DeMartini et al.; Population density, fecundity, and egg size of Panulirus marginatus 



29 



1999). Pollock {1995c) noted that P. guttatiis produces 

 unusually few, but large eggs for a shallow-water tropical 

 palinurid. 



Using the CL-to-body-weight regression listed in Table 1, 

 we estimated an inverse index of egg size (Pollock, 1997) 

 for Necker Bank P. marginatus in 1999 that was 660 eggs 

 per g total body weight. Such small eggs are typical within 

 the derived lineage of shallow-water, subtropical and 

 tropical members of the genus (Pollock, 1997). 



We could find no other studies documenting changes in 

 egg size as a response to density fluctuation in palinurid 

 lobsters. Prior to the mid-1990s, information on temporal 

 and size-related patterns of fecundity and egg size were 

 largely restricted to cold- and warm-temperate members of 

 the genus Jasi/s and Panulinif; (Pollock, 1995c, 1997). Per- 

 haps egg size, like size-specific fecundity, is phenotypically 

 labile in tropical reef species of the genus Panulirus for 

 which high and variable predation pressure makes such 

 plastic responses adaptive. More research on size-specific, 

 individual reproductive output is needed for P. marginatus 

 and other tropical reef species of spiny lobsters. 



It is unknown whether egg size lability in P. marginatus 

 has a genetic or environmental basis. One could perhaps 

 evaluate this for individual females by repetitively mea- 

 suring egg subsamples from successively brooded egg 

 masses of berried tagged and recaptured females. Fixed 

 but differing egg sizes among individual females would be 

 consistent with a genetic basis. On the other hand, changes 

 in the size of eggs produced by the same individual female 

 in successive broods would suggest that environmental 

 factors are involved. 



Management implications 



One of our observations has major relevance to the man- 

 agement of P. marginatus in the NWHI lobster fishery. 

 Based on the IRP of Kanciruk and Herrnkind (1976), egg 

 production by the Necker Bank population of P. margin- 

 atus was dominated by the 50-57 mm TW classes in 1999, 

 which together contributed >43'7f to population egg pro- 

 duction (Table 4). Even though each large (>60 mm TWi 

 individual produces a disproportionately great number 

 of eggs, large females are now so poorly represented in 

 the population that they no longer drive population egg 

 production (Table 4). The eggs produced by smaller (50- 

 57 mm TW) females are more important to the population 

 now than before exploitation. In 1996 a "retain all" size 

 policy was established for the commercial fishery, replac- 

 ing a 50-mm-TW minimum size limit used previously, in 

 part because of the high mortality of discarded lobsters 

 (DiNardo et al., 2002). If a commercial lobster fishery with 

 a minimum size limit were to be reinstated in the NWHI, 

 a minimum size larger than the previous (50 mm TW) 

 should be considered. Our findings on the size distribution 

 of population egg production indicate that smaller adult 

 females, which now produce most of the population's eggs, 

 should be further protected, perhaps by using larger escape 

 vents in traps. Doing so would increase total population 

 egg production and might assist in countering recruitment 

 overfishing (Botsford, 1991; Pollock, 1993). Panulirus mar- 



ginatus production at Necker Bank historically and pres- 

 ently dominates archipelago-wide production by the spe- 

 cies; this production is supported by empirical catch data 

 (DiNardo et al.'^) as well as modeling of its recruitment 

 dynamics (Polovina et al., 1999). Augmenting egg produc- 

 tion by the Necker Bank population might significantly 

 bolster stock-wide productivity. The body size distribution 

 of egg production by P. marginatus at other NWHI banks 

 is presently unknown, however, and egg production by 

 large females elsewhere possibly could partly offset the 

 deficit in production at Necker. Our observations on the 

 size distribution of egg production at Necker Bank none- 

 theless merit important consideration for setting size 

 limits for spiny lobster management. 



By necessity we calculated the IRP assuming that all 

 size classes produced the same (single) brood per spawn- 

 ing period because data on size-specific spawning frequen- 

 cy were lacking. We caution that, if females >60 mm TW 

 (whose size-specific egg production is greatest) produce 

 broods more frequently than smaller females (Lipcius, 

 1985), we have proportionately underestimated the con- 

 tribution of larger females to population egg production. 



Individual Panulirus marginatus of all sizes likely 

 produce multiple broods per individual spawning season, 

 based on the protracted period during which females are 

 berried (Uchida and Tagami, 1984; Polovina and Moffitt, 

 1995) and the occasional presence of new, intact (unused) 

 spermatophore plates on spent females (unpubl. data, 

 Honolulu Laboratory, NMFS). (The latter observation in 

 fact suggests that Necker Bank P. marginatus can pro- 

 duce more than one brood per molt [like P. argus; Sutcliffe, 

 1953].) There are no time-series growth-rate data avail- 

 able with which to evaluate whether females of a given 

 body size might now be producing larger broods at more 

 frequent intervals than previously. If females are now 

 growing faster, it is likely that the rates of both molting 

 and brood production are now greater Accurate estimates 

 of individual spawning frequencies and how these might 

 differ among females of varying body sizes, would be 

 needed to fully describe the compensatory increase in 

 reproduction which has occurred for the Necker Bank 

 population of P. marginatus. 



Acknowledgments 



We thank several anonymous fishery observers for collec- 

 tion of invaluable commercial catch data and R. Moffitt, 

 J. Polovina, and an anonymous reviewer for constructive 

 criticisms of the manuscript. 



- DiNardo, G. T, W. R. Haight, and J. A. Wetherall. 1998. Sta- 

 tus of lobster stocks in tfie Northwestern Hawaiian Islands, 

 1995-97, and outlook for 1998. Southwest Fish. Sci. Cent. 

 Admin. Rep. H-98-05, 35 p. Honolulu Laboratory, Southwest 

 Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, Honolulu, HI 

 96822-2.396. 



