release station. The possibility exists also that the 

 bottles at this station were leleased in an aiea of 

 mixing between north- and south -bound cunents. 



None of the 110 drift cards released on the 

 Ludington -Manitowoc transect were recovered. 



I have talked to commercial fishermen from 

 Liidington who speak freely of currents "in and out. " 

 They report that frequently currents flow in com- 

 pletely opposite directions along a north-south line 

 a short distance offshore, and report also an incon- 

 stancy of these currents, which often change from 

 one day to the next. 



Rate of drift . --The average rate of drift for all 

 bottles released on the 7 crossings ranged from 1. 

 to 2. 1 miles per day compared to 1. 3 to 5. 7 miles 

 per day for drift envelopes (table 4). The difference 

 in mean rate of drift between envelopes and bottles 

 is not as great as appears from these averages. Re- 

 coveries of drift envelopes were nearly all from re - 

 leases at inshore stations whereas drift bottles were 

 recovered from all stations. In general, rates of drift 

 for bottles released at inshore stations were higher 

 than the rates for bottles released offshore. Bias be- 

 cause of difference in recovery pattem can be elim- 

 inated partially by comparing rates only for recovery 

 of units from stations where both envelopes and bot- 

 tles were recovered. From 26 of such stations, 20 in- 

 dicated faster drift rates for envelopes than for bot- 

 tles (table 4); thus a real difference exists between 

 the two units. 



The slow drift of bottles released at offshore 

 stations (table 4) suggests the possibility of gyral 

 movement of surface water. Calculated drift rates 

 of bottles moving in curved paths to landing points 

 would be lower than actual rates of movement since 

 a straight line was used from release to recovery 

 point in determining distance traveled. 



Rates for some individual bottles were very 

 much higher than the average, especially for those 

 released in the littoral zone. Three bottles released 

 at the station nearest Grand Haven on August 19 

 traveled slightly more than 100 miles to the north at 

 a rate of approximately 10 miles per day (table 9). 

 A similar rapid drift to the north had occurred 3 

 weeks previously when 3 bottles traveled 16 miles 

 to the north in 2 days (table 9). 



General characteristics of surface-water move- 

 ments . "The surface -cunent pattem in southern Lake 

 Michigan in 1954 was not stable. Over any one tran- 

 sect the current had changed from one release date to 

 the next. The littoral current to the north off Grand 

 Haven appears to have been the most stable; it was ap- 

 parent from recoveries made from releases at four dif- 

 ferent times. A similar north -bound littoral current off 

 South Haven followed both the August 3 and September 

 15 releases (fig. 4). From the remaining areas drift 

 was mainly from west to east except that recoveries from 

 the southwestern quarter of the lake were made in equal 

 numbers along the east and west shores. 



Central and Northern Lake Michigan, 1955 



Grand Haven -Manitowoc -Sturgeon Bay transects. — 

 The Grand Haven -Manitowoc section was traveled on 

 April 26 and the Manitowoc-Sturgeon Bay leg on April 

 27. The recoveries from drift bottles released on the 

 two days were mostly from Michigan shores (282 of 

 325 units). Most bottles were recovered north of their 

 release station (figs. 9-10). Movements of bottles with 

 drags and sand -ballasted bottles released on April 26 

 were similar whereas the drift of the two types of 

 bottles differed significantly on the Manitowoc-Stur- 

 geon Bay leg (figs. 9-10). Most of the sand -ballasted 

 bottles were recovered from the eastern shores of the 

 lake (34 of 44 bottles recovered), whereas well over 

 half of the bottles with drags (29 of 41) were recovered 

 from the northern and western shores. 



The north -bound littoral current off Grand Haven, 

 found consistently in the 1954 studies, was evident 

 again as is shown by the recoveries from the liberations on 

 April 26. 



The prevailing winds for May, when most of the 

 bottles released April 26-27 were adrift, were from the 

 southwest and northwest (fig. 8, table 5). 



Ludington -Manitowoc transect. --Movements of 

 drift bottles with drags and sand -ballasted bottles re- 

 leased on the Ludington -Manitowoc transect were in 

 good agreement. The first of the 5 transects was made 

 on May 13 when 240 units were released. Bottles re- 

 leased on this date appeared in general to move in a 

 counterclockwise pattern (figs. 11-12). Most of those 

 from the 3 westernmost stations moved southward but, 

 from these stations eastward the trend was increasing to 

 the east and north. 



16 



