Florida within 53 days after release. The av- 

 erage distance traveled each day from Beaufort 

 to Cape Fear and from Beaufort to Florida was 

 7.0 miles. In 1969 elapsed time between first 

 recaptures at Beaufort and Florida was 56 days, 

 resulting in an average distance traveled of 6.6 

 miles per day. From Southport to Florida, the 

 elapsed time was 48 days or 6.1 miles per day. 

 From these recoveries, we estimate that thread 

 herring migrate south in fall at a rate of 6 to 7 

 miles per day. 



Population Size 



An estimate of the size of the thread herring 

 population moving south from Beaufort to 

 Southport, in September 1968, can be made using 

 the number tagged (less those recaptured before 

 leaving the Beaufort area), the estimated num- 

 ber recaptured at Southport, and the catch at 

 Southport (Table 3). An estimate of popula- 

 tion size from our tagging data requires the as- 

 sumption that the entire population moves as a 

 group. That assumption is supported by the 

 fact that tagged fish were recaptured with al- 

 most all thread herring catches. 



For this estimate we are given (Ricker, 

 1958) : 



Table 3. — Thread herring landings and estimated 

 number of tags recovered by area from 1968-70. 



c = 



M = 



R = 



N = 



Number of thread herring landed 



at Southport. 

 Effective number of tagged fish at 



large. 

 Estimated number of tagged fish 



recaptured at Southport. 

 Estimated population size. 



then, 



N 



M (C + 1) 

 R + 1 



or 



N = 



(1,505) (6.585,583) 

 14 



= 702.6 million fish ± 355.6 million 

 (95% confidence interval) 



This estimate, made so soon after tagging, 

 could be misleading. No adjustment is possible 

 for the degree of mixing of tagged with untagged 



' None of the landings were reported as thread herring. 

 * Fishing terminated early in October before thread herring normally 

 are caught in area. 



fish in the population. Fishing at Southport may 

 have been concentrated on the tagged portion 

 of the population. No adjustment was made for 

 tag loss from shedding and mortality. These 

 effects would produce an underestimate of the 

 stock size. On the other hand, this calculation 

 might overestimate population size because 

 we were unable to determine rate of recruit- 

 ment. 



The one tag recovery from Florida was not 

 used to estimate population size. A single re- 

 covery and a low magnet efficiency provide an 

 imprecise estimate of recaptures. 



Another estimate can be made using the re- 

 coveries and landings from September through 

 November 1969. In this case, sufficient time 

 elapsed for mixing of tagged fish in the popu- 

 lation, but tag loss or recruitment were not taken 

 into account. In this estimate: 



N 



(1,487) (37,653,241) 

 46 



= 1,217.2 million fish ± 355.1 million 

 (95% confidence interval) 



We feel these estimates, although very gross, 

 are indicative of the population size for the 

 purpose of this study. The catch of thread her- 

 ring in 1968 was approximately 1,547 metric 

 tons and in 1969 was 2,150 metric tons (Table 2) , 

 while in 1968 and 1969 the average catch of men- 



300 



