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Fishery Bulletin 89(1). 1991 



The four methodologies we employed for assessing 

 Dungeness crab movement yielded information at dif- 

 ferent scales of resolution. Beam trawling between 

 June 1985 and September 1986 helped us survey the 

 gross distribution and abundance of male and female 

 crabs 125-140 mm carapace width (CW). Trapping 

 helped us assess the distribution and abundance of 

 females greater than 145 mm CW. We previously as- 

 sessed male abundance and exploitation using trap 

 sampling data in Smith and Jamieson (1989b). From 

 the beam trawl and trapping data sets we were able 

 to infer some seasonal movement patterns, while our 

 model for analyzing mark-recovery data enabled us to 

 estimate proportional transfer rates of crabs among 

 geographical zones within our study site (see Fig. 1), 

 and mortality. Finally, by acoustic tagging and releas- 

 ing male and female Dungeness crabs during two 

 periods, August-October 1986 and November 1986- 

 February 1987, we were able to monitor the movement 

 tendencies of individual crabs during summer and 

 winter. Together, all four methodologies enabled us to 

 document a coherent description of the spatial distri- 

 bution and movement patterns of male and female 

 Dungeness crab near Tofino, British Columbia. 



Methods 



Site description 



All beam trawling, trapping, and tagging were con- 

 ducted within sheltered coastal waters near Tofino, 

 British Columbia. These waters are generally =5-15 m 

 depth and well mixed, with an annual seawater tem- 

 perature range of =6-12°C. Substrate varies from sand 

 along the exposed coast to mud near the head of Lem- 

 mens Inlet. These coastal waters have sustained a pro- 

 ductive Dungeness crab fishery for several decades 

 possibly due to local mudflats providing good substrate 

 for juvenile crab (Armstrong and Gunderson 1985). 

 The study site is within Canadian Department of 

 Fisheries and Oceans Statistical Area 24. The fishery 

 in Statistical Area 24 accounted for 13 and 20% of the 

 total weight of Dungeness crab landed in British Co- 

 lumbia in 1985 and 1986, respectively. During 1985 and 

 1986, 27 and 59 vessels, respectively, reported landings 

 from Statistical Area 24. Of the 59 vessels which landed 

 crab in 1986, 30 fished in the study site, and these 30 

 vessels accounted for approximately 80% of the 265 1 

 landed from Statistical Area 24 in 1986. The fishery 

 near Tofino was exploited year-round and fishing ef- 

 fort was sufficient to capture most males soon after 

 their molt to legal size. Annual instantaneous fishing 

 mortality was estimated at F = 5.1-6.9 (Smith and 

 Jamieson 1989b). No crab fishing occurs in marine 

 waters inland of the study site due to poor crab habitat. 



Figure 1 



Map of the coastal region near Tofino, British Columbia, 

 demarcating the geographical zones within the study site. Also 

 shown are the relative net movement vectors across bound- 

 aries between adjacent zones for both male (m) and female 

 (f) Dungeness crabs. The zone designation is indicated by the 

 numbers both on the map and within the vector circle. These 

 vectors illustrate the net directional tendencies across zone 

 boundaries and their relative magnitude under the assump- 

 tion of equal crab densities in all zones. An asterisk (*) in- 

 dicates the vector magnitude is significantly (P < 0.05) different 

 from zero. Zones 1-3 are in Lemmens Inlet; zone 5 is Brown- 

 ing Passage. 



Beam trawl sampling 



In order to assess crab spatial distribution and abun- 

 dance throughout the study site, we made more than 

 50 tows with a beam trawl (Gunderson et al. 1985, 

 Gunderson and Ellis 1986) from June until August 

 1985. In addition, in areas where crabs were abundant 

 and in a few other strategic areas, we made tows at 

 approximately monthly intervals until September 1986. 

 Date, tow depth, bottom type, and area swept were 

 recorded for each tow. Crabs were sexed and their 

 carapace widths measured. We define carapace width 

 (CW) as the distance between the notches just anterior 

 to the tenth anterolateral spines rounded down to the 

 nearest millimeter. Area swept was estimated by mul- 

 tiplying the effective swept width of the beam trawl 

 (2.3 m) by the distance towed. By ranging landmarks 

 at the beginning and end of a tow of 5-10 minutes dura- 

 tion, we were able to calculate distance towed from 

 high-resolution aerial photographs. Most tows were 

 200-500 m. Our beam trawl was assumed to be efficient 

 and equally selective for crabs up to 135-140mm CW. 

 We captured very few crabs larger than 140 mm CW 

 by beam trawl. Because it is unlikely a beam trawl cap- 

 tures all crabs in its path, minimum estimates of crab 



