26 
Fishery Bulletin 95 ( I ), 1997 
have similar feeding behaviors and if hatchery fish re- 
side in the estuary for a substantial period, then the 
effect of hatchery fish on the wild fish may be great. 
Anadromous, Inc. operated a salmon-rearing and 
release facility on the North Spit of Coos Bay, Or- 
egon in the 1980’s. From this facility millions of 
smolts are released into the bay annually, principally 
large subyearling spring-run (“spring”) chinook 
salmon, thus creating the potential for competition 
between these hatchery-produced spring chinook 
salmon and the native runs of fall chinook salmon in 
the Coos Bay drainage. 
During the late spring and summer of 1987 we 
undertook a sampling program in the lower half of 
Coos Bay to study the use of the estuary by different 
groups of juvenile chinook salmon. In 1987 two 
groups of juvenile chinook salmon were present in 
Coos Bay: fall chinook salmon from the Coos and 
Millacoma River drainages (both wild fish and fish 
released by the Salmon and Trout Enhancement Pro- 
gram | STEP]) and spring chinook salmon released 
from the saltwater rearing pens of the Anadromous, 
Inc. facility, North Spit of Coos Bay (Fig. 1). About 
400,000 STEP fall chinook salmon were released in 
tributaries of the Coos River between 30 April and 
28 June at average fork lengths (FL) of between 48 
and 94 mm, and over five million spring chinook 
salmon (123-156 mm FL) were released from the 
Anadromous, Inc. release facility on North Spit be- 
tween 19 June and 1 October. In an earlier paper 
(Fisher and Pearcy, 1990) we reported on the distri- 
butions and residence times of juvenile spring and 
fall chinook salmon in the bay. In this paper we de- 
scribe the food habits of these two groups, overlap in 
their diets, and the potential for competition for food 
between them. 
