COMMERCIAL FISHERIES REVIEW 



Vol. 28. No. 9 



Commercial fishermen reported that the heaviest run of fish up the river was encountered 

 around June 19 and that the main run may have been over by June 29, even though some schools 

 of alewives remained in the harbor. They also reported extremely large schools of alewives 

 in Lake Michigan. As funds were unavailable to continue operation of the air curtain, the 

 study was ended June 30, but the main run of the alewives was apparently encountered during 

 the study. Further migrations of alewives into the Milwaukee River was not apparent during 

 July, and caused no further nuisances. 



Generally, the visual observations revealed large numbers of dead fish below the air cur- 

 tain and smaller numbers above. The largest numbers of dead fish were noted at the junction 

 of the Menomonee River and in the area of the junction of the Kinnickinnic River. Although 

 dead fish were constantly sighted upstream, it is not known how long they had been dead. 

 Many of the fish above the air curtain were quite deteriorated. Most fish were probably noted 

 several times in the week- to- week searches. 



Fish were often observed dying downstream from the air curtain. In only a few cases, 

 however, were dying fish noted in the Milwaukee River above the air curtain. Because of in- 

 ability to determine when those fish had died, the visual method of observation was unreliable 

 for showing quantitatively the effectiveness of the air curtain. It did indicate, however, that 

 the air curtain was somewhat successful in stopping the alewives from migrating up the Mil- 

 waukee River. 



Commercial establishments in the downtown area were checked to determine whether the 

 water intakes for their air conditioning systems were affected by large numbers of alewives. 

 Personnel of these establishments reported an exceptional decrease of alewives found intheir 

 intakes during May and June. All establishments reported that around the third week of June, 

 many fish were again found in their intakes, which coincides with the time that the large run 

 of alewives was encountered and the time that the flushing tunnel was being operated. 



The effectiveness of the air cur- 

 tain may have been biased by several 

 factors. The location of the curtain 

 during the study may have hindered 

 evaluation since the fish had few alter- 

 native routes when the curtain was 

 reached. Commercial operators, while 

 attempting to fish in the test area, ran 

 into difficulties due to currents and 

 large amounts of debris that tore their 

 nets during fishing (fig, 11). Conse- 

 quently, commercial netting was dis- 

 continued after two attempts to remove 

 alewives in this area. The gill-netting 

 data showed that about 36 percent of 

 the fish near the bottom may have gone 

 through the air curtain during this 

 study. Thus, migration through the 

 curtain may have been due to the large number of fish involved, the lack of alternative routes, 

 and a "forcing" of the fish through the barrier. Commercial harvesting of the alewives in the 

 main harbor may have alleviated this problem by reducing the number of fish reaching the 

 area below the air curtain. 



Fig. 11 - Dead fish and debris in river. 



The migration of fish up the Milwaukee River may also have been affected to some ex- 

 tent by the removal of about 10,000 pounds of alewives by fishing in the harbor area by com- 

 mercial fishermen (table 2). Most of those fish were caught in the outer harbor and only one 

 small catch was made in the Kinnickinnic River. 



