2009 - 2009 Centre for Environment, Fisheries & Aquaculture Science (Cefas) Bristol Channel Bass Selectivity Survey 2009/10 - Fisheries Science Partnership
FSP Bristol Channel Bass Selectivity Survey
This work was part of the Fisheries Science Partnership (FSP), a Defra-funded collaborative programme of scientific research between the UK fishing industry and scientists. Local trawlermen working in the Bristol Channel and the South Wales Sea Fisheries Committee suggested that square-mesh panels fitted into trawls used to catch bass could reduce discards of undersize bass. A trawl was modified to incorporate a square-mesh section and was tested on board the MFV Cerulean against a control trawl. In August 2009, 46 hauls were conducted. Catches were sampled and video footage was taken of fish behaviour at the square-mesh section.
dataset
http://data.cefas.co.uk/#/View/638/
function: order
CEFASfa66b85d-c831-44ad-a259-f0ddf54026c5
http://www.cefas.co.uk/
eng
OGP
urn:ogc:def:crs:EPSG::4326
biota
revision
2011-03-25
publication
2008-06-01
-7
-2
53
51.25
revision
2010-05-18
2009-08-01T00:00:00.000Z
2009-08-31T00:00:00.000Z
publication
2017-02-14
notPlanned
Methods The gear The fishing gear normally used by the Cerulean in this fishery is a single-rig box trawl. Two single-rig box trawls are employed at different times; one of 13 fathoms the other of 14 fathoms. The trawls were of comparable design. The 14 fathom trawl had been modified previously to include a section of square-mesh netting near to the codend. This had been inserted by the skipper of the Cerulean to reduce the capture of undersized bass. For the FSP gear trials a new section of square-meshes of similar design to that used previously was fitted to the trawl. The panel was constructed from 90mm knotless square-mesh netting called Dyneema® with the guidance of Mike Montgomerie of Seafish. Both trawls had codends and extensions of 100 open meshes in the round. To account for the lack of flexibility of square netting and the narrowness of the extension, the panel was made with a width of 25 open bars with a baiting rate of 2 meshes to 1 bar for both ends of the panel. The panel was made to fit from selvedge to selvedge and 3 extra bars were used each side to allow for a 3 knot selvedge in each side. The length of the panel was agreed at 3 metres to keep it in line with other square-mesh panels used in UK, this would need a length of 68 bars (3.06m). An extra 1 bar was used each end to enable 2 bars to be laced together for extra strength at the end bar for joining on the diamond mesh. The panel was made so it could be inserted easily into either of the trawls. Two new 80mm mesh codends and lengtheners with conventional diamond meshes were used to ensure that any differences in trawl selectivity were not caused by differences in the codends. The square-mesh section was regularly changed between the two trawls to ensure any difference in selectivity was not due to the differences in the trawls. Consequently there were four trawl configurations: a 14 fathom trawl with and without the square-mesh section and a 13 fathom trawl with and without the square-mesh section. The trawl with the square-mesh section is hereafter called the experimental trawl, the trawl without, the control trawl. Sampling plan The trials took place in August, a period of good bass fishing in previous years, during 2 five-day trips. The trawl with the square-mesh section and the other without were deployed every day and the square-mesh section was swapped between the two trawls after each day. Normally only one haul was conducted at each location on the same day. This was usual commercial practice because it is believed that bass move away from an area when it is trawled. The method, therefore, assumed that the same assemblage of fish would be encountered by the control and experimental trawls during tows in similar locations during two five-day trips. The hauls were conducted in areas normally fished and were either on inshore trawling grounds off the North coast of Devon and Cornwall or on the ridges of sand banks further north in the Bristol Channel (Figure 5). The sand banks are fished specifically for bass and can yield high catches. The inshore fishing grounds are more generic trawling areas. A request for a derogation to conduct the work in Welsh waters was rejected so all hauls took place in English and EC waters. Cefas scientists measured the lengths of all fish species caught in each haul were where possible; samples of a known fraction were taken otherwise. Volumes of benthos were also recorded. Lengths were converted to weights using length-weight conversion parameters relevant to ICES Sub Area VII. Video camera During the second five-day trip an underwater video camera was used to film escape behaviour of bass and other species at the square-mesh section. A light sensitive EXPLORER 4K camera was mounted on a frame and attached to the top edge of the square-mesh panel pointing toward the codend.
Public data (Crown Copyright) - Open Government Licence Terms and Conditions apply
Public data (Crown Copyright) - Open Government Licence Terms and Conditions apply
Data Manager
Centre for Environment, Fisheries & Aquaculture Science
Cefas Lowestoft Laboratory
Pakefield Road
Lowestoft
NR33 0HT
UK
+44 (0)1502 562244
originator
Data Manager
Centre for Environment, Fisheries & Aquaculture Science
Cefas Lowestoft Laboratory
Pakefield Road
Lowestoft
NR33 0HT
UK
+44 (0)1502 562244
custodian
Data Manager
Centre for Environment, Fisheries & Aquaculture Science
Cefas Lowestoft Laboratory
Pakefield Road
Lowestoft
NR33 0HT
UK
+44 (0)1502 562244
pointOfContact
2017-02-14T10:27:07