DOI: 10.14466/CefasDataHub.87

Description

Total count and biomass in grams of taxa identified from 2m beam trawl samples of the seabed, with associated station information. Samples were collected using a 2m scientific beam trawl at sampling stations located within three experimental boxes (treatment boxes only) during a fishing impact recovery survey within the Fladen Grounds. Data were collected at three time points (before impact (time 0), immediately after impact (time 1) and 8 months after impact (time 2) during two research surveys on the RV Cefas Endeavour in April 2015 and November 2015. Three 2m scientific beam trawls, spaced a minimum of 16m apart, were collected a North South orientation against the tide in Treatment boxes only. The 2m beam trawl is designed to sample epibenthic megafauna and is comprised of a heavy-duty steel beam, and a 4mm knotless mesh liner is used in the cod-end to retain smaller organisms. The chain mat, which is used to prevent the collection of large boulders, was removed to prevent the net from filling with the soft sediment. Tow distance was measured from the time that the beam trawl settled on the seabed to the time that hauling of the trawl began. The amount of wire paid out was 3x the water depth. Tow speed was maintained between 0.5 and 1.0 knots (speed over ground). A GIS navigation system was used throughout fishing operations to log the position of the tow every 10 seconds. On surfacing, the net was cleaned by gently towing it behind the vessel before landing the catch on-board.  The net was inspected to ensure there were no signs of gear damage before the cod-end was emptied directly into large fish boxes. The contents of the fish boxes were washed on a benthos sorting table (5mm mesh) before being sorted on a sheet-steel table. The catch was sorted into taxon/species and the individual weight for all taxa were recorded for all specimens. Hermit crabs were weighed without shells and highly numerous species were sub-sampled. This involved measuring the individual weights of one quarter of the species total weight and then the whole catch was then calculated by ‘raising’ the number and weight in the known sub-sample volume. Taxa were identified using standard reference texts and a photographic reference collection was produced to aid rapid identification.

Contributors

RV Cefas Endeavour Staff / Barry, Peter

Subject

Benthos / Biota Abundance / Biomass and Diversity

Start Date

21/04/2015

End Date

03/12/2015

Year Published

2019

Version

1

Citation

RV Cefas Endeavour Staff & Barry (2019). Fladen experimental fishing impact recovery data 2015 - 2m Beam Trawl. Cefas, UK. V1. doi: https://doi.org/10.14466/CefasDataHub.87

Rights List

Open Government Licence

DOI

10.14466/CefasDataHub.87