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10In the Mediterranean Sea Nephrops (Nephrops norvegicus) is predominantly caught with 11 bottom trawls, but it is also harvested with creels. While the size selection of Nephrops in 12 bottom trawls is well documented, there is no previous information on creel size selection for 13 this species. Therefore, sea trials were carried out to assess the selective properties of 14 commercial creels with 41 mm mesh size netting mounted as a square mesh netting as 15 prescribed by the legislation. Creel size selection was assessed for Nephrops and two main 16 crustacean bycatch species: mantis shrimp (Squilla mantis) and blue-leg swimming crab 17 (Liocarcinus depurator). The influence of the soak time on creel selectivity was also 18 investigated, and no significant difference was detected between one and two day soak times. 19The average carapace length of a crustacean with 50% probability of being retained (L50) was 20 31.69 mm for Nephrops, which is 59% larger than the minimum landing size (MLS) set by 21 the fishery regulation, therefore demonstrating a mismatch between MLS and gear selectivity 22 in this fishery. Comparison of creel selectivity obtained in our study with the historical results 23 obtained from commercial bottom trawl selectivity studies for Nephrops in the Mediterranean 24 *Manuscript including abstract Click here to view linked References Sea demonstrated that the creel L50 was significantly higher than in the trawl fishery, this 25 implies that creel fishery is targeting larger Nephrops than trawl fishery. 26 27

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The Nordmøre grid is widely used in shrimp trawls to reduce the bycatch of fish species. However, small-sized fish species and juveniles still pass through the grid and enter the codend, along with the targeted shrimp. This bycatch of small fish has a negative impact on the ecosystem due to increased fish mortality, and leads to additional sorting work onboard. Some small-sized fish that enter the trawl avoid entering the codend by escaping through the outlet above the grid, without making contact with the grid itself. Design changes that promote this behavior could potentially reduce bycatch in shrimp trawl fisheries. Lightemitting diodes (LEDs) mounted around the escape outlet have previously been found to have either a negative effect, or no effect at all, on fish bycatch species. This study investigates the effect of mounting green LEDs on the lower part of a Nordmøre grid, to determine if their presence would encourage bycatch fish to rise towards the escape outlet prior to contacting the grid. Experimental fishing trials were conducted to assess the size selective properties of a 19 mm bar spaced Nordmøre grid with and without LEDs, mounted on a bottom trawl targeting Deep-water shrimp (Pandalus borealis). For the four bycatch species investigated, 51-100 % of small fish passed through the Nordmøre grid. The addition of green LEDs to the Nordmøre grid did not significantly affect the escape probability or the size selectivity of any *Manuscript including abstract Click here to view linked References 2 of the investigated species. Very few Deep-water shrimp were found to escape through the escape outlet independent of the presence of the LEDs mounted on the grid.

It is well established that increasing mesh number in the circumference of a diamond-mesh trawl codend can reduce size selection for round fish, whereas selection for flat fish species is unaffected. This effect has also been documented in Mediterranean trawl fisheries. In contrast, no information is available with regard to the effect of increasing mesh number in the circumference of square-mesh codends on the size selection of round fish and flat fish species. A field study was devised to bridge this gap and formulate proposals aimed at improving trawl fishery management. Size selection data were collected for a round fish species, red mullet (Mullus barbatus), and two flat fish species, Mediterranean scaldfish (Arnoglossus laterna) and solenette (Buglossidium luteum). Fishing trials were conducted in the Adriatic Sea (Central Mediterranean) using three square-mesh codends that differed only in mesh number around the circumference. Results demonstrated that increasing the number of meshes from 107 to 213 reduced the 50% retention length (L50) for red mullet by 2.5 cm but did not affect size selection for the two flat fish species. In some fisheries, regulatory provisions regarding the number of meshes in the circumference should therefore be carefully considered both for diamond- and square-mesh codends.

An experiment was conducted to assess the selectivity in a typical Mediterranean bottom trawl, equipped with a square-mesh panel inserted in front of the cod end, for Atlantic horse mackerel (Trachurus trachurus), European hake (Merluccius merluccius), red mullet (Mullus barbatus), poor cod (Trisopterus minutus), broadtail shortfin squid (Illex coindetii), and deep-water rose shrimp (Parapaeneus longirostris). The release efficiency of undersized individuals through the panel was low. The differences in selectivity between the gear with and without the panel were very small. The low release efficiency of the square-mesh panel was caused by the lack of fish contact with the panel as they drifted towards the cod end, since the average contact probability was estimated not to exceed 9% for any of the species investigated. A low probability of contact with the selection device was thus found to be the reason for the low efficiency of the square-mesh panel.

In hydraulic dredge clam fisheries, the onboard mechanical sorting can be considered as the main catch selection process. The catch is mechanically sorted by a sieve made up of a series of successive grids with holes of decreasing diameter. The effect of the grid hole diameter and sorting speed of the vibrating sieve of a hydraulic dredger was investigated in a field study to determine its clam selection properties and to formulate proposals aimed at improving fishery management. Data analysis demonstrates that it is technically impossible to achieve a knife-edge selection and that there is scope for improving the size selection process, for instance by increasing grid hole diameter, which, however, can be accompanied by a reduced catch of both undersized and commercial-sized individuals. An increase in the hole diameter to 21.71 mm, while ensuring less than 5% retention of undersized individuals, would entail a retention of 67% of the commercial sizes. The modelling approach applied can be extended to investigations of other dredge gear types and nonmobile benthic species.