Age and growth of the shortfin mako (Isurus oxyrinchus) in the south-eastern Pacific off Chile

Abstract

The shortfin mako, Isurus oxyrinchus, is a large pelagic shark with a widespread global distribution. However, very little is known about most aspects of this species for the south-eastern Pacific. In the present paper, the age and growth parameters of the shortfin mako, caught by Chilean swordfish longline fisheries from 2004 to 2005, are reported. Ages were estimated by counting band-pairs from sections of vertebral centra from 547 individuals, ranging from 76 to 330 cm in total length (TL). Trends in the proportion of opaque edges for all ages combined and grouped into ages 0–6 and 7–26 years indicated that they are formed during summer and showed that annually, one band-pair is formed in the vertebrae of shortfin makos. Modal-progression analysis was used to verify the first three age classes (ages 0–2 years). For both sexes, the oldest estimated age was 25+ years. Von Bertalanffy growth parameters were estimated at L∞ = 325.29 cm TL, K = 0.076 year–1 and t0 = –3.18 years for females and L∞ = 296.60 cm TL, K = 0.087 year–1 and t0 = –3.58 years for males. The results indicated that this species is highly vulnerable to exploitation and, thus, urgent conservation measures are required.