ZIMUSHKO, V. v., AND S. A. LENSKAYA. 



1970. Feeding of the gray whale {Eschrichtius gibbosus 

 Erx.) at foraging grounds. Ekologiya Akad. Nauk SSSR 

 l(3);26-35. (Engl, transl., Consultants Bureau, Plenum 

 Publ. Corp., 1971. Ekologiya 1(3):205-212.) 



g. m. wellington 

 Shane Anderson 



Marine Science Institute and 

 Department of Biological Sciences 

 University of California 

 Santa Barbara. CA 93106 



HOMING OF MORPHOLINE-IMPRINTED 

 BROWN TROUT, SALAIO TRUTTA 



Homing for the purpose of spawning is well 

 documented for lake-run brown trout, Salmo 

 trutta (Stuart 1957; Niemuth 1967), but the 

 mechanism by which they find their natal trib- 

 utary is not understood. Our own recent studies on 

 related species — coho salmon, Oncorhynchus 

 kisutch, and rainbow trout, Salmo gairdneri — 

 suggest that they become imprinted to the odor of 

 their natal tributary when they begin their 

 downstream migration and later use this informa- 

 tion for homing (Hasler and Wisby 1951; Scholz et 

 al. 1973, 1975, 1976; Cooper and Scholz 1976; 

 Cooper et al. 1976). In these experiments 18-mo-old 

 hatchery-raised fish were exposed to a synthetic 

 chemical, morpholine, for 40 days and then 

 stocked in Lake Michigan. During the spawning 

 migration the fish homed to a simulated home 

 stream which was scented with morpholine. Since 

 the life cycle of migratory brown trout is similar to 

 that of coho salmon and rainbow trout, we con- 

 ducted the present study to determine if odor im- 

 printing could be extended to brown trout. The 

 methods used in this study were similar to proce- 

 dures reported by Cooper and Scholz ( 1976) since 

 both experiments were conducted concurrently. 



Methods 



In 1972, hatchery-raised, 18-mo-old brown trout 

 fingerlings were transported to South Milwaukee, 

 Wis. (Figure 1). The fish were marked with fin 

 clips, divided into three groups of 300 each, and 

 held in separate tanks at the South Milwaukee 

 Water Filtration Plant. Lake Michigan water was 

 supplied to all three tanks from an intake crib 



Figure l. — Research area, South Milwaukee, Wis. (after 

 Cooper et al. 1976). The solid triangle indicates the location of 

 the hatchery where the fish were reared. Inset (A) shows detail 

 of: 1) the water intake for the tanks at the South Milwaukee 

 Water Filtration Plant, 2) the Oak Creek stocking site, and 3) the 

 Milwaukee Harbor stocking site. 



located 1.5 km offshore. Morpholine (C4HgN0) 

 was metered into one tank for 34 days in May and 

 June. This period was selected because it is the 

 time when brown trout would normally begin 

 their downstream migration (Stuart 1957; 

 Niemuth 1967). A concentration of 5 x 10"'^ mg/1 

 morpholine was maintained in the tank through- 

 out the exposure period. 



The morpholine-exposed group and one unex- 

 posed control group were then stocked in Lake 

 Michigan at Milwaukee Harbor, 13 km north of 

 Oak Creek (Figure 1). The second control group 

 was released at the mouth of Oak Creek. During 

 the spawning migration in fall 1972 and 1973, 

 morpholine was metered into Oak Creek at the 

 same concentration used for imprinting. The 

 stream was surveyed for marked fish by gillnet- 

 ting, electrofishing, and creel-census methods 

 (summarized in Table 1). Fish were unable to 

 move past a dam situated 1.5 km from the mouth. 

 Surveys began before the spawning migration 

 started and continued until no fish were left in the 

 river. The results are recorded in Table 2. 



293 



