FISHERY BULLETIN: VOL 78, NO. 4 



Yield Estimates 



Because the northern anchovy stock under con- 

 sideration is in a nearly virgin state, an estimate 

 of potential yield can be obtained using Gulland's 

 (1971) formula 



Y,,, = XMBo 



(14) 



where Ypot = maximum potential yield 



X = a constant coefficient [0.6 for north- 

 ern anchovy based on MacCall 

 et al. (1976)] 

 M - instantaneous natural mortality 

 rate [1.00-1.05 for northern an- 

 chovy based on MacCall et al. 

 (1976) and Pacific Fishery Man- 

 agement Council (footnote 2)] 

 Bq = mean virgin biomass, in this case 

 spawning biomass. 



SURVEY RESULTS 

 Hydrography and Plankton Volume 



In all 3 yr, upwelling activity was observed 

 along the coast, evidenced by the colder, <14° C 

 water nearshore (Figures 3-5). This is a typical 

 summer condition when winds blow mainly from 

 the north, currents tend generally to the south, 

 upwelling takes place in a narrow band along the 

 coast with resultant offshore transport of surface 

 waters (Wyatt et al. 1972; Smith 1974; Huyer et al. 

 1975; Ingraham and Hastings 1976; and others). 

 Offshore, especially beyond the continental shelf, 

 water temperatures were >14° C, well within the 

 range for successful northern anchovy spawning 

 and early development (Brewer 1976). 



Salinity contours showed that all three surveys 

 covered the inner bounds of the Columbia River 

 plume, delineated by the 311. isohaline (Figures 

 3-5). The outer bounds of the plume, defined by the 

 32.5%., isohaline (Barnes et al. 1972), were not en- 

 compassed. This plume is a persistent hydro- 

 graphic feature off the Oregon coast in summer 

 (Barnes et al. 1972). The Columbia River reaches 

 maximum outflow in June and flows southerly, 

 under the influence of prevailing winds and cur- 

 rents, as a plume of shallow (20-40 m deep), low 

 salinity, warm water on top of the more saline and 

 colder ocean water. It can extend as far as 800 km 

 offshore and as far south as northern California. 

 In 1976 the plume extended farther south and was 



closer to the coast than in 1975. In 1977 the central 

 core of the plume was much reduced reflecting the 

 extreme drought conditions of that year. High 

 salinities, >33L, along the coast were indicative 

 of upwelling. 



Chlorophyll concentrations at 3 m in 1975 and 

 1976 were greatest near the coast in regions of 

 upwelling and generally decreased with distance 

 from shore (Figures 3, 4). In 1975, relatively mod- 

 erate concentrations extended beyond the conti- 

 nental shelf in the region of the lowest salinity 

 plume water. This may be indicative of higher 

 productivity associated with nutrient rich plume 

 waters near the Columbia River mouth ( Anderson 

 1972). 



Of the 920 surface drifters released in July 1976, 

 24 or 2.6% were returned by 21 August 1976 (Fig- 

 ure 6). No additional returns were reported as of 

 February 1977. All but seven of the returns were 

 from the 2 km stations. All returns that had been 

 released off Oregon indicated southward trans- 

 port. Two returns from the 2 km station near the 

 Columbia River indicated some transport into the 

 river and one return showed northward move- 

 ment. Three drifters released 46 km off Grays 

 Harbor, Wash., were transported toward the coast 

 while three drifters from the 2 and 9 km stations 

 were transported moderate distances northward. 

 The low number of returns ( 2.6% ) probably reflects 

 the offshore component of surface drift which is 

 generally observed during the summer upwelling 

 season (Wyatt et al. 1972; Huyer 1974). 



Plankton volumes, which ranged from 30 to 

 4,726 ml/1,000 m^ in 1975 and 8 to 3,670 ml/1,000 

 m^ in 1976, were greatest on the continental shelf 

 with the highest volumes ( >2,000/l,000 m^) oc- 

 curring at stations 2, 9, and 28 km from shore 

 (Figures 3, 4). In these areas the plankton con- 

 sisted largely of phytoplankton and ctenophores 

 although at 9 and 28 km off Cape Perpetua, Oreg., 

 in 1975 it consisted mainly of copepods and 

 euphausiids. Nearshore low plankton volumes 

 <100 ml/1,000 m^ were observed at the 2 km sta- 

 tions off Grays Harbor in both 1975 and 1976 and 

 off the Columbia River in 1975. High plankton 

 volumes appeared to be mainly associated with 

 coastal upwelling with no obvious relationship to 

 the Columbia River plume. However, plume 

 waters are a near surface phenomenon while the 

 plankton was sampled from 150 m to the surface 

 possibly obscuring any relationship. 



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