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This is a pre-copyedited, author-produced version of an article accepted for publication in ICES Journal of Marine Science following peer review. The version of record Mytilineou, Herrmann, Mantopoulou-Palouka, Sala, Megalofonou. Escape, discard, and landing probability in multispecies Mediterranean bottom-trawl fishery. ICES Journal of Marine Science. 2021 is available online at: https://doi.org/10.1093/icesjms/fsab048. Commercial bycatch species and their exploitation pattern in the Mediterranean trawl fishery are little studied. The present work examines the overall size-selection pattern, both regarding the trawl in the sea and the fisher onboard the vessel, for seven commercial bycatch species using different codends. The applied selection model predicted the escape, discard, and landing probability for each species simultaneously, a useful method for providing information important for fisheries management under the ecosystem approach. Among the studied codends, the 40-mm diamond mesh codend, still in use in non-EU Mediterranean fleets, was found unsuitable for the stocks in all cases. The 40-mm square mesh codend (40S) was found appropriate for blue whiting (Micromesistius poutassou), comber (Serranus cabrilla), and bogue (Boops boops) sustainability. The 50-mm diamond mesh codend (50D) was more suitable than the square mesh codend only for the spotted flounder (Citharus linguatula). Both the 40S and the 50D codends were appropriate for picarel (Spicara smaris), whereas none ensured sustainable exploitation for the blackbelly rosefish (Helicolenus dactylopterus), and the streaked gurnard (Chelidonichthys lastoviza). The results are discussed in relation to juvenile protection, discard mitigation, and fisher selection behaviour, important factors for the sustainability of stocks and fisheries in the Common Fishery Policy for the Mediterranean Sea.

Mediterranean trawl fisheries are characterized by a critical combination of high fishing effort and low size at first capture for most commercial species. In this study we tested the use of sorting grids installed on bottom trawl nets to minimize the catch of undersized deep-water rose shrimp (Parapenaeus longirostris, DPS) and European hake (Merluccius merluccius, HKE). The catch of a traditional trawl net was compared with that obtained with the same net equipped with ad hoc designed juveniles and trash excluder devices (JTEDs) during an experimental survey. Three different JTEDs were tested: the first (G1-SM40) was built with a net of 40-mm square mesh; the second (G2-ST20) and third (G3-ST25) with vertical steel bars spaced 20 and 25 mm, respectively. The probability of retaining DPS and HKE by length class in trawl nets with and without JTED was analysed using generalized additive mixed models. With G1-SM40, the reduction of undersized individuals in the cod-end was about 60% and 44% for DPS and HKE, respectively. With G2-ST20, a 34% catch decrease of HKE individuals smaller than 20 cm total length was observed. A loss of marketable fractions of DPS was recorded with G1-SM40 (–25%) and G2-ST20 (30%). Finally, JTD G3-ST25 was efficient at reducing the catch of undersized specimens of DPS and HKE, but showed a higher loss of marketable fractions than the other JTEDs. Although further fishing trials would be required to maximize the sorting efficiency of the grids, the results obtained clearly indicated that grids can substantially reduce unwanted catches of undersized DPS and HKE in Mediterranean bottom trawl fisheries., Las pesquerías de arrastre mediterráneas se caracterizan por una combinación crítica de un alto esfuerzo de pesca y un tamaño de captura por debajo de la talla legal para la mayoría de las especies comerciales. En este estudio, probamos el uso de rejillas separadoras instaladas en redes de arrastre de fondo para minimizar la captura de la gamba rosada (Parapenaeus longirostris; DPS) y la merluza (Merluccius merluccius; HKE). La captura obtenida con una red de arrastre tradicional se comparó con la obtenida con la misma red equipada con “Juveniles Trash Excluder Devices” (JTED) diseñados específicamente para cada caso durante un estudio experimental. Tres JTEDs diferentes se probaron: el primero (G1-SM40) se construyó con una res de 40 mm de malla cuadrada; el segundo (G2-ST20) y el tercero (G3-ST25) se fabricaron con barras verticales de acero separadas 20 y 25 mm, respectivamente. La probabilidad de retener DPS y HKE según clase de talla en redes de arrastre con y sin JTED se analizó utilizando Modelos Mixtos Aditivos Generalizados (GAMM). Usando G1-SM40, se consiguió una reducción de individuos de talla por debajo de la talla legal en el copo, de 60% y 40% para DPS y HKE respectivamente. Con respecto a HKE, utilizando G2-ST20 se observó una disminución en la captura del 34% de individuos de menos de 20 cm TL. Sin embargo, se registró una pérdida de fraccion comercializable de DPS usando G1-SM40 del –25% y usando G2-ST20 del 30%. Finalmente, el JTED G3-ST25 resultó eficaz para reducir la captura de especímenes de DPS y HKE de talla ilegal, pero se observó una mayor pérdida de fraccion comercializable que con los otros JTEDs. Aunque se necesitarían más ensayos de pesca para maximizar la eficiencia de las rejillas separadoras, los resultados obtenidos indicaron claramente que las rejillas pueden contribuir a reducir sustancialmente las capturas no deseadas de DPS y HKE de talla ilegal en las pesquerías de arrastre de fondo del Mediterráneo.

