estimates of N (Table 3) using the Schnabel formula. Consequently, the 

 population size in Area 3 is considered to have been either relatively constant 

 throughout the study period or declining gradually to September. Counts of 

 lobsters by divers suggest that the population decreased in size. 



The population size in Area 4 is also considered to have been stable, even 

 though the Schnabel estimates of N indicate a population increase. Again, 

 these estimates are biased in the positive direction for reasons discussed 

 above. 



Population Turnover 



The rates of immigration and emigration were estimated using two independent 

 methods. As was stated in Population Estimation , if emigration of tagged and 

 non-tagged individuals is exactly balanced by immigration (stabile population) 

 of non-tagged lobsters, the Schnabel estimate of N increases with time. Assum- 

 ing varying rates of emigration and that tagged and non-tagged lobsters demon- 

 strate equal tendencies to emigrate, Schnabel estimates can be recalculated by 

 correcting K^ (number of tagged lobsters at large in the study area) accordingly. 

 That rate of emigration which results in a relatively constant N over time is 

 considered an estimate of the total rate of tag loss. Since the original esti- 

 mates of N considered tag loss from the animal, the above estimate represents 

 the combined effect of natural mortality and emigration. Emigration is consid- 

 ered to be the primary source of tag loss from the population. 



An average 1.5 percent emigration per day or 45 percent per month coincides with 

 a constant N for Area 3 during late April to mid-June; 2 percent (60 percent per 

 month) from mid- June through August; and 3 percent (90 percent per month) during 

 September. A 1.6 percent rate (48 percent per month) is estimated for Area 4 

 from late May to late July and 2.5 percent (75 percent per month) from late July 

 through September. A balancing of immigration with emigration, with resulting 

 increases in N over time, was not apparent in Areas 1 and 2. 



The second method of estimating rate of population turnover involves calculating 

 the percent of a given study period's tagged lobsters absent during the follow- 

 ing study period (Table 5). Data sufficient for such comparisons were available 

 only for Area 3. Four consecutive study periods are considered for this com- 

 parison: period 1 from April 22 to May 11 (20 days); period 2 from May 12 to 

 July 24 (74 days); period 3 from July 25 to August 13 (20 days); and period 4 

 from August 14 to September 22 (40 days) . Subtracting the number of resighted 

 tagged lobsters seen during a given period from the number known to be at large 

 during the previous period and expressing this as a percentage of the number 

 that were present during the previous period yields an estimate of the rate of 

 emigration for that previous period. This technique assumes that all tagged 

 lobsters present are sighted and recognized during periods 2, 3, and 4 and that 

 the accepted number of resights are made early during the mission so that the 

 calculated magnitude of emigration can be related to an accurate time interval. 

 Neither assumption is completely valid, although the resultant error in calcu- 

 lating percent emigration is relatively small. In either case the estimate of 

 emigration would be too large. 



Both methods of estimating rate of movement out of the study area indicate that 

 there was a significant rate of emigration of tagged lobsters from Areas 3 and 4 



VI-44 



