NOTE Griffith et al ; Straying of Oncorhynchus nerka into a non-natal fnatcfiery 



715 



straying in the true sense is helpful in interpreting 

 the movements of salmon during the final stages of 

 their homing migration. Most of the sockeye (38 of 

 48) that entered the UWH and were released did not 

 return again. From our data we cannot determine 

 which term (proving, exploring, or wandering) best 

 describes their behavior. However, five out of ten of 

 the sockeye that returned once returned a second 

 time after displacement. We do not understand the 

 motivation for the behavior of these fish but inter- 

 pret their persistence as evidence that they would 

 have spawned at the site and thus were considered 

 strays in the true sense. 



Why did only 10 of 48 sockeye salmon re-enter the 

 UWH? Were the others unable to locate the hatch- 

 ery or did they die prior to re-entry? The proportion 

 of chinook salmon returning to the UWH after dis- 

 placement ( nVc ) was much higher than that of sock- 

 eye salmon, suggesting that the UWH was not diffi- 

 cult to find and re-enter after displacement. The pro- 

 portion of chinook salmon returning in this study was 

 similar to or higher than those reported in previous 

 studies that displaced chinook about 5 km from the 

 UWH (Whitman et al., 1982; Brannon et al., 1986, 

 Quinn et al., 1988). A few of the tagged sockeye in 

 the present study returned over two weeks after re- 

 lease, implying that the sockeye had sufficient time 

 to find and re-enter the UWH before they were too 

 weak. 



The 48 sockeye salmon that initially entered the 

 UWH were only 0.005% of the total run of sockeye 

 salmon to the Lake Washington system during the 

 years of this study. We do not infer that this extremely 

 low rate of straying or exploring is representative of 

 spawning sites within this or other lake systems. The 

 absence of odors from conspecific juveniles and trace 

 odors from adults emanating from the UWH might 

 make it less attractive than rivers perennially used 

 by sockeye (Groot et al., 1986), and the small dis- 

 charge and lack of appropriate habitat for spawning 

 might also deter non-native sockeye from entering. 

 Likewise, the proportions of sockeye salmon stray- 

 ing and exploring in our study may not be represen- 

 tative of those for natural systems. 



Entry of sockeye salmon into UWH may differ in 

 some respects from their behavior in natural systems 

 but exploring and straying are characteristic of 

 salmon. On the basis of our results, many of the 

 salmon that enter non-natal hatcheries and that are 

 classified as strays might have left if given the 

 chance. Studies of straying based on recoveries in 

 hatcheries may thus overestimate straying rates, at 

 least in some cases (Quinn et al. 1991). The lack of 

 quantified estimates of proving or exploring behav- 

 ior makes it difficult to assess whether the high pro- 

 portion of these patterns found in our study is typi- 

 cal of sockeye or Pacific salmon in general. The dis- 

 tinction between straying and exploring is important 

 to the management of Pacific salmon because CWT- 

 based straying estimates from hatchery populations 

 are commonly used to model interactions between 

 hatchery and wild populations (Grant, 1997), and this 

 subject needs further research. 



Acknowledgments 



We thank William Hershberger, Glenn Yokoyama, 

 Heather Roffey, Jainrong Chang, and undergradu- 

 ate students for assisting with salmon collection and 

 tagging, and Andrew Dittman, Jeffrey Silverstein, 

 Fred Utter, and Carl Burger for comments on the 

 manuscript. Floy Tag Co. donated tags and a tag- 

 ging gun. Andrew Hendry was supported by the H. 

 Mason Keeler Endowment and a Natural Sciences 

 and Engineering Research Council of Canada post- 

 graduate scholarship. 



Literature cited 



Berman, C. H., and T. P. Quinn. 



1991. Behavioural thermoregulation and homing by spring 

 chinook salmon, Oncorhynchus tshawytscha (Walbaumi, in 

 the Yakima River. J. Fish Biol. 39:301-312. 