High rates of discards have been noted for shrimp fisheries worldwide and especially for the small-scale shrimp trawl fisheries of the Persian Gulf. Bycatch reduction devices (BRDs) can significantly decrease discards in shrimp trawl fisheries. We tested the performance of a square mesh panel BRD (SMP) and a juvenile and trash fish excluder device (JTED) in the small-scale shrimp trawl fishery of the Persian Gulf. Efficiency of the BRDs was determined in terms of shrimp loss, by-product loss, the reduction in discards by weight and differences in size selectivity of commercial fishes. Where a JTED was used, reductions in catch, by weight, were (mean ± 95% CI) 12% ± 2.35 for shrimp, 31.9% ± 5.22 for by-product fish and 49% ± 7.52 for discards. Similar reductions were observed when a SMP was used: 16% ± 4.19, 38.3% ± 6.41 and 45% ± 6.15 for shrimp, by-product and discards, respectively. There was no significant difference in the exclusion rate of discards between the JTED and SMP. Significant difference was found for loss of shrimp between JTED and SMP. The mean escapement rate for by-product species in trawl net with JTED and SMP were 35% and 40%, respectively. Selectivity curves of both BRDs indicated, that for each species, the length of 50% retention probability (L50) were smaller than the length at maturity (LM) and an increase in bar spacing in JTED and mesh opening in SMP would be required to delay capture until fish had reached Lm. The results indicated that SMP allows a higher proportion of sub-legal by-product species to escape the trawl, compared to the JTED used in the study. Implementing BRD requirements for the Persian Gulf small-scale shrimp fisheries would contribute to meeting strict sustainability criteria, a good outcome for this small-scale fishery.

The reduction of juvenile catch and discards are important targets in fisheries policy. This work examines how selection models can predict the size structure (LFD) of discards and landings considering the effects of area, time period, gear and fisher behaviour. Additional exploitation indicators related to the gear used, fisher's selection pattern, and discards were also estimated. The approach is demonstrated in a study concerning hake in the Mediterranean trawl fishery, focusing on high (HRA) and low (LRA) recruitment areas in the Saronikos Gulf (Eastern Mediterranean) during two periods (June, September) using two codends (40 mm square-40S, 50 mm diamond-50D mesh). The predicted discards LFDs revealed generally higher percentages in the HRA in June when using the 50D. The predicted landings LFDs showed higher percentages in the LRA in September for both codends, but undersized hake were always included. LFDs and exploitation indicators indicated that both codends were inappropriate for sustainable fishing of hake in the HRA, where 50D performed worse than the 40S. Fishing with both codends in the LRA in September revealed the lowest discards rates and minimum sizes of landings close to MCRS (minimum conservation reference size). These results can provide information to fisheries management aiming to protect juveniles and reduce discards through spatio-temporal fishing closures.

Reduction of discards from the Basque mixed bottom trawl fishery is a challenge. To improve the selective properties of the gear used by the fleet and supplement codend size selection, a square mesh panel (SMP) installed in the upper panel of the trawl was introduced in 2006. However, recent studies have shown that the release efficiency of this SMP is low due to lack of contact between the fish and the SMP. In this study, we tested the release efficiency of the SMP for four different gear configurations. We tested the effect of adding LED lights at two different positions and altering panel size and panel position in the trawl. The analyses were focused on two species: hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou). The results showed that the position of LED lights did not significantly affect the SMP’s release efficiency for any species. However, increasing panel size had a significant positive effect on the release efficiency of blue whiting, and placing the SMP in the lower panel improved the release efficiency of hake. These results highlight the challenge of simultaneously improving the selective properties of gear for species with different behaviour, especially in mixed demersal fisheries. La reducción de descartes en la pesquería de arrastre del País Vasco supone un problema importante. En 2006, se introdujo en la reglamentación la posibilidad de usar un Panel de Malla Cuadrada (SMP) en la zona anterior al copo para mejorar la selectividad de la red. Sin embargo, estudios recientes manifiestan que la eficiencia de escape de los peces es baja debido a la falta de contacto selectivo entre el pez y el panel. En este estudio, analizamos la eficiencia de diferentes configuraciones del SMP. Se analizó el efecto de luces LED colocadas en distintas posiciones, el efecto del tamaño del SMP y su localización. Estudiamos la merluza (Merluccius merluccius) y la bacaladilla (Micromesistius poutassou). La posición de las LED demostró no tener ningún efecto significativo sobre la eficiencia de escape del SMP para ninguna de las dos especies. Sin embargo, aumentar el área del panel tuvo un efecto significativo en la eficiencia de escape de la bacaladilla, mientras que el cambio de posición del SMP incrementó la eficiencia de escape de la merluza a través del SMP. Estos resultados muestran el reto que supone mejorar la selectividad de un arte de pesca simultáneamente para especies demersales con comportamientos diferentes.

Creative Commons Attribution Non-Commercial Share Alike License 3.0 CC BY-NC-ND 3.0. The current legal codends used in Mediterranean bottom trawl fisheries are at high risk of retaining undersized individuals of several commercial fish species. This entails that codends alone are unable to provide the desired exploitation pattern. A simple technological measure that potentially can provide higher release efficiency of undersized fish are Square-Mesh Panels (SMPs). SMPs are often applied in the upper section of the trawl belly, just ahead the codend. However, recent studies in the Mediterranean have demonstrated that SMPs mounted in this position provided limited release efficiency, because very few fish came into contact with their meshes. In attempt to improve SMPs efficiency in the Mediterranean bottom trawl fisheries, we applied them on the lateral sides of the last tapered section of the trawl belly, just ahead of the codend, and fitted two guiding panels in the trawl belly to enhance fish-SMP contact. We compared the catch performance of a standard commercial trawl with a 52 mm diamond-mesh codend and of a similar trawl fitted with lateral SMPs (70 mm mesh size) in the belly using a twin trawl. The study focused on red mullet (Mullus barbatus), a commercially important species, but data for gurnard (Chelidonichthys lucerna and Chelidonichthys cuculus) were also obtained and analysed. In contrast to previous research on SMPs mounted in the top panel of the trawl, in this study SMPs induced a significant effect on catch performance for red mullet, demonstrating that their lateral position involved greater fish-SMP contact. However, since the test trawl lost a significant amount of legal-sized red mullet compared with the standard trawl, the effect was not wholly positive, possibly due to an excessively large mesh size. Therefore, future studies should be encouraged to test lateral SMPs with smaller mesh sizes.

