334 



BULLETIN OF THE BUREAU OF FISHERIES 



Segregation Through Different Breeding Habits 



Most of the species are separated from one another by spawning at different 

 seasons or on different grounds. The three shoal forms (clupeaformis, quadrilaterale, 

 and artedi), wherever they occur in the basin, spawn at approximately the same 

 season — that is, in November and early December — but it is not known that they 

 congregate on the same grounds at the same time. These forms, however, are so far 

 removed from one another that it is not likely that hybridism would occur commonly. 

 What is known of the spawning habits of the other species indicates that within each 

 lake each species has a distinct breeding time or place, or both. To be sure, little is 

 known about this part of the life history of the Nipigon forms, and there are gaps 

 in our knowledge of the breeding habits of some of the forms in the other lakes. 



In Lake Michigan hoyi is the earliest spawner. It spawns in March at depths 

 of about 20 to 30 fathoms. Reighardi spawns in May, probably in shallower water. 

 Johannse spawns in August or September, presumably at depths of 60 fathoms. 

 Kiyi is said to spawn in October, also at great depths. Zenithicus and alpenx spawn 

 in November, but it is not known that they spawn on the same grounds. Data 

 indicate that the former spawns in deeper water. Nigripinnis spawns in January at 

 depths of about 60 fathoms. 



In Lake Superior it is not known when or where hoyi spawns, but certainly it is 

 not before December. Nigripinnis spawns in 60 fathoms in September. Kiyi, 

 zenithicus, and reighardi all spawn in November, as do artedi, clupeaformis, and 

 quadrilaterale, but no one knows that any two spawn on the same grounds at the 

 same time. 



In Lake Huron the breeding habits of its species are about like those of related 

 forms in Michigan, except that zenithicus spawns in late September and early October 

 and Myi may spawn in. early November. 



In Ontario reighardi is known to spawn some time in spring, probably in May. 

 Kiyi spawns in August, probably in deep water. Nigripinnis is said to have spawned 

 at about 60 fathoms in January. It is not known when hoyi spawns, but the season 

 may be as in Lake Michigan. 



The data just reviewed indicate that whatever role physiological differences 

 between the various species may have played in species formation they now are an 

 important factor in keeping the species distinct. Thus, habitat preferences separate 

 the species or groups of species into different zones, and differences in breeding 

 behavior cause each species to deposit its eggs at a different time or in a different 

 place. 



ACKNOWLEDGMENTS 



The work has been carried on with headquarters at Ann Arbor, Mich., and I am 

 indebted to the regents of the University of Michigan for the use of space in univer- 

 sity buildings and for materials. The section of this paper dealing with Lake Huron 

 was carried out under the supervision of Prof. Jacob Reighard, of the department of 

 zoology, for whose valuable assistance and constant interest I am deeply grateful. 



I am obligated to Dr. Carl L. Hubbs, of the Museum of Zoology, University of 

 Michigan, for helpful suggestions and criticisms in preparing the manuscript; to 

 Dr. John Van Oosten for his cordial cooperation in assembling certain data; and to 



