CAIN: REPRODUCTION AND RECRUITMENT OF RANGIA CUNEATA 



>. 15-, '*^° 



CO 



Figure 9.-Gonadal phases and set- 

 ting of Rangia at station C in relation 

 to salinity from 1970 to 1971. The 

 length of each shaded area represents 

 the percentage frequency of clams in 

 each category. 





 1000- 



19 7 1 



u. « 





^dX 



100- 



^4 





^_E 





OCT NOV DEC JAn'*"fEB ' MAR ' APR ' MAY ' JUN ' JUL 



DSPENT ^PARTIALLY SPENT BriPE H) L ATE ACT I VE □ EARLY ACTIVE 



and early spring. During summer and fall the 

 gonads of most clams could be recognized (Table 

 1). The ratio of females to males at station A was 

 not significantly different from 1:1. Females 

 predominated at stations B, D, and C during the 

 summer and fall months of 1970 and 1971. When 

 the clams of non-determinable sex are added to 

 the male group, there are still significantly more 

 females. 



Of the clams collected in late June 1970 at sta- 

 tion A, none measuring 5-10 mm contained 

 gonads. In the second group 50% showed signs of 

 gametogenesis and had recognizable sex products; 

 70% of the third group had discernible gonads; and 

 most clams in the fourth group contained gonads. 

 Most small clams were males, but too few were 

 examined to test the significance of sex ratios. 



Larval Setting 



The number of Rangia clams setting at each 

 station is shown in Figures 7 to 14. This number 



Table 1.— The ratio of females to males and the number of clams 

 with non-determinable (ND) gonads at each station. Summer 

 and fall seasons were tested with the ND clams added to the male 

 group. 



Seasons 



Station A 

 F ND M 



Station B Station D 



ND M F ND M 



Station C 

 F ND M 



166 9 70' 



Summer and 



fall 1970 140 153ns 209 3 57** 

 Winter and 



spring 61 53 83 46 128 35 13 44 13 29 118 66 



Summer and 



fall 1971 127 7 102ns 178 22 34** 41 5 11** 138 38 54** 



ns = not significant. 

 ** ^ highly significant. 



does not provide an estimate of survival because 

 predators were excluded by the screen cover. The 

 number of set clams at both deep and shallow sta- 

 tions by season is shown in Table 2. At stations A 

 and As a small number ( < 7) set during late July 

 and August 1970. In December 1970 through 

 March 1971 set clams were common but not very 

 abundant at these two downriver stations. Only 

 one setting period (29 individuals) was recorded 

 during the summer months at station As. Larvae 

 began setting again during the third week of 

 December 1971 with 70 at station A. Collectors at 

 both stations continued receiving set until 

 sampling was terminated on 18 January 1972. 



Setting at stations B and Bs was sporadic dur- 

 ing the spring and summer of 1970, with no more 

 than four clams in any jar. Setting began at sta- 

 tion B in mid-November 1970 and continued there 

 until late March 1971. A maximum of 42 in- 

 dividuals was collected on 8 February 1971. Set 

 clams were found on only one sampling date dur- 

 ing the next summer. Setting in the fall began in 

 late October 1971, with very large numbers during 

 late November and early December. 



Setting at station D was similar to that at sta- 

 tion B except more individuals were found during 

 the fall and winter of 1970-71. One hundred 

 eighty-five were collected in the station D bottle in 

 mid-December 1971. 



Only data beginning in September 1970 were 

 available from station C. As noted in the tissue 

 sections, spawning had commenced earlier. Set- 

 ting from early September 1970 to March 1971 was 

 very heavy, with 257 clams collected at this station 



421 



