132 



Abstract. — A commercially valuable 

 trap fishery for spiny lobster (Panulirus 

 margmatus) has existed in the North- 

 western Hawaiian Islands since the 

 late 1970s. Fisheries landings and re- 

 search trapping show that spawning 

 biomass and recruitment to the fishery 

 collapsed in 1990 in the northern por- 

 tion of the fishing ground and that 

 there has been no recovery to the 

 present, although recruitment re- 

 mained strong at banks 670 km to the 

 southeast. An advection-diffusion 

 model is used to investigate larval 

 transport dynamics between these two 

 regions. The movement model is driven 

 by geostrophic currents computed ev- 

 ery 10 days from sea surface height 

 obtained from TOPEX-POSEIDON sat- 

 ellite altimetry. The larval transport 

 simulations indicate that even though 

 larvae have a pelagic period of 12 

 months, banks differ substantially in 

 the proportion of larvae they retain 

 from resident spawners as well as the 

 proportion of larvae they receive from 

 other banks. In particular, recruitment 

 to the northern portion of the fishing 

 grounds is weak due to a very low local 

 spawning biomass and a very limited 

 contribution of lar\'ae from the area of 

 strong recruitment and high spawning 

 biomass in the southeast. The results 

 also suggest that satellite altimetry can 

 provide useful information on physical 

 dynamics for recruitment studies. 



Application of TOPEX-POSEIDON satellite 

 altimetry to simulate transport dynamics of 

 larvae of spiny lobster, Panulirus margmatus, 

 in the Northwestern Hawaiian Islands, 

 1993-1996 



Jeffrey J. Polovina 

 Pierre Kleiber 

 Donald R. Kobayashi 



Honolulu Laboratory, Southwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 2570 Dole Street, Honolulu, Hawaii 96822-2396 

 E-mail address (for J J Polovina) Jeffrey,Polovina@noaa.gov 



Manuscript accepted 18 March 1998. 

 Fish. Bull. 97:132-143 (1999). 



The spiny lobster. Pan ulirus margin - 

 atus, is endemic to the Hawaiian 

 Archipelago and Johnston Atoll. 

 The species is found throughout the 

 archipelago and is the target of a 

 trap fishery in the northwestern 

 portion of the archipelago known as 

 the Northwestern Hawaiian Islands 

 (NWHIl. From the early 1980s to 

 1990, the majority of fishery catches 

 came from two banks, Necker Is- 

 land and Maro Reef, located 670 km 

 northwest of Necker Island ( Fig. 1 ). 

 Catches during this period averaged 

 about 60^^ from Maro Reef, 40^7^ 

 from Necker Island. However, in 

 1990 there was a dramatic collapse 

 in recruitment of 3-year-old lobsters 

 to the fishery at Maro Reef, and 

 other banks north of Maro; this col- 

 lapse has been attributed to cli- 

 mate-induced change in productiv- 

 ity that has impacted various other 

 trophic levels, such as sea birds, 

 monk seals, and reef fishes (Polo- 

 vina et al., 1994). After the recruit- 

 ment collapse, the fishery reduced 

 the spawning biomass to very low 

 levels at Maro and at other north- 

 ern banks, and then fishing ceased 

 in these areas. Even with the ab- 

 sence of fishing at Maro for at least 

 six years, there is still no evidence 

 of a recovery in recruitment as in- 

 dicated from a time series of the 



relative abundance of 3-year-olds 

 obtained from a standardized re- 

 search survey (Fig. 2). However, at 

 Necker, 670 nmi to the southeast, 

 the recruitment drop at the end of 

 the 1980s was much less severe and 

 recovery has occurred in recent 

 years and has supported a fishery 

 (Fig. 2). The striking differences in 

 recruitment levels over the past seven 

 years between the two banks raises 

 the possibility that there is limited 

 larval mixing between the two banks. 

 Current management for the lob- 

 ster fishery is based on the hypoth- 

 esis that recruitment to the NWHI 

 banks comes from a well-mixed pool 

 of larvae with contributions from 

 the entire archipelago, and this pool 

 of larvae oscillates seasonally along 

 the archipelago, pushed northwest 

 in the spring and summer with 

 tradewind-driven Ekman transport 

 and pushed back southeast in the 

 fall and winter with westerly wind- 

 driven Ekman transport (MacDon- 

 ald, 1986). A genetic analysis during 

 1978-80 examined allozyme varia- 

 tion in spiny lobsters from seven 

 banks covering a substantial spatial 

 range of the Hawaiian Aixhipelago 

 and found no evidence of genetic 

 differentiation between banks (Shak- 

 lee and Samollow, 1984). However, a 

 subsequent study in 1987, using a 



