586 U. S. BUREAU OF FISHERIES 
and other animals, has shown this to be far from true. There very obviously 
is great variability in the conditions of survival, the yield varying widely 
from year to year, even in cultivated organisms. We have learned, indeed, that 
an organism must meet, in the course of its existence, periods of varying length 
in which adverse conditions of varying intensity prevail, causing great unequal 
infant mortality. 
A species in the state of nature has existed throughout the ages. It has had 
to survive the most extreme of these periods in length and intensity. Tees: 
my thought that this variability in nature has played a major role in evolu- 
tion and in the survival of species. Many characteristics of a living organism. 
are of importance from this standpoint, and theoretically, at least, it is easy 
to conceive that the reproductive power of a species must have an excess 
beyond that required by a favorable or normal year. 
I think of many characters of a species aS adapted to meet the normal or 
ordinary emergencies of the annual cycle. The power of resisting freezing, 
which many spores have, is an example. These many characters must be 
developed far beyond the ordinary in order to meet the occasional extraordinary 
conditions. For our purposes, however, I am thinking mainly of those char- 
acters that serve to bridge the adverse periods of various durations. An 
animal, developing warmth of blood, is capable of surviving more than a 
year with less loss in numbers. So, too, the young are protected by the adults. 
through the period of highest fatality, the protection in some cases lasting 
sufficiently long to bridge an ordinary long period of difficult years. 
Foremost among survival characters one must place age. The halibut 
reaches a great age, as do the elephant and man. One inevitably thinks of 
the significance of this age as a survival factor of first magnitude. The loss. 
of one year’s spawning is but a fifteenth of the total loss for the life of an 
individual, and after a period of adverse years the adult is left to spawn anew. 
But species vary widely in such characters as food, habits, age, fecundity 
or egg production—they meet the situation differently. Why can not we expect 
infinite variety in the reaction of survival characters to the strain imposed’ 
by man? The halibut is long-lived and comes to maturity at 12 years. Man’s 
attack on the adults shortens greatly the average duration of life and seems. 
to me to be undermining the very character upon which the halibut largely 
depends for its power of survival. May his fishing efforts not result in the 
inability of that Species to meet and overcome some prolonged period of 
adversity? In that case it may disappear, entirely or over large areas. The 
reverse may be true of the herring—who knows? But at all events, it may 
be fair to think that we will have as many problems as there are species. 
Perhaps, using the factors of age, food production, egg production, and 
migration, man may be able at some time to deduce some general law as to the 
productivity of a species and as to the value of characters contributing to this 
power of survival. The solution of such a problem may contribute vitally not 
merely to fisheries science but to biology. The power of survival is an essential 
part of the evolution of a species. 
The most promising method of attack seems to me to be through expe1iment, 
carefully observed by statistical method. Under known biological conditions of 
age, migration, spawning, etc., certain results may be obtained. In time a 
general law may be framed to bring these into harmony, but until then, and as. 
a means to such an end, we certainly must seek results experimentally. 
So much for the second great problem of fisheries science. Our first was to 
obtain accurate methods of observation, our second to ascertain the method of 
reaction of the species to the strain. Our third must be to devise methods of 
protection. 
After much thought concerning the halibut and other species, it seems to me 
that almost all protective measures are based upon the degree of migration 
existing. The reason for this is easy to see when the significance of a high 
degree of independence between banks is grasped. An isolated race of fish is 
depleted as a separate unit and must be rebuilt as a separate unit. With a 
homogenous, freely moving species the case must be just the reverse—it must 
be dealt with as a whole. Let us, then, set the study of migrations above all 
others when protective measures are discussed. 
It is not necessary to review at length the means of such study. Tagging, 
the finding of racial characters, of differing growth rates, of finding physical 
traces in the individual of its past life history—all these are biological studies 
of great importance. 
