Reproductive traits and spawning activity of swordfish Xiphias gladius L. in the north-western Mediterranean Sea (Corsica)

Abstract

Here we report findings regarding the reproductive biology of swordfish Xiphias gladius in Corsican waters in the north-western Mediterranean Sea. We sampled 558 swordfish (72–216 cm; lower jaw to fork length, LJFL) caught from June to September in 2019 and 2020 off Corsica's western and eastern coasts. We assessed swordfish reproductive activity using macroscopic gonad characteristics, trends of gonadal indexes for both sexes, and histological investigation of oocyte developmental stages. Size at first maturity (L50) was estimated at 139.2 ± 2.7 (95% CI) cm LJFL for females using histological techniques and 117 ± 1.7 cm (LJFL) for males using macroscopic criteria, corresponding to 3–4 and 2–3 year old-fish, respectively. Spawning occurred mainly from June to July, with a peak in July, characterized by a high gonadal index and histological and macroscopic evidence of reproductive activity. X. gladius spawning period is of relatively short duration, closely linked to SST, during which the females lay successive batches of eggs at a non-evaluated frequency. Batch fecundity (BF) and relative fecundity (RF) were estimated from five gravid females (135–209 cm LJFL) with unovulated, hydrated oocytes. BF was exponentially related to fish length with a mean BF of 1.94 ± 1.33 (mean ± SD) million hydrated oocytes in females. RF ranged from 22.29 to 37.24 (29.05 ± 5.97; mean ± SD) hydrated oocytes per gram of body weight. Our results improve knowledge regarding the sexual maturity, reproductive period, and spawning areas of swordfish in Corsican waters. These data are essential for the spatiotemporal management of Mediterranean swordfish stocks. We also provide an overview of the available information related to the reproductive biology and dynamics of Mediterranean swordfish and demonstrate the ubiquitous presence of swordfish spawning grounds throughout the Mediterranean Sea.