GEOGRAPHIC DISTRIBUTION 



The quantity of macrozooplankton and snnall 

 nekton that were taken within the upper 30 m. 

 of the water column varied substantially in 

 the study area both seasonally and geographi- 

 cally. The relative abundance of macrozoo- 

 plankton within the study area and possible 

 reasons for variations in their distribution 

 are described in the subsequent sections on 

 biomass and major taxonomic groups, 



BIOMASS 



The biomass in the surface layer, estimated 

 from the shallow oblique tows, was consider- 

 ably greater in the spring than in the fall. In 

 both seasons abundance varied widely seaward 

 from the coast and from north to south along 

 the coast. Along lines perpendicular to the 

 coast, the biomass was minimal nearshore, 

 reached a nnaximum at or near the outer edge 

 of the continental shelf (183-m. depth contour), 

 and decreased again farther offshore (figs. 4 

 and 5), The only exceptions to this general 

 distribution were in the fall along line V, 

 where all stations were located at the 183-m. 

 depth contour near the Juan de Fuca Canyon, 

 and along line VIII, where the biomass reached 

 a maximum over the 119-rn. depth contour, 

 decreased to a minimum at 183 m., and then 

 increased seaward. Neither the distributions 

 of surface temperature and salinity, nor cur- 

 rents provide an immediate explanation for 

 this general pattern. Similar distributions have 

 been reported by Mednikov (1958) for the 

 Kurile -Kamchatka region of the northwestern 

 Pacific Ocean and by St. John (1958) for the 

 Cape Hatteras region of the northwestern 

 Atlantic Ocean. 



The greatest biomass was found in the south- 

 ern part of the region. The boundary between 

 relatively high and low biomass was between 

 lines VI and VIll in spring, and shifted about 

 111 km. to the south, between lines IV and VI, 

 in fall. 



The distribution of biomass was similar to 

 the general features (Ingraham, 1967) of the 

 surface circulation (surface to 200 m.). Low 

 biomass coincided with a distinct onshore 

 movement of offshore water near the middle 

 of Vancouver Island (figs. 6 and 7). Biomass 

 was high where the circulation was charac- 

 terized by eddies or reduced flows off the 

 coasts of Washington and southern Vancouver 

 Island. There was no evidence of continuous 

 northward flow of near-shore water along 

 Vancouver Islandnorthof lat. 48 N. (Ingraham, 

 1967), 



TAXONOMIC GROUPS 



The seasonal and geographic changes in the 

 distribution of biomass were examined relative 

 to the distribution of the most important tax- 



onomic groups. Euphausiids were of primary 

 concern since they contributed the largest 

 numbers to the biomass. 



Euphausiids 



Eight species of euphausiids were identified: 

 Euphausia pacifica , Thysanoessa spinifera , 

 T. longipes , _T. raschii, Tessarabrachion ocu - 

 Tatus , Nematoscelis difficilis , Nematobrachion 

 flexipes, and Stylocheiron maximum . These 

 species constituted 90 percent, by number, of 

 the total catch (figs. 8 and 9). E. pacifica 

 and T. spinifera were the most abundant 

 euphausiid species, contributing 76 and 14 

 percent, by number, of the organisms col- 

 lected (figs. 10-1 3). The differences in biomass 

 from north to south (figs. 4 and 5) were evi- 

 dently related to the distribution of E. pacifica 

 (figs. 10 and 11). Ninety-five percent of the E. 

 pacifica , by number, were collected from the 

 area of high biomass. T, spinifera was usually 

 more prominent, relative to the total catch, 

 where the abundance of E. pacifica was low. 



The record of seasonal changes in abundance 

 and composition of euphausiids (tables 1 and 2) 

 indicate larger numbers of E. pacifica in 

 spring than in fall by a ratio of about 2 to 1. 

 Numbers of T. spinifera increased slightly 

 but their percentage of the total catch in- 

 creased markedly during the same period 

 (table 1). The substantial decrease in abun- 

 dance of E. pacifica accounted for most of 

 the reduction in biomass from spring to fall. 



The seasonal decrease in bionnass was also 

 influenced by the presence of larger speci- 

 mens of E. pacifica and T, spinifera in spring 

 than fall. Brinton ( 1962b) stated that E. pacifica 

 may live as long as 2 years and spawn at least 

 twice and that two size-classes spawn off 

 central California in a period from April to 

 June: (1) males 13 to 14mm. andfemales 13 to 

 1 6 mm., and (2) males 17 to 19 mm. and females 

 18 to 24 mm. If these size-classes represent 

 age -groups I and II, E. pacifica collected in 

 spring (fig. 14) were primarily of age-group II 

 while most of the catch in fall was of age -group 

 I, with only a remnant of age -group II. The 

 similarity in seasonal shift in the modal size 

 of T. spinifera (fig. 15) and E. pacifica (fig. 14) 

 suggests similar seasonal age-class com- 

 position of the two species. Because the mesh 

 in the 0.9-m. midwater trawl did not retain 

 euphausiids smaller than 10 mm., the O age 

 group could not be evaluated. 



Seasonal abundance and dominant species of 

 euphausiids were grossly different offshore 

 from the 914-m. contour, south of the Strait of 

 Juan de Fuca, E. pacifica was dominant in 

 spring, but T. spinifera dominated or shared 

 dominance with _E. pacifica in the fall (figs. 

 10-13). Numbers of E. pacifica were relatively 



