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Summary for Field Activity Number 1987-021-FA

Alternate Leg ID: NURP 7; DELTA Dives 622-630, 632-634

Area of Operations: New England Shelf, Middle Grounds, Block Canyon to Atlantis Canyon, United States, North America, North Atlantic

Dates: May 28, 1987 to June 03, 1987

Objectives: The purpose of the cruise is two fold: first to study the importance of the prized tilefish burrow as a lobster habitat, and second to evaluate the extent and style of sediment reworking by organisms on the outer shelf.

Type of Activity: Photography
Sampling

Information to be derived: Samples and Chemical Analysis
Morphology

Summary: This study was conducted over the open shelf in the Middle Grounds, the general area between Block and Atlantic Canyons. The specific site was chosen based on our extensive sidescan sonar surveys during 1984. We completed 14 dives, including one at night. Of these, Lance Stewart conducted one to test NURP-designed gear and another in an attempt to help URI scientists locate a missing scientific package. Most dives were centered around 725 ft. (690-840 ft.) in an area with numerous large tilefish burrows (approximately 10 ft. diameter) and abundant lobsters. Two dives immediately inshore in more shallow water (345-385 ft.) found tilefish burrows but no lobsters. We observed 85 lobsters during these dives. Most of these were moving over the open bottom as if they were taking part in the inshore migration. Many others were found in tilefish burrows and frequently lobsters and tilefish were observed simultaneously in the same vertical burrow. These lobsters usually were in larger alcoves in the upper one meter of the tilefish burrows. The shape of these smaller burrows suggested that they were dug by lobsters. Some lobsters were observed in abandoned tilefish burrows, particularly those in which the subsurface clay was still exposed. Other lobsters were observed in shallow bowl-shaped depressions as observed by other researchers. The bowl-shaped depressions were apparently of their own construction. The single night dive verified earlier observations in previous years in which we observed a marked shift in the fish fauna relative to dives during the day. This data along with extensive 35 mm and video film are still being analyzed.

USGS Project Number: LOBSTER HAB

Contact: Dave Twichell (dtwichell@usgs.gov)

InfoBank: uses the identifier P-1-87-MC. Visit this site for more information.

InfoBank: uses the identifier P-21-87-MA. Visit this site for more information.

Map for Area of Operations :

Map of field activity boundary.

Platform Info:
photo of POWELL, JW
POWELL, JW
DELTA

The following materials for this field activity are available in the Information Archives:

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