228 BULLETIN OF THE BUREAU OF FISHERIES 



RATE OF GROWTH 



The rate of growth of various organisms is of importance in any study of the fac- 

 tors that determine fouling, because of the fact that organisms become much more 

 resistant to changes in their environment as they grow older (within limits) and 

 as such are not killed off by the moving of a vessel from one port to another as easily 

 as when the growths were yoimg and succulent, and also because of the fact that 

 increase in size increases the resistance of the ship. 



It is surprising, perhaps, to learn that barnacles grow to sexual maturity in less 

 than 90 days and often attain large size in less than that time, as can be seen by refer- 

 ring to Figure 31 F, which shows the size of some barnacles collected from the 

 Nevada after she had spent 60 days in the harbor at Rio de Janiero. Figures 31 ^ 

 to E, represent the rate of growth of barnacles at Beaufort, N. C; and in Figure 32 

 is shown the amount of fouling that accumulated on a piece of wood at this harbor 

 in 60 days. Very little accurate information is recorded regarding the rate of growth 

 of these forms, although B. H. Grave (1924) has made a recent study of some of the 

 forms that cause fouling, but these results have not been published as yet. 



FRESH WATER 



HISTORICAL DATA 



It is a firmly established belief among mariners that if a "fouled vessel is placed 

 in fresh water the growths on its bottom will be removed and the boat again become 

 clean." When the cruises for vessels were less exactly timed than at present, ex- 

 perienced sea captains often put into a fresh-water harbor for this single purpose; 

 and even to-day ships passing through the Panama Canal are known frequently to 

 spend an extra day or more ia the fresh-water lakes, and it is commonly understood 

 that sea captains are anxious to have their vessels in fresh-water ports whenever 

 possible. According to Capt. Henry V/iUiams (1923), however, unfortunately there 

 is no definite information on this subject. 



It is known that certain marine organisms can and do survive in fresh water; as, 

 for example, the eel, the salmon, or the shad, all of which spend a part of their lives in 

 fresh water and the remainder in salt water. Similarly, such algae as Enteromorpha 

 and Cladophora live indifferently in fresh and salt waters; but such forms are very 

 few in number in comparison to the vast number of marine organisms that soon die 

 if placed in fresh water. 



Among the organisms that cause fouling, almost all are strictly marine forms with 

 but a small percentage able to survive in brackish waters. There can be no doubt, 

 then, that many of these organisms are killed if the vessel to which they are attached 

 is transferred to fresh water for a period of time sufficient to secure this effect. 



DATA FROM SHIPS 



During the course of this investigation it was apparent on many occasions that the 

 unusually clean condition of the boat was no doubt expficable on the basis of visits 

 into fresh waters. Thus, ia the case of the Western World (March 8, 1924) its regular 



