298 



Fishery Bulletin 90(2). 1992 



Yearl 



Eggs 

 Stage 1 



Year 2 



stage 1 

 Stage 2 

 Stage 3 



Years 



stage 2 

 Stage 3 

 Stage 4 ■ 

 Stage 5 



were collected in months with few 

 samples (Table 1). Planktonic Stage-2 

 larvae were caught in nets fished 

 deeper than either Stage- 1 or plank- 

 tonic Stage-3 larvae. The rarity of 

 larger planktonic and early metamor- 

 phic stages may reflect movement 

 deeper into the mesopelagic zone and 

 lower relative sampling effort in 

 deeper water. Late in Stage 2 (devel- 

 opmental scores 7 and 8) and in Stage 

 3 this trend appears to be reversed, as 

 these stages were caught more fre- 

 quently. If metamorphosis is a time of 

 increased vulnerability, deeper water 

 may provide a predation refuge. Alter- 

 natively, the behavior may place meta- 

 morphosing specimens in a water mass 

 that facilitates late larval transport. 

 Settlement seems remarkably grad- 

 ual, coincides with the downwelling 

 season, ends with the spring transition 

 in the oceanographic regime (Huyer et 

 al. 1979), and occurs over a very broad 

 "landing" zone (Fig. 14). Stage-3 lar- 

 vae settling outside the nursery zone 

 may experience differential mortality, 

 or their broad depth distribution may 

 reflect a process of testing the habitat 

 in search of the preferred nurseryground. Capture of 

 Stage-3 and -4 specimens in both nighttime midwater 

 and daytime bottom trawls suggests a diel vertical 

 search pattern. 



Egg and larval drift 



A proposed recruitment mechanism for Dover sole 

 (Hayman and Tyler 1980, Parrish et al. 1981) focuses 

 on inshore-offshore transport. The long planktonic 

 period of Dover sole implies that alongshore transport 

 also may be important. Our data allow some first-order 

 generalizations about the distribution of early-life- 

 history stages and may give further insight into the 

 recruitment mechanism. 



Urena (1989) found that greatest abundances of 

 Dover sole eggs were in neuston samples collected 

 beyond the 200m isobath. In April and May in the 

 upper 50 m, the current flows southward at about 

 10-15cm/second at the 200m isobath (Huyer 1977, 

 fig. 9; Huyer et al. 1979) and is even weaker further 

 offshore (Huyer and Smith 1978). At 10 cm/second, 

 eggs could be transported 260 km southward in 30 

 days, assuming that their transport was not inter- 

 rupted by offshore jets or gyres. Onshore-offshore 

 transport of eggs should be variable. During upwell- 



Month 



Figure 15 



Hypothetical time-line of development for a cohort of Dover sole Microstomus 

 pacifiaxs, off Oregon. Solid lines represent presumed peak times for the different 

 stages, and dotted lines represent the ranges. 



ing, the upper 20 m may experience an average offshore 

 velocity of 2-5 cm/second (Huyer 1983), and the upper 

 5 m may experience an average offshore velocity of 

 15 cm/second (Peterson et al. 1979). The short duration 

 of the egg stage, restricted area of high offshore 

 velocity, and the return inshore of water masses dur- 

 ing relaxation after upwelling (Peterson et al. 1979) 

 suggest that average offshore transport of eggs should 

 be slow, but nontrivial. Deepwater spawning may 

 help reduce both alongshore and onshore-offshore 

 transport. 



Stage-1 larvae also are found beyond the 200 m 

 isobath (Pearcy et al. 1977a) and, like eggs, would be 

 vulnerable to the southward flow of the California Cur- 

 rent. In fact, the large surface area of the body of 

 Dover sole larvae might facilitate such transport. 

 Although there are important seasonal changes in 

 direction (Huyer et al. 1979), on an annual basis the 

 average surface current around 100 km offshore is 

 ~0.5-1.0cm/second to the south (Hickey 1979, fig. 8b). 

 If Stage 1 lasts an average of 15 months, and assum- 

 ing a mean flow of 0.75 cm/second, these larvae would 

 travel an additional 295km southward. 



We suggest that early Stage-2 larvae move into 

 deeper water. The California Undercurrent is a north- 

 ward-flowing countercurrent located below 200 m and 



