Mesh Codend Research Articles

A simulation-based attempt to quantify the morphological component of size selection of Nephrops norvegicus in trawl codends

The selectivity for Nephrops ( Nephrops norvegicus) in trawl codends generally is poor and the lack of steepness of the selection curve results in high discard rates and/or loss of legal-sized catch. This poor codend selectivity often is attributed to the irregular shape of Nephrops, which to some extent characterizes the problem as insoluble. In the present study, the FISHSELECT methodology was used to examine the selection process of the species in order to identify ways to improve selectivity. The use of three different modes of orientation for contact (contact modes) with the codend meshes explained most of the characteristics of the selection curves for Nephrops obtained experimentally. The contact mode with the smallest cross-section was optimal for mesh penetration and, when evaluated against experimental data, 87.5% of all Nephrops encountering the gear were estimated to meet the netting in this contact mode. The range of configurations of the meshes (e.g., opening angles in the diamond mesh netting) was determinative for the selectivity, and the selective process for Nephrops was found to take place along the entire length of the codend. Simulating selectivity in a diamond mesh codend in which the closed meshes in the forward part of the codend were replaced by more open meshes revealed that the selectivity for Nephrops can be efficiently improved.

Discard mitigation increases skate survival in the Bristol Channel

The survival of fish discarded after being caught can be improved by simple gear-based technical measures aimed at reducing discards. We look at the effects of three different codends on the initial and short-term survival of trawl-caught skate (Rajidae), using a control codend (80 mm diamond mesh used as standard in the fishery) and two experimental codends (100 mm diamond mesh and 100 mm diamond mesh turned on the square). Both experimental nets reduced discarded numbers of fish by ~70%, with no commercial loss. This reduction in discards had an effect in reducing the total weight of the experimental codends by as much as 80%. We also placed 278 skate in onboard holding tanks for 48 h and evaluated the survival rates of fish caught in the different codends. Visual inspection of health at time zero was a good indicator of survival, because 86% of skate with a good score survived (p < 0.01). From a further 1539 skate assessed for health, we show that fish caught in the control codend have the lowest proportional good score (25%), followed by the 100 mm diamond mesh codend (34%) and the 100 mm square mesh codend (47%). The of the fish caught is related to codend weight (p = 0.01). We conclude that technical measures aimed at reducing discards have an additional benefit; they indirectly increase discard survival, and the benefits of mitigating discards through by-catch reduction devices may be a more powerful tool in fisheries management than previously thought.

Effect of an Increase in Codend Mesh Size on Discarding in theLoligoSquid-Directed Fishery: A Commercial-Scale Test

Discard reduction of juvenile fish and other unwanted bycatch species has been identified as a primary tool in achieving rebuilding and mortality objectives of current fishery management plans. Management of the offshore Loligo pealei squid fishery is particularly challenging because the legal codend mesh size is smaller than other regulated commercial fisheries. Co-occurrence of adult Loligo with juveniles and other Mid-Atlantic species of concern, coupled with the high volume of landings may lead to high discarding of non-target species. Accordingly, an increase in codend mesh size from the 2005 legal size of 1.875 was evaluated as a means to reduce the capture of submarket-size squid, butterfish, and other species of concern, without materially impacting the catch of market-size squid. To evaluate the influence of fishing practice, a commercial-scale test was undertaken. A 2.5 mesh codend, in addition to the desired reduction of small Loligo, resulted in a substantial decrease in the catch of intermediate-size, but marketable (10–13 cm), squid without significant reduction in the bycatch of butterfish, silver hake or spiny dogfish. To recover total catch of market-size squid with the 2.5 mesh codend would require an increase in fishing effort of 73.9%. Even with that increase, total discards of small squid would be reduced by 52.7%. However, total discards of bycatch species would be substantially increased. Codend mesh size is an effective option only if discarding of bycatch species is inconsequential or if avoidance of unwanted catch can be achieved through area management.

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

Summary 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 polyethyl- ene (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 redshrimp 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.

