the actual catch efficiency using the gear employed, which were quantified using exploitation pattern indicators in this study.

Estimating selectivity of experimental diamond (T0) and turned mesh (T90) codends in multi-species Mediterranean bottom trawl

The effect of shifting from a diamond mesh codend (T0) to a 90° turned mesh codend (T90) on the size selectivity of seven commercially important species in the Mediterranean bottom trawl fishery was evaluated. During sea trials conducted in the north-western Adriatic, two experimental codends made of 54 mm nominal mesh size netting that differed only in mesh configuration were alternately mounted on the same trawl. Overall, the size selectivity was significantly improved for all the species analysed, shifting from T0 to T90. The difference in the average expected L50values between T90 and T0 was particularly marked in European hake (Merluccius merluccius, 21.26 vs 11.26 cm total length), common squid (Loligo vulgaris, 12.06 vs 7.88 cm mantle length) and mantis shrimp (Squilla mantis, 20.78 vs 13.35 mm carapace length). Both codends had an excessive size selectivity especially for red mullet (Mullus barbatus), Mediterranean horse mackerel (Trachurus mediterraneus) and whiting (Merlangius merlangus), thus involving a commercial loss. These findings demonstrate the efficiency of the T90 codend tested at excluding undersized specimens, especially of hake, whose average L50was above the minimum conservation reference size of 20 cm. The adoption of this practical and inexpensive solution could help improve the management of the demersal resources targeted by the Mediterranean bottom trawl fishery.

Quantification of gear inflicted damages on trawl-caught haddock in the Northeast Atlantic fishery

External damages are indicators of the overall quality of fish and fish welfare. Haddock is an important commercial species widespread in the North Atlantic, but few studies related to quality have been carried out on this species. We studied the levels of external damages on haddock captured with a demersal trawl in the Northeast Atlantic. Further, we investigated to what extent the compulsory sorting grid and diamond mesh codend gear configuration employed in this trawl fishery is responsible for the external damages observed during the capture process. We evaluated external damages on 563 haddock captured over 22 hauls. In general, the results showed that catching haddock without any gear inflicted damages using demersal trawls is challenging. However, the results also showed that the severity of most damages is low and the probability to catch haddock with no external damage can be significantly increased removing the grid and changing codend design.

Length‐weight relationship of six coastal fish species from Gulf of Mannar, South‐east coast of India

The parameters ‘a’ and ‘b’ of length weight relationship of 6 species (Scolopsis vosmeri (Bloch, 1792), Engyprosopon macrolepis (Regan, 1908), Bleekeria murtii Joshi, Zacharia&Kanthan, 2012), Centriscus scutatus Linnaeus, 1758, Samaris cristatus Gray, 1831 and Iniistius bimaculatus Ruppell, 1829) are reported from the Gulf of Mannar, South east coast of India. The fish samples were collected from experimental trawling conducted twice a month during the period August to December 2012 and September to December 2013 at a depth ranging from 8.5 to 20.5 m. Three hauls were made in a day with each haul of one hour duration. The total length of the gear was 32 m with a cod end mesh size of 30 mm. The total length of the fish was measured to the nearest 0.1 cm and weight to the nearest 0.1 g.

Length‐weight relationship of seven bycatch fish species caught along the Chennai coast, Bay of Bengal, Eastern Indian Ocean

Length-weight relationships (LWRs) were estimated for seven fish species captured as bycatch along the Chennai coast, Bay of Bengal, Eastern Indian Ocean. Fish samples were collected fortnightly between June-2018 to February-2019 from the commercial boats operating bottom trawl nets with a cod-end mesh size of 35mm. The total length (L) and the wet weight (W) to the nearest 0.1 cm and 0.01 g, respectively which is followed by regression analysis. The values of exponent (b) for LWRs varied from 2.5803 (Parachaeturichthys polynema) to 3.4432 (Ostorhinchus oxina). Similarly, a value varied between 0.0037 (Bleekeria kallolepis) and 0.0258 (Archamia bleekeri). As per FishBase, a new TLmax has been recorded for four species such as Ostorhinchus oxina, Jaydia striata, Bleekeria kallolepis and Cocotropus roseus.

