46 MARINE FISHERIES OF NORTH CAROLINA 



stratification where bottom isohalines for July, 1927, are seen as tongues of 

 high salinity pointing toward the river mouths. Since warm water is less dense 

 than cold ^^ and since there is a tendency for the surface to be heated during 

 warm periods, temperature conditions may supplement the salinity stratifica- 

 tion. On the other hand, when the surface water cools, its increased density 

 opposes any stratification due to salinity but does not necessarily prevent it; 

 consequently there may be a layer of colder, fresher water toward the surface 

 (for an example of this in shallow waters see Nelson, 1928). 



Currituck Sound, many miles from the nearest inlet, is considered essen- 

 tially a body of fresh water. A salt-water guard lock prevents an inflow of 

 brackish, polluted water from the Norfolk area into the sound by way of the 

 Albemarle and Chesapeake Canal. The lock was removed in 19 13 resulting 

 in higher, more variable salinities. Largely because of the threat to the 

 unusually good production of freshwater game fishes and related forms, a 

 new guard lock was put in operation at Great Bridge in 1932. Figures 22 

 and 23 show the before and after effects of this installation. 



Albemarle Sound is also essentially fresh water as its biota indicates. About 

 the only salinity records available apply to the eastern end as given in Figure 

 22. Certainly to the westward, with the increased influence of the tributaries, 

 salinities are no higher than this.^'' 



The salinities in Pamlico Sound may be represented by Figures 15, 16, 

 and 17. The isohalines indicated form inverted cones, each of which has its 

 apex at Ocracoke Inlet and is not perceptibly modified about the other 

 narrower and shallower inlets. This suggests that practically all circulation 

 between the ocean and Pamlico Sound is through Ocracoke Inlet, or at least 

 such was the case when the records were taken in 1927. On the other hand, 

 in the earlier i88o's the salinity was high about the mouths of all the inlets, 

 according to figures published by Winslow (1886) and shown within the 

 circles of Figure 16. 



Winslow (1889) did not publish all the substantiating data but gave the 

 following very interesting account of the effects of winds on salinity in 

 Pamlico Sound: 



"It must be remembered that the condition of the water is not dependent 

 upon the wind prevailing at any particular time, but upon the wind that has 



18. Except near the freezing point. Maximum density of water is 4° C. (39.2° F.). It expands 

 with the fall of temperature below this point until it freezes, thereafter it contracts on further 

 cooling. 



19. Robert W. Luther of the Public Utility Commission of Elizabeth City has submitted 

 chloride determinations for points in the Chowan and Pasquotank rivers and Knobb Creek, 

 tributary to the latter. None of these indicate salinities even approaching i%o', however a note 

 indicates that fishermen reported water too salty to drink about 8 miles upstream from the 

 mouth of the Chowan in 1941. The note also indicates that, according to these fishermen, this 

 was the first period of such high salinity in 70 years. Figure 19 of the present paper shows that 

 1941 was a drought year with low river discharge. 



