Transcript Week3Rose
Fish capture – trawls and other active gears Craig S. Rose, Steve Patterson (NETS) April 13, 2015 Outline Review of active gears – capture based on gear movement, not fish attraction Capture mechanisms: result in Highly variable characteristics dependant on target species, bycatch and operating environment 2 Active Fishing Gears: Gear moves to the fish Beam Trawls Dredges Seines (Benthic) Otter Trawls 3 Benthic Seines – Herd fish across seafloor with cables, then capture in net http://www.crimond.com/bycatchcod.htm http://www.seafoodexport.com/ http://www.youtube.com/watch?v=ozMgLvKe0vE&feature=related 4 Scallop Dredges From "Bottom Tending Gear Used In New England" by Ronald Smolowitz (in Effects of Fishing Gear on the Seafloor of New England edited by Dorsey & Pederson) New Bedford dredge (USA) Collect bivalves from seafloor surface Toothed dredges (Europe) 5 Beam Trawls www.ilvo.vlaanderen.be/Pictures/BeamTrawlFisheries/ Net spread horizontally with a rigid beam: flatfish capture – chain mats to chase off-bottom 6 Otter trawls – nets spread by hydrodynamic spreading plates/wings (Doors) Model net in towing tank 7 Shrimp Trawls – Get shrimp up from the seafloor, then ‘filter’ them from the water – no directional response http://www.crimond.com http://www.smart-net- Systems.com/trawl_nets. Mesh size about 4 cm 8 Different otter trawl footropes used to catch flatfish Alaska U. S. east coast (45 cm diameter) 9 Pelagic trawls – Alaska pollock Very large front meshes - herding Mesh size 4 meters 10 Differences in mesh size Mesh size from 16 meters to 0.1 meters Forward – herd/concentrate Back end - enclose 11 12 13 14 15 16 Monitoring and control Sonar and echo sounders Trawl sonar – monitor shape of trawl mount and fish entrance Catch sensors – how full is the net’s codend 17 Summary Active gears – capture based on gear movement, not fish attraction Many also rely on fish reactions to concentrate herding Highly variable characteristics dependant on target species, bycatch and operating environment 18