PEARCY: MICRONEKTON AND MACROZOOPLANKTON OFF OREGON 



of advective processes rather than biological in- 

 teractions (McGowan 1971). In the headwater 

 region of the California Current off Oregon, how- 

 ever, the water type is predominantly Subarctic 

 and common species of some taxonomic groups 

 of pelagic animals are the same within and 

 among years (Pearcy 1972). 



In addition to in situ population changes and 

 changes affected by advection, small nektonic 

 animals may be able to swim or to migrate 

 horizontally. Though migrations of large nektonic 

 animals such as tuna, salmon, hake, etc., are 

 known to result in large seasonal changes in the 

 abundance of these animals off Oregon, little 

 evidence exists for horizontal movements of mi- 

 cronekton, even on a reduced scale. This is 

 another reason to expect temporal stability of 

 their populations. 



Basic differences in the structure and energy 

 pathways of neritic and oceanic ecosystems in the 

 northeastern Pacific have been inferred by differ- 

 ences in the seasonal production cycle, seasonal 

 variations in chlorophyll a concentrations, and 

 the size of individual phytoplankton and mi- 

 crozooplankton (McAllister et al. 1960; Anderson 

 1965; Parsons and LeBrasseur 1970; LeBrasseur 

 and Kennedy 1972). Inshore-offshore differences 

 in the standing stocks of pelagic herbivores and 

 carnivores, which have not been studied, are 

 therefore to be expected. 



METHODS 



Micronekton and macrozooplankton were col- 

 lected at night with 1.8-m Isaacs-Kidd mid-water 

 trawls (IKMT) and with 1-m diameter plankton 

 nets (MN) along stations west of Newport, Oreg. 

 (lat. 44°39.1'N). The stations were located 28, 46, 

 84, 120, and >120 km, respectively, offshore (Fig- 

 ure 1). Collections, made about every month, 

 totalled 243 IKMT tows between August 1962 

 and July 1967, and 179 MN collections between 

 June 1963 and July 1967. 



The IKMT had a 5-mm (bar measure) nylon 

 liner throughout. Oblique tows were made to a 

 depth of approximately 200 m, except at inshore 

 stations where about one-half the depth of the 

 water column was sampled (40 m and 130 m at 

 the 28- and 46-km stations, respectively). Tow 

 speed was 6 knots. The trawl was lowered at 50 m 

 wire/min until a 4:1 scope was attained. The 

 trawl was then retrieved at 30 m wire/min to the 

 surface. Volume of water filtered and depth of 



Figure l. — Location of the sampling stations off Newport, 

 Oreg. Stations are designed in kilometers from the coast. 

 Depth contours are in fathoms (100 fathoms = 183 m, 500 

 fathoms = 914 m, 1,000 fathoms = 1,829 m, 1,500 fathoms = 

 2,743 m). 



trawling was estimated from TSK^ depth- 

 distance recorders and flowmeters. 



The meter nets, which were made of 0.571-mm 

 Nitex, were towed immediately before or after 

 each IKMT tow. From June to November 1963 

 oblique tows were made to approximately the 

 same depths as the IKMT tows, but because of 

 difficulties resulting from preferential sampling 

 of near-surface waters, oblique tows were aban- 

 doned in favor of vertical tows in December 1963. 

 Vertical tows were from 200 m to the surface, or 

 from 60 or 150 m to the surface at the two inshore 

 stations. After a vertical wire angle was obtained, 

 they were retrieved at 50 m wire/min. Flow- 

 meters mounted in the mouth of MN's provided 

 estimates of volumes filtered. In a few instances 

 flowmeters malfunctioned. Volumes were then 

 estimated from the distance towed and 85% 

 IKMT filtration efficiency (Pearcy and Laurs 

 1966) or from the average volume of other MN 

 tows to the same depth. 



^Tsurumi-Seiki Kosakusho Co. Reference to trade names 

 does not imply endorsement by the National Marine Fisheries 

 Service, NOAA. 



71 



