14 



COMMERCIAL FISHERIES REVIEW 



Vol. 28, No. 11 



For more information, contact: Base Di- 

 rector, Exploratory Fishing Base, BCF, 5 

 Research Drive, Ann Arbor, Mich. 48103. 





North Atlantic Fisheries Explorations 

 and Gear Development 



DELAWARE COMPLETES CLAM SURVEY 



The exploratory fishing vessel M/V Dela - 

 ware completed a 29 -day surf clam survey 

 cruise on September 2. (Cruise 66-6, Aug. 

 5-Sept. 2.) Survey work was continued inArea 

 IV (see figure 1) off the coast of Maryland 

 and Delaware. Catches of surf clams varied 

 from none to 18.3 bushels per 4 -minute sur- 

 vey tow, and from none to 13.3 bushels per 

 20-minute (simulated commercial) tow. An 

 electrically-driven submersible pump was 

 tested and utilized along with the conventional 

 hydraulic jet dredge used for previous surf 

 clam survey cruises. 



518 survey tows were made in Area IV; 

 484 of these were standard tows and 34 were 

 simulated commercial tows. Also 174 other 

 tows were made to compare the efficiency of 

 the submersible pump dredge with the stand- 

 ard hydraulic jet dredge. A specially de- 

 signed 48 -inch (blade width) clam jet dredge 

 equipped with a 65 hp. electrically-driven 

 submersible pump was used during the en- 

 tire cruise (figure 2). 



The same procedure of previous surveys 

 was used. Stations were located at 1-mile 

 intervals along 1-mile spaced grid lines. 

 The 48-inch, hydraulic jet dredge, operating 

 with either the submersible pump or the deck- 

 mounted pump, was towed 4 minutes at each 

 survey site and for 20 minutes at simulated 

 commercial tow sites. 



Results: Of the 484 four-minute survey 

 tows completed, 74 (about 15 percent) pro- 

 duced catches that equaled or exceeded 1 

 bushelof surf clams. This is the highest ratio 

 of good tows that were experienced to date. 

 The largest catch for any standard 4 -minute 

 tow was 18.3 bushels. Many tows (252) pro- 

 duced catches of nearly 1 bushel; 157 tows 

 produced no surf clams. Simulated commer- 

 cial tows were made at 34 stations in one 

 section of Area IV; 12 of these produced 

 catches of 4 or more bushels. 



Fig . 2 - Surf clam dredge equipped with electrically-driven 65 

 horsepower pumping unit. 



Throughout the survey, consistent with 

 previous findings, the size and distribution 

 of surf clam catches varied with type of bot- 

 tom sediment and water depth. Best results 

 were obtained where the predominant bottom 

 sediments were coarse sand, gravel, or a 

 combination of both. The catch rate fell off 

 considerably in the nnost shallow inshore wa- 

 ters, less than 12 fathoms --apparently be- 

 cause of unfavorable bottom sediments - -and 

 in the deeper offshore waters, although for 

 the first time during survey work, occasional 

 good catches were made at depths of 23 fath- 

 oms to 25 fathoms. Generally, the best catches 

 were taken inshore where depths varied be- 

 tween 15 and 18 fathoms, and offshore where 

 the depths varied between 18 and 21 fathoms 

 (see figure 2). 



Size of Surf Clams: The 5- to 7-inch size 

 group, which is within the most valuable size 

 range for commercial utilization, was predom- 

 inant in surf clam catches. In some tows medi- 

 um-size clams of 3 to 5 inches were taken in 

 large numbers. The selectivity of the dredge 

 reduced the number below this range to almost 

 zero. The average size of clams taken in the 

 smaller catches was generally larger than that 

 from the larger catches. 



