Hobson et al.: Predation on first-year Sebastes spp. 
299 
70 
60 - 
50 
Sebastes YOY 
a) 
T3 
40 
<D 
cn 
aj 
c 
(D 
O 
a> 
CL 
30 
20 
10 
melanops mystinus decagrammus 
n = 141 n = 232 n = 191 
June-August 
B 
Other fish 
melanops mystinus decagrammus 
n = 37 n = 286 n=142 
September-May 
Figure 5 
Fish in diet of the three predators ( Sebastes melanops, S. mystinus , and S. decagrammus ) June through August com- 
pared with September through May. YOY Sebastes spp. are distinguished from other fish. « individuals with identifi- 
able food in gut. 
against attributing the precipitous decline in predation 
through late August simply to shortages of prey. 
It has been widely reported that mortality among YOY 
of a variety of fishes is greatest during and immediately 
after settlement (e.g. Doherty and Sale, 1985; Victor, 1986; 
Shulman and Ogden, 1987), but there has been virtually 
no attempt to explain this finding, other than to implicate 
predation. We propose that the intense predation of early 
summer, and its subsequent sharp decline, mirrored a pat- 
tern of vulnerability among the YOY. Abilities critical for 
survival are quickness in responding to attacks, speed in 
attaining shelter, and the ability to use shelter that is 
available. And increasingly important with time is the abil- 
ity to acclimate to novel situations — the capacity to learn. 
These abilities are based on inherent characteristics that 
can be expected to vary widely among individuals, with the 
more deficient being more vulnerable to predators. It fol- 
lows that individuals most deficient are likely to be among 
those consumed during or shortly after settlement, where- 
as individuals progressively less deficient would be con- 
sumed in diminishing numbers over the following months. 
Certainly other factors contributed to the decline in pre- 
dation during the summer. That YOY decreased in number 
and increased in size must have influenced the intensity 
of predation. There is evidence that by summer’s end most 
YOY had grown too large for predation by S. mystinus and 
H. decagrammus. The largest YOY Sebastes among the gut 
contents of either species were 5.5 cm SL (Table 2), and by 
September most in the environment were larger than this 
(based on growth evident in the representative S. mysti- 
nus sampled for study of food habits). 
Other considerations, however, argue against the impor- 
tance of prey-size in shaping the observed pattern of pre- 
dation. Sebastes melanops, which is morphologically better 
suited than either S. mystinus or H. decagrammus to prey 
on fishes (Fig. 1), was able to feed on YOY Sebastes of up 
to at least 8.0 cm SL (Table 2), yet ate very few of them af- 
ter August. Also, the great variation in size among preda- 
tors, as well as in growth among YOY would be expected to 
dampen the effects of prey-size on population-level feeding 
intensity. Another consideration is the continued presence 
of YOY as small as 4.0 cm SL (Table 2) during the late- 
summer switch to other prey. 
Although probably a combination of factors contributed 
to the decline in predation during the summer, we contin- 
ue to consider that the concentrated attacks immediately 
after settlement are mostly likely elicited by the presence 
of inherently less-adaptive individuals. This is classic nat- 