Selectivity of commercial, larger mesh and square mesh trawl codends for deep water rose shrimp Parapenaeus longirostris (Lucas, 1846) in the Aegean Sea

We investigated the differences between size selectivity of a commercial codend (40 mm diamond mesh – 40D), a larger mesh codend (48 mm diamond mesh – 48D), and a square mesh codend (40 mm square mesh – 40S) for Parapenaeus longirostris in international waters of the Aegean Sea. Selectivity data were collected by using a covered codend method and analysed taking between-haul variation into account. The results indicate significant increases in L 50 values in relation to an increase in mesh size and when the square mesh is used in the commercial trawl codend. The results demonstrate that the commercially used codend (40D) is not selective enough for P. longirostris in terms of length at first maturity. Changing from a 40D to a 48D codend significantly improves selection, with an increase of about 15% in the L 50 values (carapace length 14.5 mm for 40D and 16.6 mm for 48D). Similarly, 40 mm square mesh, which has recently been legislated for EU Mediterranean waters, showed a 12.4% higher mean L 50 value (16.3 mm) than 40 mm diamond mesh for this species. However, despite these improvements, the 48D and 40S codends still need further improvements to obtain higher selectivity closer to the length at first maturity (20 mm carapace length).

Efficiency of flexible sorting grids to improve size selectivity of the bottom trawl in the Balearic Islands (western Mediterranean), with comparison to a change in mesh cod-end geometry

In recent years several studies have been developed to improve the selectivity of the Mediterranean bottom trawl fisheries, which exert high fishing pressure on young individuals. The focus has been mainly on increasing the mesh size in the cod-end or changing its mesh geometry; few studies have assessed the efficiency of the sorting grid systems. Analysis of 21 trawl hauls carried out at depths of 117–697 m off the Balearic Islands (western Mediterranean) in October–November 2005, studied size selectivity of the trawl using flexible sorting grids with 15 (SG15) and 20 (SG20) mm bar spacing. A divided polyamide bottom trawl designed for commercial purposes demonstrated high efficiency for the simultaneous use of both sorting grid sizes at different depth intervals (DS: deep shelf; US: upper slope; MS: middle slope). The results were also compared with those from the authors’ previous studies in the area where 40 mm diamond (DM) and square (SM) mesh cod-ends were used. A saturation effect was detected on the DS for both sorting grids, due to the large amount of biomass captured at this depth interval. Size selectivity of 11 species was modelled, which showed an increase in length at first capture (L50) from SG15 to SG20. Values of L50 estimated for the main target species were: 10.9 cm total length (TL) with SG15, and 18.9 cm TL with SG20 for Merluccius merluccius; 21.1 mm carapace length (CL) with SG15, and 23.8 mm CL with SG20 for Nephrops norvegicus; and 15.9 mm CL with SG15, and 19.6 mm CL with SG20 for Aristeus antennatus. Comparison of size selectivity parameters between the sorting grids and cod-ends of different geometry showed clear differences. For most species, the highest value of L50 was obtained with SM (e.g. 26.6 mm CL for N. norvegicus and 22.1 mm CL for A. antennatus). Exceptions were the round-fish M. merluccius, the flatfish Lepidorhombus boscii, and the crustacean Parapenaeus longirostris, with values of SG20 (18.9 cm TL, 12.1 cm TL, and 25.7 mm CL, respectively) higher than with SM (15.2 cm TL, 10.2 cm TL, and 20.2 mm CL, respectively). Sorting grid selection ranges were broader than those estimated for DM and SM. Experience shows that the exchange of the DM for the SM and/or the introduction of SG20 can improve selectivity in the Mediterranean trawl, SM being more efficient than SG20 in the Balearic Islands.

Evaluation of three levels of selective devices relevant to management of the Danish Kattegat–Skagerrak Nephrops fishery

This study illuminates a range of technological options relevant to present legislation for regulating fish by-catch in a small-meshed Nephrops fishery. The selection of cod, haddock, hake, lemon sole, Nephrops, plaice, saithe, witch, and whiting were evaluated using the twin-trawl technique for: (i) a 90 mm diamond mesh codend (standard codend); (ii) a standard codend with a 120 mm square mesh panel (SMP); and (iii) a standard codend with a 35/80 mm grid mounted in the extension piece to hinder access to the codend for large individuals. We used selection models to estimate selection parameters by species and confidence bands to compare the selective properties of different gear types. For cod, haddock, hake, Nephrops, plaice, and whiting we obtained estimates for all three gear variants, whereas we obtained estimates for lemon sole and witch only with the standard and the SMP codends and for saithe only for the SMP codend. The SMP significantly ( p < 0.05) improved selectivity of haddock in terms of releasing more individuals below minimum landing size (MLS). For a narrow size range of plaice below MLS, the SMP retained more individuals than did the standard codend. No effect of the SMP was detected for any of the other species. The grid codend significantly reduced catches of all fish species above MLS, but the codend also had an increased retention of cod and haddock below MLS. Furthermore, the grid resulted in a 17% loss of marketable Nephrops.

