TABLE 15. Estimated larval winter flounder growth rales at station C in the Niantic River based 

 on linear regression, with r values, of weekly mean length and mean water temperature during the 

 first six weeks of each time period. 



nme period of weekly mean lengths used in estimating growth rate 



Mean during a 6-week period starting the week of the of the first weekly mean length used in 

 estimating the grovrth rale. 



The mean water temperature for each year was 

 calculated for a 6-week period starting in the same 

 week that the first mean length was used in the 

 growth rate calculation. Mean water temperatures 

 were similar in all years, except for 1985, which 

 was the highest and also had the lowest growth 

 rate. The slower growth in 1985 could have been 

 further evidence for an optimum temperature for 

 growth and if temperatures were too high, growth 

 rates would have decreased. Also, another pos- 

 sibility was that growth was density-dependent, 

 as Stage 2 larvae in 1985 were the most abundant 

 at station C over the 5-year period (Fig. 19). 

 Laurence (1977), in a laboratory study on larval 

 winter flounder at 8°C, reported a decrease in 

 growth rate as prey densities decreased. With just 

 5 years of data (4 of them had similar tempera- 

 tures) and no information on prey densities, it 

 was not possible to discriminate between the ef- 

 fects of temperature and food avaUabUity on 

 grovrth rates. 



The densities of larvae collected at EN provided 

 a long time-series and should have been represen- 

 tative of larval abundance in Niantic Bay. Sam- 

 pling frequency was high with 18 samples per 

 week in 1976-82 and 8 samples per week in 

 1983-87. Annual growth rates were estimated in 

 a fashion similar to station C above. A linear 

 model adequately described growth using weekly 

 mean lengths (Table 16). In general, growth rates 

 were lower in the bay than at station C. Average 



daily water temperatures were available from con- 

 tinuous temperature recorders in the MNPS intake 

 and a comparison of mean water temperatures in 

 the lower Niantic River and in the bay during 

 March through May for 1983-1987 showed that 

 temperatures in the bay were consistently lower. 

 During the 5-year period this seasonal difference 

 ranged from 0.4 to 1.5°C. Although this difference 

 was small, a similar difference in mean water tem- 

 perature in the laboratory of 5.4 to 6.9°C caused 

 significantly different growth rates (Table 14). 

 Mean water temperatures were determined for a 

 40-day period starting at the beginning of the 

 week when the first weekly mean length was used 

 in estimating the growth rate. A positive rela- 

 tionship was found between growth rate and water 

 temperature, which was described by a two -term 

 polynomial equation (Fig. 29). The increased 

 growth rate with temperature would have ac- 

 counted for the earlier dates of peak abundance 

 seen at higher temperatures and illustrated on 

 Figure 21. 



In conclusion, food availability and water tem- 

 perature appeared to have been the two most 

 important factors controlling larval growth 

 (Buckley 1982). Iloude pointed out that surpris- 

 ingly small changes in growth could have large 

 effects on subsequent recruitment in fishes. Slight 

 declines in grovrth rate caused by less than opti- 

 mum food, unfavorable temperatures, disease, or 

 pollution can lead to longer developmental times 



Winter Flounder Studies 



195 



