SEASONAL DEPTH DISTRIBUTION OF FISH IN 

 SOUTHEASTERN LAKE MICHIGAN 



By LaRue Wells, Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 

 Ann Arbor, Michigan 48107 



ABSTRACT 



This study is based on systematic seasonal bottom 

 trawling between 3 and 50 fathoms (5.5 and 91.5 m.) 

 from February to November 1964 and supplementary 

 information from other experimental fishing at addi- 

 tional depths and with other gear. The seasonal depth 

 distribution of eight common species is described, and 

 temperature relations are discussed. Catch records for 

 less common species are mentioned briefly. 



Alewives are mostly pelagic during their first 2 years, 

 but many young of the year are on the bottom in the 

 fall, and yearlings occasionally descend to the bottom in 

 substantial numbers in the spring and fall. Adults are 

 mostly on the bottom in the winter and spring, but a 

 significant portion of the population may be at mid- 

 levels in the summer and fall. Bloaters are in midwater 

 during their first 2 years, but usually on the bottom 

 thereafter. Young-of-the-year American smelt are in 

 midwater except in the fall, yearlings are in midwater 

 or on the bottom, and adults are mostly on the bottom. 



Alewives, bloaters, smelt, spottail shiners, trout- 

 perch, and yellow perch on the bottom moved into 

 shallower water in the spring and into deeper water in 

 the fall, in response to temperature changes. Slimy 

 sculpins abandoned inshore areas as water warmed in 

 the spring. Fourhorn sculpins showed a slight move- 

 ment shoreward in the spring, but changed their depth 



distribution little thereafter to the end of the trawling 

 season. 



Alewives showed the greatest seasonal change in 

 distribution. Large concentrations at 40 to perhaps 70 

 fathoms (73.2-128.0 m.) in mid-March had migrated to 

 water of less than 15 fathoms (27.4 m.) by mid-April. 

 They were in shallow water along shore or in rivers 

 until early summer; then they began a postspawning 

 movement back into deeper water which continued into 

 the fall. Depth ranges in which greatest numbers of 

 other coitimon species occurred, considering all seasons 

 as a whole, were as follows: bloater, 12 to 50 fathoms 

 (21.9-91.5 m.); American smelt, 5 to 17 fathoms (9.1- 

 31.1 m.); spottail shiners, 3 to 15 fathoms (5.5-27.4 m.); 

 trout-perch, 5 to 17 fathoms (9.1-31.1 m.); yellow perch, 



3 to 15 fathoms (5.5-27.4 m.); slimy sculpins, 15 to 40 

 fathoms (27.4-73.2 m.); fourhorn sculpins, 45 to 70 

 fathoms (82.2-128.0 m.). 



Water temperature ranges (° C.) in which the various 

 species were most abundant in summer were: alewife, 

 8 to 22; bloater, 6 to 10; smelt, 6 to 14; spottail shiner, 

 13 to at least 22; trout-perch, 10 to 16; yellow perch, 11 

 to at least 22; slimy sculpin, 4 to 6; fourhorn sculpin, 



4 to 4.5. Fluctuations in inshore water temperatures in 

 the summer caused short-term changes in depth dis- 

 tribution. 



Published records of depth distribution of fish in 

 tlie Great Lakes have been limited largely to gen- 

 eral information included as part of other studies. 

 Data on seasonal aspects of distribution are espe- 

 cially scarce, although Diyer (1966) gave consid- 

 erable information on seasonal changes in bathy- 

 metric distribution of fish in the Apostle Islands 

 region of Lake Superior. His review of current 

 literature on the depth distribution of Great Lakes 

 fish need not be repeated here. The present paper 

 describes the seasonal depth distribution of eight 



of the most abundant spe-cies in Lake Michigan 

 and gi\'es infonnation on the effect of temperature 

 on depth distribution, especially during the 

 summer. 



METHODS AND MATERIALS 



Data -were obtained from bottom tows with a 

 semiballoon trawl in 1964 off Saugatuck, Mich. 

 This net had a 39-foot (11.9 m.) headrope, 51-foot 

 (15.5 m.) footrope, and a cod end of i/^-inch (1.3 



Publislieil June 1968. 

 FISHERY BULLETIN: 



VOLL'.ME 67, NO. 1 



