OCCURRENCE OF CANCER CRAB (C MAGISTER AND 



C. OREGONENSIS) MEGALOPAE OFF THE WEST COAST OF 



VANCOUVER ISLAND, BRITISH COLUMBIA 



Glen S. Jamieson and Antan C. Phillips^ 



ABSTRACT 



The seasonal and cross-shelf occurrences of Cancer crab (C. magister and C. oregonensis) megalopae 

 in 1985 along a transect line perpendicular to the coast off Tofino, British Columbia, are presented. 

 Megalopae of both species were generally absent from surface waters during daylight hours. The two 

 species may have slight temporal differences in nocturnal surface abundance, with C. magister occur- 

 ring later in the evening and earlier in the morning than C. oregonensis. Their relative occurrence at 

 the surface during the night was used to calibrate cross-shelf megalopal abundance data. Cross-shelf 

 megalopal intermolt stage proportions were calculated, relating degree of megalopal development to 

 proximity of nearshore habitat required for successful settlement of larvae. 



Cancer magister megalopae were present from April to August, with peak abundance in May and 

 June. Megalopae were abundant in a broad band 37-148 km from shore, with peak abundance (2,871 

 10 m"^) 56 km offshore in June. In May, some late stage megalopae were collected in coastal inlets but 

 settlement appeared low in coastal study areas. Megalopal abundance decreased abruptly shoreward of 

 28 km from the coast. 



Cancer oregonensis megalopae were also present from April to August, with their pattern of cross- 

 shelf abundance basically similar to that of C. magister. However, in contrast to C. magister, abundance 

 of late stage megalopae in coastal inlets was relatively high (313 10 m"^) in June, indicating that a signifi- 

 cant settlement of megalopae of this species could have occurred. 



Evidence for cross-shelf movement of Cancer megalopae is discussed. 



Dungeness crab, Cancer magister, range from the 

 Aleutian Islands to northern Mexico in the eastern 

 Pacific (Hart 1982) and are commercially exploited 

 from northern California to Kodiak Island, AK. As 

 part of an ongoing study of Dungeness crab recruit- 

 ment off the west coast of Vancouver Island, the 

 abundance and distribution of larvae off Tofino, 

 British Columbia, are being studied to determine 

 how variability in annual recruitment is affected by 

 larval settlement. 



Dungeness crab larvae are planktonic and pass 

 through five zoeal stages and one megalopal stage 

 before settling to the sea bottom. Studies of larvae 

 prior to the 1970s primarily involved descriptions 

 of larval morphology (Mir 1961; Poole 1966), and it 

 was not until Reed (1969) developed laboratory 

 culture methods that larval environmental require- 

 ments were first described. Optimal ranges of tem- 

 perature and salinity for laboratory-cultured zoeae 

 were 10.0°-13.9°C and 25-30%o respectively, but 

 their survival was not significantly affected by the 

 temperature and salinity ranges occurring in the 



waters off Oregon, where Reed's study was con- 

 ducted, at the time of year when larvae are com- 

 monly found. Lough (1976) suggested offshore lar- 

 val movement would allow larvae to avoid lower 

 nearshore salinities, and that normal oceanic salinity 

 levels probably favor survival over the long term. 



The temporal occurrence of larvae in open coast 

 oceanic waters varies somewhat according to lati- 

 tude, with larvae present earliest in the season in 

 the southern part of the species' range. Seasonal 

 occurrence has not been well documented in the in- 

 shore waters of Georgia Strait, Puget Sound, and 

 Juan de Fuca Strait, but appears to differ signifi- 

 cantly from that in open coast waters. Larval settle- 

 ment, which typically occurs in May and June off 

 the outer coast of Washington, can occur as late as 

 mid-September in northern Puget Sound (D. Arm- 

 strong2). 



Temporal and spatial distributions of crab larvae 

 have been documented for the years 1975-80 in the 

 Gulf of Farallones and the San Francisco-San Pablo- 

 Suisun Bay complex in central California (Reilly 



'Department of Fisheries and Oceans, Fisheries Research 

 Branch, Pacific Biological Station, Nanaimo, B.C., Canada V9R 

 5K6. 



^D. Armstrong, University of Washington, Seattle, WA 98195, 

 pers. commun. December 1986. 



Manuscript accepted March 1988. 



FISHERY BULLETIN: VOL. 86, NO. 3, 1988. 



525 



