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
Abstract
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)