CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS 



TABLE 14.— Stock size estimates (tons x 10 3 ) for ICNAF Sub- 

 area 5 and Statistical Area 6, 1963-74, southern New England, 

 Georges Bank and Gulf of Maine, inclusive (strata 1-30 and 

 36-40). 



tons). Edwards obtained biomass estimates by 

 adjusting minimum biomass figures for each 

 species by a factor accounting for differences in 

 availability and vulnerability, and although 

 estimates obtained for individual species by these 

 methods differed in certain cases it can be seen 

 that, on the average, results are quite comparable. 



The data of Tables 13 and 14 again reveal 

 pronounced declines. In Table 13 (1968-75, all 

 strata) comparisons of averages for "all data" 

 between 1968-69 and 1974-75 reveal a 65% decline 

 for untransformed data and a 66% decline in the 

 case of retransformed values; with principal 

 pelagics excluded, the corresponding figures are 

 18 and 22%, respectively. In Table 14 (1964-75, 

 Middle Atlantic strata excluded) comparisons 

 between averages for "all data" for 1964-66 and 

 1973-75 reveal declines of 47% and 46% for un- 

 transformed and retransformed values, respec- 

 tively, while with principal pelagics excluded the 

 corresponding figures were 33% and 37%. The 

 greater decrease for the 1968-75 period for "all 

 data" might appear somewhat anomalous but 

 actually results primarily from appearance of the 

 outstanding 1967 mackerel year class. 



As the estimates in Tables 13 and 14 purport to 

 measure declines in biomass in SA 5 and 6, it 

 might logically be argued that they could be 

 combined in some way (use of the 1968-75 data 

 would be preferable in that survey coverage 

 extended further to the south). Paired £-tests 

 indicated no differences between corresponding 

 stock size estimates in Tables 13 and 14 for the 

 1968-75 period. Therefore, we combined the 

 1968-75 estimates in Table 13 with the 1964-67 

 estimates in Table 14 (Figures 12, 13) and 

 computed percentage changes between the means 



of the 1964-66 and 1973-75 periods, as before. For 

 "all data," we obtained declines of 51% and 47% 

 with untransformed and retransformed values; 

 with herring and mackerel excluded, the cor- 

 responding figures were 38% and 41%. 



Analysis of both untransformed and re- 

 transformed data yield essentially similar results. 

 The data of Figures 12 and 13 illustrate the ef- 

 fectiveness of the transformation in reducing 

 anomalies caused by variability in the data. For 

 untransformed estimates (Figure 12) it will be 



£ 4.000 



FIGURE 12 — Estimates of fishable biomass by year for ICNAF 

 Subarea 5 and Statistical Area 6, 1964-75, calculated with un- 

 transformed survey data. Curves were plotted by combining 

 1968-75 estimates from Table 13 with 1964-67 estimates from 

 Table 14. 



FIGURE 13.— Estimates of fishable biomass by year for ICNAF 

 Subarea 5 and Statistical Area 6, 1964-75, calculated with 

 retransformed survey data. Curves were plotted by combining 

 1968-75 estimates from Table 13 with 1964-67 estimates from 

 Table 14. 



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