FISHERY BULLETIN: VOL. 81, NO. 4 



FIGURE 1 . — Map showing locations of the Fairfield, Conn. , study site 

 (A) and the Stony Brook and Shinnecock, N. Y., study sites (B and C, 

 respectively) (Newell et al. 1982). 



Formalin 2 . This procedure was carried out during the 

 first 4 mo of study. During the remainder of the 

 study, sections of the mantle tissue and the visceral 

 mass gonadal tissue were removed, since a closely 

 related mussel of the family Mytilidae, Geukensia 

 demissa, was shown to contain one type of sex cell in 

 the mantle and the other in the visceral mass 

 (Brousseau 1982). The M. edulis tissues were then 

 prepared histologically for examination according to 

 the method described by Brousseau (1978). A mi- 

 croscopic examination was made of the mantle 

 and visceral mass gonadal tissues before assigning 

 each individual to the appropriate category of 



: Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



gonadal condition as described by Chipperfield 

 (1953). The results were based on the developmental 

 condition of the mantle tissue in all individuals 

 examined. 



Mean oocyte diameter was determined for a rep- 

 resentative sample of ripe females, selected at ran- 

 dom from each of the reported spawning periods. 

 Twenty oocytes per individual were measured using 

 an ocular micrometer. Only those oocytes which were 

 spherical in shape and ready for release were select- 

 ed for measurement. 



The reproductive condition of the mussels was 

 measured by stereology, a procedure adopted by 

 Bayne et al. (1978) and Newell et al. (1982). This 

 method is based on a procedure referred to as point- 

 counting volumetry, which is accomplished by 

 superimposing a regular point lattice on the tissue 

 section and counting the points which lie on transec- 

 tions of the sex cells (Weibel et al. 1966). The propor- 

 tion of gonadal tissue that is comprised of follicles 

 containing developing or ripe gametes is reported as 

 the "gamete volume fraction" (GVF). For any 

 individual mussel, the GVF can vary between zero, 

 for a reproductively inactive mussel, and one, for a 

 mussel showing maximal reproductive development. 

 The monthly mean GVF represents the mean of 10 

 estimates of the GVF from each mussel sampled. The 

 number of mussels included in the estimate varied 

 from 18 to 25. These proportions were then arcsine 

 transformed, and the variance for each monthly GVF 

 was calculated. 



100 



80-- 



60-- 



at 



40- - 



20- 



O N 



1980 



A M 



1982 



MONTHS 



FIGURE 2.— Proportion of Mytilus edulis population with active or inactive gonads during 1980-82. Open portions of each represent inactive 

 gonads (indifferent, no gametogenesis, or spent); solid portions represent active gonads (developing, ripe gametes, or partially spawned). 

 Observations on males and females are combined. 



734 



