23 



Abstract — Body size at gonadal matu- 

 rity is described for females of the slip- 

 per lobster (Scyllarides squammosus) 

 (Scyllaridae) and the endemic Hawaiian 

 spiny lobster (Panulirus marginatus) 

 (Palinuridae) based on microscopic ex- 

 amination of histological preparations of 

 ovaries. These data are used to validate 

 several morphological metrics (relative 

 exopodite length, ovigerous condition) 

 of functional sexual maturity. Relative 

 exopodite length ("pleopod length"! pro- 

 duced consistent estimates of size at 

 maturity when evaluated with a newly 

 derived statistical application for esti- 

 mating size at the morphometric matu- 

 ration point IMMP) for the population, 

 identified as the midpoint of a sigmoid 

 function spanning the estimated bound- 

 aries of overlap between the largest 

 immature and smallest adult animals. 

 Estimates of the MMP were related to 

 matched (same-year) characterizations 

 of sexual maturity based on ovigerous 

 condition — a more conventional measure 

 of functional maturity previously used to 

 characterize maturity for the two lobster 

 species. Both measures of functional 

 maturity were similar for the respective 

 species and were within 5% and 2% of 

 one another for slipper and spiny lob- 

 ster, respectively. The precision observed 

 for two shipboard collection series of 

 pleopod-length data indicated that the 

 method is reliable and not dependent on 

 specialized expertise. Precision of matu- 

 rity estimates for S. squammosus with 

 the pleopod-length metric was similar 

 to that for P. marginatus with any of 

 the other measures (including conven- 

 tional evidence of ovigerous condition) 

 and greatly exceeded the precision of 

 estimates for S. squammosus based 

 on ovigerous condition alone. The two 

 measures of functional maturity aver- 

 aged within 8 f » of the estimated size at 

 gonadal maturity for the respective spe- 

 cies. Appendage-to-body size proportions, 

 such as the pleopod length metric, hold 

 great promise, particularly for species 

 of slipper lobsters like S. squammosus 

 for which there exist no other reliable 

 conventional morphological measures of 

 sexual maturity. Morphometric propor- 

 tions also should be included among the 

 factors evaluated when assessing size at 

 sexual maturity in spiny lobster stocks; 

 previously, these proportions have been 

 obtained routinely only for brachyuran 

 crabs within the Crustacea. 



Manuscript submitted 2 September 

 2003 to the Scientific Editor's Office. 



Manuscript approved for publication 

 26 August 2004 by the Scientific Editor. 



Fish. Bull. 103:23-33 (20051. 



Relative pleopod length as an indicator of 

 size at sexual maturity in slipper 

 (Scyllarides squammosus) and 

 spiny Hawaiian (Panulirus marginatus) lobsters 



Edward E. DeMartini 



Marti L. McCracken 



Robert B. Moffitt 



Jerry A. Wetherall 



Pacific Islands Fisheries Science Center 



National Marine Fisheries Service, NOAA 



2570 Dole Street 



Honolulu, Hawaii 96822-2396 



E mail address (for E. E. DeMartini) edward demartinianooa gov 



Estimates of body size and age at 

 sexual maturity provide key informa- 

 tion for stock assessments and hence 

 for managing sustainable fisheries. 

 Characterizations of size at matu- 

 rity are relatively straightforward in 

 lobsters and most other crustaceans. 

 One presently accepted standard is 

 to regress percentage mature against 

 classes of some body size metric and to 

 fit a logistic model to predict the size 

 class in which 50% of the population 

 is mature. A necessary prerequisite is 

 accurate data on the maturation state 

 of individuals. In spiny lobsters of the 

 family Palinuridae, female matura- 

 tion is usually deduced from "berried" 

 (ovigerous) condition (Groeneveld and 

 Melville-Smith, 1994), the presence 

 of external morphological indicators 

 such as changes in the number of pleo- 

 pod setae (Gregory and Labisky, 1981; 

 Montgomery, 1992), relative lengths 

 of abdominal and thoracic segments 

 (Jayakody, 1989), or proportional 

 lengths of segments of walking or egg- 

 bearing appendages at the pubertal 

 molt (George and Morgan, 1979; Grey, 

 1979; Juinio, 1987; Plaut, 1993; Evans 

 et al., 1995; Hogarth and Barratt, 

 1996; Minagawa and Higuchi, 1997). 

 A major complication arises, however, 

 when the percentage mature within 

 size classes cannot be accurately 

 described. Such is the case for Scyl- 

 larides squammosus, a species of slip- 

 per lobster (family Scyllaridae) that 

 prior to closure of the fishery in 2000 



had become an increasingly important 

 target of the Northwestern Hawaiian 

 Island (NWHI) commercial trap fish- 

 ery. In S. squammosus, unberried but 

 mature females are indistinguishable, 

 based on gross external morphology, 

 from immature females. In this spe- 

 cies, the additional variance intro- 

 duced by combining falsely classified 

 "immature" with truly immature 

 females inflates requisite sample sizes 

 enough (given the sampling effort fea- 

 sible on annual research surveys) to 

 prevent characterization of possible 

 changes in size at maturity with data 

 pooled from less than several surveys. 

 Combining unberried adults with true 

 immature individuals also introduces 

 an overestimation bias (DeMartini et 

 al., 2003). 



To date only one study has provided 

 a description of the use of a morpho- 

 logical measure of maturity in a slip- 

 per lobster (Hossain, 1978). Morphol- 

 ogy-based maturity measures have 

 been described for numerous spiny 

 lobsters of the genus Panulirus, but 

 such measures for the endemic Ha- 

 waiian spiny lobster (Panulirus mar- 

 ginatus) have not been fully described 

 (Prescott, 1984). 



Our objectives are to describe the 

 development and use of an external 

 body metric for accurately and pre- 

 cisely characterizing body size at mor- 

 phological (functional) sexual maturi- 

 ty in female Scyllarides squammosus. 

 We likewise use this external metric 