Selectivity of diamond, hexagonal and square mesh codends for three commercial cephalopods in the Mediterranean

Undersized and immature commercially important cephalopods are often inadvertently caught by trawlers in the eastern Mediterranean. To evaluate the effectiveness of different mesh codends (diamond, hexagonal and square) to reduce bycatch of juvenile commercially important Mediterranean cephalopods (European squid Loligo vulgaris, broadtail shortfin squid Illex coindetii and pink cuttlefish Sepia orbignyana), a series of selectivity experiments was undertaken with a modified bottom trawl. The covered codend technique was used to capture escapees. For the broadtail shortfin squid and the pink cuttlefish, the square-shaped mesh displayed the highest 50% retention lengths ( L 50) compared to diamond and hexagonal mesh. For the European squid, selectivity could only be measured by pooling the data from all hauls for each mesh shape. For all three species, the L 50 values of square and hexagonal mesh codends were significantly different ( p < 0.01). Beyond the mesh variability, species catch was found to have a significant impact in the selection range of the broadtail shortfin squid. Furthermore, for the cuttlefish, total catch and haul duration likely account for variability of L 50 attributed to mesh configuration. For all species, regardless of the mesh shape, L 50 values were substantially lower than the minimum landing size or length at first maturity. Therefore, the current legal minimum mesh size and codend configurations for demersal trawling are not suitable for the management of these species. As such, sustainability in Mediterranean cephalopod fisheries would profit from more selective gears. This could be achieved both by an increase in codend mesh size and change in codend shape; however, being part of a mixed fishery, when these changes are being practiced, the impact on the fish catches of target species will have to be taken into consideration.

Selectivity of Square and Hexagonal Mesh Codends for the Deep Water Rose Shrimp, Parapenaeus Longirostris (Lucas, 1846) (Decapoda, Penaeidae) in the Aegean Sea

Selectivity of Square and Hexagonal Mesh Codends for the Deep Water Rose Shrimp, Parapenaeus Longirostris (Lucas, 1846) (Decapoda, Penaeidae) in the Aegean Sea

Discovery of mature freshwater eels in the open ocean

Keywords Anguilla First catch Freshwater eels Matured males Spawning areaAll freshwater eels of the genus Anguilla are catadromous,in that they perform long-distance migrations to offshorespawning area after years of growth in freshwater and near-shore habitats [1]. Finding younger and smaller lepto-cephali indicated the spawning area to be located in theSargasso Sea for European and American eels (Anguillaanguilla and A. rostrata, respectively) [2, 3] and in thewestern North Equatorial Current (NEC) area of the wes-tern North Pacific to the west of Mariana Islands forJapanese and giant mottled eels (A. japonica and A. mar-morata, respectively) [4–6]. Recent investigation couldfurther narrow down the area and timing for spawning ofthe Japanese eel (A. japonica), where a large number ofsmall pre-leptocephali (n = 130, 4.2–6.5 mm in totallength) were collected during the new moon in June 2005around 14 N, 142 E to the west of the Suruga Seamount ofthe West Mariana Ridge [7]. No matured adult eels havebeen captured or observed to date in the spawning area, notonly for the four species mentioned above, but also for anyspecies of freshwater eel. The Fisheries Agency of Japanconcerned recent declines in catches of glass eel (smalljuveniles migrating to freshwater area), and dispatched R/VKaiyo Maru to capture adult Japanese eel for collectingbiological information. Here, we report the first discoveryof fully matured anguillid eels in the open ocean.We used a large mid-water trawl net (maximum mouthopening 65 m wide and 55 m height with 7 mm mesh codend) (Nichimo Co., Ltd., Tokyo), which could be towed at4–5 knots. A total of 21 nighttime tows were performed for0.5–4 h at a depth mainly of 170–300 m in the area adja-cent to the southern part of the West Mariana Ridge(Fig. 1a) during 25 May to 9 June 2008 (Fig. 1, closedcircles). Eventually, three anguillid eels were caught in twotows on 3 and 4 June operated at 13 000 Nto13 05

