MILNEE FISHERIES OF THE GREAT LAKES. 35 



F_ECO^OMrCAL AND NATLTRAL HISTORY OF THE MORE 

 IMPORTANT FOOD-FJSHES OF THE GREAT LAKES. 



19. — Distribution of the species according- to depths. 



(19 a.) Vertebrate fauna. Observations of the net-fishing at dififerent 

 depths made the fact apparent that there are quite well defined ranges, 

 with reference to depth, in the fauna of the lakes ; not that the lines 

 are so distinct that fishes peculiar to a certain zone are not frequently 

 found straying into the ones contiguous, but still so well defined that a 

 fisherman of short experience, knowing the depths at which he is setting 

 his net, can predict with confidence what species of fishes he will cap- 

 tm"e and what he is not at all likely to take. While a few of the deep- 

 water fishes seldom or never approach the shore, there are many species, 

 of the shallow waters, never taken in deep soundings. The migratory 

 instinct of the spawning-season temporarily changes these habits in a 

 few species, and "there is considerable evidence to prove that the tem- 

 perature of the water modifies the preferences of many fishes to certain 

 depths. 



As one or two fishes of the deepest zone are the most constant in 

 their attachment to their limited range, it will be as well to begin with 

 the deeper water, in describing the ranges of the species. 



The fishes referred to are, a small Cottoid, the Triglopsis thompsoni 

 Gir.; and a Salmonoid, the hlack-iin, Argyrosomiis nigripinnis Gill, (Mss.) 

 These fishes are most abundant in seventy fathoms and deeper, and are 

 seldom taken, in the fishing-season, even in as great a depth as fifty 

 fathoms. At Grand Haven, Mich., where a line of steamers keeps the 

 harbor open throughout the winter, the fishermen take the black-fin in 

 quantities, within thirty or forty fathoms, in the month of December. 

 This fish has thus far been found only in Lake Michigan. The Triglopsis 

 is only known from specimens taken from the stomachs of larger fishes 

 in Lakes Superior, Michigan, and Ontario. The remaining species, of 

 which a few are sometimes found at the depth of seventy fathoms, are 

 the lawyer, iyo^rt maculosa Les., the salmon-trout, iSalmonamaycush~Penu., 

 the siscowet, tSalmo siscoicet Agass.,the white-fish, Coregonus alhus Les., 

 and the cisco, (not the cisco of Lake Ontario,) Argyrosomus hoyi Gill, 

 (Mss.) 



At fifty fiithoms, the nets take the five species last named abundantly. 

 This may be considered, in the deeper lakes, the zone of the Mack- 

 inaw trout and of the cisco, throughout the spring, summer, and fall, 

 with the exception, in the case of the trout, of the spawning-season. 



Between twenty and forty fathoms the gill-nets take the salmon, or 

 Mackinaw trout, with a few lawyers and ciscos. 



From twenty fathoms to the shore are found the most numerous as- 

 semblage of species: The lawyer, Lota maculosa Les., one or two small 

 Oottoids, JJranidea franlclini Agass., and U. richardsonii Agass.; the 

 sheepshead, Haploidonotus grunniens Raf<; the black-bass, Micropterus 

 nigricans Cuv. and Val. and the small-mouthed black-bass, M. salmoides 



