162 



Fishery Bulletin 89(1), 1991 



Table 1 



Serum progesterone concentrations [P] in immature and 

 mature female Dall's porpoises. Data from 1980 sample of 

 Temte and Spielvogel (1985). 



Status 



No. 



Mean [P] 

 (ng/mL) 



SD Range of [P] 



Mature 

 Pregnant (P) 

 Lactating (L) 

 non-P, non-L 



Immature* 



33 



24 



17 



14.76 



19.40 



2.63 



0.49 



0.27 



12.43 

 11.31 



3.75 



0.46 



0.0-45.3 

 0.9-45,3 

 0.0-11.4 



0.0-1.3 



* Excluding one immature female with a large follicle and 31.1 

 ng/mL progesterone. 



by Temte and Spielvogel (1985). In these samples, how- 

 ever, serum was decanted into 1.5-mL plastic ultra- 

 centrifuge tubes and frozen at - 20° C until assays were 

 performed. 



RIA for progesterone 



Progesterone RIA was identical to that reported by 

 Temte and Spielvogel (1985). This assay had previ- 

 ously been validated for porpoise serum, and chroma- 

 tography had shown an absence of interference from 

 other serum constituents. Triplicate volumes of por- 

 poise serum (10/iL for pregnant, 50^L for lactating, 

 and 100 mL for non-pregnant, non-lactating females) 

 were doubly extracted utilizing a 1:2 mixture of 

 benzene and hexane (Sawyer-Steffan and Kirby 1980). 

 The antiserum used was anti-progesterone-11-BSA, 

 No. 1337 (Gordon D. Niswender). The intraassay coef- 

 ficient of variation (COV) was 5.5%, while the inter- 

 assay COV was 5.9%. The sensitivity of this assay was 

 0.1 ng/mL. 



RIA for testosterone 



The procedure for testosterone RIA was nearly iden- 

 tical to that for progesterone. Triplicate volumes of 

 25-^L porpoise serum were doubly extracted with 1:2 

 benzene:hexane. The antiserum used was anti-testos- 

 terone, No. s-250 (Gordon D. Niswender). The com- 

 petitor was [ 3 H]testosterone (NET-553, New England 

 Nuclear). The intraassay coefficient of variation (COV) 

 was 6.3%, while interassay COV was 14.6%. The assay 

 sensitivity was 0.3ng/mL. 



Maturity criteria for females 



The mean serum progesterone for immature females 

 reported in Temte and Spielvogel (1985) was 0.27 

 ng/mL. Assuming a normal distribution, 99% of imma- 

 ture females would be expected to have serum pro- 

 gesterone levels less than 1.34 ng/mL. Based upon this 

 result, females with serum progesterone concentra- 

 tions greater than 1.34 ng/mL were considered sexually 

 mature. Whereas, this progesterone level is lower than 

 the 3.0ng/mL used by Kirby and Ridgway (1984) as an 

 indicator of ovulation in D. delphis and T. truncatus, 

 94% of the immature females and 96% of the pregnant 

 females reported in Temte and Spielvogel (1985) were 

 correctly classified using this criteria. 



Maturity criteria for males 



Since samples were collected near the peak breeding 

 period for Dall's porpoises (Newby 1982; see also Jef- 

 ferson 1989), and considering the seasonal flux of tes- 

 tosterone in other odontocetes (Wells 1984), separation 

 of immature and mature Dall's porpoises by testos- 

 terone level alone was theoretically possible in this 

 study. Although Wells (1984) regarded serum testos- 

 terone concentrations of less than 8.0 ng/mL as baseline 

 levels in S. longirostris, a natural break in the Dall's 

 porpoise data occurred between 1.7 and 5.0ng/mL. 

 However, as tissue samples were not available for 

 maturity assessment, no hormonal maturity criteria 

 could be confirmed. 



Estimation of LSM 



The proportions of mature females in each 10-cm in- 

 crement (135-225cm) were calculated. Graphical anal- 

 ysis determined the length at which the cumulative 

 probability of maturity, I(mj), equaled the cumulative 

 probability of not being mature at that length or longer, 

 1(1 -mj). This method was first used by Kasuya 

 (1972) and has been termed the summation technique 

 by DeMaster (1984). It is recommended when small 

 samples of size- or age-classes exist. 



A small total sample precluded the use of the sum- 

 mation technique in males. As a consequence, a modi- 

 fication of the regression technique (see DeMaster 

 1984) was used to identify the LSM. Because testos- 

 terone concentrations demonstrated a discontinuity 

 (see above), a continuous two-phase regression model 

 (Yeager and Ultsch 1989; review by Nickerson et al. 

 1989) was used to objectively identify the transition 

 point in the data. The transition point in the length 

 represents the point at which the discontinuity oc- 

 curred, or in this case, the LSM. 



