Selectivity of diamond (PA) and square (PE) mesh codends for commercially important fish species in the Antalya Bay,eastern Mediterranean

Size selectivity of the 40 mm nominal polyethylene (PE) square mesh codend and the 44 mm nominal polyamide (PA) diamond mesh codend were determined under commercial conditions in the demersal trawl fishery. Data were collected using the covered codend technique and analyzed by logistic equation with a maximum likelihood method. Changing the mesh from a 44 mm PA diamond to a 40 mm PE square increased the mean retention lengths (L₅₀s) of red mullet (Mullus barbatus), picarel (Spicara maena) and bogue (Boops boops) and decreased the selection ranges (SR) for common pandora (Pagellus erythrinus). For large‐eye dentex (Dentex macrophthalmus) and axillary sea bream (Pagellus acarne) mean L₅₀ and SR values were 9.6 and 11.8, and 2.4 and 2.4 cm, respectively, only in the DM44PA codend. For golden banded goatfish (Upeneus moluccensis) values for SM40PE were only 15.0 and 2.7 cm, respectively. Results showed that the 40 mm PE square mesh codend provided higher selectivity for most of the Mediterranean fishes. The results also showed that regulating mesh size and requiring square mesh openings during trawling is essential for the release of immature individuals. This practice will result in a reduction in overfishing and permit recovery of overfished stocks.     

Selectivity of commercial compared to larger mesh and square mesh trawl codends for four fish species in the Aegean Sea

Differences in size selectivity of commercial (40 mm diamond mesh, 40D), larger mesh (48 mm diamond mesh, 48D), and square mesh codends (40 mm square mesh, 40S) for hake (Merluccius merluccius), greater forkbeard (Phycis blennoides), blackbelly rosefish (Helicolenus dactylopterus dactylopterus) and four‐spot megrim (Lepidorhombus boscii) were investigated in the Aegean Sea. The study was conducted using the covered codend method. Data were analysed taking between‐haul variations into account. Results showed that changing from a 40D to 48D codend significantly improved mean L₅₀ values, with increases of about 22% for hake, 8% for greater forkbeard, 20% for blackbelly rosefish, and 11% for four‐spot megrim (P = 0.000). A change from diamond to square mesh configuration with the same 40 mm netting also significantly increased the mean L₅₀ values, with 45% for hake, 36% for greater forkbeard, and 25% for blackbelly rosefish (P = 0.000). For four‐spot megrim the mean L₅₀ value was about 10% lower, but this difference was statistically insignificant (P > 0.05). Despite the increases in L₅₀ values, this study concludes that the selectivity of the 48D and 40S codends is still not sufficient to release fish smaller than length at first maturity for these four species.     

Selectivity of a 50-mm diamond mesh knotless polyethylene codend for commercially important fish species in the Aegean Sea

This research investigated effects of changing the diamond mesh size on codend selectivity in Mediterranean fisheries. The selectivity of a typical 50‐mm diamond knotless polyethylene (PE) codend used in the Turkish fishery in the Aegean Sea was measured for commercially important species, in particular hake (Merluccius merluccius), horse mackerel (Trachurus trachurus), anglerfish (Lophius piscatorius) and John Dory (Zeus faber). Fishing trials were carried out on the commercial trawler ‘Hapulo?lu’ between 9 and 12 December 2006 using a modified trawl net. Selectivity data were collected by the covered codend method and analysed by means of a logistic equation (Maximum Likelihood Method). The mean selectivity curve was estimated from individual hauls, taking between‐haul variations into account. Mean mesh size of the codend was 49.4 mm as measured by digital calliper. Mean values for 50% retention length of hake and horse mackerel were estimated to be 11.4 and 15.6 cm total length; corresponding selection ranges were 4.1 and 5.5 cm respectively. The 50‐mm diamond mesh codend showed adequate selectivity compared to the minimum landing size (MLS) for horse mackerel, while for hake it selected specimens in a size range far lower than the MLS. No selectivity values could be determined for anglerfish or John Dory. To design a more selective codend for the Turkish demersal trawl fishery, not only mesh size regulations but also other codend characteristics and netting material properties must be urgently considered.     

