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



49 



160 



E 140 - 



• Australia, length modes 



o SW New Zealand, length modes 



□ Aasen (1963) length modes 



2 3 4 5 6 



Age (years) 



Figure 4 



Porbeagle mean lengths-at-age determined by MIX analysis of the south- 

 west New Zealand and Australian data in Figure 3, A and C, with fitted 

 linear regressions. Also shown are Aasen's ( 1963 ) northwest Atlantic length- 

 frequency modes, which were plotted assuming a 9 April theoretical birth 

 date ( 1.7 months earlier than the Southern Hemisphere) and a mean sam- 

 pling date of 9 August. 



Logjo (weight) = ^.719 + 2.916 Logjo (FL) 



(« = 100, r2=0.974) 



The Kerguelen Island embryos reported by Duhamel 

 and Ozouf-Costaz ( 1982 ) were the smallest in our sam- 

 ple, with estimated FLs of 9.6-10.4 cm. Our largest em- 



bryos were in litters of 62.0-67.0 cm, 64.2-65.6 cm, and 

 64.3-66.6 cm. Typically, all embryos in a litter were sim- 

 ilar in length, but two litters each contained one unusu- 

 ally small embryo (runt) (Table 2). Variation in length 

 within a litter increased with mean length, but the per- 

 centage range in length was relatively constant. 



