Several important developments in our winter 

 flounder program this past year included the es- 

 tablishment of a stock and recruitment relation- 

 ship and data analyses leading to increased knowl- 

 edge of the dynamics of larval and juvenile stages. 

 The three-parameter stock and recruitment model 

 helped explain the variability seen in adult abun- 

 dance and demonstrated that water temperature 

 during spawning and early life history was as im- 

 portant as the parental stock size in determining 

 recruitment success. Poor recruitment was asso- 

 ciated with wanner-than-average years and strong 

 year-classes were produced during cold years; this 

 has also been found for a number of other winter- 

 spawning marine fishes. Although strong envi- 

 ronmental (i.e., density-independent) factors were 

 implicated as important to winter flounder repro- 

 ductive success, density-dependent mortality must 

 also have been a significant stabilizing mechanism, 

 given the relatively small range within which the 

 absolute abundance of the winter flounder varies. 



The use of the Gompertz function to describe 

 larval abundance led to the fmding that the k 

 parameter (i.e., the shape parameter determining 

 the steepness of the Gompertz curve) described 

 well the magnitude and breadth of larval distri- 

 bution over time (see Figure 23). This parameter 

 was found to be directly related to February water 

 temperatures, with larger K values associated with 

 warmer years and smaller values for colder years. 

 This illustrated that in a cold year, larval abun- 

 dance, as characterized by the Gompertz function, 

 was slow in reaching a peak and had a more 

 broadly based abundance curve. Conversely, in 

 a warm year the curve peaked quickly and had a 

 narrow base. A highly significant relationship 

 was found between the k parameter and winter 

 flounder recruits 3 years later (see Figure 24). 

 This implied that in cold years somewhat fewer 

 larvae were present at any one time, but the sea- 

 son was longer in duration; the result was a 

 stronger year-class. The February temperatures 

 would have most likely affected spawning and egg 

 incubation, resulting in protracted spawning and 

 longer time to hatching. With larvae less con- 

 centrated over time, effects of predation upon lar- 

 vae may have been less and there likely would 



have been a better chance for larvae to encounter 

 adequate food densities. However, exact causal 

 mechanisms are still unknown. 



Results of both the larval analyses and the 

 three-parameter stock-recruitment model showed 

 that year-class strength was related to events in 

 the early life history of the winter flounder, for 

 which water temperature was an important factor 

 (by itself or as a surrogate for other factors). .lust 

 as the stock and recruitment relationship v/as used 

 to describe recruitment as a function of adult 

 stock and February temperatures, the relationship 

 found between the k parameter and the age 3 

 recruitment index can be used as a second and 

 independent indicator of future adult recruitment. 

 The empirical relationship between k and the age 

 3 recruitment index (R) given on Figure 24 was 

 used to appro xiinate recruitment levels from 1976 

 through 1984 (Fig. 40). For the following 3 years, 

 recruitment from the 1985 year-class was predicted 

 to be greater than from the 1986 and 1987 year- 

 classes and and close to the recruitment from the 

 1977 and 1980 year-classes. Very similar predic- 

 tions were made for the same 3 years using the 

 three-parameter stock and recruitment relation- 

 ship (see Figure 15), although somewhat smaller 

 differences in recruitment were predicted. 



Results of the larval sampling program showed 

 the greatest mortality occurring during Stage 2 of 

 development in the Niantic River. During this 

 stage, which is characterized by the transition 

 from yolk-sac larvae to first feeding and limited 

 mobility, is also when most larvae are flushed 

 from the river and when most jellyfish predation 

 may occur on larvae remaining in the upper river. 

 All of this suggests that density-dependent mor- 

 tality probably occurs during this stage of larval 

 development. 



Van der Veer (1986) pointed out that, for 

 plaice, the highest coefficients of variation for 

 yearly abundance estimates of diflerent life stages 

 occurred during larval development in late winter 

 and first settlement of pelagic juveniles in spring. 

 Much less variation was seen for post-larval young 

 during mid-summer and for age 2 recruits. He 



214 



