FISHERY BULLETIN: VOL. 70, NO. 3 



(1966) . Landings from this fishery range from 

 about 91 tons^ (200,000 lb) per month in Feb- 

 ruary to more than 907 tons (2 million lb) per 

 month in July. Total annual landings also show 

 wide variations ranging from 2,676 tons (5.9 

 million lb) as in 1969 to 7,302 tons (16.1 million 

 lb) as in 1965.' Hawaiian fishing vessels fish 

 within sight of land, mainly in the vicinity of 

 the islands of Oahu to Maui and Hawaii (Uchida, 

 1970). Thus, Hawaiian skipjack landings pro- 

 vide, in contrast to other fisheries where fishing 

 fleets may follow the fish concentrations, a time 

 sequence measure from a fixed area. 



Uchida (1967) analyzed the catch and eflfort in 

 the Hawaiian fishery and found that although 

 there has been a decline in the number of vessels 

 fishing on a full-time basis during the last 15 

 years, there is no clear evidence that this decline 

 has affected total landings. It appears that the 

 decline in the number of fishing vessels occurred 

 primarily among the smaller boats (Uchida 

 1966: Table 6) and, also, that the decline was 

 offset by increased efficiency of fishing. For 

 purposes of this paper, it is important to note 

 that the large fluctuations in total annual land- 

 ings are also reflected by the average annual 

 catch per standard effective trip (Uchida, 1967: 

 Figure 8). The annual landings of skipjack, 

 therefore, reflect availability near Hawaii. 



THE OCEAN ENVIRONMENT 

 NEAR HAWAII 



The oceanographic climate of the Hawaiian 

 Islands region was described by Seckel (1962). 

 Of interest are the North Pacific Central and the 

 North Pacific Equatorial water types and the 

 transition water of the California Current Ex- 

 tension between these water types (Figure 1). 

 Seckel (1968) defined the North Pacific Central 

 water as that with a salinity of more than 34.8/^f 

 and the North Pacific Equatorial water as that 

 with a salinity of less than 34.2^r. These sa- 

 linities are always found in the salinity gradients 

 that actually define the water type boundaries. 



' Metric tons are used throughout this paper. 



* Source: Hawaii State, Division of Fish and Game. 



The boundary of the North Pacific Central 

 water lies near the Hawaiian fishing area and is 

 displaced north-southward both seasonally and 

 nonseasonally. Usually the boundary lies just 

 south of the islands in fall and winter and within 

 or north of the islands during spring and sum- 

 mer. The boundary displacement is reflected by 

 the salinity as measured at Koko Head, Oahu 

 (Seckel and Yong, 1971). Low salinities occur 

 during spring and summer and high salinities 

 during fall and winter. During some years, 

 such as in 1957 and 1958, the islands were bathed 

 in North Pacific Central water throughout the 

 year and in 1968 the islands were bathed in the 

 transition water of the California Current Ex- 

 tension throughout the year. 



The large effect of heat exchange across the 

 sea surface tends to obscure the effect of ad- 

 vection on the sea-surface temperature. Never- 

 theless, the change of temperature due to ad- 

 veetion is apparent in graphs of the change of 

 temperature per month (Seckel, 1962). Warm 

 advection in late winter and early spring causes 

 the temperature in Hawaiian waters to rise be- 

 fore it would rise due to the onset of seasonal 

 heating across the sea surface. The temperature 

 increases and the salinity decreases southward 

 near Hawaii. Warm advection is therefore as- 

 sociated with a northward component of flow 

 that also causes a decline in the salinity. 



Extremes of temperature and salinity as ob- 

 served at Koko Head, Oahu, range fi^om about 

 22.5°C in February or March to 27.4°C in Sep- 

 tember or October and from 34.4%f in July to 

 S5.5'/(r in late fall or early winter. Inorganic 

 phosphate concentrations in the Hawaiian region 

 as well as in the North Equatorial Current are 

 about 0.3 fjig at./liter. Seasonal variations have 

 not been observed. 



In the Hawaiian region 10 to 40 cc of zooplank- 

 ton per 1,000 m" of water are filtered by a 1-m 

 net in 200-m oblique tows (King and Hida, 1954, 

 1957a, 1957b; Nakamura, 1967). King and 

 Hida (1954: Figure 16) indicate that an aver- 

 age zooplankton volume of about 25 cc per 1,000 

 m'' of water filtered near Hawaii compares with 

 20 to 25 cc in the North Equatorial Current and 

 with about 38 cc near the equator to the south 

 of Hawaii. There is no clear indication of a sea- 



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