300 
Fishery Bulletin 99(2) 
100 
80 
60 
40 
20 
n 6 6 3 
freq. 10030.7 
8 36 4 
00 00 00 
4 0 30 
0 0 0.0 0 0 
■ S. melanops 
□ S. mystinus 
□ H. decagrammus 
ft 
1 34 9 11 38 23 
000 00.0 0 7 040.8 
115 10 8 18 4 
000001 090201 
<13 
O 
c 
03 
T3 
C 
13 
JD 
03 
03 
> 
CD 
cc 
1977 1978 1979 
1980 
1981 
1982 
1983 1984 1985 
1986 1987 
Figure 6 
Inter-annual variation in occurrence of YOY Sebastes spp. in predator diets in relation to abundance of YOY in the habitats, June 
through August. Measures of YOY abundance in habitat are based on information presented in Figure 3. n = Individuals examined 
that had identifiable food in gut. 
ural selection. That predators studied in our study had es- 
sentially resumed their regular diets by the end of sum- 
mer indicated to us that YOY vulnerable to their attacks 
had by that time become scarce. 
There are other predators that follow similar temporal 
patterns in feeding on YOY Sebastes off northern Cali- 
fornia. Pacific hake, Merluccius productus, for example, 
have been reported attacking YOY S. jordani so close to 
shore that many are driven onto the beach — but only dur- 
ing June and early July of years when these prey were 
particularly abundant (Hobson and Howard, 1989). Simi- 
larly, king salmon. Oncorhynchus tshawytscha, regularly 
switch to YOY Sebastes from other prey during late May 
and June, then switch back before the end of July (Adams 
et al. 2 ). Other examples include Sebastes spp. studied by 
Hallacher and Roberts (1985) in kelp forests off Carmel, 
CA. In a chronicle that followed activities of these fishes 
over one year (with limited data from July and August of 
two other years), it was determined that S. atrovirens, S. 
carnatus, S. chrysomelas, and S. melanops fed primarily on 
YOY Sebastes during the “upwelling season” (April to Au- 
gust), but all except S. carnatus switched to invertebrates 
during the “non-upwelling season” (September to March). 
Hallacher and Roberts attributed this pattern to seasonal 
differences in YOY abundance. 
2 Adams, P. B., W. M. Samiere, and C. J. Ryan. 1986. Unpubl. 
manuscript. Prey selection and diet of marine chinook salmon, 
Oncorhynchus tshawytscha, 17 p. Natl. Mar. Fish. Ser., NOAA, 
Tiburon CA 94920. 
The decline in attacks during the summer does not lead 
to essentially an end to predation on YOY, however. At 
least one resident piscivore, the ling cod, Ophiodon elon- 
gatus, remains a regular threat (Miller and Geibel, 1973). 
In fact, Adams and Howard (1996), studying in part the 
same series of assessments used in our study, considered 
predation the major cause of natural mortality in YOY S. 
mystinus from late summer through early spring. Their 
estimates were higher during years that YOY were more 
abundant, indicating persistent density-dependent preda- 
tion, but were much lower than most other published rates 
of natural mortality for juvenile fishes, probably because 
they missed the intense predation of late spring and early 
summer. And although Hallacher and Roberts (1985) re- 
ported that most Sebastes spp. off Carmel switched to pre- 
dation on invertebrates from September to March, they 
noted that S. carnatus continued to prey on YOY Sebastes 
during that period. 
There is evidence that density-related predation con- 
tinues to dampen interannual variation in year-class size 
through entry into the fishery, which for most Sebastes 
spp. is at about age 3-4 years (Ralston and Howard, 1995). 
Arguments for the importance of postsettlement mortal- 
ity in establishing ultimate year-class size have empha- 
sized the extended effect of this mortality (e.g. Sissenwine, 
1984) but do not recognize the extent that mortality from 
predation is concentrated during a relatively brief period 
immediately after settlement. We suggest that manage- 
ment needs would be most effectively met by measuring 
year-class size soon after this period of intense predation. 
