292 
Inferannual variation in predation on 
first-year Sebastes spp. by three 
northern California predators 
Abstract —There is much interannual 
variation in numbers of first-year Sebas- 
tes that settle near shore off northern 
California, and when more abundant, 
they become prey of an increased vari- 
ety of predators. Among predators that 
concentrate on these abundances are 
the black rockfish ( Sebastes melanops); 
the blue rockfish ( Sebastes mystinus ); 
and the kelp greenling (Hexagrammos 
decagrammus). One might expect S. 
melanops to be involved in these attacks 
because it is known to be piscivorous, 
but S. mystinus and H. decagrammus 
ordinarily feed on invertebrates. The 
predation on Sebastes juveniles is con- 
centrated during a relatively brief 
period shortly after they have settled in 
nearshore habitats. Most of this preda- 
tion occurs during June and decreases 
sharply through July and August, and 
relatively little after that. We argue that 
the pattern of predation reflects removal 
of less adapted individuals during the 
period shortly after settlement. 
Manuscript accepted 3 November 2000. 
Fish. Bull. 99:292-302 (2001). 
Edmond S. Hobson 
Santa Cruz Laboratory 
Southwest Fisheries Science Center 
1 10 Shaffer Road 
Santa Cruz, California 95060 
E-mail address: ted.hobson@noaa gov 
James R. Chess 
P O Box 96 
Piercy, California 95587 
Daniel F. Howard 
Gulf of the Farallones National Marine Sanctuary 
Fort Mason, Bldg. 201 
San Francisco, California 94123 
First-year Sebastes spp. off California 
vary greatly in number from year to 
year (Stephens et al., 1984; Love, et al., 
1991), as do young-of-the-year of many 
marine fishes (Hjort, 1926; Cushing, 
1973; Ricker, 1954). It has been argued 
that this variability between years is 
set during the earliest stages of life his- 
tory, so that numbers present at settle- 
ment can be used to predict ultimate 
strength (or weakness) of year classes 
(Bailey and Spring, 1992; Myers and 
Cadigan, 1993; Ralston and Howard, 
1995). But such predictions may need 
to consider postsettlement mortality, 
which has been recognized as a den- 
sity-dependent force that reduces the 
interannual variation in year-class size 
evident at settlement (e.g. Sissenwine, 
1984). 
Early evidence that young-of-the- 
year (YOY) suffer density-dependent 
mortality after settlement came from 
studies of fishes caught by trawlers in 
temperate seas. Some of these studies 
identified predation as the main cause 
of this mortality (e.g. Lockwood, 1980), 
but most recognized predation as just 
one of several possibilities (Veer, 1986; 
Myers and Cadigan, 1993). More re- 
cently, investigators using scuba to ob- 
serve underwater have studied postset- 
tlement juvenile mortality in a variety 
of tropical and temperate species. Al- 
though some have concluded that this 
mortality is not density dependent (e.g. 
Victor, 1986; Sale and Ferrell, 1988), 
others have concluded not only that 
it is density dependent but also that 
it acts to regulate populations (Sano, 
1997) and is a result of predation (Hix- 
on and Carr, 1997; Steele, 1997). That 
predation is the major cause of mor- 
tality during and after settlement now 
seems generally accepted, and attempts 
are being made to identify the mecha- 
nisms involved under controlled condi- 
tions in laboratories (e.g. Bertram and 
Leggett, 1994; Witting and Able, 1995). 
Although there have been many 
studies of the relations between pre- 
dation and recruitment, all have been 
of short duration and thus limited as 
examinations of interannual varia- 
tions. An opportunity to draw on 11 
years of data for such a study developed 
from our work with marine commu- 
nities off northern California. There, 
an investigation of trophic relations in 
fishes overlapped annual assessments 
of YOY Sebastes spp., and during this 
period (1977 to 1987) certain preda- 
