The purpose of the exploratory fishing 

 cruises during this study was to provide in- 

 formation regarding the seasonal depth and 

 geographic distribution of certain abundant 

 and unutilized species such as alewives and 

 chubs in relation to their availability to a 

 new and growing trawl fishery. This informa- 

 tion was distributed to the fishing industry 

 in the form of cruise reports at the end of 

 each cruise. The operations were intended to 

 determine the feasibility of trawling at widely 

 separated areas at particular times. 



Southern Lake Michigan is here defined as 

 that portion of Lake Michigan south of a line 

 between Manitowoc, Wis., on the west shore 

 and Ludington, Mich., on the east shore (fig. 2), 

 A few drags made a few miles north of this 

 line are included here. A fishing log of all 

 trawl drags is given in the appendix. 



VESSELS, GEAR AND METHODS 



All the fishing explorations in this study, 

 with the exception of cruise 30, were nnade 

 with the 65-foot research vessel Kaho. 

 The research vessel Cisco made 14 trawl 

 drags in southern Lake Michigan on cruise 

 30. 



Most trawling was with a 52-foot (headrope) 

 Gulf of Mexico type fishing trawl (Gordon and 

 Browillard, I960). During phase II of cruise 

 3, 33 drags were made with a 62-foot (head- 

 rope) modified western type bottom trawl. 

 Both nets were rigged with a I -inch mesh 

 (stretched measure) cotton liner in the cod 

 end to sample young fish and small species. 

 All drags were recorded with a high- 

 resolution echo sounder with fish-discrimi- 

 nating features. 



Most trawl drags were for 1/2-hour duration 

 although 38 drags were extended for longer 

 periods (up to 2 hours) to determine rates 

 that commercial fishermen might expect and 

 65 were ended purposely before 30 minutes 

 for one of the following reasons: encountered 

 snags, avoided set fishing geair, i.e. gill nets 

 in the area, limited catch of alewives to a 

 size that could be handled conveniently, avoided 

 rough bottom, or ran out of time. Gear was 

 damaged severely on 19 occasions and mod- 

 erately on 30 drags. 



During naost cruises trawl drags were made 

 at regular depth intervals at preselected loca- 

 tions. These depth series were generally nnade 

 along the contour at 5-fathom intervals from 

 the shallowest depth possible to fish, which 

 depended on bottom conditions, to 50 fathoms 

 and at 10-fathom intervals thereafter to 70 or 

 80 fathoms (88 fathoms on one occasion). Not 

 all depth series, however, covered all depths 

 and fishing effort varied from year to year 

 and port to port (see fishing effort). Reasons 

 for incomplete depth series other than bottom 

 conditions were generally gear limitations in 



1962 or lack of tinne. Series out to 70 fathoms 

 were usually made only during cross-lake 

 transects. During this study, 84 depth series 

 were made, 38 of which covered a range of 

 40 fathoms or more. 



Bottom irregularities and currents at times 

 caused variations of several fathoms in actual 

 fishing depths. To simplify analyses, actual 

 fishing depths are rounded off to the nearest 

 5- or 10-fathom midpoint as follows: 



Depth Designated 



range depth 



Fathoms Fathoms 



Depth Designated 



range depth 



Fathoms Fathoms 



In making some depth analyses, I considered 

 three depth zones as follows: 



1. Shallow water - 3 to 17 fathoms (5- to 

 1 5-fathom intervals) 



2. Intermediate depth - 18 to 55 fathoms 

 (20- to 5Q-fathon-i intervals) 



3. Deepwater - 56 fathoms and deeper 

 (60- to 90-fathom intervals) 



During 1962, drags were made in randonn 

 directions or in opposite directions on alter- 

 nate drags; however, in 1963, biologists noted 

 that current apparently affected the size of 

 catches. Thereafter on each series, two drags 

 were made initially in opposite directions at 

 the same depth. If a drag made in one direc- 

 tion had a substantially greater catch, all 

 remaining drags in the series were made in 

 the direction producing the larger catch. 



Evaluations of fishing results are based 

 here on two methods of calculation: (1) Catch 

 rate - which is pounds produced per unit effort 

 for all drags in a particular evaluation and 

 (2) average catch for effective effort - which 

 is pounds per unit effort for only those drags 

 that contained the species being evaluated. 

 Effective fishing effort has been discussed 

 by Hile (1962). All analyses of catch rates 

 and average catch for effective effort are 

 based on l/2-hour dragging time unless speci- 

 fied. For most evaluations, total dragging 

 time was divided into 1/2-hour periods. 



To define more accurately the seasonal 

 availability of alewives to bottom trawls in 

 southern Lake Michigan, the seasonal fishing 

 depths of three commercial trawlers from 

 Saugatuck, Mich., were evaluated. Since 1961 

 these commercial trawlers have provided the 

 Bureau of Commercial Fisheries with records 