Selectivity of conventional and alternative codend design for five fish species in the Aegean Sea

Currently, traditional Mediterranean trawls are generally made with non‐selective netting and the fishing boats are involved in multi‐species fisheries. As a result, most near‐shore stocks are over‐exploited. Weather permitting, the demersal trawl fleet tends to fish in relatively deeper, international waters of the Aegean Sea, where the catch is usually higher. Therefore, the need for evaluation of the codends used in this fishery and the potential improvements to their selectivity are of prime importance. In the present study, selectivity data were collected for hake (Merluccius merluccius), blue whiting (Micromesistius poutassou), greater forkbeard (Phycis blennoides), blackbelly rosefish (Helicolenus dactylopterus dactylopterus) and fourspotted megrim (Lepidorhombus boscii) in commercial (300 MC) and square mesh top panel (SMTPC) codends. Trawling was carried out at depths of 274–426 m onboard a commercial vessel chartered for a 15‐day sea trial in August 2004. Selection parameters were obtained by fitting a logistic equation using a maximum likelihood method. Results of the selectivity analysis indicated that the commercially used 40 mm nominal mesh size PE codend was rather unselective for the species investigated in this study. In general, the square mesh top panel codend has relatively higher L₅₀ values than the commercial codend. However, except for blue whiting, even this codend is rather unselective when 50% maturity lengths (L_M50) are considered.     

Selectivity of 50 mm T0 and T90 codends for commercial shrimp species in the Turkish deepwater trawl fishery,Eastern Mediterranean

The study compared the selectivity of 50 mm mesh size conventional (T0) and 90° turned mesh (T90) demersal trawl codends for four commercial shrimp species (Aristaeomorpha foliacea, Aristeus antennatus, Parapenaeus longirostris and Plesionika martia) in the Bay of Antalya in the eastern Mediterranean. Data were collected from 27 valid hauls using the covered codend method. Selectivity parameters were obtained using the logistic equation with the maximum likelihood method and by taking into account the between‐haul variations. Results show that changing the codends from T0 to T90 increases the percentage of escapees for all four targeted shrimp species. According to species, a change in the mesh configuration significantly increases L₅₀ by 7–14%. However, for the two commercially important red shrimp species (Aristaeomorpha foliacea and Aristeus antennatus), even the L₅₀ values obtained in the T90 codend (23.3 mm) remain rather low for the release of sufficient numbers of immature specimens. First maturity sizes (FMS) for these two species are 38 and 30 mm, respectively; therefore, for their sustainable exploitation, additional management measures must be investigated including larger mesh sizes.     

Discards in bottom trawl fishery in the Aegean Sea (Izmir Bay,Turkey)

Sampling was carried out on a seasonal basis during 2007–2009, using a conventional bottom trawl net with 44 mm codend mesh size in Izmir Bay, Aegean Sea. A total of 116 valid hauls: 27 in autumn, 28 in winter, 35 in spring and 26 in summer, were conducted at depths ranging from 30 to 70 m. A total of 112 species: 15 Chondrichthyes, 83 Osteichthyes, 11 Cephalopoda and 3 Crustacea were obtained in the trawl codend. All captures were separated into commercial (C) and non‐commercial (NC) species. The C ratio was 69.6%, while NC (i.e. discards) was 30.4%. Diplodus annularis was the most abundant species in all seasons, followed by Mullus barbatus, Merluccius merluccius, Citharus linguatula, Serranus hepatus, Lepidotrigla cavillone, Spicara maena, Myliobatis aquila, Diplodus vulgaris, and Trisopterus minutus in decreasing order of abundance. These top ten species constituted 75% of total catch weight. Biomass ratios of total discards to commercial species were 0.44 : 1.     

Short‐term effect of selectivity change in a trawling fishery in the Western Mediterranean

The change of mesh size or shape as a management measure to improve selectivity as proposed by the EU should be assessed using actual fishery data, despite being tested experimentally in previous studies. This work was conducted to evaluate the consequences of inserting either a 40‐mm square‐mesh or a 50‐mm diamond‐mesh (instead of the traditional 40‐mm diamond‐mesh) at codends in commercial Spanish trawlers. Landings in terms of biomass, income and catch composition were compared under commercial conditions. Four métiers were identified in the fishery: European hake (Merluccius merluccius), red mullet (Mullus barbatus), red shrimp (Aristeus antennatus) and Norway lobster (Nephrops norvegicus). No significant differences were observed in biomass or income owing to the new mesh in either European hake or red mullet. In contrast, the total biomass of the red shrimp métier and the biomass of the Norway lobster, Nephrops norvegicus, were significantly higher after the selectivity change. Regarding the catch composition, only the European hake métier showed slight – but not significant – changes after using the new mesh. Considering these results, there was no short‐term effect (substantial biological or economic loss) as previous studies had expected. This could possibly be related to a higher performance of the new gear that may compensate for the lower retention of small sizes.     

