102 American Fisheries Society 



extensively, although the alleged hybrids have never been scien- 

 tifically identified as such; (b) the German brown trout has not 

 hybridized, but is preying extensively on the others and is becom- 

 ing predominant; (c) the eastern brook-trout has not hybridized 

 (for the obvious reason that they spawn in the fall and cannot 

 hybridize with spring-spawning species). 



3. It is the writer's impression that the streams stocked with 

 several species do not "stand up" under the drain of heavy 

 fishing quite as well as those with only one species. One of the 

 most resistant streams known to the writer is Sabino Canyon in 

 the Coronado National Forest, almost on the Mexican boundary. 

 It was stocked once with eastern brook trout in 1908, has been 

 heavily fished ever since, and showed no sign of giving out until 

 this year. Much less resistant is the Pecos River in the Santa Fe 

 National Forest, a much larger stream. It has been stocked every 

 year with black-spotted, rainbow or German brown trout, and is 

 no more heavily fished, in proportion to its size, than the Sabino. 

 These impressions are, of course, merely indicative. 



It appears therefore that available knowledge on the question 

 of mixing species, may be summarized as follows : 



1 . Species of trout spawning at the same time may hybridize. 

 More knowledge is needed on when and to what extent. 



2. These hybrids are less productive, and therefore less 

 desirable, than pure stock. More knowledge is needed on how 

 much their reproductive capacity is reduced. 



From the foregoing conclusions, the Southwestern District of 

 the Forest Service has arrived at and is now adhering to the 

 following rules of practice in stocking trout waters in the National 

 Forests of Arizona and New Mexico : 



1. Nature, in stocking trout waters, sticks to one species. 

 The Forest Service will do likewise where mixing has not already 

 occurred. 



2. Empty waters will be stocked with the species that seems 

 most suitable. Where there is danger of depletion through heavy 

 fishing, avoid rainbows. Where there is danger of the water being 

 too warm, avoid black-spotted and eastern brook-trout. Where 

 a lake is large or mud-bottomed or warm or otherwise liable to 

 produce large non-rising fish, avoid the native black-spotted trout. 



3. Stocked waters will not be further mixed. Restock with 

 the best adapted species, the native species always preferred. 



