The use of shifting rather than more stable beds as a borrow site has several ecological 

 advantages, as well the practical advantage of supplying clean sand since these beds are 

 usually composed of coarse, pure sand in contrast to fine sands with admixtures of mud, 

 silt, detritus and similar components of the more stable beds. Plants and animals are sparse 

 on shifting beds, and are either transitory or highly mobile. These communities are less 

 organized and usually are of less commercial and ecologic importance than those of the 

 more stable bottom. Also, physical effects of dredging could be erased through filling, as 

 indicated by the quick filling of borrow areas between reefs on some relatively shifting 

 sand areas off Florida. (Walter R. Courtney, personal communication.) 



Selection of such sites could be determined by grab samples and coring. Underwater 

 towed observation vehicles such as the Remote Underwater Fishery Assessment System 

 (RUFAS), developed by the National Marine Fisheries Service (NMFS), for faunal 

 assessments could be used for rapid scanning before designing a complex survey system to 

 identify bottom sediments and benthic animals. 



Dredging shifting sands could be much more extensive without ecological harm than 

 could operations on more productive, stable beds. This leads to the conclusion that even 

 extensive dredge operations on beds of shifting or unstable sands would have little direct 

 long-range ecological effect on the immediate area. The role these shifting sand areas play 

 in natural beach nourishment or in nourishment of other areas is usually unknown, but 

 should be determined before dredging. 



Dredging on stable beds is apt to be more serious because of the richer, and more 

 diverse nature of resources and the lesser mobility of most of the components of the biota. 



It is on these more stable bottoms that shellfish and commercially important finfish 

 occur in large numbers, because the more permanent and higher organized food-web 

 structure attracts more fish. Although studies have been made of recovery of channel 

 dredge areas and harbors (Reish, 1954), little helpful information is available about the 

 recovery of stable offshore dredge areas, either physically or biologically. Minor 

 excavations can hardly be viewed as serious; indeed they may be beneficial. Follow-up 

 studies on minor excavation sites would provide needed information for evaluation of the 

 effects of more extensive excavation. Expecially needed are data on (a) rates of filling of 

 borrow areas under a wide range of conditions and bottom types, and (b) rates of 

 repopulation of borrow areas by biota. In view of the needed research, extensive dredging 

 in stable sand areas should be preceded by studies on effects of minor dredging and 

 collection of more complete ecological data before and after dredging. 



The type of dredge used is another factor to be considered. Hopper dredges are suited 

 to offshore conditions, and appear to inflict the least ecological harm. To shallowly dredge 

 sand deposits over extensive areas, and allow a layer of sand to remain might cause less 

 harm than to dredge deep pits covering a limited area. Deep borrow areas hamper trawling 

 and harm level-bottom communities. The disturbance would be spread over a greater area 

 because a greater surface area would be involved in obtaining the same amount of material. 

 Safeguarding against opening a different interface through removal of all of the sand and 



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