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Midwater Assessment & Conservation Engineering Program

Crabs and Trawl Footropes: How They Interact and How Effects Can Be Reduced

trawl footropes
Figure 1.  Two trawl footropes (disk, above - roller, below) used in studying how they affect crabs that they encounter.  Photos by Carwyn Hammond.
 
 

RACE scientists completed two field projects investigating the interactions between crabs and bottom trawl footropes. Our goal was to assess the rates of bycatch and crab mortality associated with different conventional footropes and to begin developing new footrope designs to reduce those rates.

The effectiveness of different footropes at catching their target species and crab bycatch were compared aboard the fishing vessel Cape Horn from 18 June to 4 July. The Cape Horn's twin trawl system and processing capabilities allowed comparison of catches from simultaneous side-by-side tows of full scale trawls and commercial-scale catch rates. We compared disk and bobbin footropes (Fig. 1), as well as disk gears with substantially wider spacing. The wider spacing was a modification suggested by fishermen for reducing bycatch and damage.

The effects of these footropes on crabs that were not captured were investigated during work aboard the fishing vessel Pacific Explorer 10-24 August. Crabs were captured after they had passed under the footropes and examined for damage and reflex impairments. Previous work had shown that delayed mortality could be predicted from these reflex assessments. As suggested by a group of cooperating fishermen, additional tests assessed the effect of the capture process on the resulting mortality estimates, particularly the role of exposure to suspended sediments behind the footropes.

Results from both studies are being analyzed and will initially be presented to our collaborators from the fishery in November 2011.

By Craig S. Rose
 

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