LOUGH: LARVAL DYNAMICS OF DUNGENESS CRAB 



ference between the number of C. magister 

 megalopae, or the total number of larvae caught 

 in the first two series of tows. In the second series 

 of samples more larvae were caught towing from 

 surface to 150 m than from 150 m to svuface and 

 the total number of larvae decreased with time 

 (0134-0514) for both alternate types of tows. The 

 coefficients of variation (standard deviation/ 

 mean) for the total number of larvae were about 

 the same for the first two series of tows (1.25 and 

 1.31, respectively) indicating a somewhat patchy 

 distribution of the larvae in the upper 150 m of 

 water at night. Very few larvae were caught dur- 

 ing the third series of tows. 



RESULTS 



Distribution and Abundance of 

 Cancer magister Larvae 



Two larval seasons were encompassed by the 

 sampling program (Figure 3). Zoea 1 larvae made 

 their first substantial appearance during the first 

 season on 29 January 1970 at stations NH03, 

 NH05, and NHIO with maximum densities rang- 

 ing from 1,000 to 3,000/1,000 m^. The subsequent 

 zoeal stages were found most abundantly at sta- 

 tions NH05 and NHIO. Few zoea 4 and no zoea 5 

 stages were found at any of the four inshore sta- 

 tions. In general, the number of larvae captured 

 decreased from zoea 1 through 5. However, large 

 numbers of megalopae were found at stations 

 NHOl, NH03, and NH05, suggesting a general 

 inshore transport of larvae during this season. 

 Maximum densities of the magalopae ranged 

 from 1,000 to 8,000/1,000 m^, densities compara- 

 ble to those of the zoea 1 stage found earlier in the 

 year. Few megalopae appeared in the water col- 

 umn after 22 May 1970 and none after 16 July 

 1970. This indicates that the length of the larval 

 period in the plankton is approximately 130 days 

 (89-143 days). The summer upwelling conditions 

 did not appear to have any effect on the larvae 

 since the bulk of the megalopae had settled before 

 the onset of intense upwelling. 



The major appearance of zoea 1 larvae during 

 the second season occurred at about the same 

 time (18 January 1971) and stations (NH03, 

 NH05, NHIO), and at about the same densities 

 (1,000-2,000/1,000 m3). However, the density of 

 the larvae appeared to decrease more rapidly at 

 zoeal stages 2 and 3, and virtually no larvae of 

 any stage were found after zoea 3. The 30 March 



1971 cruise was the last sampling period which 

 caught any significant number of larvae. Very few 

 megalopae were found at any station through- 

 out the summer in day or night samples. 



Cancer magister was the most abundant crab 

 larvae caught at station NH45, 11-12 April 1970 

 (Nekton Cruise). Its megalopae had the highest 

 densities of any larval stage with 19/1,000 m^, 

 followed by zoea 5 at 12/1,000 m^. Fewer zoea 4 

 and 3 were present. Scattered occurrences of all 

 larval stages were present the following year, 

 1971, to 60 miles offshore in the 0.7-m bongo net 

 samples. Megalopae and zoea 3-5 predominated 

 offshore with densities usually much less than 

 200/1,000 m^, suggesting that these larvae had 

 originated nearshore and subsequently drifted 

 offshore. Larvae present at stations NH35 to 

 NH60 are under the influence of the Columbia 

 River plume as indicated by the warmer tempera- 

 tures and lower salinities measured at these sta- 

 tions during the sampling period. 



All observations indicate a dramatic difference 

 in the abundance of megalopae between the 2 yr. 

 Sampling was much more intensive during the 

 1971 season from the standpoint of day-night re- 

 plicate tows using both size samplers in the in- 

 shore and offshore areas when the megalopae 

 were sparse. 



Climate and Hydrography 1970-1971 



The winter of 1971 along the Oregon coast was 

 generally more severe than that of 1970. 

 Climatological records (U.S. Environmental Data 

 Service 1970,1971) for Newport and other ports of 

 Oregon show monthly mean air temperatures for 

 February and March 1971 to be substantially 

 lower than the same months during 1970. Also, 

 total precipitation generally was greater during 

 the winter of 1971 but showed considerable var- 

 iability along the coast. Ocean surface tempera- 

 tures correspondingly were much colder during 

 this period in 1971 than 1970. Conor et al. (1970) 

 and Conor and Elvin (197 1)^ reported Agate 

 Beach, Oreg. mean surf temperatures and Wyatt 

 and Cilbert (1971, 1972) reported monthly mean 

 surface temperatures for various ports along the 

 Oregon coast to be as much as several degrees 

 lower during the later winter of 1971 than 1970. 



^Gonor, J. J., and D. W. Elvin. 1971. Inshore sea surface 

 temperature and salinity conditions at Agate Beach, and 

 Yaquina Head, Oregon in 1971. Unpubl. data. School 

 Oceanogr. Oreg. State Univ. 



357 



