ATLAS OF THE OCEANOGRAPHIC CLIMATE OF THE HAWAHAN 



ISLANDS REGION 



By GuNTER R. Seckel, Oceanographer. Bureau of Commercial Fisheries 



A studj' of the oceanographic climate of the 

 Hawaiian Islands region is a part of the Hawaii 

 skipjack investigations conducted by tiie staff of 

 the Biological Laboratory/ Biu'eau of Commercial 

 Fisheries (Honolulu). This seasonal fishery has 

 been described by Yaniashita (1958). The catch 

 rate generally begins to rise rapidly in April from 

 200,000 pounds or less a month during the winter 

 to 2 million pounds or more in August. There- 

 after it drops off rapidly in September and October, 

 again reaching the minimum catch rate per month 

 during the latter part of the year. The fishery 

 also shows relatively large annual fluctuations 

 ranging from a low of about 6 million pounds, as 

 in 1957, to about 14 million pounds, as m 1954. 

 Because both the seasonal nature of the fishery 

 and its animal fluctuations were believed to be 

 associated with changes m the phj'sical environ- 

 ment, oceanographic studies were included as part 

 of the skipjack investigations. 



Oceanographic information for the waters bath- 

 ing the Hawaiian Islands was summarized by 

 Schott (1935) and Sverdrup et al. (1942), and 

 bathythermograph observations from 1941 to 1949 

 were analyzed by Leipper and Anderson (1950). 

 Since 1949, six oceanographic surveys were made 

 in the vicinity of the higli islands of the Hawaiian 

 archipelago (McGary, 1955; Seckel, 1955). The 

 information from these sources can be summarized 

 as follows: The Hawaiian Islands are located in 

 the trade wind zone of the Pacific Ocean, where 

 sensonal changes of surface variables are relatively 

 small. The seasonal temperature range, for ex- 

 ample, is approximately 4° to 5° F. (2° to 3° C). 

 The mean summer high is about 78° F. (25.6° C.) 

 and varies locally from 75° (23.9° C.) to 80° F. 

 (20.7° C). The mean winter low is about 74° F. 

 (23.3° C.) with local variations from 73° r22.8° C.) 

 to 76° F. (24.4° C). 



' Formerly Pacific Oceanic Fisliery Investigations (POFI). Renamed 

 December 1, 1959. 



Note.— Approved tor publication February 27, 1961. Fishery Bulletin 

 193. 



The mean salinity is about 35 °/oo, ranging 

 from 34.4 to 35.3 °/oo. Defijiite seasonal sahnity 

 variations, because of insufficient data, were 

 believed to be obscured by large annual variations. 

 Available surface inorganic phosphate data show 

 that the concentration to be found in the vicinity 

 of the Hawaiian Islands approaches the limit of 

 precision in present experimental techniques 

 (0.3/ig-at./L.). This, together with the scarcity 

 of observations, made it impossible to detect 

 seasonal changes. 



Zooplankton catches in the area have been dis- 

 cussed by King and Hida (1954, 1957) and Waldron, 

 Nakamura, and -Shippen (MS). Mean catches 

 indicate annual variations of 15 to 25 cc. per 

 thousand cubic meters of water strained in 200- 

 meter oblique hauls, with a suggestion of a similar 

 range in seasonal catch variations (King and Hida, 

 1957, figs. 7 and 8). 



Current charts generally show a weak set toward 

 the west throughout the year. Geostrophic cur- 

 rents indicate a complex flow pattern in the vicin- 

 ity of the high islands, without providing any 

 information about seasonal changes. In short, 

 these environmental parameters are well within 

 the limits within which skipjack are known to 

 occur, so that their changes appear to be insuf- 

 ficient to explain the seasonal nature of the skip- 

 jack fishery and its annual variations. 



All data, however, have not been exhausted. 

 There are many isolated observations from cruises 

 either originating or terminating in the Hawaiian 

 Islands. In addition, many thousands of bathy- 

 thermograph observations have been obtained by 

 the Bureau of Commercial Fisheries Biological 

 Laboratory (Honolulu), and otlier organizations 

 since the end of World War II. These data, if 

 treated by means of a different approach, could 

 yield information which is not now apparent. 



One can postulate, for exaini)le, that the surface 

 variables such as temperature or salinity, are not 

 randomly distributed in space, but that they are 



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