aData from Pilskaln et al. (1998) and NMFS data from 1991–1993.
bData from Churchill (1989) and NMFS data from 1991–1993.
cAssumes 5 tows/fishing day, door spread of 150 ft., and 9 nm/tow.
dAssumes observed tows equal 0.75 actual tows, door spread of 600 ft., and 9 nm/tow; total tow distributed proportionally to observed tows.
eAssumes observed tows equal 0.75 actual tows, door spread of 550 ft., and 9 nm/tow; total tow distributed proportionally to observed tows.
fAssumes observed tows equal 0.40 actual tows, door spread of 400 ft., and 9 nm/tow; total tow distributed proportionally to observed tows.
gAssumes door spread of 300 ft. and 9 nm/tow.
hAssumes door spread of 150 ft. and 9 nm/tow.
NOTE: Relative intensity of trawling between regions based on assumptions regarding area swept, estimated total fishing area, and total number of trawl tows (used with permission from Natural Resource Consultants). NA indicates that data were not available.
of large scallops (Box 6.2). However, the only fishing effort data available for that region were collected before the areas were closed. In 1993, estimates of the percentage of statistical areas swept in New England waters indicated that the effort in some areas could have swept the grounds more than four times a year, and the effort in many statistical cells resulted in swept area estimates exceeding 100 percent of the block area.
Bottom trawling off the southeastern United States and in the Gulf of Mexico is for the most part concentrated in waters <20 m deep and close to shore. Trawling in the Pacific, North Pacific, and New England regions is directed primarily at groundfish and pandalid shrimps; bottom trawling in the Gulf of Mexico and off the southeastern states is directed primarily at various warmwater shrimp species, with some seasonal effort directed at crabs or scallops. The fishing gear used to harvest shrimp is lighter than that used for most groundfish.
Data from the Gulf of Mexico show the average number of 24-hour fishing days in the region exceeded 200,000 annually from 1991 to 1999, averaging more than 4 million fishing hours per year. The data strongly suggest that the number of bottom trawl hauls per year (assuming five tows per 24-hour fishing day) in many of the statistical areas exceeded the bottom trawl effort off Alaskan coast, the contiguous Pacific states, or the New England region. The relatively large total area fished given in Table 4.1 for the Gulf of Mexico is partially an artifact of the division of the Gulf into 21 large fishing areas, some of which have very little effort. If the data were resolved into smaller statistical blocks, the total area fished would be much smaller and the percentage of the area swept per year would be