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Fishery Bulletin 90(3), 1992 



the absence of fishing). Further, a CPUE of 1.2 spiny 

 lobster/trap-haul means the exploitable population is 

 1 million spiny lobster. An independent estimate of M 



from tagging at FFS is 0.5/yr (MacDonald 1984). 



Commercial trapping effort since 1985 has averaged 

 about 1 million trap-hauls (Table 1); using the qj esti- 

 mate as catchability, annual fishing mor- 

 tality (F) is estimated as 1.2/yr or 1.7 xM. 

 With these figures and the estimates of 

 growth and age at onset of sexual matur- 

 ity, the Beverton-Holt yield equation esti- 

 mates the spawning-stock biomass per 

 recruit, when effort is 1 million trap-hauls, 

 is 40% of what it would be in the absence 

 of fishing (Polovina 1991). Thus, the ratio 

 of F to M and the relative spawning-stock 

 biomass calculations suggest that the 

 spawning biomass in 1985-86 was not 

 fished down to a level that would cause the 

 poor recruitment to the fishery 4 years 

 later (1989-90). 



Much of the variation in residuals from 

 the CPUE model is due to variation in re- 

 cruitment at Maro Reef. For example, for 

 the entire NWHI in 1990, trapping effort 

 increased 11% from the previous year 

 while the catch declined 33%, resulting in 

 a 39% decline in CPUE. However, the 

 decline in CPUE was most striking at 

 Maro Reef, where CPUE declined 42% 

 even though effort decreased by 

 37%. At Necker I., CPUE also 

 declined (40%) but effort in- 

 creased 35%. 



The estimated age-frequency 

 distributions based on research 

 cruises at Maro Reef show a 

 strong 3-year-old class in 1988 

 and a striking absence of all age- 

 classes in 1990 (Fig. 5). This is 

 consistent wdth the hypothesis 

 that recruitment of the 3-year- 

 olds to the fishery was weak in 

 1990 and subsequent fishing 

 reduced all older age-classes. 

 Necker I. had many more 2-year- 

 olds in the samples since some 

 trapping sites include nursery 

 habitat; but between years, the 

 abundance of 2-year-olds was 

 relatively constant, whereas 

 older lobsters declined in 1990, 

 likely because of the increase in 

 fishing effort (Fig. 6). 



The NWHI lobster fleet is very 

 mobile and shifts its trapping 

 locations according to abundance 

 of lobsters. By 1985, both Maro 



