Reproductive dynamics of swordfish (Xiphias gladius) in the southwestern Indian Ocean (Reunion Island). Part 1: oocyte development, sexual maturity and spawning

Abstract

The reproductive dynamics of swordfish (Xiphias gladius) was investigated from catches of the Reunion Island-based longline swordfish fishery between 19-25 ◦ S and 48-54 ◦ E. Thus, 1727 swordfish (size range 75-289 cm, lower jaw-to-fork length, LJFL) were sampled on board commercial fishing vessels during the period of May 1998 to January 2001. Reproductive activity was assessed using macroscopic gonad characteristics, trends of gonadal indexes for both sexes, oocyte size-frequency distributions and microscopic investigation of oocyte development stages. Size at first maturity (L50) for female and male swordfish was estimated in Indian Ocean for the first time. L50 was estimated at 170 cm and 120 cm (LJFL) for females and males, respectively. Spawning occurred from October to April in the vicinity of Reunion Island where sex ratio of caught populations fluctuated seasonally. The seasonal changes in sex ratio and the incidence of larger individuals at the beginning of the spawning season provide some preliminary indications of synchronized movements of swordfish between spawning grounds and neighboring regions. Our results add signif- icantly to knowledge about the reproductive biology of swordfish in the southwestern Indian Ocean. An overview of the available information on reproductive biology and dynamics of swordfish in Indian Ocean and eastern Pacific indi- cated that spawning activity is localized in discrete areas, and showed that there is incomplete information on spawning grounds in this extended area.