Crustaceans (Malacostraca and Thecostraca) from the International Minho River, Iberian Peninsula

Crustaceans (Arthropoda) are a diverse and abundant group with chitinous exoskeleton, living on coastal/estuarine environments, at community invertebrate fauna. A survey on the species of some crustacean groups found on the Minho River estuary (international section) in the Iberian Peninsula, is presented with specimens collected through glass eel fishing bycatch, grab sampler, trammel net, beam trawl and fyke net sampling methods. A total of 98 specimens were examined belonging to 7 orders, 21 genera and 23 species (17 new records from Minho River, including one for Portugal). Brief diagnosis, ecological notes, species distributions and figures are provided intending to present taxonomic support on future projects in this region.

Morphological abnormality in thornback ray Raja clavata in the Irish Sea

A free-swimming thornback ray Raja clavata specimen demonstrating significant morphological abnormality is reported, captured by beam trawl in the Irish Sea off north Wales, UK. The anterior sections of both pectoral fins were separated from the head section for a length of approximately 140 mm extending from the rostrum tip to a point posterior of the spiracles, along with abnormal morphology of the gill slits. This phenomenon has been observed elsewhere but is the first documented example of this abnormality in the eastern Irish Sea, despite widespread targeting of the species across the region by commercial and recreational fishers. Possible causes and consequences of the observed abnormality are discussed.

Sediment mobilization by bottom trawls: a model approach applied to the Dutch North Sea beam trawl fishery

Bottom trawls impact the seafloor and benthic ecosystem. One of the direct physical impacts is the mobilization of sediment in the wake of trawl gear components that are in contact with or are close to the seabed. The quantity of sediment mobilized is related to the hydrodynamic drag of the gear components and the type of sediment over which they are trawled. Here we present a methodology to estimate the sediment mobilization from hydrodynamic drag. The hydrodynamic drag of individual gear components is estimated using empirical measurements of similarly shaped objects, including cylinders, cubes, and nets. The method is applied to beam trawls used in the Dutch North Sea flatfish fishery and validated using measurements of beam trawl drag from the literature. Netting contributes most to the hydrodynamic drag of pulse trawls, while the tickler chains and chain mat comprise most of the hydrodynamic drag of conventional beam trawls. Taking account of the silt content of the areas trawled and the number of different beam trawl types used by the fleet, sediment mobilization is estimated as 9.2 and 5.3 kg m−2 for conventional 12 m beam and pulse trawls, respectively, and 4.2 and 4.3 kg m−2 for conventional 4.5 m beam and pulse trawls.

Comparison of beam trawl catch, by-catch and discard in fishing and non-fishing areas – a case study from the northern Adriatic Sea

Beam trawl fishery is highly important in the Croatian part of the northern Adriatic wherein 116 vessels have a licence for this type of fishing gear. A sharp decrease in the beam trawl catch observed since 2015 has raised concern about not only socio-economic issues but also ecological issues and the effect that beam trawl fisheries have had on exploited stocks. Besides the effect that beam trawl fisheries can have on targeted economically important species, intensive dredging can cause long-term changes in the benthic community. Therefore, this study aimed to detect the effect that this type of fishing gear has on target and by-catch species. Furthermore, survey data were compared with the official beam trawl fishery data gathered through Vessel Monitoring System data together with fishermen’s logbooks. Our research targeted two adjacent areas: an area where beam trawl fishing is allowed and an area where it is forbidden. The results demonstrate that the commercially important catch represented a minor share of the total beam trawl catch in both survey areas, while discard made up more than 93% of the total catch. The main beam trawl commercially important species in the Croatian part of the northern Adriatic Sea was Pecten jacobaeus, followed by Solea solea and Ostrea edulis. Our results suggest that beam trawl fisheries mostly affect target bivalve species and some non-commercial benthic species (e.g. sponges). The differences recorded between areas could suggest that beam trawl fisheries cause changes mostly in the P. jacobaeus population.

Mitigating seafloor disturbance of bottom trawl fisheries for North Sea sole Solea solea by replacing mechanical with electrical stimulation

Ecosystem effects of bottom trawl fisheries are of major concern. Although it is prohibited to catch fish using electricity in European Union waters, a number of beam trawlers obtained a derogation and switched to pulse trawling to explore the potential to reduce impacts. Here we analyse whether using electrical rather than mechanical stimulation results in an overall reduction in physical disturbance of the seafloor in the beam-trawl fishery for sole Solea solea. We extend and apply a recently developed assessment framework to the Dutch beam-trawl fleet and show that the switch to pulse trawling substantially reduced benthic impacts when exploiting the total allowable catch of sole in the North Sea. Using Vessel Monitoring by Satellite and logbook data from 2009 to 2017, we estimate that the trawling footprint decreased by 23%, the precautionary impact indicator of the benthic community decreased by 39%, the impact on median longevity of the benthic community decreased by 20%, the impact on benthic biomass decreased by 61%, and the amount of sediment mobilised decreased by 39%. The decrease in impact is due to the replacement of tickler chains by electrode arrays, a lower towing speed and higher catch efficiency for sole. The effort and benthic physical disturbance of the beam-trawl fishery targeting plaice Pleuronectes platessa in the central North Sea increased with the recovery of the plaice stock. Our study illustrates the utility of a standardized methodological framework to assess the differences in time trends and physical disturbance between gears.