Mollet, H.F., Cliff, G., Pratt Jr. H.L., Stevens, J.D.
(HFM Monterey Bay Aquarium, 866 Cannery Row, Monterey CA 93940; (GC) Natal Sharks Board, Private Bag 2, Uhmlanga Rocks, 4300 South Africa; (HLP) NOAA/NMFS, Narranagansett Labs, 28 Tarwell Drive, Narrangansettt RI 02882; (JDS) CSIRO Division of Fisheries, P.O. Box 1538, Hobart, Tasmania 7001, Australia
Reproductive parameters of shortfin mako, Isurus oxyrinchus
Litter data from 28 pregnant females, reproductive data from 47 mature non-pregnant females and 38 immature females shortfin mako Isurus oxyrinchus with a worldwide distribution were available. A logistic model maximum likelihood fit (N = 102) estimated 10%, 50%, and 90% of females to be mature at total length (TL) 2.59, 2.70, and 2.82 m, respectively. The gonadosomatic indices were 0.009% (s.e. 0.001), 0.21% (s.e. 0.01), and 1.9& (s.e. 0.7) for immature makos (n = 9), mature makos with inactive ovary (n = 41), and mature makos with active ovary (n = 3 only), respectively. Fecundity increased with the size of the mother (F =0.57 TL^2.55 (m), n = 18, p = 0.0160 and agreed with a model calculation. A TL-embryo vs. date regression (n = 22, r = 0.72) predicted a gestation period of 10 months (s.e. ca. 0.75) and confirmed Spring parturition in both hemispheres. A combined temporal analysis of embryo size and gondaosomatic index indicated that the reproductive cycle lasts at least 2 years. A one year gestation period followed by a one year resting period is most likely. (Session 46, Sunday June 29 (1997), Savery 239. 2:30)