Smith and Jamieson Movement and mortality of Cancer magister 



139 



densities were obtained by dividing the number of crabs 

 captured in a tow by the area swept. 



Trap sampling 



The abundance of large (>145mm CW) female crabs 

 was assessed by sampling the catch of commercial 

 fishermen onboard their vessels. The number and 

 carapace width of crabs caught were recorded as were 

 the date and location of the sample. We report two in- 

 dices of female abundance: w/trap • soak day and vir- 

 tual catch rate (Smith and Jamieson 1989a). Virtual 

 catch rate (n/trap  day) is the rate at which crabs would 

 enter a trap if initial entry rates were not reduced by 

 changes in bait effectiveness over time and agonistic 

 interactions among crabs. 



Fishing effort survey 



The number of traps fished by all local fishermen, in- 

 cluding the three fishermen who agreed to maintain 

 records of all tagged crabs recovered in the study site, 

 was determined by interviewing fishermen at least 

 monthly from April 1985 until November 1986. The 

 number of traps hauled each month in each of the seven 

 zones demarcated in Figure 1 was estimated by incor- 

 porating trap-count data with haul-frequency data. We 

 also maintained a record of the number of our own 

 research trap hauls. We validated our fishing effort 

 survey by comparing the estimated number of traps 

 in Lemmens Inlet each month, as obtained in fishermen 

 interviews, with the number of trap buoys we counted 

 in Lemmens Inlet each month. With few exceptions 

 each trap buoy indicated one trap. Trap buoys were 

 easily counted from a moving boat on calm water in 

 this enclosed body of water. Figure 2a compares the 

 estimated number of traps fished in Lemmens Inlet by 

 each method and indicates that the fishermen's inter- 

 views provided an acceptable census of trap abundance. 



Mark-recovery 



We tagged and released 4038 sublegal-sized male (x 

 142 mm CW, with 95% between 106 and 162 mm CW) 

 and 1246 female (x 150mm CW, with 95% between 

 135 and 160 mm CW) Dungeness crabs from April 1985 

 to May 1986. Blue, individually numbered, 4.1-cm T-bar 

 anchor tags (Floy Tag and Manufacturing Company, 

 Seattle, WA) were inserted through the right posterior 

 epimeral suture line, taking care not to puncture in- 

 ternal organs. Crabs to be tagged were obtained from 

 research traps, fishermen, or beam trawls. Before 

 being released, the date, location and tag number were 

 recorded, the crabs were sexed, and their carapace 

 width measured. Release and recovery locations were 



< 



IOOO- 



800- 



600- 



400- 



200- 



• TRAP COUNT 



 INTERVIEWS WITH FISHERMEN 



1 — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I 



K 2000 1 -ST 



o LEMMENS INLET 

 600 A & INDIAN ISLAND 



1200- 



800- 



400- 



rUDY SITE (excluding o,a □ ) 



BROWNING PASSAGE 

 • ELSEWHERE 



A M J J 

 1986 



DATE 



Figure 2 



(A) Time-series comparison of the number of trap buoys 

 counted in Lemmens Inlet and the number of traps estimated 

 to be in Lemmens Inlet (zones 1-3) from interviews with 

 fishermen. (B) Time-series of the number of traps estimated 

 to be fishing in different regions within the study site from 

 interviews with fishermen. 'Elsewhere' refers to traps fished 

 outside the study site (zone 7) by fishermen who also 

 fish within the study site. 



determined with a grid identification system (0.9 x 

 1.2km) and landmarks. 



Most recoveries were obtained from fishermen and 

 research traps. Three fishermen recorded the date, 

 location, and tag number of all tagged crabs they 

 recovered on special recovery forms. Females and 

 sublegal-sized males were returned to the water, but 

 legal-sized males (i.e., > 154 mm CW) were generally 

 retained. We asked other fishermen to ignore the 

 recoveries of sublegal-sized crabs, i.e., return them to 

 the water, but to retain tags from legal-sized males. 

 Tags were either given to us or our associates, or we 

 had permission to board a fisherman's vessel at the 

 dock and retrieve tags set aside. From April until 

 August of 1985 and 1986 we saw most fishermen at 

 least biweekly, at other times monthly. 



