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 significantly 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 indicated that spawning activity is
localized in discrete areas, and showed that there is incomplete information
on spawning grounds in this extended area.