composition of the large clams presently 

 being fished, and (2) to determine if small 

 clams exist in the area. 



The survey was conducted by Clam 

 Investigations and North Atlantic Fisheries 

 Exploration and Gear Research of the 

 Bureau of Commercial Fisheries. We wish 

 to acknowledge the assistance of Captain 

 Stanley T. Spink, Narragansett Marine Lab- 

 oratory, University of Rhode Island, and 

 Mr. Thayer C. Shafer, Massachusetts De- 

 partment of Natural Resources, Division of 

 Marine Fisheries. In the operation of the 

 Bureau of Commercial Fisheries vessel 

 PHALAROPE II we had the assistance of these 

 agencies and men. 



METHODS OF SAMPLING 



Gear 



The size of the area and relatively 

 low abundance of hard clams precluded the 

 use of standard sampling devices. The jet 

 dredge was selected as the principal sampl- 

 ing gear because of its success in obtaining 

 hard clams commercially. This gear would 

 also obtain samples which could easily be 

 converted into bushels per tow, an abund- 

 ance or density figure familiar to the in- 

 dustry. The M/V Sunapee, a comnnercial jet 

 dredge boat, with an experienced captain 

 and crew, was chartered from June 2 to 

 August 31, 1958. Captain Arnold Veek, her 

 owner, has had extensive experience op- 

 erating a jet dredge and was familiar with 

 clam fishing in Nantucket Sound. 



The jet dredge' used in this survey was 

 developed in the 1940's to fish areas of 

 hard bottom where the Nantucket and Fall 

 River dredges would not operate effectively. 

 It has since been used extensively on hard 

 clanns and on surf cla.ins (Spisula solidissima) 

 along the Atlantic coast. 



Unlike the Nantucket and Fall River 

 dredges, the jet dredge uses water jets to 

 loosen the bottom sediments ahead of the 

 digging blade (fig. 1). Water is supplied to 

 the jets through a 5 -inch hose attached to 

 a powerful salt-water punnp on the deck of 

 the dredge boat. At 80 to 90 pounds pres- 

 sure per square inch this pump will deliver 

 about 125 gallons of water per minute. 



*A more detailed description of the jet dredge is to be pre- 

 sented in a subsequent issue of Commercial Fisheries Review. 



Figure 1. Bottom view of the forward cage 

 of a jet dredge 



The 40 -inch wide digging blade at the 

 mouth of the dredge has an attached in- 

 clined rack of iron rods that extend to the 

 rear of the first cage. This blade can be 

 adjusted up or down to vary the digging 

 depth. The inclined rack serves to pass 

 shellfish into the dredge. Two steel frames 

 or cages form the bulk of the dredge and 

 support the jet manifold, cutting blade 

 and mesh bag. These cages slide along 

 the bottom on broad flat runners 

 (fig. 2). 



In fishing, the 1,000-pound dredge is 

 lowered by the main winch and a 5/8-inch 

 wire cable attached to a ring on the forward 

 cage towing bar. For safety in case of 

 catching on bottom obstructions, the actual 

 towing is done with a 1 -inch nnanila line. 

 The dredge is towed at slow speeds against 

 the tide to keep it on the bottom and digging 

 nearly all the time. After towing, the dredge 

 is raised to the surface and a line is at- 

 tached to a chain bridle on the rear cage. 

 This line is used to raise the rear end 

 of the dredge above the deck so it can be 

 dumped (fig. 3). 