Escapement patterns of red mullet, sole, horse mackerel and hake facing two trawl selective devices

The landing obligation implemented under the European Union Common Fisheries Policy prompted the development of selective devices for fishing gear to reduce unwanted catches. In the Bay of Biscay, a collaborative project between scientists and fishermen evaluated catch rates and length frequencies of caught species from two innovative trawl devices, which were compared to the gear that is currently used in the fishery. The experimental designs were: (1) a 90 mm square mesh bycatch reduction device inserted in the tapered section (SMBRD) and (2) a 70 mm T90 mesh codend and extension (T90). Each selective device was tested separately using the twin trawl method for catch comparison on board commercial vessels: SMBRD was tested on board vessels targeting Nephrops and T90 on board vessels targeting demersal fish. This study focused on hake (Merluccius merluccius), which is an important bycatch species, red mullet (Mullus surmuletus) and common sole (Solea solea), which have high commercial value, and horse mackerel (Trachurus trachurus), which is nearly never discarded. Horse mackerel and hake escaped through the two devices tested, resulting in fewer unwanted catches in the selective trawls without commercial loss. For sole, more individuals were caught with the SMBRD than with the standard gear. The T90 resulted in the escapement of most red mullet across its entire length range observed, resulting in significantly lower Catch Per Unit Effort of landings and unwanted catch, probably due to unsuitable mesh size and shape for that species. These results have direct application for multispecies fisheries in which fishermen have to appropriately select devices according to the specific characteristics and species composition of their fisheries.

Hiện trạng khai thác và nhận thức về tác động của biến đổi khí hậu đến nghề lưới đáy ven bờ, tỉnh Sóc Trăng

Studying on fishing status and perception of fishermen on the impact of climate change to near shore bag-net fishing at Soc Trang province was performed from January to June, 2018. Results showed that fishing boat power, length, and tonnage are recorded at 32.7±13.9 CV; 12.09±1.63 m; and 5.46±3.97 tons, respectively. Bag-net length, width, height, and cod-end mesh size are at 23.3±7.97 m; 14.2±5.02 m; 5.35±2.71 m; and 2a=12.7±0.46 mm, respesctively. The average member of fishermen is 3.63±1.56 people/boat; 47.9±13.7 years old; 80,0% at primary school level in education. The average of fishing time is 6,2±3,1 days/month and the main fishing season is from January to June annually. Fishing yield is at 191.9±152.8 kg/day/household (11.9±10,0 tons/year/household). Total investment cost is at 124.1±54.1 million VND/boat and variable cost at 1.36±0.79 thousand VND/household/day. Turnover is at 2.24±0.88 million VND/day and profit rate 0.53±0.47. There are 77.5% fishermen only working on fishing. There are 55% fishermen have aware of climate change such as stronger wind rate and increasing storm frequency, and fishing season present unusually and difficult to predict. Only 45% fishermen have some temporary solutions to cope with climate change. Generally, bag-net fishing have low production and unstable income due to extreme weather and banning regulation. Thus, the fishermen suggest suitable and integrated solutions for their better livelihood.

Assessment of bag net fishery of Narmada estuary, Gujarat: A case study

Bag net, locally known as ‘Golava,’ is an important means of fishing in the middle stretch of Narmada estuary for the livelihood security of many stakeholders. The present study was conducted during 2015-16 to find out species composition and economic evaluation of bag net fishery in the Narmada estuarine region. Bag net was operated for 7-8 months with peak duirng November to February. A total of 7-8 sets of bag nets were found to be operated from Bhadhut (21o 41' 108" N, 72o 51’ 198" E) to Mehgam (21o 40' 44" N, 72o 45’ 27" E) region. In a single set, a total of 12-22 numbers of bag nets were installed with an average individual net length of 25-27 m with 10 mm cod-end mesh size. The nets were installed in the current-driven area during low as well as high tides to harvest fishes during high tides and low tides, respectively. A total of 8-12 fishers were involved in the total installation. The operational time of the bag net is around 10-12 hours. The mean catch per unit effort (CPUE) was recorded 2.5-9.5 kg/day/ operation during the study periods. Mullets were the dominated group contributing 30% to the catch, followed by Otolithoides pama (15%), Lates calcarifer (14%), Macrobrachium rosenbergii (12%), catfishes (8%), Harpadon neherius (6%), Cynoglossus cynoglossus (4%), Eleutheronema tetradactylum (3%), juvenile Tenualosa ilisha (2%) and others (6%) during peak season (November-February). The mean profit per net per year was estimated to be 0.14 and 0.18 lakh for Bhadbhut and Mehgam centres, respectively. Due to less profit, high capital requirement, and operational cost, bag net fishery is gradually declining in the Narmada estuary. Bag net fishery was found to be destructive and needs to be replaced with alternative nets with higher mesh sizes for sustainable exploitation of the resources.Key words Bag net fishery; catch composition; profitability; sustainability; Narmada estuary

Karadeniz’de Mezgit (Merlangius merlangus euxinus) avcılığındaki trol torba seçiciliklerinin karşılaştırılması

