Spiny lobster recruitment and sea 

 level: results of a 1 990 forecast 



Jeffrey J. Polovina 



Honolulu Laboratory, Southwest Fisheries Science Center 



National Marine Fisheries Service, NOAA 



2570 Dole Street, Honolulu, Hawaii 96822-2396 



Joint Institute for Marine and Atmospheric Research (JIMAR) 

 University of Hawaii, Honolulu. Hawaii 96822 



Department of Oceanography, School of Ocean and 



Earth Science and Technology 

 University of Hawaii, Honolulu, Hawaii 96822 



Gary T. Mitchum 



Joint Institute for Marine and Atmospheric Research LIIMAR) 

 University of Hawaii, Honolulu, Hawaii 96822 



Department of Oceanography, School of Ocean and 



Earth Science and Technology 

 University of Hawaii, Honolulu. Hawaii 96822 



A relation between recruitment to 

 the fishery and sea level for the 

 spiny lobster Panulirus mar- 

 ginatus, in the Northwestern Ha- 

 waiian Islands, was supported by 

 data from 1985 through 1990 

 (Polovina and Mitchum, 1992). A 

 forecast of future recruitment was 

 made based on projected sea lev- 

 els (Polovina and Mitchum, 1992). 

 This note updates that forecast 

 with two more years of data. 



Fishery data from 1985 to 1990 

 indicated considerable inter- 

 annual variation in recruitment 

 strength of spiny lobster, Pan- 

 ulirus marginatus, between the 

 two principal fishing grounds 

 (Necker Island and Maro Reef), 

 although separated by about 700 

 km (Fig. 1; Polovina and 

 Mitchum, 1992). Recruitment 

 strength variation between the 

 two fishing areas was measured 

 as the ratio of the commercial 

 landings from Maro Reef divided 

 by the combined commercial land- 

 ings from Necker Island and Maro 

 Reef. A strong correlation was ob- 



served between this measure of 

 recruitment strength at Maro 

 Reef and the sea level gradient 

 along the Northwestern Hawaiian 

 Islands, advanced by four years 

 (Polovina and Mitchum, 1992). 

 The sea level gradient was mea- 

 sured as the difference in sea 

 level between tide gauges at 

 French Frigate Shoals, southeast 

 of Maro Reef, and Midway Island, 

 northwest of Maro Reef. A high 

 proportion of the commercial 

 landings came from Maro Reef 

 following a steep gradient, while 

 relatively few spiny lobsters were 

 caught at Maro Reef following a 

 flat gradient. The four-year lag is 

 based on the minimum legal har- 

 vest size which, for the spiny lob- 

 ster is about three years old, af- 

 ter benthic settlement. Prior to 

 benthic settlement, the larvae are 

 planktonic for about one year. 



Since sea level gradient appears 

 to lead recruitment to the fishery 

 by four years, the relation can 

 provide up to a four-year forecast. 

 Based on data through 1990, it 



was forecast that in 1991 recruit- 

 ment to the fishery at Maro Reef 

 would be weak but would recover 

 in 1992 relative to recruitment at 

 Necker Island (Fig. 2). The 1991 

 and 1992 fishery data show this 

 forecast correct (Fig. 2), although 

 the fishery for the entire North- 

 western Hawaiian Islands was 

 relatively weak in 1992. Thus, 

 while sea level gradient index 

 does forecast the relative strength 

 of recruitment at Maro Reef, it is 

 not, by itself, an index of absolute 

 recruitment strength. 



It has been argued that sea 

 level gradient measures the 

 strength of the Subtropical 

 Counter Current, which appears 

 to intersect the Hawaiian ridge as 

 three narrow eastward flowing 

 bands at 20, 24, and 26 degrees 

 north latitude (Polovina and 

 Mitchum, 1992; White and 

 Walker, 1985). Recent studies of P. 

 marginatus larval distribution 

 find a relatively high abundance 

 of late stage larvae consistently 

 present near lat. 26°N, and tracks 

 from Argos drifter buoys drogued 

 at 30 m indicate buoy entrap- 

 ment along lat. 26'N. 1 These re- 

 sults provide some additional sup- 

 port to our original hypothesis 

 that a positive relationship exists 

 between the strength of the Sub- 

 tropical Counter Current and lo- 

 cal larval survival, retention, and 

 recruitment to the fishery at Maro 

 Reef (Polovina and Mitchum, 

 1992). 



Literature cited 



Polovina, J. J., and G. T. 

 Mitchum. 



1992. Variability in spiny lob- 

 ster Panulirus marginatus re- 



1 Polovina, J.J.. and R.B. Moffitt. In re- 

 view. The spatial and temporal distribu- 

 tion of the larvae of the spiny lobster 

 {Panulirus marginatus) in the North- 

 western Hawaiian Islands. 



Manuscript accepted 11 August 1993 

 Fishery Bulletin 92:203-205 (1994) 



203 



