GREAT LAKES COEEGONIDS 



539 



the species has been of irregular occurrence everywhere and the average annual 

 yield has been low. Around the beginning of the century there was also a period 

 of low production, after which the species increased again. At that time the large- 

 meshed nets went out of use because no other species could be caught with them 

 and the quantity of trap nets and pound nets (which depended largely on the white- 

 fish for profitable employment) decreased in numbers, and with the abatement of 

 the persecution it had sustained, the stock had an opportunity to recover. At that 

 time, too, the Canadian fisheries were being exploited but little, so that there was 

 a kind of natural preserve across the border, besides which large quantities of fry 

 were planted annually. 



The present depletion is much more serious than any recorded before, and there 

 is less reason to hope that time will repair it. The use of large-meshed nets is being 

 discontinued again, but the other apparatus is not at all affected, because other 

 species, which were not marketable 20 years ago, are being taken in profitable 

 quantities; and even where whitefish are the mainstay of the fisheries the increased 

 price paid per pound, which in 1922 was over two and one-half times the average 

 price in 1903, permits the continuation of the fisheries even though the supply is 

 less. Canadian fisheries also have expanded enormously in the last 15 years, and 

 the waters across the boundary probably are as exhausted now as our own, so that 

 there is much less of a reserve stock than formerly. The recuperation of the white- 

 fish is impeded further by the excessive pollution of the Detroit and other rivers, 

 also, which, the fishermen say, has driven them off the best spawning grounds in 

 the lake. 



ABNOEMAL FOKMS 



The 11 mule whitefish." — Specimens of what are usually considered hybrids 

 between Coregonus clupeqformis and Leucichthys artedi are taken occasionally out 

 of many of the lake ports. Their occurrence has been known long, and specimens 

 have been described. These so-called hybrids are frequently of greater average 

 size than even the whitefish. I have a photograph of a male taken by W. D. Bates 

 at Kidgetown on the north shore that weighed 11 pounds, 15 ounces. 



A specimen 282 millimeters long was taken by me at Toledo, Ohio, on November 

 27, 1920. This fish was a male and showed pearl organs. A numerical expression 

 of many of its systematic characters is given in Table 93, and a drawing of the head 

 is shown in Figure 31, A. 



The body outline is elliptical in side view, like that of a deep -bodied herring. 

 The caudal peduncle also is short and thick, as in the herring alius. The premaxil- 

 laries are inclined backward, as in the whitefish, but in this specimen the angle is 

 bent little more than 90°. The long adipose and maxillary are other characteristics 

 of the whitefish. The number of gill rakers is clearly intermediate between that of 

 the two forms. The other characters exhibited by this fish are such as are common 

 to both of the supposed parents. 



Artificially reared whitefish. — The New York aquarium reared whitefish from 

 •eggs of Lake Erie parents hatched in January, 1913. An account of their treatment 

 is given by Mellen (1923). Thirty-two of these fish, which died during the years 

 1921 and 1922, were received from the aquarium authorities and are now preserved 