A large part of the total whiting (Merlangius merlangus euxinus) fishing in the Black Sea is carried out with the traditional bottom trawl nets along the coast of Turkey. Diamond mesh shape with 40 mm mesh size (40D) has been used in the codends of these trawls. In this study, the traditional trawl codend (40D) and square-mesh codend with different size (36S and 40S) were compared for whiting size selectivity in August 2014. Selectivity data were collected by using a covered codend method and analysed taking between haul variations in to account. The selectivity parameters were estimated by using CC2000 software. Results showed that commercially used 40D trawl codend is not selective enough to release immature of whiting. However, the net change in square mesh (36S and 40S) instead of a diamond-shaped (40D) mesh significantly improved the mesh selectivity for whiting. The 40S trawl codend is even higher than the first maturity size (LM50) with a length at fifty percent retention (L50) of 15.74 cm. In conclusion all square mesh codends with different mesh size tested here supplied appropriate selection considering minimum landing size (MLS) of whiting.

Quantification of bell-shaped size selectivity in shrimp trawl fisheries using square mesh panels and a sorting cone after a Nordmøre grid.

Shrimp trawlers in the Barents Sea use a Nordmøre sorting grid ahead of a small-mesh codend to avoid bycatch while catching shrimps efficiently. However, small fish can still pass through the grid to enter the codend, which increases their risk of being retained. In this study, we quantified the selectivity of a standard Nordmøre grid used together with one of two different codend designs, namely a diamond mesh codend with square mesh panels and a codend with a square mesh sorting cone section, for deep-water shrimp (Pandalus borealis), redfish (Sebastes spp.), and American plaice (Hippoglossoides platessoides). For the first time, the selective properties of these two alternative designs were estimated and compared to those of a Nordmøre grid used together with a 35-mm diamond mesh codend, which is the compulsory gear used in the fishery today. With this traditional codend, the size selectivity of both bycatch species showed the expected characteristic bell-shaped size selection pattern, with low retention probability of very small fish and bigger fish but with high retention probability of certain sizes of juveniles. Using the square mesh sorting cone significantly reduced the maximum retention risk of redfish. The maximum retention with the diamond mesh codend with square mesh panels was estimated to be 14% lower than that of the traditional codend, but the difference was not statistically significant. The two alternative codend designs did not result in any significant reduction in bycatch of American plaice.

Length-Weight Relationships for 16 Snapper Fishes fromVisakhapatnam Coast, India

This study presents the length-weight relationships (LWRs) for 16 lutjanid species from Visakhapatnam coastal waters, India (16.98°N-20°.2 N, Long. 82.19°-86.53°E). The samples were collected fortnightly between December 2013 and December 2018 from commercially operated fishing gears viz.: the reef fish trap with single and double horse necked funnel (mesh aperture size 4.5 cm) trap measured about 3 ft in length, 4 ft in width and 2.5 ft in height, having a volume of 30 cu ft. The soak time was between 18 to 22 h. Gill nets made of monofilament nylon netting with a mesh size of 80 mm were used in the collection of snapper fishes. The nets were operated 3 h before morning (sunrise) and hauled 1 h after the sunrise. The depth of the net operated varied from 3 to 8 m, whereas the head rope of the net is around 20–25 m in length. The hook number 8 to 11 is used for the fishing of snapper fishery resources in water depth more than 75 m in Visakhapatnam region. The soak time varied from 5 to 10 h. The bottom trawlers (43 mm with a cod end mesh size of 15–25 mm) a depth range of 10 to 55 m, whereas during each fishing period, 3 to 4 hauls are made with a towing period ranging from 1 to 2 h; trawlers (a depth regime of 12 to 55 m, with a mesh size of 400 mm to 25 mm at the cod end). Around 3 to 6 hauls are made during each fishing trip with a towing period of 1to 2 h. All LWRs were significant with r2 values ranged from 0.9504 for Lutjanus lemniscatus to 0.9951 for Lutjanus fulvus and ‘b’ values ranging from Pinjalo pinjalo for 2.5982 Lutjanus quinquelineatus for 3.4993. In addition, new maximum total length for each of the three species L. indicus, L. xanthopinnis and P. pinjalo was also found. The parameters are found great importance to evaluate the relative condition of populations, biology, ecology, species management and their fisheries and stock assessment.

