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



43 



25 S 



30 



35 



40 



45 



50 



55 



160 



rp,— r 



165 



170 



175 E 



— 1 1 r- 



180 



175 W 



170 

 25 S 



o Observed on longlines 

  Pregnant females 



;Macquane 

 Island 



30 



35 



40 



45 



50 



55 



160 



165 



170 



175 E 



180 



175 W 



170 



Figure 1 



Map of the New Zealand region showing start positions of tuna longUne 

 sets from which porbeagles were recorded, and capture locations of pregnant 

 females (n=35). The 250-m isobath and Exclusive Economic Zone are also 

 shown. 



Size and growth 



Porbeagles were measured in one or more of three 

 ways: precaudal length (PL; snout to the precaudal 

 pit), FL (snout to the fork in the tail), and TL (snout 

 to the tip of the tail). TL can be measured in two differ- 

 ent ways — ^with the tail in the natural position (TL^^j) 

 (Bigelow and Schroeder, 1948), or with the tail flexed 

 down so that the upper caudal lobe lies parallel to the 

 long axis of the body ( TLjj^j, ) ( Compagno, 1984 ). Observ- 

 ers probably measured TL^^, on postnatal porbeagles 

 because TLj^^j^ is difficult to measure in species with a 

 relatively rigid caudal fin. TL^^^j measurements in em- 

 bryos are not strictly comparable with TL^^.^^ measure- 

 ments in postnatal porbeagles because of the curved 

 and folded nature of the caudal fin in embryos. 



Most observers measured FL; therefore we adopted 

 that as our standard. Regression equations relating 

 FL to TL and PL are given in the "Results" section. 

 Literature reports of TL were converted to FL before 

 comparison with our data. Hereafler, FL is reported 

 unless otherwise stated. Porbeagles were also sexed, 

 weighed whole, and sometimes weighed after process- 

 ing. Data were inspected for outliers on bivariate plots 

 of PL, FL, TL, whole weight, and processed weight. 

 Obvious errors were corrected if possible, and deleted 

 if not. Before 1993, some New Zealand observers con- 

 fused porbeagles and shortfin makos. We therefore re- 

 stricted our New Zealand analyses of length, weight 

 and location to data collected from 1993 onwards. 



Initial inspection of the length-frequency data re- 

 vealed modes that might correspond with juvenile age 