Feeding behavior of adult Vinciguerria nimbaria (Phosichthyidae), in the tropical Atlantic (0°–4°N, 15°W)

Adult Vinciguerria nimbaria are the main prey of tuna during the tuna fishing season (late autumn and winter) in the equatorial Atlantic (0–4°N, and ~15°W). V. nimbaria trophic behavior in the fishing grounds was studied in relation to hydrobiological factors to determine its role in the trophic food web. Sampling stations spaced by 20 nautical miles were set up along a 15°W north–south transect from 4°N to 0°40S. At each station, the temperature and vertical fluorescence profiles were recorded. Nitrate and chlorophyll a analyses were performed on water sampled at different levels in the euphotic zone. Vertical plankton hauls were carried out at depths of 0–100 and 0–200 m using a standard WP2 net fitted with a 200-μm mesh gauze. Vinciguerria nimbaria adults were collected using a young-fish mid-water trawl net (10 × 15 m opening mouth, 10 mm cod end mesh). The weight of the stomach contents, the stomach fullness index, the number of prey, the frequency of occurrence and the prey preponderance were recorded for 20 fish from each haul. An oligotrophic typical tropical structure (TTS) was found between 1° and 4°N where small zooplankton was relatively abundant above or near the thermocline. In the TTS, V. nimbaria behaved as an epipelagic fish, feeding on the dominant small prey during the daytime. In turn, it was a prey for tuna. In the equatorial zone, where zooplankton was more abundant than in the north equatorial zone, V. nimbaria behaved as a mesopelagic fish and as an opportunistic mesozooplankton feeder. It consumed a wide range of sizes of food, feeding on the most abundant species of zooplankton as well as the largest zooplankton species, possibly while migrating towards the surface in the late afternoon or in the deep layer.

Discarding in the North Sea and on the historical efficacy of gear-based technical measures in reducing discards

We describe and analyse newly available catch and discard data from the English and Welsh fishing fleet operating in the North Sea. In this fleet we estimate that between 2003 and 2006 discard rates averaged 36% by number and 25% by weight. Additionally, we analyse historical discard data from the fleet to evaluate the efficacy of square-mesh panels and increases in codend mesh size. These various gear-based technical measures have been introduced into the fisheries for the purpose of reducing discarding; we demonstrate that these technical measures have been effective in this respect.

The effect of varying cod-end circumference, inserting a ‘flexi-grid’ or inserting a Bacoma type panel on the selectivity of North Sea haddock and saithe

A comprehensive set of experiments using the twin trawl technique were conducted in the North Sea to assess the selectivity of haddock ( Melanogrammus aeglefinus), cod ( Gadus morhua) and saithe ( Pollachius virens) in 120 mm mesh cod-ends with (i) 100, 80 and 60 meshes in circumference; (ii) a 35 mm ‘flexi-grid’ mounted in the extension; (iii) a 110 mm ‘Bacoma’ style square mesh panel. For haddock, cod-end type and catch size had a significant impact on 50% retention length (L50) and only cod-end type influenced selection range. Reducing the number of meshes in circumference from 100 to both 80 and 60 increased the L50 of haddock. The Bacoma panel gave a similar selection for haddock to the 60 mesh round cod-end, while no difference was found between the ‘standard’ 100 meshes round cod-end and the trawl with the flexi-grid fitted. For saithe, the cod-end with 60 meshes in circumference was significantly more selective than the cod-end with 100 meshes around. The cod-end with 80 meshes in circumference had an estimated selectivity between that of the cod-ends with 60 and 100 meshes in circumference, although it did not differ significantly from either. Catch size was not found to influence the selectivity of any of these three cod-ends. Insufficient data were obtained to estimate either the selectivity of saithe in the cod-end with a Bacoma panel or grid. A stock predictive model was used to illustrate the possible long-term effects of improving gear selectivity on the biomass, yield and discarding of haddock in the North Sea.

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

Summary 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 ‘Hapuloglu’ 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.

