-; 20 



o 



X 



X 



I- 



LU 



Q 



40 



50- 



January | February | March 



April 



May 



June I July 



MONTH 



August I September] October | November | December 



Figure 4. — The pattern of seasonal movements of alewives In souttiern Lake Michigan based on bottom trawl catches by 

 commercial trawlers out of Saugatuck, Mich. When sufficient data were available, tabulations were made for three 

 periods each month, the 1st to the 10th, the Uth to the the 20th, and the 21st to the end of the month. 



From the beginning of July to about mid- 

 September the lake is stratified by tem- 

 perature, and the depth distribution of 

 alewives appears to be controlled by 

 temperature. Catch rates and bottom 

 temperatures taken from July 15 to 

 July 23, 1964, indicate that catch rates 

 decrease generally with temperature and 

 few alewives are taken in trawl catches 

 in areas where the bottom temperature 

 is colder than 50 F. The availability of 

 alewives from Jialy to mid-September 

 can also be related to depth since most 

 of the alewives are caught in 15 fathoms 

 or less and few are taken deeper than 



25 fathoms. Catch rates begin to drop 

 off during July and through this period. 

 From mid-September through most of 



November the fish are scattered and 

 taken in trawls from shore to about 35 

 fathoms. The largest concentrations are 

 taken generally between 15 and 20 fa- 

 thoms. Catch rates are low during this 

 period. 



From the end of November to the end of 

 the year the fish remain scattered, the 

 best catches vary from day to day at 

 depths from 15 to 30 fathoms, and fish 

 concentrations must be searched for 

 daily. The movement to deep water is 



apparently rapid but has not been docu- 

 mented yet. This deepwater movement 

 apparently takes place sometime in late 

 Decennber or early January. Catch rates 

 during this period are also low and 

 sporadic. 



Alewives were taken in commercially sig- 

 nificant amounts by the Kaho in every month 

 except January and June. Only 13 drags were 

 made in January, and none was deeper than 

 30 fathoms. Catches of 3,000 and 3,400 pounds 

 in 1/2-hour drags taken on February 3, and 

 catches of 750 and 1,000 pounds per one-half 

 hour made on December 17 indicated that ale- 

 wives might be available in commercial 

 amounts in January. The 65 drags in June 

 1962 were made in 10 fathoms or deeper when 

 spawning alewives were in water shallower 

 than 10 fathoms. Commercial trawlers have 

 made large significant catches during January 

 and June. 



Catch rates varied during the year. Catch 

 rates were highest during the inshore spawn- 

 ing migration and spawning and were high 

 when schools were in deep water in winter. 

 After major spawning (about July 1 ) to the 

 end of the year, catch rates were lower, be- 

 cause alewives dispersed and were not con- 

 centrated on the bottom. 



12 