This is a pre-copyedited, author-produced version of an article accepted for publication in ICES Journal of Marine Science following peer review. The version of record Cuende, E., Arregi, L., Herrmann, B., Sistiaga, M. & Aboitiz, X. (2020). Prediction of square mesh panel and codend size selectivity of blue whiting based on fish morphology. ICES Journal of Marine Science is available online at: https://doi.org/10.1093/icesjms/fsaa156 Square mesh panels (SMPs) are selective devices used extensively to supplement codend size selectivity in trawl fisheries. Therefore, predictions of the effect of mesh size in both SMPs and codends on size selectivity are valuable. Here, we established a framework to predict the size selection of blue whiting through different SMPs and diamond mesh codends based on the morphological characteristics of this species. We hypothesized that size selection for an SMP is determined by different fish contact angles, whereas different mesh opening angles determine size selection for the codend. Based on these hypotheses, we first developed a model that enabled us to predict which sizes of blue whiting are able to pass through meshes of different sizes and shapes. We then tested whether the selectivity for blue whiting of the SMP, the codend, and the combination of both could be explained by the models. Finally, we predicted the size selectivity of multiple combinations of SMPs and diamond mesh codends. The method presented here can potentially be applied to make predictions for species other than blue whiting.

Many fishing methods result in significant catches of non-target species or individuals that are too small to be retained for economic values or within quota regulations. In the Baltic Sea trap fishery, the major problem is the bycatch of juvenile and non-marketable whitefish (Coregonus maraena) which constitutes a threat to the sustainability of the fishery and a time-consuming problem for the fishers. This study evaluates the effectiveness of a modified fish trap in reducing such bycatch. An encircling selection panel consisting of 50 × 50 mm square mesh netting was installed in a pontoon fish chamber of a salmon/whitefish trap. Comparative fishing was conducted against a control trap without selection panel in the inshore waters of the Bothnian Sea. Comparisons of catch compositions between the traps showed that there was a 72% reduction in juvenile whitefish catch in the experimental trap. The length at 50% retention (30.1 cm) corresponded well to the minimum market size (>30 cm) of whitefish that are desired for the local market. Fishers are advised to use a netting panel of 50 × 50 mm square mesh for their traps to reduce undersized whitefish. The results are important for the sustainability of whitefish stocks in the Baltic Sea.

Many jurisdictions have introduced management regimes prohibiting or limiting discarding, and a key objective of the European Union Common Fisheries Policy is the gradual elimination of discards. One way of reducing the catch of unwanted fish is to use more size-selective gears. Gear-based management options can best be explored using models that predict size selection across a wide range of variables related to gear design. Such a model is developed for haddock (Melanogrammus aeglefinus) through a meta-analysis of 21 trials of codend selection and 19 trials of the combined selection of the codend and a square mesh panel. Individual-haul estimates of the 50% retention length (l50) and the selection range (SR) are related to a set of explanatory variables through a structural model that describes the dual process of panel and codend selection. Codend l50 and SR are positively related to codend mesh size and negatively related to the codend twine diameter. Codend l50 is also negatively related to the number of open meshes around the codend circumference. Panel l50 increases with panel mesh size. The panel contributes more to gear selection as it is moved closer to the codline. The panel is most effective between November and January and least between May and July, periods which broadly coincide with peak and poor haddock condition. The results are illustrated for a typical trawler targeting haddock in the Scottish whitefish sector, and the utility of the model for gear design and legislation is discussed.

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.

This is a pre-copyedited, author-produced version of an article accepted for publication in ICES Journal of Marine Science following peer review. The version of record Sistiaga, M.B., Herrmann, B., Grimaldo, E., Larsen, R.B., Olsen, L., Brinkhof, J. & Tatone, I. (2017). Combination of a sorting grid and a square mesh panel to optimize size selection in the North-East Arctic cod (Gadus morhua) and redfish (Sebastes spp.) trawl fisheries. ICES Journal of Marine Science. 75(3), 1105-1116 is available online at: https://doi.org/10.1093/icesjms/fsx231 Sorting grids and square mesh panels are the two most-applied technical devices to supplement codend size- and species-selection in demer- sal trawls. In the Barents Sea gadoid fishery, the compulsory size-selectivity system comprises a mesh section with a sorting grid followed by a diamond mesh codend. We tested the size-selective performance of a new sorting section that comprised a sorting grid combined with a square mesh panel as a potential alternative for the grid sections currently in use. The new sorting section was shorter and therefore more maneuverable than the existing sorting grid sections. The investigation was carried out on cod and the bycatch species redfish. The grid was found to contribute to the largest proportion of fish release, and the release through the square mesh panel was low. But, the results showed that the grid was successful at guiding fish not escaping through the grid to a second selection process in the panel. However, the square mesh panel did not result on the intended release efficiency except for the smallest sizes of fish, most likely because the guiding angle of the grid and the square meshes in the panel used did not provide a suitable escape path for the desired size range of fish. Therefore, optimizing the mesh size/shape in the panel and/or the guiding angle for the grid potentially could lead to the desired selectivity pattern in the new sort- ing section.

This paper quantifies the effects of a square mesh codend bycatch reduction device (BRD) and turtle excluder device (TED) in the deepwater eastern king prawn (Melicertus plebejus) fishery on the southeast Queensland coast, based upon on a 10-day research charter. The bycatch comprised 224 taxa, mainly gurnards, flatheads, sandpaper fish, hermit and charybdid crabs, mantis shrimps, sand dollars (i.e. sea urchins), dragonets, snipefish, carids and lizardfish. The total mean bycatch rate was comparatively low (1114.0 g ha−1 from the standard diamond mesh codend), mainly because of the relatively deep waters associated with the fishery. When the TED and square mesh codend BRD were used together the total mean bycatch rate was significantly reduced by 29% (796.0 g ha−1) compared to the standard codend, with no significant effect on the prawn catch rate or size frequency distribution. Several bycatch species experienced very large reductions in mean catch rate, due to the square mesh codend, including Graham's conger Gnathophis grahamii (98.2% reduction), dumpling squid Euprymna tasmanica (95.9%), shortsnout threadsail Aulopus curtirostris (90.6%) and sandpaper fish Aulotrachichthys sp. (90.0%). Multidimensional scaling indicated that bycatch assemblages were more affected by latitude and depth than codend type. Based on the results, we recommend that the 47.6 mm square mesh codend be made mandatory in the deepwater eastern king prawn fishery as a highly effective BRD.