Analysis on the body size selectivity for multi-species of discarding juvenile fishes in the bottom trawl

Discarding juvenile fishes under girth 16 cm nearly equal to inner perimeter of codend mesh size collected by a cover net method in bottom trawl. The body size of the main five species (mackerel, horse mackerel, sea bream, melon seed and black throat seaperch) was measured for their body length, girth, weight, height and width and analyzed size selectivity. Frequency of penetrating fish as retention in a cover net was less than 40% of total number of juvenile discarding fish. The most of body length or girth of five species were significantly different between in the codend and in the cover net. The 50% selection girth in the cover net ranged 8-11 cm were smaller than those in the codend ranged 9-13 cm by the species respectively. The 50% selection body length was significantly related with the ratio of body height (H) by body width (W) both for in the codend or in the cover net while 50% selection girth was not significantly related with H/W. Furthermore 50% selection fish size by fish species between in the codend and in the cover net was not significantly different both in body length or girth. Therefore, the girth selectivity represented possibly as one unique value regarding fish body shape was considered as more useful method for multi-species catch in trawl.

Analyses of the non-target catch from the Egyptian Mediterranean trawlers, off Port Said

The present study aimed to analyze the non-target catch in the Egyptian Mediterranean waters, off Port Said, during the period from spring 2017 to winter 2018. The analysis revealed that from 75 non-target species, fish constituted about 69.4% of the total catch weight, whereas invertebrates reached about 30.6%. For non-target fish, 51 fishes were identified (50 bony fishes and one elasmobranch), of which 17 lessepsian species were found. The high percentage of fish (82.67%) was with an average length between 4.0 and <9.0 cm. The highly represented fish species by numbers were: Engraulis encrasicolus (25.608%), Herklotsichthys punctatus (23.711%), Terapon puta (9.572%), Equulites klunzingeri (9.342%), Gobius niger (7.177%), Argyrosomus regius (6.280%), Alepes djedaba (4.155%), Gobius paganellus (3.397%), Sardinella aurita (2.525%), Ariosoma balearicum (1.093%) and Diplodus annularis (0.803%). Total analysis, seasonal analysis and an index of diversity (H′) for the non-target catch species were provided. On the other hand, length-weight relationship, condition factor and age composition were described for the most dominant species. For non-target invertebrates, 24 species were identified among which 13 lessepsian species were found. Shrimps and mantis shrimp Erugosquilla massavensis were the main constituents during the period of study. The authors propose to change the cod end mesh size from 2.5 cm to 4.0 cm to minimize the high percentage of non-target catch and preserve recruits of valuable species from over fishing along the Egyptian coast of the Mediterranean Sea while doing experiments to ensure the best results. Further, continuous monitoring and managements of trawlers must be put into consideration.

Effect of three different codend designs on the size selectivity of juvenile cod in the Barents Sea shrimp trawl fishery

Shrimp trawlers often use a Nordmøre sorting grid ahead of a small mesh codend to avoid bycatch of juvenile fish while allowing shrimps to be efficiently caught. However, small fish can pass through the grid to enter the codend and risk being retained. The risk of retention for fish of different sizes depends the size selection in the Nordmøre grid and the size selection in the subsequent codend, which makes the process complex and often results in a bell-shaped size selection curve. In the Barents Sea shrimp fishery, cod (Gadus morhua) is one of the species of concern because of its great commercial value. We studied the size selection of juvenile cod when the trawl was equipped with the compulsory gear in the fishery: a 19 mm Nordmøre grid followed by a 35 mm diamond mesh codend. As expected, the size selection curve showed a bell-shaped signature, with a certain size range of juveniles having high retention risk, while the risk for smaller and bigger cod was smaller. The retention risk was highest for cod between 12 and 20 cm in length. We also tested two alternative designs in the aft section of the gear: a codend with 35 mm square mesh panels and a square mesh sorting cone section. Neither of these designs affected the size selection in the trawl significantly.

Further improvements in sorting grids for the crustacean trawl fishery off the Southern coast of Portugal

Bottom-trawl fishing for crustaceans off the Portuguese south and southwest coasts is a very important segment of the Portuguese fishing fleet, where annual rates of discarding have ranged from approximately 38% to as much as 70% of the total catch. Past experiments to address this problem encompassed the testing of different codend mesh sizes and configurations, square mesh windows and rigid grids to enhance species and size-selectivity. While the use of a Nordmøre grid has proved quite efficient in separating out blue whiting (Micromesistius poutassou), it also led to some losses of the two main crustacean target species, Norway lobster (Nephrops norvegicus) and rose shrimp (Parapenaeus longirostris). The present study addresses that limitation by using a modified grid with 20 mm bar spacing and two open sections, designed with the purpose of separating fish and crustacean species into upper and lower codends. Good separation was achieved, with about 80% of the blue whiting (in number) directed towards the upper trawl section and caught in the upper codend, while a similar percentage of Norway lobster was caught in the lower codend. The grid bars had 50% retention for Norway lobster at 34.1 mm carapace length. The results herein will enable this gear configuration to be fine-tuned with regard to codend mesh sizes and bar spacing, so as to optimize both retention of Norway lobster and exclusion of blue whiting. For example, compared to using the minimum 70 mm diamond mesh size, using an 80 mm diamond mesh upper codend would reduce Norway lobster catch weight by just 1.6% but reduce the number of blue whiting caught by 42%.

