24 



Fishery Bulletin 103(1) 



to estimate size at maturity of females of the Hawai- 

 ian spiny lobster, for which functional maturity can be 

 accurately described by using a combination of other, 

 more apparent external features. We also estimate body 

 size at gonadal maturity by microscopic examination of 

 histological preparations of ovaries of each species and 

 use these results to validate the functional maturity 

 characterizations. We contrast the benefits of the dif- 

 ferent approaches for estimating functional maturity in 

 these two lobsters and discuss the potential importance 

 of applying efficient measures of maturation for manag- 

 ing the NWHI lobster fishery. 



Materials and methods 



Specimen collection 



A research vessel was used to set and retrieve lobster 

 traps. All specimens of spiny lobster used in this study 

 were taken from Necker Bank surrounding Necker Island 

 (23°34'N, 164°42'W), NWHI. All the slipper lobsters used 

 were taken from Maro Bank, located about 600 km to 

 the northwest of Necker at 25°25'N, 170°35'W. Lobsters 

 were caught from bank terraces at median depths of 15 

 fm (slipper lobsters, Maro) and 17 fm (spiny lobsters, 

 Necker) with molded plastic (Fathoms Plus", San Diego, 

 CA) traps baited with 1 kg of mackerel (Scomber japoni- 

 cus) and left for a standard (overnight) soak. 



Shipboard processing 



All specimens were processed alive within minutes 

 of trap retrieval. Tail width (TW), as defined for slip- 

 per lobster by DeMartini and Williams (2001) and for 

 Hawaiian spiny lobster by DeMartini et al. (2003), was 

 measured with 0.1 mm accuracy. Berried females were 

 scored by egg-development stage with a gross visual 

 proxy (brooded eggs noted as either orange or brown 

 in color to the unaided eye). Female spiny lobsters 

 were scored by the presence or absence and by condi- 

 tion ("smooth"=unused, "rough"=partly used) of sper- 

 matophoric (sperm) mass (Matthews, 1951; Berry and 

 Heydorn, 1970) on the sternum. Female S. squammosus 

 in almost all cases lack a sperm mass and the presence- 

 absence of this feature provides no useful information. 

 In 1998-2000, ovaries were dissected from a maximum 

 of two living specimens for each 1-mm TW class of the 

 two species and fixed in 10% (sea water buffered) for- 

 malin for subsequent histological analyses. Egg-bear- 

 ing "tails" (abdominal segments) were flash-frozen at 

 -20 C. 



During 1997-99, pleopods of each species were mea- 

 sured aboard ship to evaluate measurement accuracy 

 under field conditions. Maxima of 10 live individuals 

 per 1-mm TW class of each species were measured as 

 described below. Two independent measurements of 

 each specimen were made by each of two measurers 

 (one inexperienced and one experienced). In 2000-01, 

 pleopods for a larger series of morphometries were simi- 



larly measured aboard ship to evaluate production- 

 scale numbers (500-1000 specimens per species on each 

 cruise) based on a single measurement per specimen 

 taken by one measurer. 



Laboratory measurements 



Beginning with specimens collected in 2000, the lengths 

 of exopodites on first pleopods were measured for a 

 representative sample of berried and unberried tails of 

 each species, after the tails were thawed overnight in a 

 refrigerator at 3 C. Preliminary observations indicated 

 that the first pleopod was disproportionately large in 

 berried females; measurements of the first pleopod of 

 all (berried and unberried) females moreover were the 

 most precise, i.e. the measurements were more likely to 

 be obtained again — probably because the first pleopod 

 was the easiest to measure. The straightline distance 

 between base and tip of exopodite on the first pleopod 

 (exopodite length=EL) was measured with dial calipers 

 to 0.01 mm. An analogous measurement of exopodite 

 width (EW) was taken perpendicular to the EL axis at 

 the structure's widest point. The left exopodite in ven- 

 tral aspect (Fig. 1) was routinely measured because the 

 ventral aspect was easier to measure for live animals 

 aboard ship. Measurements of the right exopodite (of 

 the same specimen) in dorsal aspect were taken for a 

 range of body sizes to evaluate the possible influence of 

 aspect (dorsal vs. ventral) or body side (left vs. right) on 

 the measurement that was taken. Replicate measure- 

 ments (independent, with calipers reset to zero between 

 measurements) were used to assess inter-measurer and 

 inherent measurement error. Formalized ovaries were 

 weighed (blotted damp-dry) to the nearest 0.01 g after 

 fixation for at least a month. 



Histological validation 



Fixed ovary specimens of each species were dehydrated, 

 imbedded, and sectioned by using standard techniques, 

 and were stained with hematoxylin and counter-stained 

 with eosin to differentiate protein and yolk materials 

 within oocytes. Histological slides were viewed under a 

 compound microscope at 150x magnification. For each 

 specimen, the diameters (average of major and minor 

 axis) were measured for 10 oocytes (randomly chosen) 

 within the largest size class of oocytes present. The 

 median diameter was used to characterize oocyte size 

 for that specimen; the median diameter based on 10 

 measurements yielded CVs (100% x standard error/mean) 

 <10% (DeMartini et al., 2003). Developmental staging 

 followed Minagawa (1997) and Minagawa and Sano 

 (1997): females were scored as mature 1) if unberried 

 in developing or ripe ovarian stages II and III, respec- 

 tively; 2) if berried in ripe and redeveloping stages 

 IV and V, respectively; or 3) if recently spent (stage 

 VI) with heavily setose pleopods (P. marginatus only). 

 Inactive females in stage I were scored as immature. A 

 gonad index, calculated as GI = (OWx 10 5 /TW 3 ), where 

 OW = ovary weight in g, was used to complement his- 



