Hobson et al.: Predation on first-year Sebastes spp. 
295 
120 r- 
100 - 
80 - 
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 
Month 
| S. melanops Q S. mystinus Q H. decagrammus 
Figure 2 
Monthly sampling of predators used in study of predation on YOY Sebastes spp. near shore off 
Mendocino. 
erect from gut contents often had been damaged beyond 
recognition as species. Owing to their distinctive morphol- 
ogy, 8. jordani juveniles were identifiable even when ex- 
tensively damaged, but they are excluded from our report 
because they were in the study area for reasons other than 
those accounting for the presence of the other Sebastes 
species (Hobson and Howard, 1989). 
Results 
YOY Sebastes 
The number of YOY Sebastes varied greatly from year to 
year (Fig. 3). Their initial appearance near shore tended 
to be earlier in the season during years of greater abun- 
dance; thus the earliest first sighting was during April of 
the year that YOY were most numerous (1987), and the 
latest first sighting was during June of the year that YOY 
were least numerous ( 1983). Upon arrival, these fish were 
<4.0 cm SL, often numerous, and still showed the silvery 
hues characteristic of their pelagic stage. Our record of 
first arrivals was limited. Ordinarily, visits to the Men- 
docino study sites at this time of year were separated by at 
least a week, sometimes up to a month (during extended 
periods of inclement weather), and our efforts were con- 
centrated close to the seabed. Observations in the surface 
canopy of bull kelp came mostly during brief surveys fol- 
lowing more extensive observations at greater depths. 
Once alerted to their presence, however, we intensified our 
search (even during the same day) and often found a few 
individuals or small groups among the rocks below. Most 
of these were 4.0 to 4.5 cm SL and showed darker hues 
more appropriate to reef settings. 
Numbers of juveniles increased rapidly over the weeks 
that followed (except during years of low abundance, e.g. 
1983) to reach maximum levels between mid June and 
early July. Throughout this time, and over subsequent 
months, the juveniles aggregated at varying distances 
from the seabed or kelp — some in mixed species aggrega- 
tions. Their distance from these structures was influenced 
by the water’s transparency, however, and this affected 
our ability to measure abundance. When visibility was re- 
duced, as during phytoplankton blooms of late spring and 
early summer, the juveniles stayed closer to shelter — ma- 
ny often out of sight among the rocks. It was often dif- 
ficult to assess their abundance under these conditions, 
even when visibility was sufficient to perform the counts. 
In contrast, when visibility was extended, as when oce- 
anic waters flowed shoreward with relaxation of upwell- 
ing during the fall, the juveniles ranged farther from shel- 
ter and were readily counted. Thus, although the greatest 
numbers were recorded during a period of exceptionally 
clear water during July 1987, counts were at times higher 
during September or October than during June or July 
(Table 1), even though we assumed that there were fewer 
individuals present. This circumstance did not affect in- 
terannual comparisons because the pattern was basically 
the same each year, but it effectively precluded compari- 
sons between months or seasons. 
Sizes of YOY available to predators during the five 
months after settlement can be approximated from data of 
the YOY S. mystinus sampled from June through October 
for study of gut contents. The 82 from June were 3.7 to 5.8 
