DRYFOOS, CHEEK, and KROGER: ATLANTIC MENHADEN MIGRATIONS 



Table 16. — Actual and comparative values of catch, effort, catch per unit effort (CPUE), percent 

 recapture, availability index and population size for menhaden landings in Chesapeake Bay, 1967-70 

 using 1967 as the base year. (Comparative values are in parentheses.) 



threefold between 1969 and 1970, the avail- 

 ability index more than tripled, so the difference 

 in the population size was relatively small. 

 Table 16 suggests that most of the variation in 

 catch during 1967-70 in Chesapeake Bay results 

 from the reduction in effort and the fluctuations 

 in availability rather than actual changes in 

 fish abundance. 



Anomalies in survival rates calculated from 

 tagged fish or age composition data provide 

 another indication of fluctuation in availability. 

 When availability is high and a larger than 

 normal catch is made, a correspondingly large 

 number of fish are recaptured. Then, compared 

 to a normal year, the survival rate is overes- 

 timated when the high number is the numerator 

 and underestimated when it is the denominator. 

 Such an anomaly was noted in our estimates of 

 survival rate based on tag recoveries and also 

 in age composition data for Chesapeake Bay 

 in the summer of 1968 (Henry, 1971). 



Differences in monthly catches between 1967 

 and 1968 from June to September also suggest 

 changing rates of availability. The catch for 

 these months in 1968 was up to 28% over the 

 previous year, but nearly three-fourths of the 

 difference occured in July. Most of these fish 

 were caught near the Maryland border in the 

 vicinity of Tangier Island. Since the time and 

 location of large catches was so restrictive, the 

 large catch probably resulted from fish moving 

 from Maryland to Virginia, rather than a gen- 

 eral increase in the number offish in the Bay. 



Vulnerability appears to have varied in re- 

 cent years in Chesapeake Bay. The proportion 

 of the weekly catch made on Mondays in Chesa- 

 peake Bay has increased since 1962, coinciding 

 with an increase in fishing effort in the early 

 1960's and a decrease in relative abundance 

 during the decade (Nicholson, 1972b). Although 



this phenomenon had not generally been ob- 

 served in other areas, it demonstrates one type 

 of fluctuation in availability. 



SUMMARY 



From 1966 through 1969, over 1 million 

 adult Atlantic menhaden were tagged in the 

 major fishing areas from Long Island Sound to 

 Florida. We estimate that more than 200,000 

 tags have been recaptured. 



Tag recoveries demonstrate a seasonal mi- 

 gration of menhaden along the coast: North- 

 ward in spring and early summer and south- 

 ward in fall. As the fish grow older and larger 

 they migrate farther northward each spring. 

 Maximum migration speeds from one area to 

 another along the coast vary from 11 to 16 

 km/day. 



Rates of interchange between fishing areas 

 were determined from recoveries of the 1967 

 and 1968 releases. An important feature of the 

 data is that 21% of the recoveries from fish re- 

 leased in Chesapeake Bay in 1967 and 1968 

 occurred off the coasts of New York and New 

 Jersey 1 yr later. These fish from Chesdpeake 

 Bay made up 72% of the catch in New York and 

 New Jersey. 



Preliminary estimates of population param- 

 eters were made from tag-recovery data. 

 Survival rates were estimated by several meth- 

 ods; i.e., ratio of recoveries in successive years, 

 Robson-Chapman catch curve analysis tech- 

 nique, and age composition of catch for 1966 to 

 1968. Rates determined yearly from ratio of 

 recoveries varied due to fluctuations in avail- 

 ability. Annual survival rates were based upon 

 Robson-Chapman catch curve analysis and age 

 composition of catch. Both use several years 

 data and agree closely, averaging 0.23. Better 



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