DRAGONET II, AN OPENING-CLOSING QUANTITATIVE TRAWL FOR THE STUDY OF MICROVERTICAL DISTRIBUTION OF ZOOPLANKTON AND THE MEIO-EPIBENTHOS

Abstract

Scientists, in their efforts to reduce the difficulties of studying the marine benthos, have produced an abundance of bottom sampling instruments. These have been reviewed recently by HoLME (1964) and HoPKINS (1964). In recent years most emphasis has been placed on corers and grabs which, if used properly, give the most precise samples of bottom sediments and their biocontents. Trawls have slipped somewhat into disrepute, but nevertheless many naturalists still use them surrepti-tiously. In order to determine the microdistribution of zooplankton near the bottom, and of epibenthic animals just above the sea floor, we here add a super-gadgeted trawl to the over-long list of bottom sampling devices. Where depth, visibility and other factors permit, diving and manual manipulation of collecting apparatus as described by FAGER, FLECHSING, FoRD, CLUTTER and GHELARDI (1966) can eliminate many of the errors that attend the use of remotely controlled apparatus including trawls, and we have used that approach with this apparatus whenever feasible. However, the Dragonet is primarily designed for remote operation. Some may recognize Drago net II as a modification of the EBD's and EBTOC's (epibenthic dredge, epibenthic trawl, opening closing) built by BRADSHAW and BIERI some years ago (GuNTER, 1957). Although there are several new features in this trawl, its two unique characteristics are a changing bridle attachment and an in situ sorter. While lowering, the bridle is attached above the center of gravity. This assures that the trawl will land right side up and thus permits the design of an asymmetrical trawl. When the trawl reaches bottom, the s~spension point shifts forward and lower, for towing over the bottom. The lower and forward towing position reduces drag during