THE WHITEFISH PRODUCTION OF THE GREAT LAKES, 651 
true whitefish, but this is uncertain. It may cover in part the range of the 
blackfin (Argyrosomus nigripinnis), which is stated by Ward to be in Lake 
Michigan rare in less than 40 fathoms. I have placed the inshore range of the 
whitefish of Lake Superior at 10 fathoms, although Rathbun and Wakeham 
make no statement on this point, but say merely that the fish ranges ‘“ outward 
into depths of 40 to 50 fathoms, seldom farther, and in some places coming 
close upon the shore during the spawning season and in the spring.” I 
have assumed the inshore range on Lake Superior to be about the same during 
most of the year as in the other lakes. 
The most careful investigation of the food of the whitefish and of the 
related fishes we owe to Ward (1896), who finds as a result of the examination 
of 14 individuals taken in summer that on the average 63 per cent (by volume) 
of the food of the true whitefish consists of small bottom crustaceans, 26 per 
cent of small mollusks, 5 per cent of insect larva and 2 per cent of small fish. 
Small brown stones were also found commonly in the stomachs. ‘The con- 
siderable part played by the mollusks and insect larve, both of which are 
strictly bottom forms, shows that the common whitefish is to a large extent a 
bottom feeder. This view is strengthened by the down-pointed sucker-like 
mouth of the fish as well as by the presence in the stomachs of numbers of small 
stones, which were undoubtedly snapped up with some morsel of food” (Ward, 
1896). The food of the longjaw Ward found to consist of small crustacea to 
the extent on the average of 97 per cent of the whole (volume), while the food 
of the two specimens of blackfin examined contained crustacea to the extent of 
97 percent of the volume. ‘The absence of stones, mollusks, and insect larve from 
the stomachs of these two forms and the presence in them of free swimming crus- 
tacea, as well as the form of the mouth of the fish themselves, show that they 
feed not on the bottom, but just above it. All of these whitefishes therefore 
feed on the bottom or just above it, but differ in their depth range during the 
greater part of the year, the true whitefish ranging from 10 fathoms outward, 
but rarely being taken in more than 35 fathoms, the longjaw ranging from 20 
fathoms outward, occurring in greatest abundance between 20 and 25 fathoms 
and reaching in winter a depth of 116 fathoms, the blackfin occurring rarely in 
less than 40 fathoms and most abundant at 70 fathoms and upward. 
The ranges indicated above as occupied by the whitefish are its feeding 
grounds during eight or nine months in the year. It enters shallow water 
in the southern lakes in June and July, and returns again to the deeper water 
about the ist of August. The cause of this shoreward migration is dis- 
cussed by Milner (1874), but he does not mention one very probable cause, 
namely, that the period of this shoreward summer migration is that when the 
insect larvee upon which the migrating fish feed (Kiel, 1874) are most abundant. 
It is quite possible that the migration takes place as a search for a more abundant 