Based on size selectivity data for more than 25 000 cod (Gadus morhua) collected during experimental trawl fishing with six different codends, all of which included a square mesh panel, we investigated the effect on cod-release efficiency based on the size of the square mesh panel area, position of the square mesh panel, and stimulation of the escape response. Based on the results, we were able to explain why the BACOMA codend, applied in the Baltic Sea cod directed trawl fishery, releases juvenile cod efficiently, whereas other designs, including a square mesh panel with similar mesh size, are less efficient. Our main findings reveal that the release efficiency of the square mesh panel in the BACOMA codend depends largely on the overlap of the square mesh panel and the catch-accumulation zone in the codend, where cod do not have the option of just drifting further back in the trawl when proximate to the panel. On the contrary, the reduction in panel size by 50% did not significantly affect the release efficiency when the panel overlapped with the catch-accumulation zone. It was possible to stimulate an escape response for cod to achieve a release through a square mesh panel positioned away from the catch-accumulation zone. Our findings demonstrated that this release was as efficient as for a panel mounted in the catch-accumulation zone of the codend. Devices that stimulate behaviour may improve the release efficiency of cod through square mesh panels in other fisheries where this is a problem.

Five modified trawl codends were assessed for their utility in simultaneously improving the size selectivity of cod ( Gadus morhua ) and plaice ( Pleuronectes platessa ) in the Baltic Sea. The modifications included refining the selective performance of the current Bacoma codend by increasing the mesh size of the lower panel from 109 mm double twine to 129 mm single twine and increasing the mesh size in the upper square mesh panel from 132 to 147 mm, and also making the lower panel the same design as the upper panel; i.e. a full square mesh codend. These three experimental designs were tested in conjunction with the currently legislated codends; Bacoma and T90. The most favourable selective properties with regard to simultaneously improving the selectivity for round and flatfish, considering the current minimum landing sizes (MLS) for cod (38 cm) and plaice (25 cm) in the Baltic Sea and the fish population size structures during the sea trials, were found to be the T90 codend and the Bacoma codend with a modified lower panel. For the T90 codend, the selection parameters (L50 and SR) were 43.4 and 6.7 cm for cod, and 24.7 and 2.1 cm for plaice. The selection parameters for the most effective modified Bacoma codend were 41.1 and 8.3 cm for cod and 25.2 and 3.9 cm for plaice

This study was predicated by a recent management proposal to mandate square-mesh codends in an Australian estuarine squid trawl fishery, based on their improvements to the selectivity of penaeid trawls deployed across comparable temporal and spatial scales. The assumption of no impacts of a codend cover on the performance of a squid trawl was validated before it was used to quantify the size and species selection of a conventional codend made from 41-mm diamond-shaped mesh and two new designs made from 29- and 32-mm mesh hung on the bar (i.e. square shaped). Compared to the 41-diamond codend, both square-mesh designs incrementally and significantly reduced the catches of a small legally retained teleost (whitebait Hyperlophus vittatus), but had no significant effect on discarded catches (termed ‘bycatch’). The 32-square codend also significantly increased the sizes at 50% probability of retention for the targeted squid (Luminous Bay squid Loliolus noctiluca and broad squid Photololigo etheridgei), across narrow selection ranges and, because all sizes are retained, consequently reduced their total landed catches. The results support the utility of square-mesh for consistently improving and maintaining lateral openings in codends, but the management of this fishery means that such configurations would result in economic loss, and for the 29- and 32-square codends, no concomitant reduction in bycatch. This study reiterates the need for bycatch issues to be clearly identified and defined on a fishery-specific basis, and prior to the implementation of mitigation measures.

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).

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 Nephrops .

Broadhurst, M. K., and Millar, R. B. 2009. Square-mesh codend circumference and selectivity. – ICES Journal of Marine Science, 66: 566–572. Despite the wide-scale assessment and the use of square-mesh codends in demersal trawls, relatively few studies have tested the effects of configurations other than mesh size on their selectivity. We investigated the consequences of increasing the circumference of square-mesh codends used in an Australian penaeid fishery from the expected optimal configuration of ∼33% of maximum diamond-mesh extension to ∼56 and 75%. Three square-mesh designs comprised 27-mm polyamide mesh throughout and had the same length (100 bars, B), but different circumferences (90, 150, and 200 B, respectively). Paired simultaneous comparisons (using twin trawls) of each treatment codend against a small-meshed control revealed significant effects of circumference on the efficiency of the trawl for a small teleost (pink-breasted siphonfish, Siphamia roseigaster) and commercial size classes of school prawns (Metapenaeus macleayi). Compared with the 90 codend, pink-breasted siphonfish catches and prawn count (numbers per 500 g) were both significantly greater in the codends of larger circumference, and these effects are attributed to concomitant (i) convoluted or reduced lateral openings of meshes and (ii) lesser probabilities of organisms encountering meshes in the posterior section. These differences would not preclude the use of codends of larger circumference in the fishery, but they do highlight the need to select appropriate configurations in future studies to reduce the potential for including the confounding effects of different geometries.

Rotherham, D., Broadhurst, M. K., Gray, C. A., and Johnson, D. D. 2008. Developing a beam trawl for sampling estuarine fish and crustaceans: assessment of a codend cover and effects of different sizes of mesh in the body and codend. – ICES Journal of Marine Science, 65: 687–696. An experiment was carried out in the Clarence River (New South Wales, Australia) to test the hypotheses that fish and crustacean catches in an experimental beam trawl were affected by a codend cover and the sizes of mesh in the body and codend. The cover had no obvious effects on the catches retained in the codend. Similarly, in comparisons between trawl bodies made from 26- and 41-mm diamond-shaped mesh, there were no differences in the assemblages of fish caught, or in the mean numbers entering the codends. For one species of fish (Acanthopagrus australis), however, there were differences in the proportions caught between the trawl bodies across different size classes. There was also some evidence to suggest that mesh size in the body of the trawl influenced the size selection of school prawns (Metapenaeus macleayi). For most finfish, there were no differences in catches between codends made from 20-mm and from 29-mm mesh hung on the bar (i.e. square-shaped mesh). In contrast, mesh size in the codend was important for the size selectivity of school prawns, with smaller carapace lengths at 50% retention in the 20-mm codend. We conclude that use of a 41-mm mesh in the body and a 20-mm square mesh in the codend of the beam trawl would be appropriate for future sampling with this gear in estuaries of New South Wales. A similar experimental approach to ours is needed in adapting the beam trawl to estuaries in other parts of the world, or in developing other types of research trawl.