Size selectivity of three diamond mesh codends for the European hake (Merluccius merluccius) and the tub gurnard (Trigla lucerna) in the Sea of Marmara, Turkey

The effects of an increase in the codend mesh size from 44 to 56 and 80 mm on size selectivity of the two by‐catch species (the European hake Merluccius merlucius and the tub gurnard Trigla lucerna) commonly captured in the shrimp fishery in the Sea of Marmara, were evaluated. The parameters of the logistic selectivity model were estimated by maximum likelihood. Length at 50% retention, L₅₀, was found to increase with mesh size for both species. The L₅₀ values of 44, 56 and 80 mm were, respectively, 19.8, 21.5 and 33.4 cm for European hake, 17.9, 17.7 and 25.6 cm for tub gurnard. The main conclusions are that 44 mm and 56 mm diamond mesh codends retain a considerable amount of undersized hake and tub gurnard as by‐catch in the shrimp fishery. With 80 mm mesh size codend, most juvenile European hake are released. For the tub gurnard, however, even this mesh size does not provide a good enough selection. From the biological point of view, it is concluded that the legal 44 mm diamond mesh codend does not provide satisfactory selection for European hake and the tub‐gurnard in trawl fisheries of the Sea of Marmara.     

Comparison of the size selectivity of diamond (PA) and square (PE) mesh codends for deepwater crustacean species in the Antalya Bay, eastern Mediterranean

The aim of this study was to compare selectivity results of currently used 44 mm nominal polyamide (PA) diamond mesh- and alternatively suggested 40 mm nominal polyethylene (PE) square mesh- codends in the deepwater crustacean trawl fishery in the Antalya Bay, eastern Mediterranean. Selectivity experiments were carried out during targeted trawling of four commonly harvested crustacean species: giant red shrimp Aristaeomorpha foliacea , 'blue and red' shrimp Aristeus antennatus , rose shrimp Parapenaeus longirostris , and pandalid shrimp Plesionika martia . A conventional bottom trawl of 600 meshes around the fishing circle was operated onboard a commercial stern trawler between 6 and 18 June 2007. Depth of the fishing area varied between 441 and 630 m. Data were collected using the covered codend technique, and analyzed using a logistic equation with maximum likelihood for individual and pooled hauls. The commercially used trawl codend was unable to release immature crustaceans. Selectivity parameters of the three species of crustaceans were distinctly lower when collected with the polyamide diamond mesh than with the polyethylene square mesh, except in the case of giant red shrimp for which values were similar. However, the present and previous results show that in square mesh codends, mesh sizes must be more than 40 mm in order to keep catches clear of specimens below minimum landing sizes or 50% sexual maturity sizes of crustaceans in the Mediterranean. This study suggests that regulating mesh size by requiring square mesh openings during deep water crustacean trawling of the eastern Mediterranean is essential for the release of immature individuals.     

The impact of fisheries on vulnerable habitats: the case of trawling on circa-littoral grounds in the Strait of Sicily (central Mediterranean Sea)

The Council Regulation (EC) no. 1967/2006 introduced the adoption of the 40 mm square-mesh or alternatively a 50 mm diamond-mesh codend for trawlers of EU Member States. In this context, the main aim of the current study was to compare the catch composition of Lampedusa’s shallow-water trawl fishery, in terms of retained and discarded fraction, using the 24 mm square-mesh codend (illegal and supposed unselective) and the 50 mm current diamond-mesh codend (legal and supposed selective). During 2012, 21 hauls were performed, under commercial conditions, with the 24 mm square mesh codend and 27 with the 50 mm diamond mesh codend in an area of the Strait of Sicily at depths from 40 to 80 m. The introduction of a 50 mm diamond-mesh, although not significantly, reduced the CPUEs of retained and discarded fraction compared with the 24 mm mesh. Moreover, for most target species and their size classes (especially immature individuals), the legal mesh recorded a lower mean number of specimens than the banned mesh size. All these advantages aside, the discard of the shallow-water trawl fishery, in Lampedusa, represented a very important part of the total catch (more than three-quarters) by both mesh sizes and a large amount of this was represented by species and habitat of conservation concern. Our results suggest that spatial restrictions, such as no-take zones, could be a more effective management tool to protect this sensitive ecosystem in the area than the technical measures (e.g. reduction of mesh size) imposed today by the EU.     

