Mitigation of seabird mortality on factory trawlers: trials of three devices to reduce warp cable strikes

Abstract

Experimental trials were conducted onboard a stern trawler to identify the relative efficacy of three emerging mitigation measures (tori lines, warp scarer and Brady baffler) designed to reduce seabird mortality caused by warp cable strikes. The use of mitigation measures was clearly shown to substantially reduce seabird mortalities from collisions between seabirds and warp cables. Based on an established significant relationship between contact rate and seabird mortality, when using contact rate as an index of mortality there was a clear performance hierarchy of the three measures. Tori lines and the warp scarer were significantly more effective at reducing contacts than the Brady Baffler, whilst tori lines represent a smaller, but still significant, improvement on the warp scarer. While further testing would be required under local environmental and operational conditions, our findings are likely to have application for many trawl fisheries around the world.

Appendices

Appendix 1

Contact codes describing interactions between seabirds and trawlers (AFMA protocol; Wienecke and Robertson 2002) .

Field	Code	Definition
Age	A	Adult
	SA	Sub-adult
	Ja	Juvenile
Contact code (birds)	1	Bird on water, very light contact with vessel/gear
	2	Bird on water, heavy contact with vessel/gear, causing at least part of the bird to be dragged underwater
	3	Bird flying, light contact with vessel/gear, bird does not deviate from course
	4	Bird flying, heavy contact with vessel/gear, bird deviates from course and/or dragged underwater
	5	Bird snagged on loose wire ends (eg. splice ends)
	6	Bird has high speed collision with vessel gear
	7	Bird caught in net
	8	Bird snagged on net while attempting to feed
	9a	Bird hauled on trawl door
Contact point	1	Warp wire
	2	Trawl doors
	3	Backstops, brides and sweeper
	4	Net
	5	Vessel
	6	Paravanes (includes towing wires)
	7a	Ropes on bird scaring device
	8	Other
Fate of bird	1	No apparent damage
	2	Possible minor injury
	3	Possible major injury
	4	Death
	5	Unknown
	6a	Bird seen wrapped around warp wire (suspected death)

1. ^acategories added by SAST

Appendix 2

Environmental variables recorded during observation periods .

Variable	Code	Level
Relative wind direction	1	Ahead
	2	45°
	3	90°
	4	135°
	5	Stern
BBA abundance	1	1–10
	2	11–50
	3	51–200
	4	201–500
	5	501+
	6	Present
Sea state (Beaufort scale)	1	≤2
	2	3
	3	4
	4	≥5
Sea height (m)	1	0
	2	>0,<0.5
	3	≥0.5
Swell (m)	1	0
	2	0.5
	3	>0.5,<1
	4	1
	5	>1

1. BBA Black-browed albatross