FISHERY BULLETIN: VOL. 86, NO. 2 



processes of the Oregon coastal zone. Daily up- 

 welling indices derived from barometric pressure 

 data (Fig. 3; A. Bakun"*) indicated that in April 

 and May, local winds varied in direction and 

 strength, with one extended period of stormy 

 weather with southwest winds (negative index 

 values). Temperature and salinity profiles during 

 these months showed relatively little variation 

 along the transect within a sampling period (Fig. 

 4a, b, c). Chlorophyll a peaks and low salinity 

 near shore may have been due to the influence of 

 water exiting Yaquina Bay. The highest chloro- 

 phyll a values were observed following periods of 

 northwest winds, and the highest temperatures 

 occurred after a period of very light winds and 

 high insolation. 



The hydrographic regime was altered by the 

 onset of northwest winds in June (Fig. 3), which 

 induced the upwelling of cold, more saline 

 nutrient-rich water along the coast. Strong up- 

 welling [defined by Small and Menzies (1981) as 

 a daily index value >50] was sporadic in June but 

 nearly continuous in July. Temperature, salinity, 

 and chlorophyll a profiles rapidly changed in re- 

 sponse to the upwelling-favorable winds (Fig. 5a, 

 b, c). 



During the 8-10 June cruise, low temperature 

 and high salinity water was found within 5 km of 

 the coast. Low salinity, warm water more than 15 

 km offshore apparently was the plume of the Co- 

 lumbia River. By 19-20 June, continued offshore 

 transport of the surface layer pushed the inshore 

 edge of the plume to 40 km off the coast. Low 

 chlorophyll a concentrations, low temperatures, 

 and high salinity near shore on 19-20 June indi- 

 cated the occurrence of active upwelling. 



Upwelling persisted through the end of July. 

 Temperature and salinity profiles were similar to 

 those observed during the second June cruise, 

 with the patterns of increasing temperature and 

 decreasing salinity farther offshore continuing to 

 the limits of sampling of 90 km on 8 and 9 July 

 and to 70 km on 23 and 24 July. During the up- 

 welling in July, a dramatic phytoplankton bloom 

 occurred in the surface waters within 30 km of the 

 coast. Chlorophyll a concentrations here were 

 denser and broader in offshore extent than the 

 surface and subsurface biomass concentrations 

 previously observed off Oregon (Small and Men- 

 zies, 1981). 



+ 200 



« 



T3 



C 



c 



0) 



a 



3 -200- 



U 



I ||'|||l||l ll'l' f |'l|| '1 11 1 T 



lll.i„lil 



yt4 y^ /N /K yfs yT\ xTs xl\ 



"•A. Bakun, Pacific Environmental Group, National Marine 

 Fisheries Service, Monterey, CA 93940, pars, commun. August 

 1984. 



M J J 



1984 



Figure 3. — Daily upwelling indices for spring-summer 1984. 

 Positive values >50 indicate occurrence of winds inducing 

 strong upwelling. Arrows indicate dates of sampling cruises. 



Ichthyoneuston 



A total of 107 Manta net and 142 neuston trawl 

 samples collected 48 taxa of larval, juvenile, and 

 adult fishes. Larvae <10 mm and a few juveniles 

 were collected by the Manta net, while large 

 numbers of juvenile fishes up to 60-70 mm were 

 taken by the neuston trawl. Size-frequency data 

 for three of the commonest species (Fig. 6 a, b, c) 

 illustrate the relative ability of the nets to cap- 

 ture different sizes of fishes. 



Nighttime sampling (59% of the Manta net 

 tows and 62% of the neuston trawl tows) ac- 

 counted for 93.3% of all fishes in the Manta net 

 catch and 96.5% of the fishes taken in the neuston 

 trawl (Table 1). Four Manta net and 8 neuston 

 trawl tows made during twilight collected 5.4% 

 and 2.9%, respectively, of the total number of 

 fishes taken with each gear type (Table 2). Only 

 1.3% of the Manta net catch and 0.6% of the neu- 

 ston trawl catch was made during daytime (Table 

 2). 



Only two species were not collected predomi- 

 nantly at night. Larval Pacific saury, Cololabis 

 saira, were taken in both day and night Manta 

 net samples. Larval northern lampfish, Steno- 

 brachius leucopsarus , were abundant only in the 

 twilight samples from early June (Tables 1, 2). 



Arbitrary criteria on frequency of occurrence 

 (in >15% of the night samples of either net) or 

 abundance (peak densities >40/l,000 m"^) indi- 

 cated that nine taixa of larval, juvenile, and adult 

 fishes were dominant components of the ichthy- 

 oneuston. Most taxa were characterized by dis- 



302 



