FISHERY BULLETIN: VOL. 75, NO. 1 



The species richness value in 1972 (Table 7) was 

 lower than in 1971, indicating that fewer species 

 were present. 



Offshore Assemblage 



During the sampling period, 148 samples were 

 taken (45 at night, 14 at dusk or dawn, 89 in 

 daylight) in the offshore assemblage. The 141 

 positive samples yielded 7,381 larvae or a 

 standardized total [2 (number of larvae under 10 

 m 2 sea surface in each sample)] of 10,868. 



Species Composition and Dominance 



Fifty-two taxa in 21 families were taken in the 

 offshore samples (Table 2). Of these, 43 were 

 identified to species, 6 to genus, and 3 to family. 

 The species richness value, based on Margalef's 

 (1958) formula for diversity, was 5.73 for the 

 offshore assemblage, which was lower than the 

 value of 7.43 for the coastal assemblage. 



The top 10 dominant (BI) taxa (see footnote 15) 

 in the offshore assemblage accounted for 94.3% of 

 the total number of larvae in this assemblage 

 (Table 8). Nine of these 10 taxa also were among 

 the 10 most abundant although in different order, 

 with Microstomas pacificus (total standardized 

 abundance 81.74) replacing Hemilepidotus 

 spinosus. 



The two major dominants were Sebastes spp. 

 and Stenobrachius leucopsarus, which together 

 accounted for 70% of all larvae taken offshore. 

 Tarletonbeania crenularis and Lyopsetta exilis 

 were also dominant in the offshore assemblage in 

 terms of overall abundance and frequency of 

 occurrence. Fifth ranked Engraulis mordax oc- 

 curred in concentrations (standardized numbers 

 per positive tow) equivalent to Sebastes spp. and 

 Stenobrachius leucopsarus (Table 8) although it 



was less frequently taken. The top six dominant 

 taxa composed 91% of the total larval abundance 

 compared with 13 taxa contributing that per- 

 centage in the coastal area. 



Seasonality 



In 1971, 94% of all larvae were taken between 

 February and July, as in the coastal area, and 83% 

 were taken during the 3-mo period from May to 

 July (Figure 6). The winter (February-March) 

 peak of abundance noted in the coastal area was 

 absent offshore. Larval abundance decreased in 

 August and remained low for the rest of the year. 

 The minor increase in numbers in October was 

 solely due to small Citharichthys (probably 

 sordidus) larvae 37 to 46 km offshore. Since only 5 

 mo of data were available for the offshore as- 

 semblage in 1972, seasonal trends could not be 

 assessed. 



Dominant taxa (BI>1) within the May-July 

 peak abundance period in 1971 were essentially 

 the same as those (Table 8) for the entire lVfe-yr 

 sampling period. These wereS. leucopsarus (BI = 

 3.10), Sebastes spp. (BI = 3.08), L. exilis (BI = 

 1.96), andT. crenularis (BI = 1.47). Together they 

 made up 88% of the total larvae taken in that 

 spring-summer period. 



As in the coastal zone, some taxa had restricted 

 spawning periods and their larvae were present in 

 the plankton for a relatively short time, e.g., E. 

 mordax and L. exilis (Table 9). Both species 

 showed distinct growth trends. Hemilepidotus 

 spinosus was also present during a short period 

 although the larvae in the offshore zone were 

 usually larger than those in the coastal area (Ta- 

 ble 6). Glyptocephalus zachirus was taken as small 

 larvae only in April to June indicating a rather 

 restricted spawning period, but large larvae were 

 present through September. The larvae grow 



Table 8. 



-Offshore dominants based on all larvae collected 37 to 111 km offshore in 1971 and 1972. 

 [BI = Biological Index modified from Fager (1957)]. 



1 The sum of the standardized numbers (number under 10 m 2 sea surface) of larvae from each sample 



138 



