Polovina and Mitchum: Recruitment of Psnulirus marginatus relative to sea level in NW Hawaiian Is 



489 



Reef and Necker I. had gone through a period of fishing 

 down the pre-exploitation population; the relative 

 change in catches between the 

 two banks may reflect changes in 

 their relative recruitment. Since 

 both banks are not always fish- 

 ed each month, we pooled the 

 catches by quarter. A 3-quarter 

 moving average of the ratio of 

 quarterly catches at Maro Reef 

 to the combined quarterly catches 

 at Necker I. and Maro Reef shows 

 considerable variation (Fig. 7). 

 For example, catches from Maro 

 in 1985 and 1988 represented 

 almost 80% of the catches from 

 the two banks, but in 1990 they 

 represented less than 20%. A 

 3-quarter moving average of the 

 residuals from the CPUE model 

 shows the same trend as the ratio 

 of catches from Maro Reef rela- 

 tive to Necker I. and Maro Reef 

 combined (Fig. 7). This suggests 

 that the variation in recruitment, 

 catchability, or both at Maro 

 Reef is responsible for most of 

 the variation not explained by 

 fishing effort observed for the 

 entire NWHI. 



height of the sea level ridge stretching across the 

 Pacific. The height and location of this sea level ridge 



1986 



1988 



Year class 



1987 



1990 



3 4 



Year class 



Figure 6 



Age-frequency distributions of spiny lobster Panulirus marginatus, based on research 

 sampling in 1986-88 and 1990 at Necker I. (N = no. of spiny lobster in the sample). 



Variation between 

 sea level and the SCC 



Differences in sea level over the Pacific, be- 

 tween a year when the FFS-Midway sea level 

 was high and a year when it was low, appear 

 as a ridge of positive values, extending from 

 southwest to northeast, that parallels a 

 trough of negative values to the northwest 

 (Fig. 8). Midway lies in the trough, Honolulu 

 is on the ridge, and FFS lies on the gradient, 

 which corresponds to the region of the most 

 energetic geostrophic flow anomalies. This 

 ridge and trough indicate that the change in 

 the FFS-Midway sea level from low to high 

 reflects the increase in a ridge extending 

 across the western Pacific. The increase in 

 the ridge and trough pattern represents an 

 increase in the current flow along the gradi- 

 ent of this ridge. The path of this gradient or 

 flow across the Pacific is consistent with the 

 general path of the SCC. Thus FFS-Midway 

 sea level measures a large-scale oceano- 

 graphic feature which is represented by the 



Figure 7 



Three-quarter moving average of the ratio of quarterly landings of spiny 

 lobster Panulirus marginatus at Maro Reef to quarterly landings at Maro 

 Reef and Necker I. (D), and 3-quarter moving average of the residuals 

 from the fit of the CPUE model to monthly spiny lobster CPUE (♦). 



