FISHERY BULLETIN: VOL. 81, NO. 3 



gives some insight into what factors may limit sur- 

 vival, and thus year class strength, in the P. jordani 

 fishery. Surface seawater temperatures in 1971 and 

 1972 (Fig. 5) were different in several respects. The 

 regression analysis draws attention to months from 

 June through August. In these late months of larval 

 development, temperatures were several degrees 

 higher at nearshore stations in 1971 than in 1972. 

 Evaluation of laboratory rearing experiments showed 

 that survival was highest at 11° to 12°C, and it de- 

 creased rapidly above that range (Rothlisberg 

 1979). 



DISCUSSION 



Movements of adult Pandalus jordani associated 

 with reproductive events have not been well defined. 

 In contrast to other pandalids, e.g., P. borealis 

 (Haynes and Wigley 1969; Horsted and Smidt 1956) 

 and P. montagui (Lebour 1939, 1947; Mistakidis 

 1957; Allen 1963), there is no evidence of an inshore 

 migration of female P. jordani prior to hatching of 

 eggs they bear. Dahlstrom (1970) found that P. jor- 

 dani at Morro Bay, Calif., moved 2 to 3 nmi farther 

 offshore to spawn in the winter. Lukas and Hosie 

 (1973) reported that female P. jordani left their study 

 area 10 to 20 nmi off Tillamook Head, Oreg., in the 

 fall. Numbers in March were greater at the south end 

 of their grid than to the north, but there was no 

 evidence of inshore or offshore movement associated 

 with hatching. During the present study off Newport, 

 Oreg., we found highest concentrations of adult P. 

 jordani between 20 and 25 nmi offshore. While trawl- 

 ing was casual, and results are not reported here, 

 there was no evidence of shoreward movement of 

 ovigerous females during the period of hatching. 



Prevailing wind and resultant currents could have 

 transported larvae to the nearshore zone during the 

 present study. Differences in wind and current be- 

 tween 1971 and 1972 are reflected in larval dis- 

 tributions for the two years. Furthermore, extended 

 alongshore sampling in 1972 showed that shifts in 

 distribution along the Newport line were representa- 

 tive of shifts along the whole coast. Shifts were not 

 restricted to areas of high adult abundance. 



Widespread distribution of early zoea in early and 

 mid-March 1971 can probably be attributed to the 

 mixed winds of February and to the spell of 

 northwest wind in mid-March. More dramatic 

 offshore displacement was seen in early May 1971, 

 when larvae were found in abundance at 50 and 60 

 nmi. Numbers decreased markedly after May, pro- 

 bably through continued offshore displacement 

 beyond the sampling area. More limited offshore dis- 



placement of early larvae in 1972 coincides with 

 stronger, more consistent southwest winds in Feb- 

 ruary and March of that year. Older larvae were 

 generally closer to shore in 1972 than in 1971. 

 Offshore displacement by upwelling probably was 

 reduced in 1972 by the advanced larval development 

 at the initiation of upwelling compared with 1971. 

 Since older larvae live deeper in the water column 

 (Rothlisberg and Pearcy 1977), late onset of upwell- 

 ing with respect to the development sequence will 

 produce less offshore displacement. 



Year-to-year fluctuations in seasonal winds, upwell- 

 ing, and surface advection in the northwest Pacific 

 have been repeatedly described (e.g., Wickett 1967; 

 Hubbard and Pearcy 1971; Peterson and Miller 

 1975). However, until the upwelling index was 

 developed by Bakun (1973), it was difficult to corre- 

 late strength of upwelling in a long sequence of years 



with variations in productivity at any level. This now 

 can be done, although specific processes involved 

 may remain obscure. Several of the features of up- 

 welling may act to change production of a given life 

 stage or species. The correlation we found between 

 upwelling index and larval survival is something of a 

 surprise. Earlier studies (Winnor 1966; Wickett 

 1967; Hubbard and Pearcy 1971) stressed the advec- 

 tive nature of upwelling. Thus we expected greater 

 larval "wastage" to seaward for years with early onset 

 and greater strength of upwelling. The colder tem- 

 peratures also might be supposed detrimental to P. 

 jordani because they should slow development. The 

 unexpected, high, positive correlation of larval sur- 

 vival and June to August upwelling can be explained 

 by other knowledge of larval physiology in P. jordani. 

 Laboratory rearing experiments have shown optimal 

 larval survival at 1 1° to 12°C (Rothlisberg 1979). Up- 

 welling maintains these relatively low temperatures 

 through the summer months, whereas weaker up- 

 welling allows summer warming (Patullo et al. 1969). 

 Temperatures above 14°C in June 1971 would have 

 been harmful and may have contributed directly to 

 low larval survival in that year. 



The reproductive strategy of P. jordani appears to 

 rely on the complex advection of late winter and 

 spring. Many demersal species of the Pacific 

 northwest spawn in winter and spring, apparently to 

 maximize onshore drift of larvae and retention in 

 coastal nursery grounds (Parrish et al. 1981). Pan- 

 dalus jordani larvae, on the other hand, hatch in late 

 winter and have a planktonic phase extending 

 through the transition from northward-onshore to 

 southward-offshore currents. They should usually 

 encounter 1) onshore retention in early stages and 2) 

 offshore displacement of later stages during subse- 



470 



