299 



Abstract.— Reproductive data fnim 95 

 mature female shortfin mako sharks, 

 Isurus oxyrinchiis Rafinesque. 1810. 

 including 35 pregnant females, together 

 with data on 450 postnatal fish were 

 collected from around the world. Size 

 at birth was approximately 70 cm total 

 length (TL) and litter size varied from 

 4 to 25. increasing with maternal size. 

 Embi-yo length-at-capture data predicted 

 a gestation period of 1.5-18 months and 

 late winter to midspring parturition in 

 both hemispheres. A temporal analysis 

 of uterus width index and gonadoso- 

 matic index of pregnant and postpartum 

 females indicated that the reproductive 

 cycle is three years. The median TL- 

 at-maturity of females from the west- 

 ern North Atlantic ( 2.98 m ) was gi'eater 

 than that of females from the South- 

 ern Hemisphere (2.73 ml and they were 

 16-19% heavier in the TL range of 2.5- 

 3.5 m. 



Recently ovulated females and a litter 

 with 2.6-3.3 cm TL embryos having 

 external gills, a large yolk sac, and still 

 inside their egg cases, are described. 

 We describe a litter of embryos (52.0 cm 

 TL) with huge yolk-filled stomachs. Lit- 

 ters of 59.9- and 68.8-cm-TL embryos 

 showed a decline in the mass of the 

 yolk-filled stomach from 29.1^i to 10.9'7( 

 of total mass and an increase in hepa- 

 tosomatic indices from 3.7% to 7.0% as 

 gestation advances. When the mass of 

 the yolk-filled stomach was excluded, 

 the mass-length relationship of short- 

 fin mako embryos could be fitted with 

 a power regi'ession similar to that for 

 postnatal fish. The condition factor of 

 lamnid embryos (including yolk-stom- 

 ach mass) reaches a maximum between 

 20 and 35 kg/m-' when the embryos 

 are midterm and have the largest yolk 

 stomachs. The condition factor of alo- 

 piid embryos remains constant, indi- 

 cating that no large yolk-filled stomach 

 develops. 



Reproductive biology of the female 

 shortfin mako^ Isurus oxyn'nchus Rafinesque, 

 1810, with comments on the embryonic 

 development of lamnoids 



Henry F. Mollet 



Monterey Bay Aquarium 

 886 Cannery Row 

 Monterey, California 93940 

 E-mail address molletiSmbaynet 



Geremy Cliff 



Natal Sharks Board 



Pnvate Bag 2 



Umhianga Rocks 4320, South Afnca 



Harold L. Pratt Jr. 



Narragansett Laboratory 



28 Tarzwell Drive 



Narragansett, Rhode Island 02882 



John D. Stevens 



CSIRO Manne Research 



P O Box 1538 



Hobart. Tasmania 7001, Australia 



Manuscript accepted 23 November 1999. 

 Fish. Bull. 98:299-318 (2000). 



The shortfin mako, Isurus oxyrin- 

 chus Rafinesque, 1810, is a pelagic 

 species with a circumglobal dis- 

 tribution in tropical and temper- 

 ate seas (Garrick, 1967). It is fre- 

 quently taken by commercial fish- 

 eries, mainly as bycatch of tuna 

 and swordfish longlining, and is an 

 important recreational species (e.g. 

 Casey and Kohler, 1992; Pepperell, 

 1992), It is one of five species in the 

 family Lamnidae comprising the 

 genera Isurus, Carcharodon, and 

 Lamna (Compagno, 1984), All 1am- 

 nids are large, active pelagic sharks 

 that regulate their body tempera- 

 ture (Carey et al,, 1985; Goldman, 

 1997). Reproduction in lamnids is 

 oophagous (Swenander, 1907; Loh- 

 berger, 1910; Bass et al,, 1975; Gil- 

 more, 1993; Francis, 1996), 



Our knowledge of shortfin mako 

 biology and reproductive parame- 

 ters has increased considerably in 

 the last 30 years, Garrick (1967) 



showed that the 12 nominal species 

 of Isurus represent a single world- 

 wide species, /, oxyrinchus; these 

 findings were confirmed by Heist et 

 al, (1996). Both males and females 

 were thought to mature at around 

 1,8 m TL (Bigelow and Schroeder, 

 1948; Gubanov, 1978; Cailhet et al,, 

 1983). With the collection of more 

 extensive data it has become appar- 

 ent that females mature at a much 

 larger size than males (2,7-2,8 m; 

 Pratt and Casey, 1983; Stevens, 

 1983;Chffetal., 1990), 



Our review of available reproduc- 

 tive data showed that female short- 

 fin makes have similar reproductive 

 characteristics in all regions. Based 

 on a small number of mostly near- 

 term litters, litter size is 4-16 in 

 Australia (Stevens. 1983) and 9-14 

 in South Africa (Cliff et al, 1990). 

 Litter sizes from other parts of the 

 world are reported to be between 

 6 and 18, with the exception of a 



