Evidence of summer parturition in shortfin mako (Isurus oxyrinchus) sharks from New Zealand waters

Abstract

A litter of eight near‐term shortfin mako (Isurus oxyrinchus Rafinesque 1810) embryos is described from a 317.5 cm total length (TL) female caught off Hawke Bay, south‐east North Island, New Zealand on 5 February 1999. The embryos (3 males and 5 females) were 67.2–77.0 cm TL. Embryo length, condition, hepato‐somatic indices, and mass of yolk in their stomachs all indicate they were close to birth. This is the first shortfin mako litter reported from New Zealand and is outside the late winter‐early spring parturition period predicted from estimated embryonic and juvenile growth rates. Uterine width data from four mature non‐pregnant females and age‐0+ length‐at‐capture data suggest parturition occurs from September to late February (late winter‐mid summer) but is infrequent after January. We suggest that shortfin makos have an extended parturition period, possibly year‐round, with peak parturition occurring in late winter‐spring.

Keywords:

• shortfin mako
• Isurus oxyrinchus
• embryos
• juveniles
• summer parturition
• New Zealand