FISHERY BULLETIN: VOL. 75, NO. 4 



animal is equally abundant at all depths, then 

 oblique tows will adequately estimate its abun- 

 dance. If an animal is restricted to a narrow sur- 

 face layer, then its abundance will be underesti- 

 mated by deeper tows relative to shallower ones. 

 Recent work by ourselves and Myers (1975) has 

 shown that highest zooplankton abundances are 

 found within the top 20 to 30 m of the water 

 column. Therefore, our oblique tows from depths 

 greater than about 30 m do underestimate zoo- 

 plankton abundances. This becomes a problem for 

 tows taken at stations farther from shore as the 

 water depth increases, because an increasing frac- 

 tion of the water column sampled contains few 

 animals. Therefore, abundance gradients should 

 not be considered to be real between stations NH 1 

 (water depth = 20 m) and NH 10 (water depth = 

 80 m) unless abundance differences are greater 

 than a factor of four. 



Abundances are also underestimated for many 

 copepod taxa because the small copepodite stages 

 could easily pass through our 240-/u.m mesh net. 

 Copepodites of species of Pseudocalanus and Acar- 

 tia younger than stage III were seldom seen in our 

 samples. Probably only stages IV and V were sam- 

 pled quantitatively. 



The data set gains its value from being a 3-yr 

 time series of samples collected in exactly the 

 same manner at the same stations. As such, these 

 are good baseline data to which future work can be 

 compared. Point estimates of abundance have lit- 

 tle meaning, but comparisons of abundances be- 

 tween seasons and years at a set of stations are 

 valid and meaningful. 



RESULTS 



Frequency of Occurrence of 

 Zooplankton Taxa 



Copepods were the most frequently occurring 

 and the most abundant members of the zoo- 

 plankton community in the nearshore region off 

 Newport, Oreg. Fifty-eight species were seen in 

 our samples (Table 1). Thirty-eight species were 

 found in the summer samples and 5 1 species in the 

 winter samples. During our study, species from 

 the Subarctic, Transition, and Central Pacific 

 faunal groups (McGowan 1971) were taken. 



The copepods in Table 1 can be grouped on the 

 basis of patterns of occurrence. Eight species occur 

 commonly during both winter and summer 

 months: Calanus marshallae , Paracalanus par- 



TABLE 1. — A checklist of copepod species taken off Newport, 

 Oreg., in summer ( S) and winter ( W) months during the period of 

 the study. 



[C = Common, occurrence in >50% of the samples taken, U = 

 Unusual, occurrence in <50% but >5 samples taken, R = Rare 

 occurrence <5 samples.] 



1 Pacific representatives of the genus Pseudocalanus are not adequately 

 described They are being studied by B. Frost. 



2 Two morphs of the genus Metridia were separated on the basis of the shape 

 of the prosome in lateral view. The M. pacifica type is more robust and has a 

 steeply sloping forehead. Detailed morphological analysis of the two types has 

 not been done. 



vus, Psuedocalanus sp., Metridia lucens, Acartia 

 clausii, A. longiremis, Oithona similis, and O. 

 spinirostris. Seven species were found only during 

 the summer months and probably have northern 

 affinities: Aetideus pacificus, Gaidius imma- 

 tures, Gaetanus immatures, Racovitzanus ant- 

 arcticas s.l., Metridia pacifica, and Oncaea media 

 hymena. Eurytemora americana occurred very 

 rarely in the sample series, but it is a common 

 form in all of the local estuaries (Frolander et al. 

 1973). Only one species was common during the 

 summer and uncommon during the winter: Cen- 

 tropages abdominalis. This species has northern 

 affinities. A group of six species had the opposite 

 characteristic; that is, they were common during 

 the winter but uncommon or rare during the 

 summer: Calanus tenuicornis, Clausocalanus ar- 

 cuicornis, C. pergens, Ctenocalanus vanus s.l., 

 Acartia tonsa, and Corycaeus anglicus. All of these 

 species are common in warmer water south of 

 Oregon. 



The majority of the copepod species (43) were 



718 



