Discard sampling of Dutch bottom-trawl and seine fisheries in 2011

Helmond, A.T.M. van; Uhlmann, S.S.; Bol, R.A.; Nijman, R.R.; Coers, A.


In the European Union, the collection of discard data is enforced through the Data Collection Regulation or Framework (DCF) of the European Commission (EC). To comply with this ruling, approximately ten trips of discard-intensive beam-trawlers are being monitored annually since 1999 (Helmond and Overzee, 2010). In 2009, revisions to the DCF (2008/949/EG), required member states to increase sampling intensity to i) improve the precision of their estimates and ii) the number of sampled métiers. To meet this requirement within an affordable budget, the Institute for Marine Resources and Ecosystem Studies (IMARES, part of Wageningen University and Research) set up a collaborative project between the Dutch fishing industry and the research institute to recruit a ‘reference fleet’ of vessel owners willing to participate in a selfsampling programme. In the self-sampling programme, trips were pre-determined from a reference fleet of participating vessels. In total, 155 trips were sampled in 2011, of which 27 trips (17%) were considered invalid due to missing or incomplete information. During the 128 valid self-sampling trips 248 hauls were sampled. While the majority of observations were done on board beamtrawl vessels with mesh sizes ranging between 70 and 99 mm targeting flatfish, data was collected from eight other metiers as well. These included beam trawls with other mesh sizes or target species assemblages, otter trawls and seines. This led, apart from a considerable increase in sampling effort for some métiers, to an increase in the temporal and spatial spread of sampling compared to the previous observer-based sampling. Samples from previously unsampled northern and eastern parts of the North Sea were available now. The spatial distribution of sampling locations matched that of the total effort of the fleet for intensivelysampled métiers. Large-mesh beam- and otter trawls (100-119 mm) on average landed more than they discarded. In the other métiers, combined fish and benthos discards exceeded the volume of landings. The majority of discards comprised of benthic (invertebrate) species such as common starfish (Asteria rubens); sand star (Astropecten irregularis); swimming crab (Liocarcinus holsatus); and serpent star (Ophiura ophiura). Most frequently discarded fish species of no commercial value included: dragonet (Callionymus lyra); grey gurnard (Eutrigla gurnardus); scaldfish (Arnoglossus laterna); solenette (Buglossidium luteum); and lesser weaver (Echiichthys vipera). Among commercially-valuable fish, common dab (Limanda limanda) and European plaice (Pleuronectes platessa) were the most frequently discarded species.