FACTORS INFLUENCING THE ORIENTATION 

 OF MIGRATING ANADROMOUS FISHES 



By Gerald B. Collins, Fishery Research Biologist 



HISTORICAL BACKGROUND 



Tli(> oiieiitation of migrating fislies lias been tlie 

 subject of investigation and conjecture for many 

 years. Migration paths liave been outlined by 

 tagging experiments, and n wealth of valuable 

 information on the physiology, development, and 

 behavior of migratory fishes has been acquired 

 through the persistent eiforts of many able in- 

 vestigators; but the means by which the fish are 

 directed on their migrations are still largely a 

 matter of speculation. 



The purpose of the study presented here was to 

 investigate the influence of certain physical and 

 chemical factors upon the orientation of migrating 

 anadromous fish of the genus Pomoloii/s. In 

 the course of this investigation an effort was made 

 to determine experimentally if the migrating fish 

 would orient to differences in the physical and 

 chemical characteristics of water. 



The existence of difl'erences in physical and 

 cliemical factors in natural waters to which fish 

 might respond has long been known. Slight 

 gradations usually exist in the relative amounts 

 of dissolved gases, in ^H, in temperature, and in 

 other physical and chemical characteristics of a 

 stream from the source to the mouth. Such 

 gradients are usually so slight that the differences 

 I let ween points miles apart are still below tlie 

 tJireshokls of the sensory perception of fish. 



Much greater gradients are found at stream 

 junctions and at stream entrances into lakes or 

 into the sea. In these gradients there frequently 

 are chemical and physical differences between 

 points a few feet apart which are large enough to 

 be detected by the fish. The existence of these 

 gradients at crucial points along the migration 

 paths of anadromous fishes where they might in- 

 fluence the fish in the selection of a stream has led 

 In speculation on (heir possible role in directing 

 tlie migration of the fish. 



The author is greatly indebted to Prof. George 

 L. Clarke of Harvard University for his encour- 



agement, helpful suggestions, and criticisms dur- 

 ing this research. The work was done in partial 

 fulfillment of the requirements for (he degree of 

 doctor of philosophy at Ilarvaid University, De- 

 partment of Biology. 



TJianks are due also to Prof. .VI tied C. Redfield 

 and many other members of Harvard University 

 and the Woods Hole Oceanographic Institution 

 for their advice and aid in securing funds and 

 special equipment. The research during the 

 summer of 1949 was done wiiile occupying a re- 

 search fellowship at the "Woods Hole Oceano- 

 graphic Institution. 



The cooperation of the town of Bourne, Mass., 

 is acknowledged for permission to work in 

 Herring Eiver and to use town property at 

 Bournedale. 



A special debt is gratefully acknowledged to 

 Director Francis W. Sargent and John Burns 

 of the Division of Marine Fisheries, Massachu- 

 setts Conservation Department, for their interest 

 and aid which made this investigation possible. 

 The research in the .spring of 19i9 was done as an 

 emplo3-ee of the Massachusetts Division of Ma- 

 rine Fisheries. 



The encouragement and aid of Dr. Lionel A. 

 Walford, Ralph P. Silliman. Clinton E. Atkin- 

 son, and others of the Fish and Wildlife Service 

 are also acknowledged. The research in the 

 spring of 1950 was done as an employee of the 

 U. S. Fish and Wildlife Service. 



MAJOR THEORIES ON ORIENTATION 



Currently, two major concepts on the orienta- 

 tion of migrating anadromous fishes have gained 

 wide support; and, while not nuitually exclusive, 

 they are, as the frequent clashes in the literature 

 suggest, not entirely compatible. 



One of these theories regards the upstream 

 migration of the fish as a purposeful "homing" 

 to the part of the river system in which it was 

 hatched or in which it spent the early stages of 



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