DRYFOOS, CHEEK, and KROGER: ATLANTIC MENHADEN MIGRATIONS 



leased within the area 

 and season divided by 

 total number of indi- 

 vidual fish landed with- 

 in the area and season. 

 2. Maximum-monthly Highest monthly ratio 



density 



3. Last-month-of- 

 season density: 



of number of recoveries 

 from releases within 

 the area and season to 

 the total number of in- 

 dividual fish landed 

 during the month. 

 Number of recoveries 

 during the last month 

 of fishing from releases 

 within the area and 

 season divided by the 

 total number of indivi- 

 dual fish landed during 

 the month. 



If the areas were truly closed to recruitment, 

 immigration and emigration, and if there were 

 rapid dispersal of tagged fish throughout the 

 population in each area, any one of these ap- 

 proaches would provide adequate density in- 

 dices. 



We observed that the maximum density was 

 not always achieved at the end of the season 

 and believe that the effects of recruitment and 

 migration near the end of the fishing season 

 confound the third approach. We believe that 

 selecting the month with the highest density 

 may also be misleading due to nonrandom dis- 

 tribution of tags within each area. We selected 

 the season average as a robust statistic for de- 

 termination of an index of achieved tag density. 



After obtaining the index of density (the 

 season-average density) for each area, we de- 

 termined the standardization factor necessary 

 for each area to achieve an arbitrarily selected 



MASS 



PENN 





SPRING AND SUMMER 



, MASS 



CONN^ 



PENN 



FALL AND WINTER 



Figure 3. — Generalized movements of lagged Atlantic menhaden. 



727 



