A plot of fish size by area of catch showed 

 that larger fish were usually caught farther 

 offshore. Separating the fish sizes into two 

 categories, we found fish averaging smaller 

 than 7 kg. concentrated in six 20-minute areas 

 near Niihau and Kauai, in eight areas around 

 Oahu, and in only two isolated, offshore 20- 

 minute areas south of Kauai and Oahu (fig. 11). 

 Most of the areas with fish averaging larger 

 than 7 kg. were far offshore. 



Spatial and temporal distributions of sight- 

 ings and catches . --The vessels, concentrating 

 their fishing in those areas where skipjack tuna 

 showed the greatest tendency to aggregate in 

 the past, obtain a major portion of the skipjack 

 tuna catch each year from waters to the south- 

 west of Oahu. Commonly called "shitaba" 

 (which means lower ground in Japanese) by the 

 fishermen, this leeward fishing ground off Oahu 

 is calm almost year-round and close to the 

 home port of Oahu-based vessels as well as to 

 Pearl Harbor, one of two major baiting grounds 

 in the Hawaiian Islands. We arbitrarily divided 

 the fishing grounds around Oahu into four sec- 

 tors and found that out of 971 sightings for 

 which positions were recorded, nearly half 

 were in waters to the west of Oahu, 34 percent 

 to the south, about 13 percent to the east, par- 

 ticularly north of Molokai, and only 5 percent 

 to the north (fig. 12). 



Sightings varied not only by geographic loca- 

 tion, but also by time of day. The number of 

 sightings in relation to time of day increased 

 rapidly from daybreak to a peak at midmorning 

 (0801-0900), followed by a slight dip at 1001- 

 1100 and a second peak at 1301-1400 (table 13 

 and fig. 13). We believe that reduced scouting 

 intensity during mealtimes may have caused 

 the slight dip at midday. Data on mealtime 

 aboard the seven vessels showed that on nearly 

 half of the trips, the crewmembers ate lunch at 

 1001-1100, which coincided with the slump in 

 sightings (table 14). Undoubtedly, insufficient 

 light and scarcity of birds at 0501-0600 and at 

 1801-1900 affected sightings, but the time taken 

 for breakfast and dinner also may have had 

 some effect on scouting intensity. 



Data collected during a research cruise of 

 the Charles H_. Gilbert in April 1953 showed 

 similar variations in sightings, by time of day 

 (Royce and Otsu, 1955). Sightings, recorded 

 by fishermen maintaining a continuous watch, 

 dipped at midday and peaked at 0700-0800 and 

 at 1400-1600. Royce and Otsu stated that there 



Table 13. — Number and percentage of schools 

 sighted and of schools with catches, tabulated 

 by time of sighting and start of fishing, for 

 seven Hawaiian skipjack tuna vessels, June- 1 

 August 1967 



Time 



Schools 



Sighted 



With catches 



Number Percent 



Number Percent 



0001-0100 



— 



— 



— 







0101-0200 



— 



— 



— 







0201-0300 



— 



— 



— 







0301-0400 



— 





— 







0401-0500 



— 



— 



— 







0501-0600 



11 



0.9 



1 







2 



0601-0700 



60 



4.7 



21 



3 



4 



0701 -osnn 



119 



9.4 



36 



5 



8 



0801-0900 



144 



11.3 



66 



10 



6 



0901-1000 



130 



10.2 



67 



10 



8 



1001-1100 



112 



8.8 



50 



8 



1 



1101-1200 



121 



9.5 



60 



9 



7 



1201-1300 



122 



9.6 



70 



11 



3 



1301-1400 



124 



9.8 



56 



9 







1401-1500 



91 



7.2 



62 



10 







1501-1600 



97 



7.6 



46 



7 



4 



1601-1700 



72 



5.7 



42 



6 



8 



1701-1800 



52 



4.1 



26 



4 



2 



1801-1900 



16 



1.2 



17 



2 



7 



1901-2000 













2001-2100 













2101-2200 













2201-2300 













2301-2400 













Totals 



1,271 





620 







0501 0701 0901 IIOI 1301 1501 1701 



I I I I I I I 



0600 0800 1000 1200 1400 1600 1800 



TIME OF SIGHTING OR FISHING 



Figure 13. — Frequencies of school sightings and 

 schools with catches, by time of day for seven 

 Hawaiian skipjack tuna fishing vessels, June- 

 August 1967. 



18 



