Reproductive biology of the female shortfin mako, Isurus oxyrinchus Rafinesque, 1810, with comments on the embryonic development of lamnoids
Mollet, H.F.; Cliff, G.; Pratt Jr., H.L.; Stevens, J. (2000). Reproductive biology of the female shortfin mako, Isurus oxyrinchus Rafinesque, 1810, with comments on the embryonic development of lamnoids. Fish. Bull. 98(2): 299-318
In: Fishery Bulletin. US Government Printing Office: Washington, D.C.. ISSN 0090-0656; e-ISSN 1937-4518, more
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| Authors | | Top |
- Mollet, H.F.
- Cliff, G.
- Pratt Jr., H.L.
- Stevens, J.
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| Abstract |
Reproductive data from 95 mature female shortfin mako sharks, Isurus oxyrinchus 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. Embryo length-at-capture data predicted a gestation period of 15-18 months and late winter to midspring parturition in both hemispheres. A temporal analysis of uterus width index and gonadosomatic index of pregnant and postpartum females indicated that the reproductive cycle is three years. The median TL-at-maturity of females from the western North Atlantic (2.98m) was greater than that of females from the Southern Hemisphere (2.73m) 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. Litters of 59.9- and 68.8-cm-TL embryos showed a decline in the mass of the yolk-filled stomach from 29.1% to 10.9% of total mass and an increase in hepatosomatic 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 shortfin mako embryos could be fitted with a power regression similar to that for postnatal fish. The condition factor of lamnid embryos (including yolk-stomach mass) reaches a maximum between 20 and 35 kg/m³ when the embryos are midterm and have the largest yolk stomachs. The condition factor of alopiid embryos remains constant, indicating that no large yolk-filled stomach develops. |
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