A covered-codend experiment was done to assess the size selectivity of a codend made from 27-mm mesh hung on the bar (i.e. square mesh) for school prawns (Metapenaeus macleayi) across 10 vessels within the New South Wales (NSW) estuarine penaeid-trawl fishery. Prior to starting the experiment, a codend cover (18-mm diamond-shaped mesh) was tested and demonstrated to have no effect on the catching efficiency of a typical estuarine trawl, thereby validating its use for assessing size selectivity. There was substantial variability in the estimated carapace lengths at 50% probability of retention (L50 ± S.E.: between 7.90 ± 0.97 and 13.76 ± 0.23 mm) and selection ranges (SR: between 2.70 ± 0.18 and 6.71 ± 1.72 mm) of the 27-mm square-mesh codend among trawlers and estuaries. Multi-level, generalised linear mixed-effects modelling demonstrated that this variation was explained by: (i) the catch weight of school prawns; (ii) the particular estuary being fished; and (iii) random between-tow and -trawler variability. The results are discussed in terms of the various operational, biological and environmental factors unique to each fishing operation. Despite the variability in the performance of the 27-mm square-mesh codend, an overall improvement in size selectivity compared to conventional diamond-mesh designs, combined with a high survival rate of escapees, justifies its adoption and legislation throughout the NSW estuarine penaeid-trawl fishery as a means for mitigating unwanted fishing mortalities. We also conclude that similar codends may have application in other penaeid-trawl fisheries around the world.

In the continuing drive to reduce discards of juvenile gadoids (whiting, cod, haddock) in the Farn Deeps Nephrops directed fishery in the North Sea, we examine the efficacy of the square-mesh panels (SMP) which are currently fitted to the trawls in that fishery. We find that discards can be further reduced by around 40% through simple modification to these square-mesh panels. While some basic measures to improve their efficacy have been identified, we have not yet described the ‘optimal square-mesh panel’ and thus we indicate areas for further research in this field which may yield further dividends in discard reduction.

Trials were carried out to evaluate the effects of a square mesh panel on the catches of a demersal trawl during normal commercial fishing operations over a period of 1 year. A 100 mm cod-end fitted with a 90 mm mesh square mesh panel between 6.3 and 9.3 m from the cod-line was compared with an identical cod-end with no panel, attached to the same net, using the alternate haul method. The square mesh panel significantly reduced the catch of undersized whiting (by an estimated 34%; p

A catch comparison method was used on a commercial vessel to assess the potential of a Swedish grid and square-mesh codend in reducing fish bycatch, in particular cod, in the Farn Deeps Nephrops fishery (England). A standard trawl with a diamond mesh codend, as currently used in the fishery, was compared against a trawl with a Swedish grid and against a trawl with a Swedish grid and square-mesh codend. The trawl with the grid and diamond mesh codend caught no cod of marketable size and fewer large whiting, plaice and haddock than the standard trawl. However, that trawl caught twice the number of small cod and more haddock (and more Nephrops), as did the standard trawl. The trawl with the grid and square-mesh codend caught less cod, haddock and whiting in all length classes, but Nephrops catches were around half that of the standard trawl. Using the grid meant a ∼75% reduction in revenue from bycaught fish and squid landings, and when combined with the square-mesh codend, a further reduction of 50% in revenue from Nephrops landings. The implications of these economic findings are evaluated.

In order to improve the capacity of bottom trawl fishing gears to reduce catches of young fish and discards in a highly exploited demersal trawl fisheries in the Mediterranean, the size-selection performance of a 36-mm square-mesh codend and two sorting grids with 20 and 15 mm bar spacing was assessed. Alternate hauls were used to assess the selectivity of 36-mm square-mesh codend. Selectivity of sorting grids was assessed using a double codend in which fish that escaped through the grid were captured in the lower codend while other fish were guided into the upper codend. The mean selection length (L50) for European hake was 18.5 cm and that for the Atlantic horse mackerel was 14.0 cm with the 36-mm square-mesh codend . These values are close to their current minimum landing sizes (20 cm for hake and 12 cm for horse mackerel). The sorting grid with 20-mm bar spacing showed L50 value of 13.3 cm for hake, suggesting that a larger grid-spacing would be needed to obtain sufficient sorting performance. Similarly, for Atlantic mackerel the estimated L50 of 14.3 cm indicates that larger grid spacing is required to attain an L50 that would be close to the current MLS (18 cm). For Atlantic horse mackerel and red mullet, the L50 obtained with the sorting grid with 20-mm bar spacing was close to the MLS of these species (the MLS of red mullet is 11 cm). The selectivity of the sorting grid with 15-mm bar spacing was generally very poor. Size-selection performance of sorting grids was assessed for the first time in the local fisheries. In order to effectively improve size-selection, seasonal and depth-dependent differences between target and by-catch species must be taken into account, which is a good indicator of the difficulty of implementing a single mesh size or grid spacing in the Mediterranean demersal trawl fishery. Con el propósito de mejorar la capacidad de las redes de arrastre de fondo para reducir las capturas de peces juveniles y descartes en una pesquería multiespecífica altamente explotada en el Mar Mediterráneo, se evaluó la selectividad de las tallas de diversas especies demersales mediante el uso de una malla cuadrada de 36 mm y dos rejillas con separación entre barras de 20 y 15 mm. Se usó el método de lances alternativos para evaluar la selectividad del copo de malla cuadrada. La selectividad de las rejillas se evaluó mediante un doble copo. Los peces que escaparon de la rejilla se capturaron en el copo inferior y el resto del pescado se guió y capturó en el copo superior. Con el copo de malla cuadrada, la talla media de madurez (L50) de la merluza y el jurel fue respectivamente de 18,5 cm y 14,0 cm. Estos valores se aproximan a la talla mínima de selección (MLS para la merluza es de 20 cm y para la jurel es de 12 cm). Con la rejilla con separación entre barras de 20 mm, la L50 de la merluza fue de 13,3 cm, lo cual sugiere que sería conveniente aumentar la separación entre barras para obtener una L50 más próxima a la MLS. La caballa se seleccionó con una L50 de 14,3, por debajo de la MLS de 18 cm. El jurel y el salmonete mostraron L50 cercana la MLS (MLS del salmonete es 11 cm). La rejilla con espacios de 15 mm fue muy poco selectiva. Este es el primer trabajo que se realiza en el área en el que se compara el funcionamiento de la malla cuadrada y las rejillas separadoras. La tecnología de las rejillas separadoras se aplicó por primera vez con el objetivo de mejorar la explotación de las pesquerías locales. La mejora en la selección de tallas requiere tener en cuenta la variación estacional y en profundidad de las especies objetivo y especies acompañantes, lo que demuestra la dificultad de implementar una sola malla o rejilla en toda la pesquería demersal de arrastre del Mediterráneo.