Trawl codend design (44 mm diamond PE mesh) and the effect on selectivity for Pagellus erythrinus and Pagellus acarne, two species with different morphometrics

The effects of different body shapes on size selectivity were analysed. Relationships between total length and fork length, height, width and girth were estimated and the selectivity parameters of a 44 mm PE diamond mesh codend determined for common pandora (Pagellus erythrinus) and axillary sea bream (Pagellus acarne). Two data sets were collected during demersal trawl trials carried out in Izmir Bay (Aegean Sea) between May 1996 and February 1997. Regression analyses were used to determine the relationships between total length and other measured dimensions of the species. However, selectivity parameters were estimated from pooled data by using the logistic equation with the maximum likelihood method. Fork length, height, width and girth were found to increase linearly with total length for both species (R² > 0.90, except TL–W for axillary sea bream, 0.76). Ratios of average body thickness (W/H) were 0.45 (±0.002) for common pandora and 0.52 (±0.002) for axillary sea bream. L₅₀ and SR values were found as 12.4 (±0.44) and 2.2 (±0.51) from the eight valid hauls for common pandora and as 13.6 (±0.13) and 1.9 (±0.26) from the three valid hauls for axillary sea bream, respectively. The difference between the size selectivity of the two species in the same family can be explained by the body shape and fish behaviour distinctions.     

Alternative codends to improve the size selectivity for nylon shrimp (Heterocarpus reedi) and yellow squat lobster (Cervimunida johni) off the Chilean coast

The size selectivity of alternative codends for nylon shrimp and yellow squat lobster was studied off the Chilean coast using the covered codend technique. Various mesh sizes (47 and 63 mm mesh opening) and shapes (diamond and square) in the codends were used. For both species, substituting the DM47 codend with the DM63 codend significantly increased 50% retention length (l₅₀). The change of diamond (DM47) to square mesh (SM47) had a positive effect in size selectivity for nylon shrimp. For yellow squat lobster, no significant effect was observed when changing the diamond (DM63) to square mesh (SM63). Selectivity data were modeled by considering explanatory variables such as ‘codend catch weight’ and ‘vessel’. Increases in the catch significantly reduced the l₅₀ for both species whereas the vessel factor was not significant. Finally, using the length at first maturity as a reference value, the authors concluded that the DM47 codend failed to protect the immature portion of either stock, thus the DM63 codend is recommended.     

Comparison of a rigid grid to a square‐mesh panel in size selection for commercial fishing in the Persian Gulf shrimp trawl fishery

Two bycatch reduction devices (BRDs): a juvenile and trash fish excluder device (JTED) and a square‐mesh panel (SMP), were tested in the Persian Gulf shrimp fishery from a small‐scale shrimp trawler in October–November 2012. Each device was alternatively tested by using a small‐mesh cover net to retain individuals that escaped the BRDs. Three valuable fish species—tigertooth croaker (Otolithes ruber), silver pomfret (Pampus argenteus) and silver sillago (Sillago sihama)—were selected for detailed analyses. Average escapement rates by number for commercial species in the trawl nets with either JTED or SMP were calculated as 24% and 33%, respectively. There were significant differences in escapement rates for Otolithes ruber and Sillago sihama between JTED and SMP (p < .05). In both BRDs, Pampus argenteus had the smallest escapement rate. A two‐sample Kolmogorov–Smirnov test detected a significant difference (p < .05) in the length‐frequency of Sillago sihama, and Otolithes ruber captured in the codend and cover net equipped with JTED. Selectivity curves of both BRDs indicated that for each species, the length of 50% retention probability (L50) was substantially smaller than the length at maturity (Lm), except for Otolithes ruber. From an ecological perspective, the codend equipped with SMP was superior to the codend equipped with JTED because it retained substantially fewer under‐sized fish and had the smallest selection range. It therefore seems that replacing the standard codend with a codend equipped with SMP provides the best outcome for the fishery whereby fishermen will increase their catches of larger fish while simultaneously reducing their under‐sized fish catches.     

