TRAWLING FOR FORAGE ORGANISMS IN CENTRAL PACIFIC 



283. 



r.\BLE 8. — Volume and number of organisnix obtained with 

 the Isaacs-Kidd traivls on Hugh M. Smith cruise 27, 

 central North Pacific, 1955 



Item 



Station 23: 

 rosltlon: 



Latitude 



Longitude 



Date - -- 



Time of haul (zone time).. 



Estimated maximum depth (m.) 

 Ciitcli ner liour's hauling: 



Volume (ml.) 



Number of organisms 



Station 25: 

 Position: 



Latitude 



Longitude- 



Hate 



'I'inio of haul (zone time) 



Estimated mavimura depth (m.) 

 (^atch per hour's hauling: 



Volume (ml.)-. _. 



Number of organisms,. 



Station 28: 

 Position: 



Latitude.- 



Longitude _. 



Date.- --- -- 



Time of haul (zone time) --_ 



Estimated maximum depth (m.) 

 Catch per hour's hauling: 



Volume (ml.) 



Number of organisms 



Average (all stations): 

 Per hour of hauling: 



Volume (ml.) 



Number of organisms- 



Per 1,000 m.3 of water strained: 



Volume (ml.) 



Number of organisms 



6-foot 



10-foot 



8 shows that many groups of vertebrates and in- 

 vertebrates were common to the catch of all four 

 trawls. In an attempt to determine whether there 

 were wide differences in the catch composition, 

 we counted the major categories appearing in each 

 list and assembled the results in table 9. The 

 same number of phyla and classes was sampled 

 by all four trawls. The major differences were in 

 the families of invertebrates and the families and 

 genera of fishes, with the most-frequently used 

 trawl catching the greatest variety of organisms. 



VARIATION OF TRAWL CATCH ' 



DIURNAL VARIATION 

 Size of Catch 



Although our data indicate that catches made 

 at night greatly exceeded day catches both in vol- 

 ume and number of organisms (table 10), the in- 

 formation available is insufficient to describe the 

 diurnal variation in forage abundance. On Man- 

 ning cruise 9 (appendix table 1) two series of 

 four hauls each were made with the 6-foot beam 

 trawl with the stations at various distances from 

 shore, one series in the daytime (1000-1800 hours) 

 and the other at night (2000-0300 hours). The 

 day hauls yielded an average volume of 8.6 ml. 

 per hour of hauling and the night hauls 38.6 ml. ; 

 the night/day volmne ratio was therefore 4.49. 

 With respect to number, day liauls produced an 

 average of 123 organisms and the night hauls 134, 

 for a night/day ratio of 1.09. The difference be- 

 tween these two ratios indicates a difference in the 

 size of organisms in the night and day catches. 

 "\^nien the average volume is divided by the aver- 

 age number in the catch we obtain a value of 0.07 

 ml. for the average individual size of the organ- 

 isms in the day catches and 0.29 ml. for the indi- 

 \ndual size in the night catches. 



In April-June 1953, the 1-meter ring trawl was 

 used repeatedly at two "fixed" stations in Ha- 

 waiian waters, one located to windward and the 

 other to leeward of the islands. The stations were 

 about 75 miles apart, and both were thought to 

 represent open ocean conditions. On each of the 

 Gllhert cruises 11, 12, and 13, the windward sta- 

 tion (station A) was visited during the early after- 

 noon hours and the leeward station (station D) 



Table 9. — Number of taxonomic groups in the catch of the four trawls and in the stomach contents of tuna 



I See footnote 4, p. 295. 

 637256 O— 62 3 



