bottom areas de<>pci" than those of the standard 

 series, and (to a limited extent) to other portions 

 of the Lake. 



Common and scientific names of the species men- 

 tioned in tlie text, listed below, follow the list pub- 

 lished by the American Fisheries Society (1960). 



Common niimc Scioitific immc 



Alewife Alosn. psei(doliarengus 



Gizzard shad Dorosomacepedianum 



Bloater Coregonus h oyi 



Shortnose cisco Coregonus reigh-ardi 



Lontrjaw cisco Coregonus alpenae 



Kiyi Coregonuskiyl 



I^ake herrinp- Coregonus arted'd 



Lake whitefish Coregonus elupeiiforinis 



T>ake tront Salveliwusnxt.may(Hsh 



American smelt Osmeriis mordax 



Spottail shiner Notropis hiidsoniu.s 



Emerald shiner IVotropis atherinoides 



Carp Cyprimis carpio 



Quillback Carpiodes cyprimis 



White sucker Catostoinus (■oinmi'ixoiii 



Burbot Lotalofa 



X inespine stickleback. Pungltius jmngltkis 



Trout-perch Percopsisomiscomaycvs 



Yellow perch Perca.-flavescens 



Johnny darter Etheostoma nigruni 



Logperch Percinacaprodes 



Slimy sculpin Cothis cognatiis 



Spoonhead sculpin __ Coitusricei 



Fourhornscidpin M yoxocephahis fpmdri- 



cornis 



THERMAL CHANGES 



The Lake was vertically homothermous at all 

 sampling stations on February 13 and March 11. 

 Bottom temperatures close to shore were near 

 freezing (0.1° ('.) and increased with depth to near 

 :).0° C. at 50 fathoms (table 1). Homothermous 

 conditions continued through early May except 

 near .shore. On May 26 bottom temperatures had 

 risen to 1L8 and 11.5° C. at 3 and 12 fathoms, re- 

 spectively, and some thermal stratification had de- 

 veloped at depths greater than 12 fathoms. From 

 mid-June until late August bottom temperatures 

 i)f water 15 fathoms and deeper remained cold 

 (3.9-6.5° C), and thermal stratification became 

 more i^ronounced. In water shallower than 15 



fathoms (and especially at depths less than 12 

 fathoms) bottom temperatures in summer fluc- 

 tuated and varied widely (7.9-22.3° C. at 3 fath- 

 oms). By October 15 the epilimnion had cooled 

 and thickened so that the water was near 12° C. 

 from surface to bottom at all stations out to 25 

 fathoms. Cooling progressed little from October 

 15 to November 4 because of unseasonably warm 

 weather. A detailed account of seasonal thermal 

 changes in Lake Michigan has been published by 

 Church (1942,1945). 



DEPTH DISTRIBUTION 



ALEWIFE 



Alewives are the most widely distributed of any 

 species in Lake Michigan. Depending on the time 

 of year and life stage, they occupy all depths along 

 the bottom and all waters above the bottom. Ver- 

 tical distribution is discussed first, in general terms, 

 then bottom distribution is described in more 

 detail. 



Young-of-the-year alewives, which hatch mostly 

 in June and July, live at midlevels until late siun- 

 mer or early fall. They have been observed near 

 the surface in early September in midlake and 

 probably occur from shore to shore. They are al- 

 ways caught on the bottom in large numbers by 

 October and have been taken in bottom trawls off 

 Saugatuck as early as August 31. Many, however, 

 are probably at midlevels even in the fall. Nearly 

 all of the young on the bottom, regardless of date 

 of capture, have been 1.5 to 3.5 inches (3.8-8.9 cm.) 

 long, compared with an average calculated 1st- 

 year growth of 3.7 inches (9.4 cm.). Thus, it ap- 

 t)ears that young alewives ai'e on the bottom only 

 at a certain size, and because the spawning season 

 is rather long, all are not on the bottom at the same 

 time. Possibly some alewives, particulai'ly those 

 which move into midlake in their earlier stages, 

 may not go to the bottom at all in their first year. 

 High winds and resultant turbulent conditions in 

 the fall ajjparently cause most of the young on the 

 bottom to ascend to midlevels temporarily. 



Alewives after their first year tend more strongly 

 toward a bottom existence as they grow older. 

 Yearling alewives (age-group I) are essentially 

 pelagic, but occasionally substantial numbers are 

 on the l)ottom in the spring and fall, and a few 



FISH DISTKIBCTIOX IN SOUTHEASTERN LAKE MICHIGAN 