Rockall and the Scottish haddock fishery

Rockall Bank, lying to the west of the Rockall Trough, has supported a fishery for more than 200 years. Whilst the Rockall grounds were opened up by cod fishermen, it has been the haddock fishery which has had the most economic significance with the stock being exploited historically by various nations but now fished mainly by the UK and Russia. Prosecution of this fishery has varied over time with resulting variable landings but the effort expended by the fishing fleets does not appear dependent on the size of the available haddock stock but more on other external considerations, e.g. politics, economics and the success, or otherwise, of ancillary fisheries such as squid. Due to the isolated position of the Bank the amount of scientific data gathered on Rockall haddock has been sparse and several erroneous assumptions concerning depth, and consequently spatial, distribution have been made. Recent investigations have improved the biological knowledge of the haddock stock but although this should lead to more robustness in stock assessment there are new uncertainties. Two main fleets now operate at Rockall–Russian vessels generally fishing with small mesh sizes (40–70 mm) and retaining all of the fish they catch and a European fleet using nets with cod-end meshes of 120 mm and above which entails some discarding. This dichotomy presents a challenge in providing accurate stock forecasts. In addition the regional regulatory authorities (EU and NEAFC) are introducing closed areas but it is unclear, given the sparse information available, whether the correct areas have been chosen and whether there can be effective surveillance of the closed areas.

Sorting grid trials to improve size selectivity of red mullet (Mullus barbatus) and annular sea bream (Diplodus annularis) in Turkish bottom trawl fishery

Summary Sorting grids with two different bar spacings (12 mm and 14 mm) were tested to improve size selectivity of the commercially important fish species, red mullet (Mullus barbatus) and annular sea bream (Diplodus annularis), in Turkish bottom trawl fishery. Fishing trials were carried out with R/V ‘Egesuf’ between April and May 2003 in Izmir Bay, Aegean Sea, using a traditional bottom trawl. Selectivity data were collected by the top cover method and analyzed by means of a logistic equation with the maximum likelihood method. Selectivity parameters for individual hauls were obtained with the software program cc 2000. Mean selectivity was also estimated and compared using the EC Model software that takes between-haul variations into account. The codend catch size as an additional explanatory variable was used in the comparison. The Kolmogorov–Smirnov (K–S) test was also applied to detect differences between length-frequency distributions in the upper and lower bags of the 12 and 14 mm bar spacings for red mullet and annular sea bream. The mean L50 values of red mullet were 8.7 and 10.0 cm with the 12 and 14 mm grids, respectively. The L50 value of 14 mm was comparable with the L50 value of the codend mesh size; however, the 12 mm value was rather low. The mean L50 values of 12 and 14 mm bar spacings were 8.8 and 10.4 cm for annular sea bream, respectively; the value of 14 mm bar spacing was very close to 50% size at sexual maturity of the species (10.5 cm). The K–S test indicated length distributions of red mullet and annular sea bream in the 12 and 14 mm upper and lower bags as significantly different (P < 0.05). These results show that improving the size selectivity in a multi-species fishery using a single selective device is rather difficult. However, higher size selectivity can be obtained when considering the minimum landing size or the 50% sexual maturity size for a given species.

Size selection by diamond- and square-mesh codends in multi-species Mediterranean demersal trawl fisheries

Mediterranean demersal trawl fisheries traditionally operate using small diamond-shape meshes in the codend, which tend to retain almost all animals. We investigated the effect of mesh configuration on the size selectivity of nine species (the scaldfish Arnoglossus laterna, the broad-tail shortfin squid Illex coindettii, the European hake Merluccius merluccius, the red mullet Mullus barbatus, the Norway lobster Nephrops norvegicus, the common pandora Pagellus erythrinus, the deepwater rose shrimp Parapenaeus longirostris, the Mediterranean horse mackerel Trachurus mediterraneus and the poor-cod Trisopterus minutus capelanus) commonly captured in the Mediterranean demersal trawls. Two codends having meshes with the same opening (ca. 38 mm) but different mesh configuration (DM38: diamond-mesh and SM38: square-mesh configuration) were fished daily and alternately on the same trawl. They demonstrated a substantial improvement in selectivity with square-mesh. Selectivity was measured using the covered codend technique, the cover being supported by circular hoops. The results were analysed taking into account the between-haul variation in selectivity. Two other important external variables were identified: the trawling depth and the codend catch, which for some species influenced between-haul variation, but there was no evidence of a coherent effect on selectivity parameters. The selectivity of 40 mm diamond-mesh codend has been reported to be rather poor because a large proportion of the codend catch is immature and smaller than the minimum landing size (MLS) or first maturity size. With the exception of the flatfish ( A. laterna), the effect of a change of mesh configuration from diamond- to square-mesh on size selectivity positively affected the retention length at 50% ( L 50). However, square-meshes were found to be unsuitable for flat and/or deep-bodied fish as these escape more readily from diamond-meshes. The Council Regulation (EC) No. 1967/2006, concerning management measures for the sustainable exploitation of fishery resources in the Mediterranean, establishes the MLS of marine organisms. However, the increase in L 50 with square-mesh would not avoid some of the existing contradictions in allowing the use of codend mesh which leads to lower L 50 than the MLS.

