Evaluating Distribution Of Trawl Marks Relative To Fishing Effort On The Northern California Shelf And Slope
Current Status of Accomplishment or Milestone: A manuscript, "Sidescan-sonar Mapping Of Benthic Trawl Marks On The Shelf And Slope Off Eureka, California," (1.6 MB) (authors Friedlander, A.M., G. W. Boehlert, M. E. Field, J. E. Mason, J. V. Gardner, and P. Dartnell) was published in Fishery Bulletin (Vol. 97, pp 786-801).
Background: Understanding essential fish habitat requires that we understand the impacts of fishing. This objective requires a combination of different techniques, ranging from direct study on small scales to more indirect, but rapid, means of assessing habitat and habitat impacts.
Purpose of Activity/Goal of Project: The purpose was to assess the potential of side-scan sonar to evaluate the frequency of trawl tracks on soft bottom environments. The abundance and orientation of trawl marks was quantified over an extensive portion (> 2700 km2) of the Eureka, California outer shelf and slope. This is an important commercial bottom trawling ground for such high value species as rockfish, sole, and sablefish.
Description of Accomplishment and Significant Results: Fishing logbook data were compared with high-resolution sidescan-sonar images. The latter revealed deep gouges on the seafloor, caused by heavy steel trawl doors that act to weigh down and spread open the bottom trawls. These trawl marks are commonly oriented parallel to bathymetric contours and many could be traced for several kilometers. The number of trawl marks observed on the sidescan images was positively correlated to the number of annual trawl hours logged within reporting areas, suggesting that acoustic remote sensing is a promising independent approach to evaluate fishing effort on a scale consistent with commercial fishing activities.
Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic plan Goals): Bottom trawling gear is known to modify seafloor habitats by altering benthic habitat complexity and by removing or damaging infauna and sessile organisms. Identifying the extent of trawling in these areas may help determine the effects of this type of fishing gear on the benthos and develop indices of habitat disturbance caused by fishing activities.
Problems: None
Key Contact: George Boehlert (831-648-8515, gboehlert@pfeg.noaa.gov)