Vol. 44 No. 4, 2005

Reproduction and Embryonic Development of the Shortfin Mako, Isurus oxyrinchus Rafinesque, 1810, in the Northwestern Pacific

Shoou-Jeng Joung* and Hua-Hsun Hsu

Department of Environmental Biology and Fisheries Science, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung, Taiwan 202

Shoou-Jeng Joung and Hua-Hsun Hsu (2005) The reproductive biology of the shortfin mako shark, Isurus oxyrinchus Rafinesque, 1810 is described based on 750 females and 498 males (including 24 pregnant females) collected from Oct. 2001 to Mar. 2004 at Nanfangao fish market, northeastern Taiwan. The size at maturity was 210 and 278 cm total length (TL) for males and females, respectively. Size at birth was approximately 74 cm TL, and litter size ranged from 4 to 15, with a mean of 11.1; there was no increase in litter size with maternal size. The mating period is from Jan. to June, and pupping occurs between Dec. and July. We estimated the gestation period to be 23-25 mo and the corresponding reproductive cycle to be 3 yr. Embryos are nourished by oophagy, and develop a grossly distended abdomen as their“yolk stomach”fills with ova. Small embryos, 15-22 cm in TL, are able to swallow egg capsules, but do not yet have teeth. Teeth form in embryos at about 26 cm TL, and they begin shedding at 42 cm TL. A subsequent set of teeth are formed at 61 cm TL. Uterine cannibalism (adelphophagy) occurs occasionally, most likely due to unequal embryonic growth.

Key words: Shortfin mako, Isurus oxyrinchus, Reproduction, Uterine cannibalism.

*Correspondence: Tel: 886-2-24622192 ext. 5039. Fax: 886-2-24623986. E-mail: f0010@mail.ntou.edu.tw