Francis and Stevens: Reproduction, embryonic development, and growth of Lamna nasus 



47 



Males (n = 230) 



Females ;n= 133) 



75 100 125 150 175 200 225 250 



Fork length (cm) 



Figure 3B 



The mean lengths of the modes for southwest New 

 Zealand and Australia were plotted against age, which 

 was calculated from a theoretical birth date of 1 June 

 (see below) and mean sampling dates of 5 May and 

 16 Jime, respectively (Fig. 4). Thus the ages classes 

 were sampled near their respective birth dates. We 

 interpret the five Australian modes as representing 

 sharks that were recently bom, and 1^ years old, 

 and the three southwest New Zealand modes as those 

 representing sharks that were 1-3 years old. The first 

 length mode in the northeast New Zealand distribu- 

 tion was substantially shorter than the first southwest 

 New Zealand mode and the second Australian mode, 

 and we are uncertain about assigning an age to it. At 

 age 1 year, southwest New Zealand and Australian por- 

 beagles were similar in length, but for older ages New 

 Zealand sharks were slightly larger Growth in both re- 

 gions was linear over the range of the data (Fig. 4): 



Australia: 



FL = 65.4 + 16.1 (Age) {r^=0.997) 



Female length at maturity and reproductive 

 development 



Maturity status was not recorded; therefore we cannot 

 estimated length at maturity. However, 37 pregnant 

 females ranged from 167^-199 cm (mean=185 cm), 

 suggesting that female maturity is reached around 

 165-180 cm. 



The Macquarie Island female had four embryos 

 21.5-23.2 cm long. The right ovary was of the "inter- 

 nal" type, which is typical of lamnid sharks (Pratt, 

 1988). It weighed 2.75 kg (2.359^ of total weight) and 

 was undergoing active oogenesis. The entire ovary was 

 packed with ova; other than a thin external envelope 

 it had no macroscopically visible ovarian tissue. There 

 was a single large efferent pore in the ovary, from 

 which ova are shed (Stevens, 1983; Gilmore, 1993). 



southwest 

 New Zealand: 



FL = 66.5 -I- 19.8 (.Age) (/•2=1.000) « FL of 167 cm was calculated from a PL of 151 cm. 



