forest and stream 
546 
active and keen, hunting more carefully, with 
greater persistence than usual, and consequently 
with greater effect. For awhile, at least, the re¬ 
duction process is thus continued and the food 
supply, or species preyed upon, falls below nor¬ 
mal. Finally, however, the enemies also are re¬ 
duced either through starvation or movement to 
other localities until their population is also 
brought below normal numbers in harmony with 
the reduced resources of the habitat. This 
gives the food species opportunity to increase 
once more to abnormal numbers and the process 
begins over again in a diminishing degree. Thus 
an oscillation is started that may take consider¬ 
able time to subside to stable normality. 
There is a certain definite maximum of popu¬ 
lation beyond which a species cannot go. We 
have many evidences of this. One of the most 
obvious was the case of the Bluebird in the 
winter of 1894-5 when this common species was 
almost wiped out in the south. For five years 
the species increased rapidly to normal popula¬ 
tion and then stopped short. As far as we can 
see no new factor was introduced, no enemy ab¬ 
sent during the five years of growth was present 
in the sixth year, the food supply and birth rate 
seemed constant throughout, but the increase was 
definitely and positively checked during the fifth 
year. It is obvious that a limit to the Bluebird 
population had been reached. 
In estimating the effects of any set of condi¬ 
tions upon the lives of a species, there will al¬ 
ways be found one or more factors having a 
predominating influence upon it. With the above 
principle in view, let us consider the effects of 
cormorants and other birds of prey upon salmon. 
The number of adult salmon is the result of 
birth rate, modified by the amount of food sup¬ 
ply, less the numbe' taken by enemies before 
reaching breeding maturity. The birth rate we 
can assume as being sufficient under normal con¬ 
ditions. But the introduction of man with his 
efficient and deadly methods of taking fish after 
they have passed the gauntlet of natural enemies, 
has introduced a decidedly adverse and abnormal 
influence against the species. The mature fertile 
fish is nature’s finished product, the outcome of 
that fine balance it has taken ages of adaptation 
to evolve and secure. Loss at this stage will be 
more keenly felt by the species than at any other 
time in its life-history and, unless compensated 
for, is bound to have a marked effect upon the 
total numbers. It is not only the individuals 
themselves that are lost in this case, but the gen¬ 
eration they are about to give rise to, and for 
which the whole economy of the species has been 
formed to produce. The proper correction for 
this is the hatchery which, in so far as it com¬ 
pensates for the eggs of those fertile individuals 
taken by man, should be sufficient to keep the 
salmon to the standard allowed by the resultant 
of other forces. However, no increase in final 
population beyond the normal capacity of the 
stocked waters can be expected from these 
menas unless there is food supply for an 
increased number of the species at all ages. 
This food supply has to be considered through¬ 
out the species’ range. The salmon in the sea 
seem to feed largely upon such fish as herring, 
and upon Crustacea, both of which are plentiful, 
and there is little probability of their insuffi¬ 
ciency. In the streams it is another question 
and a determination is less easily arrived at. 
The fry undoubtedly feed upon microscopic an¬ 
imalcules, the sufficiency of which may be ten¬ 
tatively assumed with moderate safety, but we 
have yet to learn the food supply of the finger- 
lings or parr. The water of the streams visited 
is absolutely clear, the bottoms are clean gravel 
and rock, with no visible abundance of algal, 
plant, or insect life. There is undoubtedly a 
certain amount of some such food, but it is too 
scattered to attract the attention and is obviously 
insufficient for the support of an unlimited num¬ 
ber of fish. 
We found that the parr do eat fry of their 
own species most greedily. As all the fry in 
the salmon streams are those of salmon and a 
few trout the inference is plain, that a large part 
of the parr are supported by fry. How many 
fry it takes to raise a parr to the smolt stage we 
cannot tell, but it must be an enormous number. 
The shelldrakes (mergansers) are accused of 
devouring the salmon ova. Considering that the 
ova is buried in the sand immediately after being 
fertilized and is guarded by the male, while this 
is in process, it is not likely that the number 
taken by these birds can be a very large propor¬ 
tion of the whole and must be small in compari¬ 
son with the number of fry taken by the parr. 
At this stage, the worst enemy of the salmon is 
undoubtedly the salmon itself. 
The parr, to the smolt stage, are thus obvious¬ 
ly limited in number by the amount of fry in the 
river. If it can be established that the kelt or 
grilse eat in fresh water they are probably the 
parr’s worst enemy. If not, that distinction falls 
to the lot of the kingfisher who undoubtedly 
consumes considerable numbers of them. 
