262 Roosevelt Wild Life Bulletin 



spring." In another place in the same report he says (p. 84), " The 

 results from the Lawrence fishway are particularly interesting, inas- 

 much as some of the foremost fish experts in the United States have 

 held the opinion that the pollution of the Merrimac River would 

 prohibit the use of a fishway by anadromous fish, and that fresh- 

 water species would make little use of such a structure. We now 

 know that alewives have passed through the fishway in spite of the 

 pollution, and that the fishway has been used by various species of 

 fresh-water fish." 



The table of records of fish which were observed in the fishway 

 including anadromous fish above it, from May 25 to July 6, com- 

 prised 72 alewives, 19 suckers, 105 shiners and dace, 44 eels, 3 

 trout, I sturgeon, and i carp. 



This proves nothing beyond the fact of the possible efficacy of the 

 fishway. Nothing is stated concerning the extent of the pollution 

 at this time in the particular place under observation. Furthermore, 

 even if large numbers of alewives had passed up, there is nothing 

 to indicate that they would have found suitable spawning places, or 

 if they had that the young would have endured the pollution. 

 Shelf ord ('18) very well indicates, that to all toxic substances the 

 vounger or smaller fish, down to the smallest fry, are more sensitive 

 than older ones, and that in one instance under observation the resis- 

 tance of the ^gg falls gradually from the time of fertilization to the 

 time of hatching. The point is that " tests of the minimum quantity 

 of poison which will prove fatal must be made on the most sensitive 

 stage; the strength of the chain is the strength of its weakest link." 



Again, while the pollution may have been comparatively slight or 

 even absent at the time, there is no evidence that at a corresponding 

 season another year, the pollution would not have prohibited the 

 ascent of alewives. 



As concerns sawdust, to which Evermann referred, while the im- 

 mense deposits of the lower St. Croix River in Maine and New 

 Brunswick apparently did not prevent the ascent of salmon, it is 

 positively known that they could not breed upon sawdust-covered 

 spawning beds. 



A stream may be polluted iii one part and not in another. This 

 l)eing found to be so in any instance, and having ascertained to what 

 kind of fish the unpolluted portion is in every way suited, it may be 

 stocked, provided measures are taken that it shall not be subse- 

 quently polluted. The advice here offered is not to attempt to stock 

 polluted waters. If waste can be diverted elsewhere and the water 

 purified, see that it is done before^ attempting to stock. It will be 

 economy, with gratifying results. 



In addition to pollution to which reference has been made there 

 are conditions which may be called natural pollution. Besides those 

 v/ith which almost everyone is more or less familiar, if he has given 

 any attention to aquatic conditions, such as the generation of nox- 

 ious gases, etc., from decaying vegetable matter, there is one condi- 

 tion in particular that should be mentioned. It is concerned with 

 acidity of the water. It has been found that bog-water — particularly 



