Sakuma and Larson: Distribution of Cithanchthys sordidus and C stigmaeus 



517 



and summer upwelling season, when the associated 

 offshore advection of surface waters can adversely 

 affect marine organisms with pelagic life stages 

 (Parrish et al., 1981; Bailey and Francis, 1985; 

 Roughgarden et al., 1988), the effect of upwelling on 

 pelagic-stage sanddabs was also investigated. 



Methods 



Data collection 



Pelagic Pacific and speckled sanddabs were collected 

 in conjunction with the annual juvenile rockfish sur- 

 veys conducted by NMFS Tiburon Laboratory scien- 

 tists aboard the National Oceanic and Atmospheric 

 Administration (NOAA) research vessel David Starr 

 Jordan. Standard stations extending from Point 

 Reyes to Cypress Point (Fig. 1) were sampled with a 

 26 x 26 m modified Stauffer midwater trawl with a 

 codend liner of 9.5-mm stretched mesh (Wyllie 

 Echeverria et al., 1990). Standard trawling depth was 

 30 m except at shallow-water stations where trawls 

 were conducted at 10 m. At certain standard stations 

 a series of three depth-stratified trawls 

 (depths=10 m, 30 m, and 110 m) were 

 conducted to determine bathymetric 

 distributional patterns (Fig. 1). As time 

 permitted, additional trawls, both stan- 

 dard depth and depth-stratified, were 

 conducted at nonstandard stations. All 

 trawls were 15 minutes in duration and 

 were completed between the hours of 

 2100 and 0600. Stations were sampled 

 during a 10-day "sweep" of the survey 

 area. Three replicate sweeps were com- 

 pleted from mid-May to mid-June of 

 each year; in some years one additional 

 sweep was completed in early April. 



CTD (conductivity, temperature, and 

 depth) casts were made at each trawl sta- 

 tion to obtain temperature and salinity 

 information at depth. Additional CTD 

 casts were made during the day along 

 tracklines interspersed between the trawl 

 station lines (Schwing et al., 1990). Sur- 

 face temperature and salinity were also 

 recorded continuously by a thermo- 

 salinometer aboard the vessel. CTD and 

 thermosalinometer data were used to 

 determine the relation between upwelling 

 and the spatial distributions of the dif- 

 ferent pelagic stages of both sanddabs. 



Although the annual juvenile rockfish 

 surveys began in 1983, sanddabs were 



not identified to species before 1987. Therefore, data 

 were analyzed only from the 1987 through 1991 sur- 

 veys. In addition to the May-June surveys in each 

 year, sampling was carried out in April of 1987, 1988, 

 and 1990. Sanddabs were identified and enumer- 

 ated on board the research vessel at sea. In 1990 

 and 1991, samples were frozen after identification 

 and enumeration and brought back to the labora- 

 tory where standard length (SL) and stage of meta- 

 morphosis were additionally recorded for each speci- 

 men collected. Five metamorphic stages, based on 

 the staging system used by Pearcy et al. ( 1977), were 

 defined as follows: 



Stage 1 = left and right eyes positioned sym- 

 metrically on both sides of head; 



Stage 2 = right eye has begun to move dorsally; 



Stage 3 = upper edge of right eye within close 

 proximity to the top of the right side 

 of the head; 



Stage 4 = right eye has begun to cross over to 

 the left side of the head; 



Stage 5 = right eye completely crossed over to 

 left side of the head. 



38 



I 



37 



124 



Standard Depth 

 i-Strati fied 



Longitude (°W) 



Figure 1 



Location of standard trawling stations for Pacific and speckled sanddabs, 

 Citharichthys sordidus and C. stigmaeus, collected during 1987-91. 



