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Fishery Bulletin 99(2) 
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Fish 
lH S. melanops n = 178, 20.0 to 47.5, x = 31.9 (SE 0.39) cm SL 
□ S. mystinus n = 518, 15.1 to 39.2, x = 26.5 (SE 0.23) cm SL 
| | H. decagrammus n = 333, 22.8 to 37.5, x = 29.9 (SE 0.1 5) cm SL 
Foods 
Figure 4 
Foods consumed by the three predator species ( Sebastes melanops, S. mystinus, and S. decagrammus) 1977-87 (n = 
individuals with identifiable food in gut). 
tion in YOY abundance (Fig. 6). Evidence of predation was 
strongest during years when YOY were most numerous in 
the habitat (1977, 1979, 1985, and 1987), and there was 
virtually no evidence of predation during the years when 
YOY were least numerous in the habitat (1983, 1984, and 
1986). Furthermore, it was only during the years that YOY 
were more numerous that we found them among the prey 
of S. mystinus — 1985 being the year we found the most. 
We saw no indication that distributions of adult S. mela- 
nops, S. mystinus, or H. decagrammus were influenced by 
the presence of YOY Sebastes. Even when YOY were most 
numerous, attackers seemed limited to residents of the im- 
mediate area. This finding should have been expected be- 
cause each year’s relative abundance was in effect coast 
wide. 
Discussion 
Much predation is opportunistic; thus predators often are 
drawn to concentrations of organisms that would not oth- 
erwise be their prey. Consider, for example, that when 
the squid Loligo opcdescens deposits great masses of eggs 
on sediment off central California, various fishes, marine 
mammals, and birds converge from surrounding habitats 
to forage on what is for them an unusual food (Morejohn 
et ah, 1978). Similarly, when the herring Clupea pallasi 
deposits eggs in great abundance on the seabed in San 
Francisco Bay, these become food for the brown rockfish, 
Sebastes auriculatus, which otherwise feeds mainly on 
decapod Crustacea and fishes (Ryan, 1986). Another exam- 
ple is an incident during 1962 in the Gulf of California, 
where a 1-m moray eel (Muraenidae) was observed thrash- 
ing at the water’s surface in a vigorous attempt to feed 
from a dense swarm of larval fishes, each no more than 
1 cm long (Hobson, 1968). Certainly this predator was 
behaving in a manner that was contrary to its usual mode 
of feeding. So perhaps it should have been expected that 
YOY Sebastes in exceptionally large numbers would draw 
attacks from predators not otherwise prone to show them 
interest. 
But the level of predation on YOY Sebastes off Mendoci- 
no involved more than relative abundance of prey. The 
attacks were concentrated during June, declined sharply 
through July and August, then remained at low levels dur- 
ing the rest of the year. This pattern did not follow the 
number of YOY present. These YOY gained abundance 
through most of June to attain maximum numbers late 
that month or during July, and then remained abundant 
after predation had subsided to low levels at the end of 
August. Often our counts of YOY were higher during Sep- 
tember or October than during June or July, and although 
to a considerable extent this higher court was related to 
increased visibility in clear water, it nevertheless argues 