Length‐weight relationships of 10 coastal fish species from the Visakhapatnam coast, India

We analysed the length‐weight relations (LWRs) of 10 fish species inhabiting different habitats from Visakhapatnam, Coast of India. Samples were obtained between August 2013 and December 2016 from commercial trawlers at the local fish landing centre (16.98°N–20.20°N, Long.82.19°–86.53°E). Fishes were captured between 100 and 300 m depth with demersal trawl net (head rope length: 46 m and cod end mesh size: 40 mm with a 38 m high speed. Total length (TL; nearest to 0.1 cm) and body weights (nearest to 0.1 g) were taken from each individual. This study provides new maximum length data for two species (Archamia bleekeri (Gunther, 1859) and Ostorhinchus fleurieu (Lacepede, 1802), and LWR estimates for rare deep reef associated fishes are provided for the first time. All LWRs were significant with r² values ranging from .908 for Sargocentron praslin (Lacepede, 1802) to .981 for Parapercis pulchella (Temminck & Schlegel, 1843) and “b” values ranged from 2.5216 for Parapercis pulchella (Temminck & Schlegel, 1843) to 3.4746 for Ostorhinchus fleurieu Lacepede, 1802.

Comparing size selectivity of traditional and knotless diamond-mesh codends in the Iceland redfish (Sebastes spp.) fishery

The size selectivity and usability of two diamond mesh codends, a traditional two-panel codend versus an experimental four-panel ultra-cross knotless mesh codend, were compared using the covered codend method in the Iceland redfish (Sebastes norvegicus and S. viviparous) fishery. Results showed that there was no significant difference in size selectivity between the codends at lengths greater than 29 cm for S. norvegicus and 19 cm for S. viviparous. At smaller lengths, size selectivity was undetermined due to small catches at those sizes. For S. norvegicus, both codends demonstrated a high retention ratio (93.4 and 92.9%, respectively) above the minimum reference length (MRL; 33 cm), but also had a high retention below MRL (90.9 and 83.4%, respectively). However, the actual proportion of catch below MRL was low due to few small fish on fishing grounds. Since these fish are difficult to tell apart and have similar morphologies, we investigated the size selectivity of the two codends for both species combined, resulting in similar results of no difference in size selectivity, but a large increase in actual catches below MRL, which were primarily S. viviparous. This study concludes that the experimental codend does not improve the size selectivity or usability in the Iceland redfish fishery and both codends will retain large proportions of undersized fish if present on fishing grounds; however, few undersized fish were present in the study area.

Growth, Mortality, and Exploitation Rate of Penaeus merguensis in the North Coast of Central Java, Indonesia

One of the most-caught shrimp in north coast of Central Java is Penaeus merguiensis. However, little is known on the population biology of the organisms. This study was aimed to investigate length-weight relationship, growth, length at first capture (Lc50), mortality rate, and exploitation rate of P. merguiensis in Western part of Central Java’s northern coastal waters. The study was conducted from May 2016 to July 2017 using survey method. Samples were taken for 15 times (month) from 9 coastal fishing ports. The result shows that the relationship of the carapace length and weight is negative allometry. The growth parameters of CL∞ and K were 52.5mm and 1.3 y-1 (male) and 57.25mm and 1.2 y-1 (female). Total mortality rate (Z), natural mortality rate (M), and fishing mortality rate (F) were 4.51 y-1, 1.86 y-1 and 2.65 y-1 (male), and 5.36 y-1, 1.72 y-1, and 3.64 y-1 (female), respectively. The exploitation rate (E) of male banana shrimp was 0.59, and for female shrimp was 0.68. The result shows that the exploitation level has exceeded the optimum level (E&gt;0.5). Recruitment of P. merguiensis may occur the whole year, but it peaks were in March and August (male), April and August (female). Carapace length of first captured (CLc50) was 20.63mm (male) and 18.28mm (female). It means that the sized of captured P. merguiensis is less than the size of first mature (CLm50) or growth overfishing and as a result, disrupting the availability of adult shrimp. The condition occurs due to the size of cod-end mesh measured 0.75inc.

Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms of the Iberian Mediterranean. Bottom trawling impact

Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms of the Iberian Mediterranean. Bottom trawling impact

English

English