9-21 



similar except for anomalously low concentrations in the June, July and 

 August, 1975 data. Phytoplankton total cell counts wore not corres- 

 pondingly low and chlorojjhyll data for this time period aro ;;u:;poct (sc>o 

 Section 4) . It therefore does not seem likely that low food supply was 

 the cause of the observed high mortality. The only known predator of 

 adult oysters found in great numbers near Harbor Station (epibenthic 

 trawl station 8) was the seastar Aster ias forbesi which was occasionally 

 found in the experimental trays. Table 9-10 shows the monthly occurrence 

 of A. forbesi in epibenthic trawls at Harbor Station from 1974-1976. 

 The greatest densities of seastars, May-October 1974, were not correlated 

 with the highest oyster mortalities. May- July 1975. It does not seem 

 likely that predation was the cause of the observed high mortality, but 

 that poor initial health as indicated by low condition indices was. 



Table 9-2 indicates percent survival of oysters by month at 



both Harbor Station and Fort Hale during the period 1973-1977. Data 



from 1973 were not included in the hypothesis testing analysis because 



time periods during which measurements were taken were different than in 



subsequent years. However, a correlation analysis (alpha = 0.05) shows 



that monthly change in percent survival at both experimental stations 



was very similar for 1973 and all subsequent years. Table 9-11 gives 



correlation coefficient (r) values for 1973 versus all subsequent years 



at both Harbor Station and Fort Hale. These values ranged from 0.77 



(1975, Harbor Station) to ,0.97 (1977, Harbor Station; r„ ^^ = 0.4). 



0. 05 



These results imply that the same pattern of mortality was exhibited in 



1973 as in subsequent years, i.e., mortality was not significantly 



different between stations (r = 0.97, alpha = 0.01), mortality was 



significantly higher in 1975 than in 1973 (r = 0.77, r„ „^ = 0.84) and 



. 05 



mortality was similar between years 1973 and 1974, 1976, 1977. These 

 results corroborate the conclusions of the tests of hypothesis 1) that 

 pre- and postoperational mortalities were similar and that no effect can 

 be discerned on oyster mortality with respect to the operation of New 

 Haven Harbor Station. 



