Table l.— Summary of efFort spent in monitoring Oak Creek 

 during the spawning migrations of brown trout in fall 1972 and 

 1973. Creel-census surveys were conducted three to five times 

 each day and electrofishing surveys were made once or twice 

 each week. A total of 51 marked brown trout were caught by 

 anglers; 17, by electrofishing; and 2, in gill nets. 



Fall 



Creel census 



Electrofishing 



Gill net 



1972 

 1973 



274 



451 



Number of trips 

 11 

 24 



62 

 54 



Table 2. — Recoveries of brown trout at Oak Creek in fall 1972 

 and 1973 from those released in spring 1972. Morpholine- 

 exposed and control fish were released 13 km north of Oak Creek 

 and a second control group was released at the mouth of Oak 

 Creek. Fin clip: RP, right pectoral; LP, left pectoral; LM, left 

 maxillary. 



Results 



A total of 53 morpholine fish (17.7% of the total 

 number originally stocked) were captured as com- 

 pared with 3 control trout (1.0%) released at Mil- 

 waukee Harbor and 14 control trout (4.7%) re- 

 leased at Oak Creek. Thus, the data show that 

 morpholine-exposed brown trout returned to the 

 scented stream in larger numbers than either con- 

 trol group. Both control and morpholine fish ex- 

 perienced uniform stocking procedures after the 

 initial treatment. If the selection of the morpho- 

 line-scented stream were attributed to a cue 

 learned after the treatment, we would have ex- 

 pected to capture as many control fish as 

 morpholine-treated fish in the scented stream. 

 The fact that this was not the case implies that the 

 cue was morpholine. Therefore we conclude that 

 morpholine-exposed brown trout used morpholine 

 as a cue for homing. To locate the scented stream 

 morpholine fish were able to search a distance of at 

 least 13 km. This experiment should be repeated 

 because of the low numbers offish stocked but the 

 results are of interest because of the high percent- 

 age of morpholine-exposed fish captured in the 

 scented stream. 



Discussion 



Scotland. In one case brown trout were marked in 

 one branch of a forked stream which flowed into 

 the reservoir. After the fish had migrated to the 

 reservoir, all of the water from the home fork was 

 diverted into a new channel. The original channel 

 was also maintained with water from the second 

 fork. During the spawning migration, adult trout 

 homed to the new channel in preference to the 

 channel by which they had entered the reservoir. 



In the second instance Stuart reported that, 

 when a different stream broke its banks, the 

 stream bed below the break dried up and the en- 

 tire flow of water was diverted into a marsh 

 through which it percolated into the reservoir. 

 During the spawning migration, brown trout con- 

 gregated off the marsh where the percolating 

 water entered the reservoir and not off the dry 

 stream mouth. 



Both of Stuart's observations clearly indicate 

 that the fish homed to water originating from the 

 home tributary, rather than to a specific home 

 location and are, thus, consistent with our conclu- 

 sion that it is a characteristic of the home water, 

 specifically odor, which provides brown trout with 

 homing cues. 



Acknowledgments 



We thank Sy Drezweicki, Rod Smith, Terry 

 Chapp, and Peter Johnsen for their help in the 

 field. We acknowledge Dale Madison for advice in 

 all aspects of this study; and Ron Poff, Russ Daly, 

 Paul Schultz, and Jim Holzer of the Wisconsin 

 Department of Natural Resources for technical 

 and logistical support. The assistance of Ed Muel- 

 ler and his advanced biology high-school students 

 at South Milwaukee High School, and John 

 Skorupski and Don Geiger at the South Mil- 

 waukee Water Filtration Plant is also ap- 

 preciated. Supported by grants to A. D. Hasler 

 (NSF Grant GB 343, University of Wisconsin Sea 

 Grant Program, Department of Commerce, NOAA 

 2-35209) and the Wisconsin Department of 

 Natural Resources. 



Literature Cited 



COOPER, J. C, AND A. T. SCHOLZ. 



1976. Homing of artificially imprinted steelhead (rain- 



In view of our findings it is of interest to consider 

 two unpublished observations made by Stuart^ on 

 homing of brown trout at Dunalastair Reservoir in 



'Pers. commun. T. Stuart to A. D. Hasler, 7 March 1958. Letter 

 No. Pu. 9 from Freshwater Fisheries Laboratory, Faskally, Pit- 

 lochry, Perthshire, Scotland. 



294 



