Progressively evaluating a penaeid W trawl to improve eco-efficiency

Abstract

The W trawl is a proposed innovation for more eco-efficient penaeid trawling—via reduced energy intensity and benthic contact. A significant portion of the drag-generated, netting tension of the W trawl is directed away from the wings to centre-line bracing ropes that are connected to a central towing wire through an intermediary sled. This configuration facilitates substantially smaller otter boards than normal, and consequently less drag and seabed contact. Here we compared the engineering and catching implications of subtle, progressive rigging changes to a W trawl paired against a standard Florida flyer trawl; both rigged with another eco-efficient modification, termed the ‘batwing’ otter board (suitably sized for each trawl). The W-trawl refinements included: (i) securing netting at the wing ends to prevent sliding; (ii) moving the headline forward and footrope aft; and (iii) inserting dan lenos at the wing ends. The first two modifications resulted in a maximum drag reduction by the W trawl of up to 11% for a 1.14×increase in spread. Catches ha−1 of mostly retained (commercially important) large brachyurans and cephalopods were maintained, but penaeid catches were reduced in the W trawl (by at least 33%), which was mostly attributed to less than optimal ground-gear contact. This study provides a base for future research to concurrently reduce the energy intensity and habitat impacts of penaeid trawls, via holistic modifications.