Whether they seriously reduce the final num¬ 
ber that go to the sea as smolt is a question of 
more than one aspect. A reduction of parr 
means an increased number of fry and, there¬ 
fore, more food for the remaining parr who be¬ 
ing better fed may be stronger and more fitted to 
survive later dangers. If the birth rate is mark¬ 
edly greater than the food capacity of the 
streams, kingfishers may have no harmful effect. 
They should not be finally condemned until this 
point is investigated. 
The population of fry produced by the birth 
rate is greater than can be raised and the surplus 
must necessarily be reduced, if not by one agent, 
then by another. There is a point to be reached 
when even an immense increase in the number 
of fry introduced into the streams will be inef¬ 
fective in increasing the output of smolt. As the 
birth rate has been evolved under present condi¬ 
tions of food supply and enemy factors, the nat¬ 
ural conclusion is. that the kingfisher and the 
shelldrakes are compensated for in it. The nat¬ 
ural increase was sufficient to stock the river in 
the past to abundance, in spite of these enemies, 
and there is no reason to suspect that it is less 
effective now. Hence if man introduces suffi¬ 
cient fry to compensate for the ova that should 
he laid by the breeding fish he captures, probably 
the highest possible efficiency of ihei streams un¬ 
der present food conditions will be reached. If 
this is done shelldrakes and kingfishers can be 
neglected except to see that they do not increase 
to an abnormal extent. 
As the smolt go to sea they pass the gauntlet 
of the cormorants, but these, I think, we see, 
have little or no effect upon their number and 
can be neglected. 
What happens at sea to the smolt, grilse, and 
salmon at present none can tell. In the teeming 
abundance of marine life lh ;r food can be as¬ 
sumed to be plentiful. The rapidity with which 
a fingerling smolt grows to a five pound grilse is 
sufficient evidence of this. The most serious lim¬ 
itation to numbers at s^a must come from the 
salmon’s many enemies. In the final stage of the 
salmon’s existence before maturity lies probably 
the factor that determines how many will re¬ 
ascend the streams to procreate their species and 
incidentally become available for human use. As 
said before, a food species is consumed by its 
enemies until it becomes too scarce to be profit¬ 
ably hunted. A notable increase of food supply 
attracts new consumers and the resultant popu¬ 
lation is apt to be little, if any, greater than be¬ 
fore. With the enemy factor controlling the sit¬ 
uation the number of resultant food fish seems 
to become a matter of population per unit area 
of ground occupied. 
For example, assume that ten salmon per acre 
is scarce, i. e., that population is too scattered to 
be profitably hunted, and the expended energy in 
finding and capturing a meal o! salmon is con¬ 
siderably greater than would be expended in pur¬ 
suit of other species or in other quarters; the 
salmon under these conditions and assumptions 
will cease to be systematically hunted by its ene¬ 
mies, and, except for occasional and accidental 
encounters, will enjoy comparative immunity. 
Shou’d the population be suddenly increased to 
fifty or a hundred per acre, it will be salmon sea¬ 
son for their enemies who will abandon other 
usual prey for the new abundance. Should the 
resident enemies find more than they can con¬ 
sume neighboring competitors will be attracted, 
and it will not be long before the population is 
reduced again to the old ten per acre and com¬ 
parative peace will be resumed. 
It is evident, then, that any method of raising 
this deep sea salmon population above the eco¬ 
nomic mean of ten per acre (number here arbi¬ 
trarily assumed) will be wasted energy and ex¬ 
pense unless the enemies at this critical time can 
be controlled. If, as seems likely, the deep sea 
condition is the controlling element in the life 
of the salmon, increasing the number of fry, 
feeding parr or destroying fresh water enemies 
wi'l have little if any effect on ultimate numbers. 
Protection at other times will no more increase 
the number of mature salmon than enlarging two 
ends of a pipe while leaving a constricted length 
in the middle, will increase its flow capacity. 
In conclusion it may be said that 
I. The total effect of bird enemies upon sal¬ 
mon is small, if an}'. 
II. Hatcheries and fry planting will compen¬ 
sate for the toll of mature fish taken by man. 
III. The number of smolt that go to sea is 
dependent upon the food supply in the streams. 
IV. The number of returning salmon is gov¬ 
erned by the extent of their deep sea habitat and 
the number of enemies there. 
V. While planting may return an exhausted 
stream to its normal capacity the number of fish 
cannot be indefinitely increased without a read¬ 
justment of other critical conditions. 
VI. Eliminating the question of poaching, 
stream defilement, and other abnormal conditions 
the problem of increasing the salmon run in the 
rivers, above the natural capacity of the streams, 
lies between increasing the parr food in them 
or reducing the enemies of the salmon in the 
deep sea habitat. 
