ABUNDANCE OF CONNECTICUT RIVER SHAD 



255 



Table 6. — Estimated total population, annual fishing rate, 

 and escapement of shad in the Connecticut River shad 

 fishery, 1935-51 



entering the river, (2) uniform fishing effort 

 throughout the season, and (3) catch statistics by 

 groups. 



Although the runs may vary from year to year 

 with regard to the length of time they last, the 

 number of groups in the runs can be assumed to 

 be uniform each year. Certain river conditions 

 may speed up or retard the passage of the entire 

 run through the fishery, but such a situation is 

 the sum of the effects of the river conditions on 

 the individual groups. A large run may take 

 longer to pass through the fishery, but in this case 

 the individual groups can be considered to be 

 larger in size and require a longer period of time 

 to move up the river. Because of the nature of 

 the Connecticut River shad fishery, the fishing 

 effort can be considered to be uniform throughout 

 a given season. Catch records cannot show the 

 catch by groups because of mixing of groups 

 within the river; therefore, the number of fish in 

 each group cannot be determined. For this rea- 

 son, I have treated the runs as a unit. The results 

 obtained by treating the runs either as a whole 

 or in parts are identical. The same estimates of 

 total population and escapement prevail. 



FACTORS AFFECTING THE SIZE OF 



CONNECTICUT RIVER SHAD RUNS, 



1940-51 



FISHING 



The total population of shad in any year in- 

 cludes fish which are susceptible to capture for 

 the first time and fish which, although they were 

 suseeptible to capture the previous season, have 



managed to escape the fishery and return to the 

 river to spawn again. The expressions, "catch- 

 able recruits" and "repeaters," will be applied to 

 these two groups of fish. 



The ages of nearly 2,000 fish taken in the 1951 

 commercial catch were determined by a scale- 

 reading technique developed by J. P. Cating 

 (1953) . Of the catchable recruits, 90 percent were 

 4- or 5-year-old fish that were spawning for the 

 first time. The remaining 10 percent were shad 

 returning to the river for the first time as 3-, 6-, 

 and 7-year-old fish and a few 4-year-old males 

 that had spawned once, but, as will be pointed 

 out later, were too small to be caught by the com- 

 mercial gear the first time they spawned. 



The three major components of the total popu- 

 lation are 4-year-old catchable recruits, 5-year-old 

 catchable recruits, and repeaters. The relation- 

 ships among total population in year i, escapement 

 or brood stock size in year i— 5, escapement or 

 brood stock size in year i— 4, and escapement in 

 year t— 1, can be evaluated by means of multiple 

 regression. Further, the amount of information 

 furnished in advance by the escapement data can 

 be determined. The following data are incorpo- 

 rated in table 7: Total population for each year 

 from 1940 to 1951 with the corresponding escape- 

 ments 1, 4, and 5 years earlier; predicted total 

 populations, Y; the deviations from regression, 

 Y—Y; the regression equation; the partial cor- 

 relation coefficients; an analysis of variance for 

 multiple regression; and the multiple correlation 

 coefficient. 



The R value obtained is significant at the 1- 

 percent level; it can be inferred that 83 percent of 

 the variation in total population can be accounted 

 for by changes in the escapements from the fishery. 

 Of the three partial correlation coefficients shown 

 in table 7, r YX 3 -X x X 2 is highly significant, and 

 'YX\- X 2 X 3 approaches significance; on the other 

 hand T YX 2 -X 1 X i , although positive, is small. The 

 low value of T YX 2 -XiX 3 may be explained by the 

 possibility that the 4-year-old catchable recruits 

 did not contribute as greatly to the runs in years 

 prior to 1951 as they did in 1951 when the major 

 components of the runs were determined from 

 commercial scale samples. Further scale collec- 

 tions from the commercial catch will yield more 

 information on this. 



