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Research Technical Report

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http://fishbull.noaa.gov/1131/lindholm.pdf

Ecological Effects of Bottom Trawling on the Structural Attributes of Fish Habitat in Unconsolidated Sediments Along the Central California Outer Continental Shelf

Lindholm, J., M. Gleason, D. Kline, L. Clary, S. Rienecke, A. Cramer, and M. Los Huertos (2015)

Fishery Bulletin 113(1):82-96.

ABSTRACT

Bottom trawling has been shown to affect the seafloor and associated biological communities around the world. Considerably less is known about the dynamics of impacts to structural attributes of fish habitat, particularly in unconsolidated sandy sediments of the continental shelf. We collaborated with commercial fishermen to conduct experimental trawls, with the type of small-footrope trawl required for trawling on the continental shelf, along the 170-m isobath in an area off Morro Bay in central California. The bottom trawling intensity we applied was based on the historical range of fishing effort in the study area and included low-intensity and high-intensity treatments. A remotely operated vehicle was used to collect continuous video and still photographs in trawled and in untrawled control plots, before trawling and at 2 weeks, 6 months, and 1 year after trawling. Scour marks from the heavy doors of the trawl were observed in the seafloor and persisted for at least a year. Although data extracted from the collected imagery showed some smoothing of the seafloor in trawled plots, the minimal differences between trawled and control plots in microtopographic structure on the seafloor were statistically significant only during one sampling period. Further, there were no significant differences between trawled and untrawled plots with respect to structure-forming invertebrates (e.g., sea whips) and mobile invertebrates (e.g., sea stars). The results of our study, part of ongoing efforts to understand and manage fishing impacts, indicate that bottom trawling with a small-footrope gear may have limited effects in some sand habitats.

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