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In management of fisheries, knowledge about the species is crucial due to differences in life history traits. The first step is therefore species identification. For many species this task is straightforward, however for some species e.g. the two species of Atlantic redfish Sebastes mentella and Sebastes norvegicus , it can be difficult for an untrained eye. With the goal to separate the two species, we analysed otolith shape variation of S. mentella and S. norvegicus caught on the continental slope of East Greenland using the R package “Shape R”. Results were evaluated against genetic analysis of the same fish, and compared to results of both a visual identification of the two species and a separation based on a linear discriminant analysis on standardised values of fish length, fish weight and otolith weight. It was concluded that the objective otolith shape analysis using the Shape R package analysis achieve a reasonable classification success, however with a clear bias towards S. mentella . Classification using the otolith weight achieved a slightly higher success than the shape analysis making it a promising method. Furthermore, the method is at the same time both objective, less time consuming than the otolith shape analysis and less expensive than genetic analysis. However, the visual classification method of the whole fish had the highest success rate of the three tested methods, which despite the need for trained technicians makes it the most successful method. [ABSTRACT FROM AUTHOR]

Most demersal trawl fisheries are conducted in a multispecies setting, and the catch consists of several different species. An inherent challenge in such fisheries is to provide both biologically and economically sustainable exploitation of individually fluctuating stocks and vessel- or fleet-specific quotas. The topless trawl design was developed to improve species-specific selectivity in such fisheries. In a topless trawl, the foot rope is located more forward than the headline to allow fish to escape upwards, whereas the headline is located in front in traditional trawl designs. In this study we conducted twin trawls with a topless trawl towed parallel to a similar standard trawl; we tested a topless trawl design on a small trawl with a low headline height and on a larger trawl with a high headline height. We conducted the tows in the Nephrops ( Nephrops norvegicus ) directed mixed fisheries. For both the small and large trawls, we found a significant topless effect for haddock ( Melanogramus aeglefinus ) and no effect for Nephrops . For Atlantic cod ( Gadus morhua ) we found a significant topless effect for the low headline trawl but no effect for the high headline trawl. In both the eastern and western Atlantic, topless trawls have been introduced as legal cod-selective trawl designs. However, this study demonstrates that identical gear modifications made to similar trawls of different sizes and used in the same fishery can lead to different results. [ABSTRACT FROM AUTHOR]

Abstract: The critical condition of the North Sea cod stocks has resulted in restrictions on not only cod, but also haddock and other species that are caught together with cod. Thus full exploitation of the haddock stock is unachievable unless cod can be excluded from the haddock catch. We designed a selective trawl based on the behavioral differences between haddock and cod as they enter a trawl, i.e., cod stay close to the seabed whereas haddock rise above it. The trawl''s fishing line is raised ∼60cm above the seabed to allow cod to escape beneath the trawl while haddock are retained. To collect the escapees, three sampling bags were attached beneath the raised fishing line. The selective haddock trawl reduced the total catch of cod by 55% during the day and 82% at night, and 99% of the marketable haddock was caught during the day and 89% at night. Cod escape rates were highly length dependent: smaller cod escaped the trawl in greater numbers than did larger individuals. Whiting, saithe, lemon sole, and plaice were included in the analysis. [Copyright &y& Elsevier]

Abstract: A rigid separator frame with three vertically stacked codends was used to study fish behaviour in the extension piece of a demersal trawl. A video camera recorded fish as they encountered the separator frame. Ten hauls were conducted in a mixed species fishery in the northern North Sea. Fish behaviour was analysed using the camera observations from several of these hauls by assigning seven descriptive attributes and also using catch data. Gadoids, in particular haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and saithe (Pollachius virens), were caught in the upper codend, whereas Nephrops (Nephrops norvegicus) were caught in the lower codends. Catches of flatfish were more uniformly distributed among the three codends. Unlike the flatfish, gadoids reacted to the presence of the separator frame. The camera method and the separator frame yielded different information about fish behaviour within the trawl, and together the two methods provided a more complete picture of the catching process. Behavioural observations, vertical distribution, and the methodology are discussed, as is the potential for improving species separation in demersal trawls. [Copyright &y& Elsevier]

Abstract: Two biologically distinct species, Penaeus semisulcatus and P. esculentus, are caught in the tiger prawn component of Australia''s Northern Prawn Fishery. These species are recorded and marketed together as ‘tiger prawns’. A generalised linear model is used to separate the logbook catches of ‘tiger prawns’ into catches by individual species, even though only fragmentary historical survey data are available. We also consider generalised additive model and generalised linear mixed model approaches, and the extra benefits they might allow. [Copyright &y& Elsevier]

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