A Dynamic Model of the Deformation of a Diamond Mesh Cod-End of a Trawl Net

A dynamic model of a diamond mesh cod-end subject to harmonic forcing is developed. The partial differential equations governing the displacements of the cod-end and the tension in the twine are first derived and then analyzed using the harmonic balance method by substituting a harmonic series for the dependent variables and the forcing term. A closed-form solution is derived for the case of rigid-body motion, where there is no deformation of the cod-end geometry, along with the conditions for the forcing under which this motion occurs. A pressure loading, which varies linearly over a portion of the cod-end and varies harmonically with time, is then introduced as a first representation of the loading on the cod-end that results from the pressure and acceleration forces on the catch due to surge motion of the towing vessel. The resulting sets of equations for the static and the first and second harmonic terms are solved numerically in a sequential manner, and the results presented for a number of cases. These results show that, due to the nonlinearity of the system, the oscillatory motion of the cod-end is asymmetric, and that the deformation of the net and the amplitude of oscillation increases as the region over which the forcing is applied increases. The model is the basis for a more complete coupled catch/cod-end model.

On the presence of the brachyuran crab Macropodia tenuirostris (Crustacea: Decapoda: Majidae) on the Levantine coast of Turkey

The majoid crab, Macropodia tenuirostris is now reported off the Samandag coast, Hatay, south-eastern Turkey. One male specimen of Macropodia tenuirostris was found on 31 January 2007 on a sandy bottom with a sea grass meadow, Halophila stipulacea (Forskal) Ascherson at a depth of 25 m (GPS coordinates: 36°01′24″N 35°58′33″E) by bottom trawl, with a cod-end mesh size of 22 mm. It is one of the six species of Macropodia in the Mediterranean Sea, and is widely distributed in the eastern Atlantic (Faeroe Islands, North Sea, all British coasts, southwards to Western Sahara, Cape Verde Islands) and in the entire Mediterranean. Macropodia tenuirostris as here reported presents the first record of this species for the Turkish part of the eastern Mediterranean Sea.

Evaluation of a simple means to reduce discard in the Kattegat-Skagerrak Nephrops ( Nephrops norvegicus) fishery: Commercial testing of different codends and square-mesh panels

Discarding of fish species in the Kattegat-Skagerrak Nephrops directed fisheries remains at high levels. In this work we have tested four sets of codends pair-wise with the catch comparison technique under full commercial conditions to assess their potential in reducing the catch of undersized commercial species, in particular cod. We investigate the position of a 90 mm square-mesh panel (SMP), the effect of increasing the mesh size from 90 to 120 mm in the SMP, the effect of inserting a 90 mm SMP in an 80 mm codend and the effect of increasing the codend mesh size from 90 to 120 mm in a total of 89 hauls. Inserting the SMP 3–6 m from the codline compared to 6–9 m from the codline, reduced catches of cod above the minimum landing size (MLS) and Nephrops above and below the MLS. Increasing the mesh size in the SMP from 90 to 120 mm increased the catch of cod above the MLS in weight with an overall increase of 12% in the revenue. The effect of installing a 90 mm SMP 6–9 m from the codline in a nominal 80 mm codend had no effect on the catch of cod. Increasing the nominal codend mesh size from 90 to 120 mm reduced the catch of all species below the MLS, except monkfish. Catches of Nephrops above the MLS were, however, reduced by approximately one third and the total loss in revenue was 21%.