FISHERY BULLETIN: VOL. 87, NO. 4. 1989 



Figure 1. — Map of the Lake Washington watershed showing the 

 locations of the release site on Lake Union (LkU) and the hatcheries 

 at the University of Washington (UW), Seward Park (SP), and 

 Issaquah Creek (Iss). 



Treatment of Juveniles 



In 1985 we initiated a study of patterns of 

 imprinting and homing in the Lake Washington 

 watershed. The basic experimental design was 

 to expose coho salmon to the odors of Seward 

 Park (SP) or Issaquah Creek (Iss) hatcheries and 

 release them from those hatcheries or from a site 

 2.2 km downstream from the UW hatchery (Fig. 

 1). (The SP hatchery had been used for produc- 

 tion of rainbow trout but not coho salmon prior 

 to this experiment. Water for the SP hatchery is 

 pumped from Lake Washington). Another gi'oup 

 was reared in UW water and released at the 

 downriver site. 



Between 18 and 25 November 1985, adult coho 

 salmon that had returned to the UW hatchery 

 were spawned and the fertilized eggs incubated 

 at the UW hatchery in dechlorinated city water. 

 This is not the water source normally used in the 

 hatchery; fish are normally incubated and reared 

 in water pumped from the ship canal draining 

 Lake Washington into Puget Sound (Fig. 1). The 

 eggs hatched in January and yolk absorption was 



completed in March. In late March the fry were 

 separated into three groups. Group 1, the con- 

 trol, was held at the UW hatchery and exposed 

 to ship canal (UW) water during the smolt 

 phase, from 20 May until 10-11 June, when the 

 fish were tagged with internal coded wire tags. 

 Fish in this study were judged to be smolts by 

 their downstream migratory behavior and 

 silvering. Only fish with silvery coloration and 

 lacking parr marks were given coded wire tags. 

 Group 1 fish were released into Lake Union, 2.2 

 km downstream from the UW hatchery, on 17 

 June. Groups 2 and 3 were transported to the SP 

 hatchery on 21 March and reared there. They 

 were tagged on 13 June (Group 2) and 14 June 

 (Group 3). Group 2 fish were released into Lake 

 Union on 1 July and Group 3 fish were released 

 from SP on 27 June. Table 1 summarizes infor- 

 mation on the treatments of the these groups. 



On 19 March 1986 coho salmon at the Iss 

 hatchery were marked by excision of the left or 

 right ventral fin (10,000 fish per treatment). 

 These salmon had emerged as fry in 1985 and 

 smolted after one year in freshwater (average 



770 



