FISHERY BULLETIN: VOL. 74, NO. 1 



grams/1,000 m^, Tables 3 and 4, Figure 6) were 

 found intermediate distances off the Oregon 

 coast, namely over the continental slope at sta- 

 tions 46 and 84 km offshore. A trend for maxima 

 at intermediate distances offshore has been re- 

 ported for other regions. Standing stocks of zoo- 

 plankton were highest at the edge of the shelf or 

 over the inner slope off New York (Grice and Hart 

 1962), intermediate distances from shore off 

 California (Smith 1971), and near mid-shelf in 

 the Florida Current off Cape Hatteras, N.C. (St. 

 John 1958). Macrozooplankton and micronekton 

 collected with a 0.9-m IKMT off Vancouver Is- 

 land, Canada and Washington were maximal 

 over the outer edge of the shelf (Day 1971). The 

 reduced feeding activity of pink, chum, and sock- 

 eye salmon as they approach the coast is pur- 

 portedly explained by the low macroplankton 

 concentrations in neritic waters and higher con- 

 centrations in offshore waters of the northwest- 

 ern Pacific off Kamchatka (Andrievskaya 1957; 

 Mednikov 1958). All of these studies indicate that 

 small intermediate consumers may achieve 

 maximum importance in the pelagic food chain in 

 deep waters beyond the inner shelf (see also 

 Wilhams et al. 1968). 



The reason why catches of micronekton and 

 macrozooplankton were higher offshore than 

 nearshore may be related to their vertical migra- 

 tions. Most of the species of micronekton and 

 euphausiids caught in upper waters at night 

 undertake diel vertical migrations (Pearcy and 

 Laurs 1966; Pearcy and Forss 1966; Brinton 

 1967; Pearcy and Mesecar 1971); hence they may 

 be most abundant in waters deep enough to 

 permit vertical movements but where productiv- 

 ity is enhanced near land (Pearcy 1964). If they 

 drift over the shelf, they may be eaten by large 

 benthic or pelagic predators (Isaacs and 

 Schwartzlose 1965; Pereyra et al. 1969). 



The inshore-offshore changes in standing 

 stocks of micronekton for the two seasons (Figure 

 4) suggest that these distributions are interre- 

 lated. Movement of animals may be correlated 

 with seasonal oceanographic changes. During the 

 summer, when the biomass increases greatly 

 from 46 km to a peak at 84 km, large inshore- 

 offshore gradients also occur in physical proper- 

 ties because of upwelling, and there is an offshore 

 component of nearshore surface waters (Pillsbury 

 1972). During the winter, when biomass from 

 46 to >120 km is relatively uniform, inshore- 

 offshore gradients are weak, surface currents are 



onshore, and downwelling occurs (Hebard 1966; 

 Laurs 1967). The significant increase in biomass 

 at 46 km in the winter may be caused by inshore 

 advection of surface water and animals and the 

 concentrating effect of shallow water near the 

 edge of the shelf on vertical migrants. The peak 

 at 84 km in the summer, though far from the 

 coast, may be related to upwelling. Sometimes 

 Laurs (1967) found maximum biomass of carni- 

 vores at 65-84 km and maxima of lower trophic 

 levels closer inshore off Brookings, Oreg., during 

 the summer, suggesting a succession of trophic 

 level maxima such as reported by Sette (1955), 

 King ( 1958), and Vinogradov and Voronina ( 1962) 

 in areas of oceanic upwelling in equatorial 

 waters. 



Herbivore: Carnivore Ratios 



Others have also found that the herbivore: 

 carnivore biomass ratios decrease from shal- 

 low, eutrophic waters to oceanic waters. Grice and 

 Hart (1962) reported that well over one-half of 

 the zooplankton by volume in shelf waters off 

 New York herbivorous, while in the Sargasso Sea 

 only about one-half belonged to this trophic level. 

 The percentage of herbivores in the zooplankton 

 catches decreased from inshore waters that were 

 affected by upwelling into offshore waters of the 

 California Current off Baja California (Longhurst 

 1967). Greze ( 1970) reported that the biomass and 

 production of herbivores and carnivores was a 

 larger percentage of that of primary producers in 

 the Equatorial Atlantic or Ionian Sea than the 

 shallow waters of the Black Sea or Sevastopol 

 Bay. These trends suggest that (a) a smaller 

 fraction of the herbivorous biomass is captured 

 in oceanic than neritic waters because of escape- 

 ment through coarse mesh or avoidance, (b) pro- 

 duction per unit biomass of herbivores is higher 

 relative to that of carnivores in offshore waters, 

 or (c) that ecological efficiences (food consumed by 

 tropic level n + 1 to food consumed by trophic 

 level n ) are higher in oceanic than neritic waters. 



ACKNOWLEDGMENTS 



This research was supported by the National 

 Science Foundation (Grant GB-1588) and the 

 Office of Naval Research (Contract NOOO 14-67- 

 A-0369-0007 under project NR 083-102). I am 

 grateful to Harriet Lorz, Henry Donaldson, Lyle 

 Hubbard and others who helped with the field 



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