612 U. S. BUREAU OF FISHERIES 



have not applied such restrictions to the Great Lakes, most probably 

 because they are so large. It is this immensity in size that sustains 

 the general belief in the inexhaustibility of their resources. Most 

 people believe that water is all that any fish requires and that any 

 and all fish can survive and thrive if only there is water, but the fisher- 

 man knows that the maintenance of the fish supply is dependent on 

 other things as well. Certain species occur only within certain depth 

 limits, and within these limits only where certain bottom conditions 

 obtain. Thus in Lake Superior, for example, with its area of some 

 32,000 square miles, there are hundreds of miles of shore line where 

 whitefish are practically unknown, and in over one-fourth its area 

 there occurs no marketable species of fish. Yet, in spite of this, 

 Govei'nments on both sides of the international boundary expend 

 money every year planting fish in virgin waters, in which, if the fish 

 could find suitable conditions, they most probably would have 

 flourished from the beginning. 



Even if the Great Lakes were suited throughout their extent for 

 all kinds of fish and were they ever so much larger than they are, the 

 supjDly must nevertheless just as certainly be in danger of exhaustion 

 if at any time the bulk of the species came within human control. In 

 the Great Lakes this dangerous control may be exerted in the case of 

 most species during the spawning season. The individuals of the 

 more important species congregate to spawn near the shores where 

 bottom conditions are favorable, usually within limits which, in 

 comparison with the normal range of the fish, are extremely resti'icted. 

 During the excitement of the mating act they not only approach the 

 bottom, and thus come within the range of influence of the nets, but 

 they appear also to lose there awareness of the netting,* a faculty 

 which protects them to some extent from capture at other times, and 

 they are taken in an abundance unknown at other seasons. 



For the benefit of those, if any such there be, who believe that the 

 practice of commercial fishing must necessarily, in itself, deplete 

 any body of water, I present an abstract of an article written by 

 Dr. J. Heuscher,!" in which he gives the history of Lake Sempach, a 

 Swiss lake of approximately 5}4 square miles area, which, under 

 judicious control, maintained a commercial fishery on a large scale for 

 over 400 years and which was depleted only when fishing operations 

 were allowed to go on uncontrolled. 



The lake has a maximum depth of about 47 fathoms over an area 

 of nearly 2 miles, and limnological conditions in this lake approxi- 

 mate those in the Great Lakes. At one time this body of water 

 supported immense numbers of a whitefish, related to those in our 

 lakes. Fishing rights in Lake Sempach were legally established as 

 early as the tenth century. In 1394 these rights came into the posses- 

 sion of the city of Lucerne, which disposed of them in various ways at 

 various times, mainly in the form of leases stipulating the cession to 

 the city of a certain percentage of the fish caught. The city's docu- 

 ments record the number of fish thus taken annually from 1418 to 

 1853. The catches varied from year to year, chiefly between 100,000 

 and 600,000 fish. 



« It can not be doubted that the fish are aware of gill netting in the shallower waters. The pnnciple 

 of the pound net and all trap nets is based on the ability of the fish to perceive the lead, which is of a mesh 

 large enough to permit them to swim through it uninjured. To reason further in the same strain, if they 

 are aware of their food in deeper water they must likewise retain the capacity of sensing the presence of 

 the netting. 



10 Swiss Fishery Journal, Vol. IH, 1895. 