Experiments were conducted in the Baltic Sea to measure mortality of cod that escape through trawl codend meshes under commercial fishing conditions. Three codend types were tested: a 120 mm diamond mesh codend, a Danish type 105 mm escape window codend, and a 105 mm square mesh top-panel codend (Bacoma-window). In total, 30 tows were carried out in three different experiments. Mean tow duration was 3 h and average codend catch 536 kg (range 47–2592 kg). Escapees were collected during the last 20 min of each haul by a caging method. These fish were then held in cages anchored on the seabed and checked daily by divers. Average number of escapees in cage was 133. Average caging duration was 9.5 days. The mortality of escapees was low in normal water temperatures (

The effects of an increase in cod end mesh size from 65 to 70 and 80 mm and a change of mesh configuration from 65 mm diamond to 65 mm square mesh on the size selectivity of horse mackerel (Trachurus trachurus), hake (Merluccius merluccius) and axillary seabream (Pagellus acarne) of the shallow groundfish assemblage off the Portuguese southwest coast were evaluated. The increase in mesh size had a small but significant effect on size selectivity for the three species, while the change in mesh configuration led to a much more pronounced increase in the selectivity parameters. For horse mackerel, the L50 estimates ranged from 14.4 to 16.0 cm in the diamond mesh cod ends-values that are close to the minimum landing size of 15 cm. For hake, L50 of 17.0 and 18.3 cm were estimated for the 70 and 80 mm diamond cod ends respectively, while for the axillary seabream the L50 estimated was 13.9 cm for the 80 mm diamond mesh cod end. These values are well below the minimum landing sizes of 27 and 18 cm for these species. The corresponding estimates in the square mesh cod end were 21.9, 32.4 and 19.6 cm, with the loss of a high percentage (76%) of horse mackerel above the minimum landing size. For all the cod ends tested, the observed retention was presented as a function of maximum girth/mesh perimeter, which allowed a better understanding of the selection process for the species in study. Selectivity estimates for horse mackerel and hake were also compared to those obtained by Campos et al. (2003) for the same species in 1993 off the south coast, where they are captured as a by-catch in the crustacean fishery.

An industry-modified Nordmore-grid was tested on its own and with a composite square-mesh panel as a secondary bycatch reduction device (BRD) at two different positions (aft and forward) in codends. Compared to the control codend (which had no BRDs), all three combinations (Nordmore-grid only, Nordmore-grid and aft composite square-mesh panel and Nordmore-grid and forward composite square-mesh panel) reduced catches of prawns (mostly western king prawns, Penaeus latisulcatus). However, prawns were found to escape out of the Nordmore-grid—not through the composite square-mesh panels. The Nordmore-grid with the aft composite square-mesh panel significantly reduced the weight of bycatch (by 49%) and the numbers and weights of several commercially and non-commercially important bycatch species (by up to 75.7%). No other significant differences were detected. The results are discussed in terms of the likely factors influencing the performance of the various designs, including the behaviour of fish in codends, influences of hydrodynamics on their escape and the importance of the positioning of BRDs in codends.

Square mesh panels are often inserted in the codend or extension of a fishing net to allow under-sized fish an extra opportunity to escape. The effectiveness of the panel can be quantified by placing a small-mesh cover over the panel to catch all the fish that escape through it. This paper develops methodology for modelling the data from such covered panel experiments. The selection process is modelled in two stages: first, selection in the panel area, and second, conventional codend selection. Several different curves describing selection in the panel area are investigated. These include curves that separate the process of fish “contacting” the panel from the selection of the panel itself. Parameter estimation, inference, and methods for assessing goodness-of-fit are described. The methodology is illustrated using haddock and whiting data.

Selectivity experiments were carried out in the northern North Sea at the Fladen Ground and the East Ground from a Danish commercial vessel. A conventional 70 mm Nephrops codend and a similar codend with a 90 mm square mesh panel window inserted in the top panel were tested simultaneously in a twin trawl rig. Selectivity parameters and differences in catches of the target species Nephrops and the by-catch species whiting, haddock and cod were estimated. The logistic function was found to give the best description of fish selection ogives, whereas the asymmetric complementary loglog function described Nephrops selection best. The Fryer model was used to describe and compare the selection ogives for haddock, whiting, cod and Nephrops in the two codends. Due to low catches of cod and Nephrops only four out of 11 hauls could be used for modelling the selection of these two species. Selection factor and selection range were larger for the window codend for all fish species. The codend catch size had a significant negatively correlated influence on l50 and selection range for whiting in the window codend. There were large significant reductions in numbers of cod and haddock under the Danish MLS with the window codend. Catches of small cod, however, were low. Very few whiting under MLS were retained in either codend but there was a large significant reduction in individuals over MLS with the window codend. A large proportion of the Nephrops in the codends were under MLS. A reduction in catch weight of Nephrops over MLS was found for the window codend, but catches of Nephrops were low for several hauls.

