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CHAPTER IV.—THE NATURE OF LIVING MARINE RESOURCES, JURISDICTION OVER THEM, 
AND CONCEPTS FOR MANAGING THEIR USE 
A. The nature of living resources 
The basic factor in dealing with living resources, as differentiated from non- 
living, is that they are continuously renewing themselves. They do this in re- 
lation to general laws of nature, and in accordance with special conditions that 
are not only specific to each individual species, but frequently differ among the 
races or homogeneous stocks within a species. 
In general a male and female from one generation will produce at such a rate 
that in a state of natural equilibrium the result will be just exactly one male and 
one female in the following generation. Different sorts of resources react to the 
vicissitudes of their environment by providing different reproductive surplus’ to 
counter the different mortality rates the stock has encountered historically. For 
instance, fur seals produce one pup (more rarely two) per year after the adult 
stage is reached, and such a slow rate of reproduction is typical among elasmo- 
branchs (sharks, skates and rays). For instance the dog fish shark will produce 
six or eight young every two years. In the fin fishes the reproductive rate is 
highly diverse but generally more liberal. The viviparous perch will produce a 
few dozen young per year; the salmons, trouts, herrings, anchovies, etc., will 
produce a few thousand young per year; the ocean perch will produce a few 
tens of thousands of young per year; and so on up to the tunas, cods, etc., that 
will produce a few million young per year. This range, roughly speaking, is char- 
acteristic also of the wide range of invertebrate resources normally called 
shellfish. 
But the general rule holds. Nature anticipated expected mortality rates for the 
stock by producing sufficient young so that in a state of balance two animals 
beget two in one generation, and no more or less. 
Man may (and does) intervene in this process in various ways. This can be 
done to his benefit or harm. Whether the intervention will be harmful or bene- 
ficial depends absolutely upon knowledge of the species of animal, the principal 
characteristics of its specific life history, the rates of natural mortality, the rate 
of growth of the individuals in the stock, the rate of recruitment (reproduction), 
the effect of addition of artificial (fishing) mortality on the stock, and the effect 
of variations in the environment on these factors. 
There are no short cuts. A great deal of expensive and time consuming research 
of a high order of sophistication must be done to have the ingredients for know- 
ing how to manage the use of a resource to any effect, either beneficial or harmful. 
Research done on such a population dynamic problem for one species of animal 
is of very little use in dealing with another species of animal, because its vital 
processes will be different. This is frequently the case for separate homogeneous 
populations within a particular species. 
Generally speaking, when animals are removed from the population by fishing 
or gathering the total number of animals in the population decreases, the average 
size (age) of individuals in the population decreases, the catch per unit of 
effort decreases, and the reproduction efficiency of the population as a whole in- 
creases (so that two ean still beget two under these additional stresses and the 
population still survive). 
As the rate of fishing pressure (mortality) increases the amount of the catch 
increases, while the abundance (numbers) and weight of the remaining popula- 
tion decreases. This condition continues to exist up to a certain point where the 
added rate of artificial mortality (fishing) plus the natural mortality inherent 
in the stock and its relations to its environment, begins to exceed the total pos- 
sible reproductive capability of the population. This is called the point of maxi- 
mum sustainable yield (MSY), a phrase often encountered in dealing with fishery 
management. 
Beyond this point of MSY, if fishing effort is still increased, the catch will 
either level off (under conditions where there is enough reproductive surplus 
escaping the fishery to provide all the young the environment will support) or 
drop more or less sharply (depending upon the dependence the reproductive rate 
of the population has on the number of reproducing adults left by the fishery in 
the population). Under the latter condition that total rate of mortality can get 
so high in relation to reproductive capabilities that it, possibly aided by adverse 
environmental conditions, can extinguish the stock and species (the case of the 
passenger pigeon and the saber-toothed tiger), or drive it below the threshold 
of commercial importance (the case of the Pacific sardine). Under either situa- 
