JAMIESON and PHILLIPS: OCCURRENCE OF CANCER CRAB MEGALOPAE 



south of Cape Flattery (Hickey 1979). Along the 

 eastern Pacific coast, Cape Flattery marks a sig- 

 nificant change in nearshore oceanography, and 

 this study to investigate larval crab distribution in 

 open coast waters is the first one north of this 

 landmark. 



GENERAL OCEANOGRAPHY OFF 

 VANCOUVER ISLAND 



A seasonal surface current moving northward 

 from about lat. 32°N to 51 °N (northern Vancouver 

 Island) typically exists in nearshore waters from 

 October to March (Fig. 2). South of Cape Flattery, 

 this is called the Davidson Current (Hickey 1979) 

 whereas off British Columbia, it appears to consist 

 of two components. Nearshore, there is the year- 

 round, northward flowing Vancouver Island Coastal 

 Current, about 20-30 km wide, and further offshore, 

 there is the seasonal Shelf-Break Current, perhaps 

 a continuation of the Davidson Current, which 

 reverses direction in response to changes in the 

 large-scale wind field (Freeland et al. 1984). The 

 Davidson Current off Oregon has an average 

 northward flow of 50 cm/s for 30% of the time 

 (Boisvert 1969), sufficient to transport larvae sig- 

 nificant distances northward during their develop- 

 mental period if they remained continuously in the 

 current. The California Current is a seasonal, south- 

 ward moving, surface current of similar magnitude 

 and location to the Davidson Current. It occurs off 

 Vancouver Island (Hickey 1979) in the spring and 

 summer, along with the seasonal, southward flow- 

 ing, Shelf-Break Current on the outer continental 

 shelf (Freeland et al. 1984). These currents could 

 transport larvae located off Vancouver Island dur- 

 ing the spring and summer southwards (Fig. 2). 

 North of Vancouver Island, outer continental shelf 

 currents are poorly described, but off Cape St. 

 James (southern tip of the Queen Charlotte Islands), 

 the surface flow is strongly southward almost year- 

 round, turning northward only in March and April 

 (Freeland et al. 1984). The Vancouver Island Coastal 

 Current originates at the mouth of Juan de Fuca 

 Strait, and so could transport larvae out of the Puget 

 Sound-Georgia Strait complex. 



MATERIALS AND METHODS 



General Methodology 



Sampling was largely done along an offshore 

 transect line perpendicular to the coast off Tofino, 

 British Columbia (Fig. 1), with stations located at 



0, 9.3, 18.5, 27.8, 37, 46, 55.6, 74.1, 92.3, 111.2, 

 148.2, and 185.3 km from shore. Stations were more 

 closely spaced nearshore where larval abundance 

 was expected to be greatest, but the transect ex- 

 tended well beyond the shelf break to determine 

 what the seaward distribution of megalopae might 

 be. 



Six offshore samplings were made along the tran- 

 sect from February through August 1985, but only 

 three extended the full 185 km. Dates of sampling 

 were 27 February-4 March, 17 and 18 April, 30 and 

 31 May, 14 and 15 June, 6 and 7 July, and 24 and 

 25 August. February-March, June, and July sam- 

 plings were terminated 74 km, 130 km, and 111 km 

 offshore, respectively, because of poor weather and 

 time constraints. 



At each station, a neuston tow and an oblique 

 bongo tow to 250 m, or to within 5 m of bottom, 

 were made, and a temperature profile was recorded 

 by means of an expendable bathythermograph. On 

 all cruises, bongo tows were done during daylight 

 hours and neuston tows at night; late-stage crab 

 larvae congregate near the water surface at night 

 (Booth et al. 1985). On 17 June 1985, an hourly, noc- 

 turnal series of neuston tows was made at one loca- 

 tion, 9.3 km offshore, to identify patterns of night- 

 time abundance of megalopae in surface waters. 



To supplement offshore sampling along the tran- 

 sect, neuston tows were made after dusk in the in- 

 lets around Tofino biweekly from early May through 

 August 1985 to monitor presence and movement of 

 larvae. In addition, a beam trawl and epibenthic sled 

 were used in inshore waters in July 1985 to sample 

 for newly settled larvae in an effort to establish time 

 and magnitude of larval settlement. 



The RV G. B. Reed was used for all offshore 

 sampling except for the June sample, which was 

 collected from a 27 m charter vessel. Inshore sam- 

 pling was conducted from a 7 m aluminum herring 

 skiff except for mid-June, when the charter vessel 

 was again used. 



Gear 



The neuston sampler was a modified otter surface 

 sampler (Mason and Phillips 1986) with a square 

 mouth opening 45 cm on each side; under calm sea 

 conditions, it sampled the top 35 cm of the water 

 column. A General Oceanics flowmeter^ in the 

 mouth of the net was used to establish volume of 

 water filtered. Netting was black, 500 pt Nitex, and 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



527 



