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



45 



estimate was made of the total number present by 

 counting ova in six weighed subsamples. 



The four MNHN embryos from Kerguelen Island 

 were measured for TL, FL, and weight in December 

 1997. Because there was a mean shrinkage of 4.4% 

 from the original TL measurements (Duhamel and 

 Ozouf-Costaz, 1982), we applied an equivalent shrink- 

 age correction to the 1997 FL measurements. Fresh 

 embryo weights were not reported by Duhamel and 

 Ozouf-Costaz (1982), and we have not used the 1997 

 weights because they probably underestimate the orig- 

 inal weights due to dissolution and leaching of lipids 

 from the yolk in the stomach. Similarly, measure- 

 ments from the Museum of New Zealand (NMNZ) em- 

 bryos are not included here because of likely shrink- 

 age and weight loss following preservation. 



North Atlantic embi-yo lengths and dates of cap- 

 ture were obtained from the literature for comparison 

 with Southern Hemisphere data (Swenander, 1906, 

 1907; Shann, 1911, 1923; Nordgard, 1926; Bigelow 

 and Schroeder, 1948; Templeman, 1963; Gauld, 1989; 

 Moss^; Newton'*). For some litters, only one or two 

 embryos were measured. Data were used only if they 

 specified the month of capture, and some measure- 

 ments that were known or thought to have been made 

 on preserved specimens were corrected for shrinkage. 



Sea surface temperature was recorded at about 

 hourly intervals during hauling of each longline in 

 New Zealand. The number of sharks caught per 1000 

 hooks (CPUE) was determined for each set and plotted 

 against the mean of the hourly SSTs. There was no ap- 

 parent trend in CPUE between 9.85°C (the minimum 

 set temperature) and 19.5°C (mean CPUE=1.82, max- 

 imum=44.8, n = 1292 sets). Between 19.5 and 23.0°C, 

 mean CPUE was lower (mean=0.54, maximum - 5.0, 

 M=105), and above 23.0°C no porbeagles were caught 



Most pregnant females were caught in the cooler 

 southern waters of New Zealand and Australia (Figs. 

 1 and 2 ), and some were taken from the subantarctic 

 Auckland, Macquarie, Heard, and Kerguelen Islands 

 ( 50— 54°S ). However, two were also caught in northeast 

 New Zealand. For longline-caught females, SST was 

 10.2-17.2°C (mean 12.9°C, /i=32 ), and bottom depth at 

 the capture locality was 600^300 m (mean=2104 m, 

 n = \\). The two Heard Island pregnant females were 

 taken by bottom trawl at depths of 248 and 259 m and 

 bottom temperatures of 2.9 and 2.5°C, respectively. 

 The Auckland Islands female was caught by midwater 

 trawl at 160-164 m and a temperature of 11.9°C. Por- 

 beagles have also been caught by bottom trawl near 

 Macquarie Island at temperatures of 1°C (Williams^). 



Results 



Geographical distribution 



Porbeagles have a wide latitudinal distribution. In the 

 New Zealand region, they range from the Kermadec 

 Islands (30°30'S) to Macquarie Island (53°52'S) (Fig. 

 1). In the Australian FEZ, they range from near the 

 Tropic of Capricorn in southern Queensland (23°44'S) 

 to south of Tasmania (45°44'S) (Fig. 2). The large num- 

 ber of capture records from northeast and southwest 

 New Zealand, and around Tasmania, reflect concentra- 

 tion of fishing effort, and not necessarily high shark 

 densities. Porbeagles also occur near Heard Island 

 (51-52°S), and Kerguelen Island (5rS) in the southern 

 Indian Ocean (Duhamel and Ozouf-Costaz, 1982). 



Porbeagles were caught off southern Queensland 

 (Fig. 2, north of 31°S) only in winter (June-Septem- 

 ber), when water temperatures were lowest. Sea sur- 

 face temperature (SST) at the time of capture of 

 six sharks off Queensland in July-August 1997 was 

 21.3-21.6°C, about 4°C lower than normal. 



3 Moss. S. A. 1995. University of Massachusetts, North Dart- 

 mouth, MA 02747, USA. Personal commun. 



■• Newton. A. 1996. The Marine Laboratory, P.O. Box 101. Aber- 

 deen, Scotland. Personal commun. 



Length, weight, and growth 



The relationships between PL and FL (both in cm) for 

 New Zealand porbeagles were as follows: 



PL = -1.366 + 0.907 FL 

 FL - 1.990 + 1.098 PL 



(n=866, r2=0.995, 

 range 61-223 cm FL, 

 54-208 cm PL 



The relationships between TL and FL (both in cm) for 

 Australian porbeagles were as follows: 



rL = 4.165 -I- 1.098 FL 

 FL = -0.567 -I- 0.881 TL 



(?i=173, /•2=0.967, 

 range 63-180 cm FL, 

 71-202 cm TL) 



Length-weight data were available for 641 New Zea- 

 land porbeagles (330 males, 309 females, and 2 un- 

 sexed) over the range 61-228 cm FL and 3-153 kg 

 weight. However 96.7% of the sample was less than 

 150 cm FL; therefore the results represent only juve- 

 niles. There was no evidence from the raw data, or 

 the residuals from a log-log regression, of a difference 

 between the sexes. The regression equation for com- 

 bined sexes was as follows: 



^ Williams. R. 1997. Australian Antarctic Division. Tasmania, Aus- 

 tralia. Personal commun. 



