Cailliet, G.M., Mollet H.F.
Preliminary demographic analysis of the shortfin mako, Isurus oxyrinchus.
(HFM) Monterey Bay Aquarium, 866 Cannery Row, Monterey CA 93940, (GMC) Moss Landing Marine Laboratories, P. O. Box 450, Moss Landing CA95039
We have evaluated existing and added new life history information on the shortfin mako, Isurus oxyrinchus, including size frequencies, marginal increment analysis, tag-recapture growth rates, reproduction (see Mollet et al., AES abstract), and catch curves for use in a demographic analysis. We assume that the female mako shark lives ~25 years, has an instantaneous natural mortality coefficient (M) between 0.175 and 0.264 year-1, matures at 4-6 years, and has a two year reproductive cycle, a gestation period of ~ 12 months, and fecundities which increase with female size. From adjusted catch curves for females off Southeastern Australia and based on two different mass-length equations, total instantaneous mortality coefficients (Z = F + M) were estimate to be 0.30 (s.e. 0.0s) and 0.34 (s.e. 0.02). Our preliminary demographic analysis provided estimates of net reproductive rate (Ro) between 1.08-1.61, generation time (G) of 9.7-9.9 years, and instantaneous rate of population increase (r) of 0.048-0.0084 year-1. These suggest that the mako shark could vulnerable to both directed fishing and by-catch from other fisheries despite its relatively fast growth.
(Session 46, Sunday June 29, Savery 239, 2:45)