Experiments were carried out during two cruises in 1995 to test a prototype species-selective bottom trawl for separating cod from haddock and saithe, in the Norwegian bottom trawl fisheries in the Barents Sea. A sorting system incorporating a horizontal square mesh panel (150 mm bar length) dividing the trawl’s body and extension sections into upper and lower compartments, leading aft to verticallyoriented trouser codends, was installed in a commercial roundfish trawl. During the first cruise approximately 90% of the haddock and 70% of the saithe were caught in the upper codend, with 70% of the cod in the lower codend. During the second cruise 90% of the haddock and 60% of the saithe were caught in the upper codend, with 65% of the cod caught in the lower codend. In situ video observations showed that fish, apparently haddock, entered the trawl at all levels, but subsequently many of those in the lower half attacked upwards and through the separating panel along its length as they passed towards the trouser codends. The diVerences in the results by species and season are discussed, along with the applicability of the sorting system to commercial fisheries. ? 1998 International Council for the Exploration of the Sea

A study to examine damage to fish escaping from prawn trawl codends was carried out in tropical Australian waters of the Gulf of Carpentaria and is the first of its kind in Australian or tropical fisheries. Fish passing through two sizes of square meshes (38 mm and 45 mm) were compared with fish passing through the standard 45 mm diamond-mesh codend. Escapees were captured in a fine mesh (16 mm) codend cover and brought on board in a water-filled scoop into which the fish were released. Individuals of species selected for damage assessment were placed in a lethal dose of MS222. These fish were examined for damage. Five species were collected in sufficient numbers (n>10) for statistical analyses to be carried out. The results indicate that, fish escaping through either 45 mm codend mesh have minimal damage. Those fish escaping through the 38 mm square codend mesh incurred more severe damage than those escaping from the 45 mm diamond-mesh codend.

The position of a square-mesh panel in a 70-mm Nephrops trawl of the type widely used in the Irish Sea was varied to examine the effect on catch rates of whiting (Merlangius merlangus) of different sizes. Panels of 75-mm mesh size and 3 m length were positioned either 1 m in front of the cod-end extension, conforming with United Kingdom (UK) legislation, or 7 m in front of the extension, conforming with Irish (IRL) legislation. Forty-three tows of a twin Nephrops trawl were carried out from a commercial fishing vessel of the type using this gear in the Irish Sea, with different panel positions in the two nets. In a subsequent experiment, the twin trawl was separated into two single trawls and 40 parallel hauls were carried out from two smaller commercial trawlers typical of the single-rig Nephrops fleet in the Irish Sea. In each experiment, the trawls were deployed over a range of depths. Rigged as a twin trawl, the IRL net consistently caught fewer whiting below the minimum landing size (MLS) of 27 cm than did the UK net (mean catch rates of 72±10 and 131±14 fish per hour, respectively). Catch rates above MLS were almost identical in most hauls. In contrast, the panel position had no significant effect on catch rates of whiting of all sizes when the same nets were towed in parallel by the two smaller vessels. Possible reasons for these differences in results are discussed. As catch rates of whiting above MLS were not affected by panel position in both sets of trials, it is concluded that the more forward panel position would be most appropriate for Nephrops fisheries involving both single and twin trawls.

Large quantities of 0-group fish and small undersized shrimp on many inshore shrimp fishing grounds in Iceland have frequently prevented shrimping for extended periods. Many experiments have been carried out to solve this problem, but none of them was successful. The paper describes experiments with square mesh netting in the codend which reduced the by-catch of 0-group fish drastically and the catch of undersized shrimp to a great extent. The reduction of some 10–20% in the shrimp catch was easily accepted by fishermen as it was mainly due to small shrimp that could not be utilized. All boats in the inshore shrimp fishery are now using square mesh netting in the codends in their trawls to reduce the manual work of sorting out the by-catch and to increase the value of their quota by landing larger and more expensive shrimp.

To assess possible management strategies for conserving small, immature Atlantic mackerel ( Scomber scombrus L.), selectivity trials were undertaken in the western English Channel aboard F.V. Marbella (H99) during the period 24 January to 6 February 1990. An experimental codend of 60 mm polypropylene knotless square netting was attached to a 3700 Ijmuiden stores midwater trawl (Type No. P.101.B) used with superkrub doors. This experimental gear was fished against a similar trawl fitted with a codend constructed from 40 mm knotted nylon mesh rigged in the conventional diamond configuration. A total of 14 successful tows were made, nine using the trawl fitted with the experimental codend and five using the standard trawl. An estimated total catch of some 470 tonnes of mackerel was taken using both gears, and mackerel were caught on all tows except one. The size composition of the mackerel caught ranged from 18 to 37 cm, well within the expected selection range for the gear under test. A comparison of the length-frequency distributions indicated that there was no difference in the size composition, and hence selection, of fish taken by the two gears.

