300 



FISHERY BULLETIN OF THE FISH AND "WILDLIFE SERVICE 



SUMMARY 



1. The staff of the Honolulu Biological Labora- 

 tory is trying to determine the environmental con- 

 ditions which influence the local availability of 

 skipjack. Commercial catch records are a source 

 of information. 



2. Methods and sources of error are considered. 

 Fish catch reports for 1952 (a poor year) and 

 1953 (a good year) were summarized by areas 

 of the fishery and biweekly fishing periods. The 

 unit of fishing effort, the productive fisherman- 

 trip, is discussed. 



3. The distribution of catches and effort in the 

 2 years was generally similar, with leeward Oahu 

 contributing one-half the catch. Hawaii, wind- 

 ward Oahu, and Kauai fell well below leeward 

 Oahu in productivity, while Maui and the oceanic 

 region contributed insignificant proprotions. 



4. Pounds cauglit per unit of effort increased 

 from southeast to northwest in the fishery and 

 from inshore to offshore, but these trends may re- 

 sult from differences in the fishery rather than to 

 distribution of fish. 



5. There was a positive correlation between the 

 average weight per skipjack caught in various 

 zones of the fisliery and catch per unit of effort. 



6. Catches (in pounds) daring the fishing 

 periods of 1953 were, with few exceptions, larger 

 than those made during the corresponding periods 

 of 1952. 



7. In comparison with the seasonal trend in the 

 fishery, the effects of rough weather (as indicated 

 by periods of small craft warnings), were un- 

 important. 



8. Large skipjack, from their appearance in 

 the catches, seemed to have arrived first in lee- 

 ward areas, and at the end of the season they last 

 appeared in catches from leeward areas. In June 

 and August of both years, concentrations of sea- 

 son fish occurred in windward Oahu and leeward 

 Oahu, respectively. 



9. The numbers of small fish taken by the Oahu 

 fishery in 1952 and 1953 were approximately 

 equal, but almost three times as many large fish 

 were caught in 1953. In the Oaliu region, there 

 was almost one and one-half times the fishing ef- 

 fort in 1953 in comparison with 1952, and a much 



larger proportion was directed toward catching 

 large skipjack. 



10. Catch, effort and catch per unit of effort 

 indexes have similar seasonal variations. The 

 positive correlation between catch and catch per 

 unit-of -effort is so close that there is little to be 

 gained in using the catch per unit-of -effort as an 

 index of apparent abundance in the fishery. 



11. During the middle of 1953, the average 

 weight of large skipjack increased at 0.25 pound 

 per week, the growth rate for Hawaii skipjack 

 estimated by Brock. This suggests that fish of 

 the same age were constantly available to the 

 fishery during this period. 



12. The number of small skipjack in the catch 

 varied inversely with the number of large fish. 



13. A hypothesis for the structure of the skip- 

 jack population supporting the fishery is offered. 

 The population has four groups: (1) season fish 

 and (2) extra-large fish, both of which are migra- 

 tory, and (3) a semiresident and (4) a migratory 

 group of smaller skipjack. 



LITERATURE CITED 



Brock, V. E. 



1954. Some aspects of the biology of the aku, Katsu- 

 ivonus pelamis, in the Hawaiian Islands. Pacific 

 Science 8(1) : p. 94-104. 



June, F. C. 



1951. Preliminary fisheries survey of the Hawaiian- 

 •Line Islnnds area. Part III. The live-bait skip- 

 jack fishery of the Hawaiian Islands. U.S. Fish 

 and Wildlife Service, Commercial Fisheries Review 

 13(2) : p. 1-18. 



Kendall, M. G. 



1951. The advanced theory of statistics. Vol. II. 

 Third edition. Charles Griffin & Co., Ltd., London, 

 England. 521 p. 



RoTCE, W. F., and T. Otsu. 



1955. Observation of skipjack schools in Hawaiian 

 waters, 1953. U.S. Fish and Wildlife Service, 

 Special Scientific Report — Fisheries No. 147, 31 p. 



Snedecor, G. W. 



1956. Statistical methods, 5th edition. The Iowa 

 State College Press, Ames, Iowa. 534 p. 



Yamashita, D. T. 



1958. Analysis of catch statistics of the Hawaiian 

 skipjack fishery. U.S. Fish and Wildlife Service, 

 Fishery Bulletin 134, vol. 58, p. 253-278. 



Yuen, H. S. H. 



1959. Variability of skipjack response to live bait. 

 U.S. Fish and Wildlife Service, Fishery Bulletin 

 160, vol. 60, p. 87-106. 



U. S. GOVERNMENT PRINTING CFICE : 1962 O -596560 



