FISHERY BULLETIN: VOL. 78, NO. 1 



The egg diameter frequencies shown in Figure 2 

 indicate Atlantic mackerel are serial spawners, 

 i.e., several batches of eggs are shed by individuals 

 throughout the spawning season. The presence of 

 multiple modes in the egg diameter frequencies 

 (Figure 2a-c) and ripening eggs in partially spent 

 ovaries (Figure 2d) are indicators of serial spawn- 

 ing (Clark 1935; MacGregor 1957). A cytological 

 study by Bara ( 1960) has shown that eggs are not 

 shed continuously as stated by Cunningham 

 (1889) but are shed in several batches during the 

 2-mo spawning period. 



The potential number of batches spawned was 

 estimated by determining the ratio of ripe eggs to 

 all yolked eggs in six running ripe ovaries. Atlan- 

 tic mackerel eggs, from plankton samples, ranged 

 from 1.01 to 1.29 mm diameter (Berrien 1975; 

 Ware 1977); therefore, in this study, eggs 1.05 mm 

 and larger were assumed to constitute the next 

 egg batch to be spawned. The ratios ranged from 

 13.7 to 21.7% and averaged 17.0%. Thus the po- 

 tential number of batches spawned per individual 

 was five to seven and averaged six batches. 



Fecundity estimates ranged from 285,000 to 

 1,980,000 eggs for fish between 307 and 438 mm 

 FL. Preliminary plots indicated a curvilinear rela- 

 tionship existed for fecundity-length and a linear 

 relationship for fecundity-weight and fecundity- 

 age. However, correlation coefficients (r) were 

 higher for the logarithmic relationships of 

 fecundity-weight and fecundity-age, therefore, all 

 variables were transformed and linear regression 

 equations of the form log Y = a + b(\og X) were 

 calculated. Data plots and the equations relating 

 fecundity to fork length, gutted weight, and age 

 are shown in Figures 4-6. 



DISCUSSION 



Spavming by the southern contingent of Atlan- 

 tic mackerel apparently peaked during the 2-wk 

 period between 21 April and 4 May 1977. This 

 2-wk period represents the mean peak spawning 

 time within the study area (Maryland to Rhode 

 Island) since there is a north and eastward pro- 

 gression of spawning during the spring migration 

 (Bigelow and Schroeder 1953; Berrien 1978). Ber- 

 rien et al.^ observed the north and east progression 



*Berrien,P. L., A. Naplin, and M.R.Pennington. 1979. At- 

 lantic mackerel, Scomber scombrus, egg production and spawn- 

 ing population estimates for 1977 in the Gulf of Maine, Georges 

 Bank, and Middle Atlantic Bight. Int. Counc. Explor. Sea 

 ICES/ELH Symp./DS:9, 17 p. 



1.70 



1.50 



30 



log F 8.346 + 5.544llog FLI 



N 218 



r 88 



Si X 0.066 



360 380 



FORK LENGTH(mm) 



Figure 4. — Relationship of fecundity and length and the pre- 

 dictive logarithmic (base 10) regression for Atlantic mackerel 

 in 1977. 



3 90 



O 



log F 1721 + 1.547 Hog GWI 



N 218 



r 81 



Sy X 081 



.'•>::'Vi' '■ ■• 



300 



400 500 600 



GUTTED WEIGHT I g) 



700 



800 



900 



Figure 5. — Relationship of fecundity and weight and the pre- 

 dictive logarithmic (base 10) regression for Atlantic mackerel 

 in 1977. 



in plankton mackerel egg densities. They found 

 spawming intensity in the Middle Atlantic Bight 

 was low during mid-April and increased rapidly 

 by late April, and maximum egg densities oc- 

 curred about 25 April. Spawning continued at a 

 reduced rate throughout May and then decreased 

 steadily during June. Very similar results are in- 

 dicated from my analysis of gonad somatic indices 

 during the 1977 spawning season. 



106 



