674 



Glude, John B. , and Warren S. Landers. 1953. 



Biological effects on hard clams of hand raking and power dredging. U.S. 

 Dept. Interior, Fish Wildl. Serv., Spec. Sci . Rept. - Fish. 110, 43 p. 



Three test areas in Narragansett Bay, Rhode Island were established to study 

 the relative biological effects of power-dredging and hand raking on a 

 population of hard clams. A clamshell bucket was used to census clam 

 populations. One area was exclusively bull-raked, one was clammed with a 

 Nantucket dredge, and the control area was not harvested at all. During 

 the 2 years (1949-1950) breakage of commercial sized clams by bullraking 

 averaged 0.2%, breakage by dredging averaged 0.95%. During the same period 

 a population survey was conducted using a power dredge. This dredge re- 

 ported 1.0% breakage on smooth bottoms and 2.9% clam breakage on rocky 

 bottoms. Undersized clams (below 47-48 mm in length) were not broken in 

 significant numbers by either method of clamming. The dredge takes mainly 

 clams above 60 mm, but there was no significant breakage of clams below 60 

 mm in the dredged areas. Neither dredge nor bullrake appeared to cause 

 mortalities by smothering clams. There was no significant difference in 

 bottom composition (physical and biological) between dredged and raked 

 areas, but both had fewer living forms than the control area. Efficiency 

 ratios for bullrake and dredge were determined. Maximum efficiency for the 

 rake was for clams above 55 mm long, but some 36-55 mm clams were retained. 

 Maximum efficiency of the dredge was for clams above 70 mm with partial 

 efficiency for clams between 35 and 70 mm. It was concluded that there is 

 no biological basis for restricting bullraking or dredging. (Abstracter's 

 note: it must be assumed that biological overharvesting is avoided.) - D.L. 



675 



Godcharles, Mark F. 1971. 



A study of the effects of a commercial hydraulic clam dredge on benthic 

 communities in estuarine areas. Fla. Dept. Nat. Resources, Mar. Research 

 Lab., St. Petersburg, Tech. Ser. 64, 51 p. 



The gear was a Maryland soft clam escalator dredge. Virtually everything in 

 its path was collected. The dredge was much more efficient than hand tools, 

 inflicted fewer mortalities, and can bring into production clam beds with 

 marginal population densities. Water jets penetrated the substrate to 18 

 inches and uprooted seagrasses and benthic algae. Traces of tracks were 

 visible 1 to 86 days after dredging. In most cases the substrate hardened 

 within a month but some spots remained soft for over 500 days. Trenches in 

 grass bed stations remained visible longest, and were deepest in shallow 

 water where propeller wash scoured loose sediments. Differences in silt/clay 

 content at experimental and control sites immediately after dredging were 

 negligible after a year. Seagrasses and algae did not recolonize dredged 

 areas, and such areas should not be dredged. On other substrates little or 

 no damage was seen. Increased efficiency and reduced damage could be 

 realized by adding slats to the conveyor belt and installing a propeller 

 guard.- Unpublished data from the Long Island Sound hard clam fishery showed 

 that continued use of escalator harvesters increased catches of littleneck 

 and cherrystone clams and catches of chowder clams declined. No increased 

 set was seen in any test area in Fla. - J.L.M. 



676 



Godcharles, Mark F., and Walter C. Jaap. 1973. 



Exploratory clam survey of Florida nearshore and estuarine waters with 

 commercial hydraulic dredging gear. Fla. Dept. Nat. Resources, Mar. 

 Research Lab., Profess. Pap. Ser. 21, iii+77 p. 



Fla. clam production has been dominated by three species, Mercenaria 

 mevoenavia, M. campechiensis, and Maoroaallista nimbosa. Some Rangia cuneata 

 are taken. Quahog landings have been reported for almost 100 yrs. Sampling 

 was done from Fort Pierce on the east coast (27°30' N) south to part way 

 down the Keys, and north and west to the vicinity of Panama City (30°10' N) . 

 Greatest depth sampled was 14 m. The southern quahog was found from 

 Alligator Har. to Shark Pt. (Everglades), most abundantly in Lower Tampa 



189 



