FISHERY BULLETIN: VOL. 82, NO. 2 



suggestive of ambisexuality. This is consistent 

 with the conclusion of Loosanoff (1953) that the 

 sexes are separate. The sex ratio, however, was 

 particularly imbalanced in favor of males. In the 

 69 quahogs considered less than fully mature, 55 

 were males and 14 were females, while in the 28 

 sexually mature specimens, 19 were males and 9 

 were females; the observed ratios were 4:1 and 2:1, 

 respectively. The data were subjected to goodness 

 of fit tests under the hypothesis of a 1:1 ratio 

 between the sexes; results indicated highly signif- 

 icant (P<0.01) and significant (P<0.05) dif- 

 ferences, respectively. 



Microscopic examinations of gonadal tissue 

 squashes of the 199 clams collected in 1980 re- 

 vealed an overall sex ratio of 96 males and 103 

 females. These results were not significantly dif- 

 ferent from parity (1 male:1.07 female), but by 

 separating the data into 10 mm size groups, a 

 significant difference (P 0.05) in favor of males 

 was indicated in the size group 80-89.9 mm, and a 

 highly signficant difference (P < 0.01) in favor of 

 females was indicated in the 100-110 mm size 

 group (Table 2). 



Figure 11 shows the combined observations of 

 clam size and sex obtained from the 1978 and 1980 

 samples. In these samples, males tended to 

 decrease in occurrence relative to females with 

 increasing shell size. 



TABLE 2. — Occurrence of male and 

 female ocean quahogs, Arctica islan- 

 dica, within 10 mm size groups off 

 Long Island, N.Y., August 1980. 



too 



DISCUSSION 



The time of sampling, sample size, and capture 

 of small quahogs provided a basis for detection of 

 the differentiated and sexually mature stage at 

 younger ages and smaller sizes as compared with 

 the study of Thompson et al. (1980b). In the pres- 

 ent study, 5- and 6-yr-old quahogs 41 and 36 mm 

 long, respectively, were considered sexually ma- 

 ture; the youngest mature quahog reported by 

 Thompson et al. (1980b) was a 42 mm male 11 yr 

 old. The intermediate gonadal condition was 



80 - 



-J 60 



1 



k 



0. 



.' 



N= 170 d*o* 126 $9 

 1 :074 



J_ 



_L 



_L 



L 



< 20-29 40-49 60-69 



SIZE CROUPS 



80-89 



100-109 



FIGURE 11. — Sex of ocean quahogs. A rctica islandica, relative to 

 shell length (mm) in collections off Long Island, N.Y., 1978 and 

 19S0 



found to occur at lower ages and smaller sizes than 

 by Thompson et al. (1980b), and slightly smaller 

 sizes were found for sexually mature quahogs. 

 Variability in attainment of sexual maturity at 

 age/size was observed in both studies. 



The onset of sexual maturity at young ages has 

 been reported for several bivalves. The bay scal- 

 lop, A rgopecten irradians, attains maturity at 1 yr; 

 the hard clam, Mercenaria mercenaria, soft clam, 

 Mya arenaria, and blue mussel, Mytilus edulis, 

 matures at 1-2 yr ( Altman and Dittmer 1972). Surf 

 clams, Spisula solidissima, from an inshore 

 habitat showed precocious sexuality in a few post- 

 larvae or juveniles; they spawned at 1 yr, but 

 reached full maturity at 2 yr (Ropes 1979a). Sea 

 scallops, Placopecten magellanieus, spawned at 

 about 1.5-2 yr after forming the first growth ring 

 (Naidu 1970). In apposition to more mature 

 gonadal conditions, some scallops in his collec- 

 tions were considered undifferentiated and dif- 

 ferentiated male and female immature specimens. 

 Lucas (1966) observed precocious sexuality in a 

 scallop (Chlamys varia) and two clams 

 (Glycymeris glycymeris and Venus striatula) from 

 waters off France. The development of the repro- 

 ductive potential during the early life history of 

 these several bivalves seems consistent with esti- 

 mates of their life span, which are as short as 2 yr 

 for the bay scallop and as long as 30 yr for the surf 

 clam (Belding 1906; Ropes 1979a). In contrast, the 

 present study revealed that ocean quahogs attain 

 maturity at 5-10 yr of age, and Thompson et al. 



264 