Length–weight relationships of 11 deep‐sea fishes from the western Bay of Bengal and Andaman waters,India

Length–weight relationships (LWRs) are presented for 11 deep‐sea fishes caught in the western Bay of Bengal and Andaman waters during August 2010 using a 38 m high speed demersal trawl II (HSDT II, crustacean version, codend mesh size 40 mm) and a 45.6 m Expo model demersal trawl (codend mesh size 30 mm). The b values ranged from 2.34 to 3.3 and the coefficient of variation (r²) ranged from .82 to .98. LWR estimates of eight deep‐sea fishes are provided for the first time. The estimated LWR values were compared with the Bayesian LWR estimates available in FishBase, based on models developed to improve the accuracy and predictability of species‐specific growth parameters of data‐poor species.     

Effect of codend mesh size increases on the size selectivity of commercial species in a small mesh bottom trawl fishery

The effects of increasing codend mesh size from 11.6 to 25 and 28.7 mm (inside stretched mesh) on the selectivity of greater lizardfish (Saurida tumbil), squid (Loligo sp.), and penaeid shrimp caught by an inshore otter trawling fishery at Nha Trang City, Vietnam were assessed. The proportion of escaping trash fish from the studied codends was also examined. In general, the lengths at 50% retention (L₅₀) of the studied species increased with increasing codend mesh size. L₅₀ values of greater lizardfish for the 25 and 28.7 mm codends were 109.4 and 145.9 mm, respectively. The 11.6, 25, and 28.7 mm codends selected shrimp at L₅₀s of 8.33, 11.86, and 13.92 mm, respectively, and squid (mantle lengths) at 13.1, 36.1, and 41.9 mm, respectively. The mean proportions of escaping trash fish were 0.06, 0.68, and 0.85 for the three codends, respectively. A minimum mesh size of 25 mm is a good compromise between management goals and fishery demands.     

Effect of codend mesh size on the performance of the deep-water bottom trawl used in the red shrimp fishery in the Strait of Sicily (Mediterranean Sea)

The influence of different codend nets mounting diamond-shaped (16, 20, 24, 28 and 45 mm, mesh side) in the performance of the commercial bottom trawl presently in use in the Strait of Sicily (Central Mediterranean Sea) to catch deep-water red shrimps, Aristaeomorpha foliacea and Aristeus antennatus, is analyzed. In two surveys carried out in fishing grounds in spring and summer 1993, 93 daylight hauls (of 3 hours each) based on the covered codend (cover of 14 mm mesh side) method were carried out. The composition and quantity of the combined, retained and escaped catch for the most relevant species and mixed categories of the different gear configurations (codends + cover) were analyzed and compared by applying both univariate (ANOVA) and multivariate (clustering and multidimensional scaling) techniques. The reduction of by-catch, the economic loss and the economic efficiency were used as indexes of the retention performance of the different codends. The overall catch was 6398 t (23 kg/h); Aristaeomorpha foliacea accounts for most of the catch in number, weight (48% of the total) and value (87% of the total value). Bony fishes, cartilaginous fishes and other crustaceans are the by-catch, representing, respectively, 26%, 16% and 9% of the catch in weight, the rest belonging to cephalopods. The use of the different codends does not influence the overall performance of the gear. No saturation was detected, with the escapement ratio uninfluenced by the amount retained. Considering the retention characteristics, results indicate that the 16 mm and 20 mm mesh codends are not selective, whereas the 24/14 and 28/14 configurations produce increased escaping ability. The 45 mm mesh sieves out 79% of specimens, indicating that no masking effect was induced by the cover. Regarding economic efficiency, the 20/14 configuration provides values comparable to those obtained with the 24/14, whereas the 16/14 configuration is as efficient as the 28/14. The lowest efficiency was obtained using the 45/14 configuration. Multidimensional scaling and clustering techniques (performed on 20, 24 and 28 mm codends) allow to discriminate the escapement ability of the 28/14 gear configuration only. Present results support the introduction of the 28 mm mesh codend in the deep-water red shrimp fisheries in the view of a precautionary management of the resources.     

Length‐weight relationships of five deep‐sea anglerfishes from Andaman and Nicobar waters

Length weight relationships are presented for five deep‐sea anglerfishes collected from Andaman and Nicobar waters during April 2016 using a 38 m high speed demersal trawl II (HSDT II, crustacean version, codend mesh size 40 mm). The b values ranged from 1.80 to 2.76 and the coefficient of variation (r²) ranged from 0.82 to 0.97.     

