478 



Fishery Bulletin 101(3) 



The adjusted number of tagged animals released during the 

 field studies effectively available to the fishery is equal to 



with variance 



V(N^^j) = Np(\-p). 

 The field study recapture rate (t) is defined as 



t = 'n(Kd?-\ 

 where m = the number of tags returned. 



(1) 



(2) 



(3) 



The variance of < can be calculated by using conditional 

 theory and an approximate variance of (iV^j.)"' (Seber, 

 1982). In this study, we used Monte-Carlo simulations to 

 obtain the 90% confidence interval (CI) for /. The simula- 

 tions were carried out in two steps to include variability 

 associated with tag loss from the initial N animals tagged 

 and released, and variability in recapture rate. First, as- 

 suming that the number of tags retained (A^,,,;,) follows a 

 binomial distribution with parameters N andp, a random 

 number (N^j.) was selected from a Binomial(N,p), where N 

 was set equal to the number of animal tagged during a par- 

 ticular study, andp equal to the proportion of tag retention 

 estimated from the aquarium study. With this simulated 

 ^adj ^ conditional value of < was derived as 



<c.='"„W„,^,)-'. 



(4) 



where "-" 

 m,. 



the simulated value; and 



the observed number of recaptures in a field 



study. 



Secondly, a value for m was obtained from a binomial dis- 

 tribution with parameters N^^- and a conditional recapture 

 rate t^.. A simulated recapture rate was calculated as 



t = m{N^^j)-K 



(5) 



The process was repeated 1000 times and the 90% CI for t 

 was defined as the 5% and 95% quantiles of the resulting 

 1000 Monte-Carlo values of ^ 



Results 



Aquarium observations 



Tag-induced mortality was observed within 30 min of tag- 

 ging for two lobsters tagged in the late premolt stage ( 1.5%) 

 and for four in postmolt stage (2.1%) but not for lobsters 

 tagged in early premolt and intermolt stages. The autopsies 

 revealed that all of these lobsters died from perforation of 

 the pericardial sac and these lobsters were not used in our 

 experiments. 



Tag loss of premolt lobsters was associated solely with 

 tag-induced mortality and this was restricted to 10% (13) 

 of the late premolt lobsters (Table 1). Autopsies revealed 

 that six lobsters died within three days of tagging from 

 the rupture of the dorsal thoraco-abdominal membrane, 

 one died after one day from the perforation of the peri- 

 cardial sac, and six died between three to sixteen days 

 after tagging from a perforated hepato-pancreas (Table 

 2). In contrast, only 4% (7) of postmolt lobsters died from 

 tag-induced mortality (Table 1). Autopsies revealed that 

 all deaths were associated with the rupture of the dorsal 

 thoraco-abdominal membrane. Another death was not 

 related to tagging (Table 2). 



