FISHERY BULLETIN: VOL. 71, NO. 3 



MM I 'fl M I I I I I I I i f l M I I I I M I U^ I I I 

 STATIONS OCCUPIED- 1969 



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Figure 1. — Stations occupied during survey of waters off 

 Oregon, May to October 1969. 



Micronekton and zooplankton were sampled 

 with a 6-foot Isaacs-Kidd midwater trawl 

 (IKMT) equipped with a 5-mm mesh liner and a 

 0.571-mm mesh cod end, paired 0.7 m (mouth 

 diameter) bongos with 0.571-mm mesh nets, 

 and a 5-m long 1.0-m-mouth diameter net (MN) 

 with a 0.571-mm mesh. 



The bongos were located 3 m above the bridle 

 of the IKMT on the same tow line. Hauls were 

 made obliquely, usually from 200 m, depth per- 

 mitting, to the surface at a tow speed of 5 knots. 

 Eight hundred meters of wire, assuming a 

 4:1 wire length to depth fished ratio, was let 

 out at 50 m/min and retrieved at 30 m/min. A 

 usual haul required about 40 min effective 

 towing time. Surface tows (upper 10-20 m) 

 were made horizontally at the same stations as 

 deep (200 m) oblique tows on the June and July- 

 August cruises for comparison. Three of these 

 surface tows did not have paired samples from 

 deep hauls. For MN hauls, the ship remained 

 stationary as the net was lowered at 10 m/min 

 to 200 m on 200 m of wire, depth permitting, 

 and hauled vertically to the surface at 30 m/ 

 min. Effective tow time was usually about 8 

 min. At depths < 400 m only the upper half of 



the water column was sampled by the IKMT 

 and bongos. Bongos were not used on the May 

 or August cruises. MN samples were not always 

 taken in conjunction with IKMT samples. All 

 tows were made between dusk and dawn. 



A flow meter was situated inside the mouth 

 of each net to record volume of water filtered. A 

 depth distance recorder (Pearcy and Laurs, 

 1966) was also used in the IKMT to record the 

 distance travelled vs. depth. 



Temperature (BT) and salinity (induction 

 salinometer) of surface waters were determined 

 at each station. 



All biological samples were preserved at sea 

 in 10% buffered seawater Formalin. ^ Later the 

 IKMT samples were transferred to 36% isopro- 

 pyl alcohol. Fish larvae were sorted from 

 bongo (one side only), MN (some of which had 

 been split a varying number of times with a 

 Folsom plankton splitter), and IKMT samples 

 (not split). They were later identified and 

 measured. Measurements, reported to the 

 nearest millimeter, refer to standard length 

 (SL = snout tip to notochord tip preceding 

 development of caudal fin, then to end of hypural 

 plate). For convenience, the term larvae in this 

 paper sometimes includes early juvenile stages, 

 e.g., anchovies, scorpaenids, and osmerids. 



The taxonomic listings follow the scheme of 

 Greenwood et al. (1966). Species names corre- 

 spond to those listed by the American Fisheries 

 Society (Bailey, 1970). The following discussion 

 is based on the deep tows of the bongos and 

 IKMT unless indicated otherwise. 



RESULTS AND DISCUSSION 



Comparison of Gear 



The three types of gear were compared for 

 the number of taxa taken, estimates of larval 

 abundance, and frequency of occurrence of 

 major taxa. The IKMT samples contained the 

 greatest number of taxa followed by the bongos 

 and MN (Table 1). Many of the bongo and MN 

 samples, but not IKMT samples, had been split 

 prior to removal of fish larvae. This process 



* Reference to trade names does not imply endorse- 

 ment by the National Marine Fisheries Service, NOAA. 



698 



