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



27 



1989; DeMartini et al.^). Density-dependent 

 changes in somatic growth, survival rates, 

 and body sizes at sexual maturity have been 

 described for numerous other palinurid spe- 

 cies (Pollock, 1995a, 1995b). At least one case 

 study provides further evidence for reproduc- 

 tive compensation. Chittleborough (1979) doc- 

 umented a decreased interval between broods 

 as a response to increased exploitation in the 

 Western Australian rock lobster, P. cygnus. 

 Prior to the present study, the study of De- 

 Martini et al. (1993) was the only published 

 record of changes in size-specific fecundity in a 

 spiny lobster, perhaps attributable to density 

 declines resulting from exploitation, although 

 perhaps only reflecting natural interannual 

 variation independent of fishing (Pollock, 

 1995b). 



The fecundity update for 1999 in this ar- 

 ticle further supports DeMartini et al.'s (1993) 

 original interpretation of an increase in size- 

 specific fecundity as a density-dependent re- 

 sponse at lower population densities. Other 

 data on body size at sexual maturity for the 

 period 1988-99, to be reported elsewhere (De- 

 Martini et al.'), extend the temporal pattern 

 of smaller body size at sexual maturity first documented 

 during 1986-87, after 10 years of exploitation, by Polovina 

 (1989). The observed decrease in size at maturity could 

 have been caused by slower growth (Pollock, 1995a) re- 

 sulting from lower levels of oceanic productivity (Polovina 

 et al., 1994, 1995). However, if smaller size at maturity 

 has been a proximal response to decreased rather than in- 

 creased per capita food availability, it is inconsistent with 

 the simultaneous increases in size-specific fecundity and 

 egg size which have occurred. Evidence for changes in the 

 nutritional status of P marginatus at Necker Bank dur- 

 ing 1991-95 is equivocal (Parrish and Martinelli-Liedtke, 

 1999). Resolution of whether the lower densities of spiny 

 lobsters at Necker Bank have resulted from natural de- 

 clines in productivity, increased fishery exploitation (or 

 both) would require comparative evaluations for lobsters 

 collected from fished as well as unfished control areas at 

 the bank; unfortunately, as of 1999 unfished lobster habi- 

 tat at Necker Bank does not exist. 



The observed increase in size-specific reproductive 

 output of P. marginatus probably has been a phenotypic 

 response to lower densities and higher per capita food 

 availabilities at Necker Bank. It is unlikely, given the 3-yr 

 generation time of P. marginatus (Uchida and Tagami, 

 1984) and relatively short (20-1- yr) period over which 

 the responses have occurred, that a genetic, rather than 

 phenotypic, dynamic has been involved. More extensive 

 comparisons of the egg productions of P. marginatus popu- 

 lations among Necker and other NWHI banks differing in 

 natural and fishery-induced densities would be necessary 



1 DeMartini, E. E., R. B. Moffttt, and P. Kleiber 2002. Unpubl. 

 data. Honolulu Laboratory, Southwest Fish. Sci. Cent., Natl. 

 Mar. Fish. Serv., NOAA, Honolulu, HI 96822-2396. 



to further distinguish natural variation from fishing ef- 

 fects. Complete resolution of this issue would require 

 quantitative comparisons of growth rates and ages at ma- 

 turity for a lengthy series of year classes off! marginatus 

 at Necker Bank and elsewhere. 



Egg size Our data demonstrate that egg size can vary 

 substantially among same-size P. marginatus collected 

 during the midpoint of a single breeding season, as does 

 fecundity among same-size females. It should not be 

 surprising, then, that average population egg size has 

 covaried with fecundity, even if egg size is body-size inde- 

 pendent. The observed change in mean egg size between 

 1991 and 1999 could not have been due to either develop- 

 mental or subseasonal changes because we evaluated egg 

 size by consistent methods, using only early-development 

 broods collected during the month of June. It is possible, 

 although unlikely, that the larger eggs (hence larvae) pro- 

 duced in 1999 were somehow of inferior quality and had 

 lower hatching success and poorer subsequent sur\'ival. 



Intraspecific variation in egg size has rarely been de- 

 scribed in spiny lobsters (Pollock, 1995a, 1997). Annala 

 ( 1991) suggested that egg size increases with body size for 

 a cold-temperate species, Jasf^s edwardsii, from mainland 

 New Zealand. Egg size is unrelated to female body size 

 in tropical Panulirus argus (Fonseca-Larios and Briones- 

 Fourzan, 1998). In one particularly detailed study of the 

 egg size dynamics of a small-bodied Caribbean palinurid, 

 P. guttatus, Briones-Fourzan and Contreras-Ortiz (1999) 

 detected no relation of egg size to female body size, even 

 though egg size varied nearly twofold among females 

 ranging over twofold in carapace length. 



Few studies have documented temporal changes in egg 

 size for palinurid lobsters. A seasonal decline in egg size 



