where the model components are defined in Table 2. There is no error 

 term in this model because proportion data are multinomial. The theoreti- 

 cal variance (BV) is approximately 821/n where n is the average number 

 of individuals in each sample (Bartlett 1947) . The total sum of squares 

 was apportioned following Krumbein and Tukey (1956) and the expected 

 mean squares determined. Because changes in the relationship among taxa 

 were of interest, F values for significance tests were calculated only 

 for terms that included taxon crossed with some other factor. The F 

 ratios for testing the significance of the taxon x period and taxon x 

 year interactions were "manufactured" by taking the ratio of the sum of 

 two mean squares. The appropriate degrees of freedom were calculated 

 using the method given by Snedecor and Cochran (1967) . Table 3 summarized 

 the effects of interest and composition of the F ratios. Determination 

 of expected mean squares and all calculations were completed using the 

 computer program PROC ANOVA from SAS79. 



RESULTS 



Since 1973, 152,223 fish representing 82 taxa have been collected 

 from the trawl hauls. The species caught, their actual catch and relative 

 percent composition are presented in Table 4. 



The following 12 taxonomic groups were considered 'important' and 

 were selected for further analysis. Winter flounder ( Pseudopleuronectes 

 americanus) was the dominant demersal species, making up 42% of the 

 total catch. Scup ( Stenotomus chrysops ) was the second most abundant 



12 



