FISHERY BULLETIN: VOL. 70, NO. 4 



Table 1. — Depths of paired oblique pankton hauls taken 



by the three research vessels in EASTROPAC II (net 



lowered by paying out 300 m of towing cable). 



Table 2. — Hour of day that paired oblique plankton 

 hauls were made from the three research vessels par- 

 ticipating in EASTROPAC II (midtime of haul used). 



ington usually were taken at approximately 

 0630, 1200, 1800, and 2400; and hauls from 

 Undaunted at 0500, 1200, 1730, and 2400. At 

 least some hauls were taken during every hour 

 of the day. 



EFFECTIVENESS OF SAMPLING FISH 



LARVAE IN DAYLIGHT HAULS AS 



COMPARED WITH NIGHT HAULS 



Catches of fish larvae for selected families 

 in day hauls compared to night hauls or to hauls 

 taken within ± 1 hr of sunrise or sunset are 

 summarized in Table 3. For all categories of 

 larvae combined, the catch was 212.0 larvae per 

 daytime haul and 480.4 larvae per night haul, 

 a difference in catch of 2.27 X. Hauls taken 

 within ± 1 hr of sunrise or sunset had an av- 

 erage catch of 347.0 larvae, intermediate be- 

 tween day and night catches. 



Difference between day and night collections 

 was somewhat less than for ETP I; on that sur- 

 vey the average count of larvae in night hauls 

 was 2.76 X as many as in day hauls (Ahlstrom 

 1971, Table 4). On both surveys gonostomatid 

 larvae had the most marked differences in 

 catches between night hauls and day hauls: 

 4.3 X as many, on the average, in night collec- 

 tions compared with day on ETP I, 2.9 X as 

 many in night collections on ETP II. Night-day 

 diflferences in catch per haul of myctophid lar- 

 vae were less marked between the two surveys: 

 3.0 X on ETP I as compared with 2.6 X on ETP 

 II. Night-day differences in average catches of 

 bathylagid larvae were similar on the two multi- 

 vessel surveys: 1.5 x as many per haul on the 

 average, in night collections compared with day 

 collections. Sternoptychid larvae, which were 

 sampled almost as well in day hauls as in night 

 hauls on ETP I, showed a somewhat greater 

 night-day diflference on ETP II: 1.7 X for ETP 

 II as compared with 1.2 x for ETP I. 



Scombrid larvae were taken in lesser num- 

 bers per haul in both day and night hauls on 

 ETP II compared with ETP I; in contrast to 

 ETP I, however, (where a night-day difference 

 of 3.7 X was observed) no difference was ob- 

 tained in night and day collections on ETP II. 



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