DeMartim et al.: Validated morphological metric for lobster size at maturity 



31 



100 



Panulirus marginatus 



curve: histological criteria 



P x = 100/(1 +exp-(-9.415+0.233TW)) 

 l 2 = 0.907 



curve: berried + 

 sperm mass criteria 



P x = 1 00 / (1 + exp-(-1 8.836+0.532 TW)) 

 ^=0.895 



50 60 



Tail width (TW, mm) 



80 



Figure 6 



Scatterplots and fitted curves for the relations between 

 body size (tail width, TW) and percent sexual maturity 

 based on functional maturity gauged by presence-absence 

 of sperm mass and berried condition (dotted curve), 

 overlaid on gonadal maturation gauged by microscopic 

 examination of ovaries (dark-line curve); the pleopod 

 length-based morphometric maturation point (MMP) 

 estimate of size at functional maturity is indicated 

 by the large circle with cross-hairs (©), for Hawaiian 

 spiny lobster (Panulirus marginatus). Two-parameter 

 logistic equations were sufficient to fit both the dotted 

 and dark-line curves. 



truly immature from mature, but reproductively inac- 

 tive, females generates an inflated "immature" class, 

 and the estimates of median size at sexual maturity 

 thus obtained with logistic equation fits are biased high. 

 Variances of median-size estimates based on sample 

 sizes available on single research surveys are often so 

 large that 3-parameter logistic applications (necessary 

 to scale maturity to 100%) fail to converge, and reliable 

 individual-year estimates are impossible (DeMartini 

 et al., 2002). Unfortunately, the temporal dynamics 

 of targeting species by fishermen in the NWHI trap 

 fishery and the rapid phenotypic responses in fecundity 

 and maturation size to harvesting, fluctuating natural 

 productivity, and changing population densities that 

 have been observed in P. marginatus (DeMartini et al., 

 2003), require that size at maturity be re-estimated at 

 short (one-to-several-year) intervals for this species at 

 least and possibly for S. squammosus as well. 



The accurate and precise estimates of median body 

 size at sexual maturity made possible by using the 

 pleopod length metric enable such yearly re-evaluations 

 for S. squammosus and provide a second reliable and 

 independent estimator for P. marginatus. Our success- 

 ful applications for a scyllarid as well as a palinurid, 

 together with prior observations for numerous other 

 spiny lobster species, indicate that easily measured 

 appendage length-to-body size relations are generally 

 suitable for assessing functional sexual maturity in 

 lobsters and other decapods. We recommend that these 

 relations be explored for other commercially exploited 

 crustacean stocks and wherever possible routinely ap- 

 plied to provide cost-effective and timely information 

 on size at maturity for stock assessments. Managers 

 responsible for the assessment of lobster and other crus- 

 tacean stocks will then have a more complete toolbox 

 of methods generally available for assessing the size 

 at maturity and harvestability of stocks, particularly 

 for species like S. squammosus in which conventional 

 morphological measures are inadequate. 



Acknowledgments 



We thank D. Yamaguchi for assistance with Figure 1 

 and G. DiNardo and J. Polovina for constructive criti- 

 cisms of the manuscript. 



unconstrained by a conspicuous but perhaps inaccurate 

 feature like berried condition. 



Literature cited 



Management implications 



Estimates of body size at sexual maturity can provide 

 key information to various stock assessment models, but 

 only if the estimates are accurate and sufficiently pre- 

 cise. For the slipper lobster (S. squammosus), DeMartini 

 et al. (2002) have shown that estimates made by using 

 percent berried as the lone maturity criterion, the only 

 morphological metric previously available, are both 

 inaccurate and imprecise. The inability to distinguish 



Aiken, D. E., and S. L. Waddy. 



1980. Reproductive biology. /« The biology and manage- 

 ment of lobsters, vol. I, physiology and behavior (J. S. 

 Cobb and B. F. Phillips, eds.), p. 215-276. Academic 

 Press, New York, NY. 



Berry, P. F., and A. E. F. Heydorn. 



1970. A comparison of the spermatophoric masses and 

 mechanisms of fertilization in Southern African spiny 

 lobsters (Palinuridae). S. Afr. Assoc. Mar. Biol. Res., 

 Oceanogr. Res. Inst. Invest. Rep. 25, 18 p. 



