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



55 



2.0 



1.5 



1.0 



0.5 



0,15 - 





0-05 - 



00 



Yolk 

 weight 



V 





• Embryos 

 o Juveniles 





20 30 40 



Intestine contents 

 weight 



50 



60 



• •• 



^ i /*^ 



vi*^ 









Percent yolk 

 weight 



••• 



...V 



80 



60 



40 



- 20 



20 



30 40 50 60 



• Percent intestine 



contents weight 







20 30 40 50 60 



12 



Fork length (cm) 



Figure 11 



Variation in the weight of yolk, intestine contents, and liver with length (left panels), and the 

 percentage of the total weight contributed by yolk, and percentages of yolkfree weight contributed 

 by intestinal contents and liver (right panels) for porbeagle embryos. Comparable data for five 

 small juveniles are also shown 



Discussion 



Geographical distribution 



Porbeagles occur throughout the New Zealand EEZ and 

 the southern half of the Australian EEZ. On the east 

 coast of Australia, they reach subtropical waters ( to 

 23°44'S), but only during winter. At the other extreme, 

 porbeagles are found in subantarctic waters in the In- 

 dian and southwest Pacific Oceans, reaching almost 

 54°S. Our results are consistent with observations of 

 porbeagles between about 28 and 58°S across the entire 

 South Pacific between New Zealand and Chile (Yatsu, 

 1995). Porbeagles are caught only north of 30°S in win- 

 ter-spring (August-November), and they penetrate far- 

 ther south during summer and autumn (Yatsu, 1995). 



Sea surface temperature at locations where porbea- 

 gles were caught was 9.9-22.6°C, but catch rates were 

 low above 19.5°C. This is similar to SSTs reported pre- 

 viously for porbeagles in the South Pacific by Stevens 

 et al. ( 19831 (7.&-22.8°C, with most captures less than 

 16.7°C) and Yatsu (1995) (5-20°C with most captures 

 less than 15 °C). Temperatures at the actual depth of 

 capture would be similar to these because most long- 

 lines fished at 50-100 m depth, which is shallower 

 than the depth of the mixed ocean layer in autumn- 

 winter. Bottom temperatures for trawl-caught porbea- 

 gles were as low as 1-3°C, which is consistent with 

 temperatures of 1.7°C (Svetlov, 1978) and 3.1-t.l°C 

 (Templeman, 1963) reported elsewhere. Thus the tem- 

 perature range inhabited by porbeagles in the South- 

 em Hemisphere is probably about 1-23°C, with abun- 



