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Fishery Bulletin 89(1). 1991 



only a small proportion per month (0.01) entering 

 Lemmens Inlet from zone 6. The monthly proportional 

 transfer rate of crabs from zone 2 to zone 1 (£21) of 

 0.50 seems high compared with transfer of crabs from 

 zone 1 to zone 2 (Q 2 i) of 0.15, but this might be ex- 

 plained by zone 1 (upper Lemmens Inlet) being poor 

 crab habitat and the possibility that only a small pro- 

 portion of male crabs are successful in escaping this 

 habitat. 



The proportional transfer rates for females have 

 large standard errors and must be interpreted cautious- 

 ly. However, a notable result is the 0.63 proportional 

 transfer rate for £ 36 compared with <0.01 for Q es , 

 thus indicating that a greater proportion of tagged 

 females vacated lower Lemmens Inlet than entered 

 Lemmens Inlet. The monthly proportional transfer rate 

 of 0.84 for females escaping the poor habitat in zone 

 1 (Q12) is high compared with males, but might indi- 

 cate females are more capable of recognizing the en- 

 vironmental clues leading to more suitable substrate. 

 The transfer rates of females in both directions be- 

 tween zone 1 and zone 2 are notably higher than the 

 male transfer rates, and since the largest release of 

 tagged male and female crabs was in zones 1 and 2, 

 this result might indicate females are generally more 

 mobile than males. 



Proportional transfer rates alone are an incomplete 

 interpretation of movement trends, since the zones 

 differ in area and therefore also in crab abundance. 

 Consequently, the high transfer rate for Q 36 when 

 compared with Q 63 is in large part a result of zone 6 

 having an area of 7.56km 2 , whereas zone 3 has an 

 area of 0.40km 2 . Relative movement vectors were 

 therefore calculated from the transfer-rate estimates 

 under the assumption that crab densities were equal 

 for all zones. For example, if crab density is A crabs 

 per km 2 , then the estimated number of crabs transfer- 

 ring from zone 6 to zone 3 in a one-month period is 

 7.56AQ 63 . 



Figure 1 diagrams net movement tendencies, under 

 the assumption of equal crab densities in all zones, 

 across those zone boundaries where transfer rates in 

 both directions were estimated. Two notable features 

 for males are the strong indication of net movement 

 of males into upper Lemmens Inlet, and a tendency for 

 males to vacate lower Lemmens Inlet and the waters 

 near Indian Island. As previously mentioned, the net 

 movement into upper Lemmens Inlet might be a result 

 of a low proportion of males escaping this poor habitat. 

 It might also indicate dispersion from zone 2 where 

 many males were tagged and released in spring 1986. 

 A large number of males 125-140 mm CW were tagged 

 in zone 2 in spring 1986 because they occurred in high 

 density (> 1200/ ha) and were readily captured by beam 

 trawl. Beam trawling indicated these crabs apparent- 



ly dispersed, or molted to legal size and were caught, 

 by summer 1986 (see previous section). For females 

 there is a general, although non-significant, tendency 

 to vacate Lemmens Inlet and Browning Passage. This 

 result is consistent with our beam-trawl and trapping 

 results (previous section) which also demonstrate a net 

 seaward movement of females from Lemmens Inlet. 



We estimated the annual rate of disappearance of 

 tagged crabs with reasonable confidence at S = 2.54 

 (SE 0.13) and S = 1.28 (SE 0.27) for males and females, 

 respectively. Corroborating these high estimates for 

 S, our analysis estimated that only about 2% and 7% 

 of tagged males and females, respectively, left zones 

 1-6, i.e., moved to zone 7, over the time-period of our 

 study. In other words, the distribution over time of tag 

 recoveries in zones 1-6 could not be well explained by 

 a high transfer rate into zone 7 where crabs might not 

 be recovered due to a low fishing intensity. Thus these 

 estimates for S were obtained despite our model struc- 

 ture providing an exaggerated opportunity for crabs 

 to disperse to zone 7 as an alternative explanation for 

 the disappearance of tagged crabs, i.e., as an alter- 

 native to mortality. This conclusion appears to validate 

 our original assumption that few tagged crabs left our 

 study site during the study period (Smith and Jamieson 

 1989b). 



Based on a double-tagging study, Smith and Jamie- 

 son (1989b) concluded that tag loss by sublegal-sized 

 crabs is low and therefore unlikely to be an important 

 source of tag disappearance. Observations of tank-held 

 crabs over several months did not reveal differential 

 mortality of tag and untagged crabs. Thus we conclude 

 that the values for S estimated in this study represent 

 mainly natural mortality and, in the case of males, tag 

 disappearance due to molting to legal size with subse- 

 quent exploitation. However, because only about 5% 

 of tagged sublegal-sized males were reported caught 

 as legal-sized crabs (210 recovered when legal-sized of 

 the 4038 released when sublegal-sized), despite high 

 fishing mortality (F = 5.1-6.9) and apparently good 

 compliance in reporting recovered tags (=87%), we con- 



