rNTRODUCTION 



This report deals with research results achieved by the 

 BCF (Bureau of Commercial Fisheries) Biological Lab- 

 oratory in Honolulu from January 1, 1967 to June 30, 1968. 

 Highlights of the reporting period include: 



1. Attempts to improve the efficiency of the present 

 Hawaiian pole-and-line fleet for skipjack tuna (Katsuwonus 

 pelamis). Skipjack tuna are the basis of by far the largest 

 fishery in Hawaii, but the fleet takes only a minuscule part 

 of the potential annual yield of central Pacific skipjack 

 tuna, which has been estimated as being hundreds of thou- 

 sands of tons. 



2. Experiments aimed at establishing an independent 

 bait-fishing industry. At present the vessels of the fleet 

 seine for their own bait, the preferred species being the 

 nehu, a kind of anchovy. Much time is spent catching bait, 

 when it could be better spent catching tunas. 



3. The search for an alternate or supplemental bait. 

 The threadfin shad, a fish introduced into Hawaii as forage 

 for bass, apparently is as effective as the nehu in attracting 

 skipjack tuna. 



4. Analytical studies of day-to-day operations of the 

 Hawaiian fleet. These investigations have produced data 

 of kinds and quantities never available before. 



5. Use of continuous-transmission, frequency-modu- 

 lated sonar to study the movements of tunas underwater. 

 The sonar is being used both in the active mode, in which 

 a signal from the ship is reflected by the body of the fish. 



and the passive, in which a "sonic tag" fed to a fish sends 

 out signals that are detected by the sonar. By both means, 

 fishes underwater can be tracked for periods of hours. 



6. Discovery that the skipjack tuna caught in the west- 

 ern Pacific Ocean are genetically distinct from those caught 

 in the eastern and central Pacific. The dividing line be- 

 tween the groups apparently lies far west of Hawaii. 



7. Delineation of commercial shrimp resources off the 

 Hawaiian Islands. Several beds of shrimp have been found 

 that might supply a local specialty market, even though a 

 large commercial fishery appears out of the question. 



8. Continuing studies of the longline tuna catches of 

 the South Pacific, as they are reflected in the landings at 

 American Samoa. The fishery now extends almost the 

 breadth of the South Pacific Ocean. 



9. Confirmation of the theory that the principal 

 changes in the temperature of the waters around Hawaii 

 during the first 7 months of the year are due not to the 

 changing seasons, but to the advection of warm water into 

 the area from the south and southeast. This warm water, 

 less saline than that which prevails during the winter, 

 appears to be associated with the large summer catches of 

 skipjack tuna. 



10. Depiction of a pronounced wake effect in the lee of 

 tiny Johnston Island. Predicted by theory, the wake was 

 clearly defined in a cruise made early in 1968. A wake was 

 also found off the island of Hawaii. 