A traditional codend (40 mm diamond mesh) and an experimental codend (40 mm square mesh) made of 2.6 mm diameter knotless PA netting were tested on a commercial trawl net on a sandy-muddy bottom (~70 m depth) of the Adriatic sea in order to assess the size selectivity of European hake (Merluccius merluccius) and the reduction of the discards in a demersal multi-species trawl fishery. The catch was sorted as target species and bycatch and the selectivity with respect to European hake was investigated using the covered codend method. The square-mesh codend allowed a reduction of about 37% of the fraction discarded at sea. The mean catch obtained with the experimental codend was lower than that obtained with the traditional codend (about 14 kg per haul) but the short-term economic losses were low (~12%). The square-mesh codend was also more selective than the traditional codend, giving the juveniles of European hake a good chance of escape: the mean selection length (L50) was 7.60 cm in DM and 12.98 cm in SM. Moreover, the mesh configuration did not affect the gear’s performance. Thus, the square-mesh codend could be an easy, inexpensive and useful solution for a more sustainable management of the resources in Adriatic multi-species fishery., Se han probado copos de malla tradicional (rombo de 40 mm) y una malla experimental (cuadrada de 40 mm), hechas en fibra de 2.6 mm de diámetro sin nudo en PA, en una red de arrastre comercial sobre fondos fangosos (~ 70 m de profundidad) en el Adriático, con el fin de conocer la talla de selectividad de la merluza (Merluccius merluccius) y la reducción de los descartes en una pesquería demersal mutiespecífica. La captura fue separada en especies objetivo y especies acompañantes. Para conocer la selectividad de la merluza se utilizó el método del sobrecopo. El copo de malla cuadrada obtuvo una reducción del 37% de la fracción descartada al mar. La captura media obtenida mediante el copo experimental fue menor que la obtenida con el copo tradicional (14 kg por lance aproximadamente), pero las pérdidas económicas a corto plazo fueron bajas (~ 12%). El copo de malla cuadrada fue también más selectivo que el copo tradicional, dando a los juveniles de merluza mayor probabilidad de escape; la talla de selección (L50) fue de 7.60 cm en malla de rombo y 12.98 cm en malla cuadrada. La configuración de la malla no afectó el funcionamiento del arte. De este modo, el copo de malla cuadrada podría representar una fácil, barata y práctica solución para conseguir una gestión más sostenible de los recursos en la pesquería multiespecífica del Adriático.

In the flatfish beam trawl fisheries the by-catch by weight of invertebrates is several times the amount of marketable fish. In order to reduce the impact of beam trawling on the benthic communities, a number of benthos escape modifications to the trawl were tested. A drop-out opening (escape zone without netting) and large diamond and square mesh escape zones just behind the groundrope were not effective in releasing the benthos by-catch and induced an unacceptable decrease in commercial catch. Square mesh windows inserted in the belly just in front of the cod-end were more promising. With these devices a significant reduction in weight and number of most benthic species could be realised. The penalty is some loss of commercial catch but the results indicate that with an appropriate mesh size in the square mesh window, a balance may be found between a significant benthos by-catch reduction and an acceptable loss of marketable fish.

The performance of square-mesh codends (as opposed to the conventional diamond mesh) was examined as a discard and by-catch reduction device for the Shark Bay saucer-scallop trawl fishery. Of the three different-sized square-mesh codends (50, 55, 60 mm) tested against the standard 100-mm diamond-mesh codend, the 50-mm square-mesh codend performed poorly with relatively high retention of small (

This study investigates the effects of increasing the lateral mesh openings in codends on the size and species selectivity of lagoon and river seines and a stow net used to target penaeid prawns (eastern king (Penaeus plebejus), school (Metapenaeus macleayi) and greasyback prawns (M. bennettae)) in Wallis Lake, New South Wales, Australia. Compared with conventional codends made from 36-mm diamond-shaped mesh, new designs made from 25- and 29-mm mesh hung on the bar (i.e. square-shaped mesh) significantly reduced the catches of non-target fish (by between 58 and 95%) and improved size selection for the targeted penaeids in the stow net and lagoon seine. In contrast, owing to gear-specific operational characteristics such as a slower hauling speed, there were few detectable effects of altering mesh openings in the codend of the river seine. The results are discussed in terms of the differences in the gears used and their particular selection mechanisms. We conclude that, pending further trials, codends made from a mesh size approaching 29 mm, hung on the bar, would provide appropriate size- and species-selection for Wallis Lake stow nets and lagoon seines. Further research is required, however, to examine the utility of operational changes to river seines and/or alterations to mesh size and configuration in the wings and body to improve selectivity.

Two experiments were done in the oceanic penaeid prawn-trawl fishery in New South Wales to investigate (i) the optimal positioning of behavioural-type by-catch reduction devices (BRDs) involving square-mesh panels; and (ii) the relative performances of two industry-developed square-mesh panels against a composite square-mesh panel developed by scientists. In the first experiment, three codends, each containing one square-mesh panel (located on the tops of the codend at distances of 0.7, 1.2 and 1.6 m anterior to the last row of meshes respectively) significantly reduced the catches of some small fish and total discards compared with a control codend that held no BRD. Rates of reduction significantly increased with proximity of the square-mesh panel to the end of the codend. There was, however, a significant reduction in catches of prawns from the codend containing the square-mesh panel at 0.7 m. Based on these results, the optimal position for these sorts of BRDs was determined to be at 1.2 m anterior to the last row of meshes. In the second experiment, at this position, two codends containing industry-developed plastic and metal square-mesh panels were less effective in excluding by-catch than a codend containing the composite square-mesh panel. The results are discussed in terms of species-specific differences in behavioural responses and swimming ability and the future development and testing of behavioural-type BRDs in penaeid prawn trawls.

As attempts to manage New England's groundfishery by mesh size regulations become more refined, interest in use of square mesh sections in nets has increased. To determine if the effects of use of square mesh seen in Europe hold true in New England's mixed species fishery, two studies have been undertaken. A short study in Massachusetts was completed in the summer of 1986 while a larger study in Maine is is underway at the time of this writing. Study techniques and preliminary findings are given here. To date, the improved selectivity of square mesh seen in Europe has not been shown in in New England. However, improved catch rates and consistant observation of lower discard rates indicate that further study is warranted.

An apparatus, consisting of a plastic latticed tray, fitted with a lid, and lined with 50 μm aperture square mesh bolting nylon and 2 mm aperture square mesh polyester is described. The apparatus is used to study the colonization of sediments by meiofaunal groups. The finer mesh size restricts movement of the meiofauna, the larger permits migration into the isolated volume of sediment, that can be considered as an artificially-isolated habitat island. Manipulation of species assemblages is readily possible, allowing studies of species interactions, as well as studies of the spatial and temporal distribution of species. The full results are to be published elsewhere.