Species selectivity in the Eastern Mediterranean demersal trawl fishery using grids to reduce non‐target species

Scientific studies have been conducted on size selectivity of trawls with grids in the Mediterranean; however, none has focused on species selectivity. The aim of the present study was to analyze the value of sorting grids with 20 mm bar spacing for species separation, in a demersal trawl fishery mainly targeting deep water rose shrimp (Parapenaeus longirostris) in the Eastern Mediterranean. Fishing trials were carried out 17–24 August 2008 onboard the commercial trawler ‘Hapulo?lu’, using a modified bottom trawl net. The separation rate for silver scabbard fish (Lepidopus caudatus) was highest among all species with 98% by weight and 97% by number in 44 mm diamond (44D) and 40 mm square mesh (40S) codends, respectively. The exclusion of European hake (Merluccius merluccius) by the grid shows differences between 85 and 93%, in weight and 64 and 83% in number for codends of 44D and 40S, respectively. Excluding the ratio for greater forkbeard (Phycis blennoides), the angler fish (Lophius piscatorius) and broadtail short fin squid (Illex coindetii) varied between 93 and 97% in weight, and 81 and 86% in number in both codends. Losses of legal sized rose shrimp were determined as 23 and 25% in 44D and 40S, respectively. The results obtained in the present study demonstrate that substantial separation of fish and shrimp can be achieved in this Mediterranean demersal trawl fishery. However, further developments should be explored; for this purpose the behaviour of species has to be studied in relation to trawl and grid design and where commercial consequences of changes in gear technology need to be considered.     

Effect of the number of meshes in the protective bag circumference on size selectivity of demersal trawl codends

This study investigated the effect of the number of meshes in the protective bag circumference on size selectivity of a demersal trawl codend. Circumferences of 50‐mesh (NMPB50) and 215‐mesh (NMPB215) protective bags rigged on the 44 mm diamond mesh codend were tested. Fishing experiments were carried out on the commercial trawler ‘Hapulo?lu’ between 20 and 27 August 2010, using a modified trawl net. Data were collected using the covered codend method and analyzed using the logistic equation with the maximum likelihood method. Mean selection curves were analyzed and compared using the between‐haul variations model. The mean L₅₀ values of NMPB50 and NMPB215 were, respectively, 16.4 ± 0.1 mm and 16.5 ± 0.1 mm carapace length for deep‐water rose shrimp, 10.7 ± 0.1 cm and 12.2 ± 0.1 cm total length for hake, and 16.0 ± 0.1 cm and 16.7 ± 0.1 cm total length for horse mackerel. In conclusion, increasing the number of meshes around the protective bag resulted in a 14% and 4% increase in the L₅₀ for hake and mackerel, respectively; however, these differences were not statically significant (P > 0.05).     

Selectivity of diamond, square and hexagonal mesh codends for Atlantic horse mackerel Trachurus trachurus, European hake Merluccius merluccius, and greater forkbeard Phycis blennoides in the eastern Mediterranean

Knowledge on selectivity is considered essential for an adequate management of the trawl fishery. This paper compares the selectivity of conventionally used codends of 44 mm diamond mesh, 40 mm square, and hexagonal mesh for Atlantic horse mackerel, European hake and greater forkbeard in the eastern Mediterranean. Data were collected using the covered codend method and analyzed using the logistic equation with the maximum likelihood method. Mean selection curves were analyzed and compared using the between-haul variations model. The mean L ₅₀ v alues of diamond, square and hexagonal mesh codends are 14.7, 15.9 and 17.1 cm total length (TL) for horse mackerel, 10.4, 14.4 and 11.0 cm TL for hake and 12.2, 15.8 and 12.7 cm TL for greater forkbeard, respectively. For horse mackerel, the differences among the codends are statistically significant (P   <   0.05); however, the L ₅₀ values for all three meshes are higher than the minimum landing size (13 cm TL). For hake and greater forkbeard, the L ₅₀ value for the square mesh codend is significantly different from the values for diamond and hexagonal meshes (P   <   0.01), whereas there is no significant difference between diamond and hexagonal meshes (P   >   0.05). Regardless of the mesh shape, L ₅₀ values were substantially lower than the minimum landing size or size at first maturity for hake and greater forkbeard. To enable more effective solutions, research on species-selective trawls is required for the Mediterranean demersal trawl fishery.