382 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



36 



35 



E: 34 



35 



34. 



10° 



15° 



20° 

 NORTH LATITUDE 



25° 



30° 



Figure 10. — Mean meridional salinity profile 10° to 

 30° N. between 155° and 160° W. Panel A, April to 

 August; panel B, November to February. 



rises at an average rate of .13°/oo per degree of 

 latitude to 35.15°/oo at 23° N. It then increases 

 to the maximum of 35.35°/oo at about 28° N., at 

 a rate of .04°/oo per degree of latitude. Of im- 

 portance here is the high salinity gradient within 

 and slightly to the north of the Hawaiian Islands. 

 This is indicative of a transition zone or boundary 

 between different types of water. Data from in- 

 dividual months indicate that this boundary also 

 moves seasonally with the previously described 

 35°/oo isopleth, with which it is closely associated. 



During the winter months or high salinity pe- 

 riod in Hawaii (fig. lOB), the salinity decreases 

 from 34.3°/oo at 10° N. to a mmimum of 34.2 °/oo 

 at 12° N. and then increases rapidly to 35.05°/oo 

 at 19° N., at an average rate of .12°/oo per degree 

 of latitude. North of 19° N. the salinity con- 

 tinues to increase to its maximum of 35.4°/oo at 

 about 27° N., at an average rate of .04°/oo per 

 degree of latitude. Of interest here is the south- 

 ward shift of the high salinity gradient to south 

 of 19° N. and the salmity decrease at 12° N. from 

 34.65 °/oo during the April to August period to 

 34.2°/oo during the November to February period. 



Finally, two salinity charts were constructed 

 (appendix B, chart III). Data were again 

 grouped as above into the April to August and 



November to February periods. The charts will 

 therefore reflect distributions for high and low 

 salinity periods within the main islands area, but 

 not for high and low periods for the remainder of 

 the region. 



Presenting data for groups of months reduces 

 the differences in the distribution between months 

 of extreme conditions. For example, figure 8 

 shows that the extreme positions of the 35°/oo 

 isopleth, corresponding to the months of July and 

 January, are located farther apart than the equiva- 

 lent isopleth on chart III. This is particularly so 

 in the western portion of the region, where the 

 mean April to August position of the 35°/oo iso- 

 pleth does not indicate its brief northward move- 

 ment during July and August. 



Despite this shortcoming, the charts provide in- 

 formation about the salinity distribution in the 

 vicinity of Hawaii. During the April to August 

 period the high salinity gradient between 20° and 

 25° N. is well defined in the eastern half of the 

 region. Another high salinity gradient is indi- 

 cated in the southeast corner of the region. Of 

 particular interest is the appearance of two cells in 

 which the salinity is higher than 35.4°/oo. A por- 

 tion of one is located in the northeast corner and 

 the other in the northern half of the region west 

 of 172° W. 



The salinity distribution for the November to 

 February period when compared to the April to 

 August distribution, suggests that the salinity 

 gradient in the southeast corner of the region has 

 moved northwestward and the gradient formerly 

 in the Hawaiian Islands area has shifted south- 

 ward. These then combined to form the more or 

 less continuous salinity gradient illustrated in 

 figure lOB. 



In the northern portion there is now only one 

 cell of high salinity (>35.4°/oo), which extends 

 westward from about 157° W. This may mean 

 that either the two high salinity cells of the April 

 to August period have combined to form one, or 

 that both have shifted eastward or westward, so 

 that only one cell is apparent. Data collected by 

 the Bureau of Commercial Fisheries during Janu- 

 ary to March, 1954 (McGary and Stroup, 1956: 

 55), suggest that the former is the case. 



Reviewing the various fragments of informa- 

 tion, one notes that to the north and south of the 

 Hawaiian Islands low and high salmities occur 

 approximately at the same time as low and high 



