Rev. biol. mar. oceanogr. 49(3): 427-447

Article

Reproductive activity of swordfish Xiphias gladius, in the Atlantic Ocean inferred on the basis of macroscopic indicators

Jaime Mejuto¹ and Blanca García-Cortés¹

¹Instituto Español de Oceanografía, P.O. Box. 130, 15080 A Coruña, España

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Regions with intense maturation-reproduction processes versus other regions showing less frequent, sporadic and non-existent maturation events were characterized on the basis of the gonadal index of 18,279 female swordfish. Females larger than 145 cm lower jaw-fork length (LJFL) may present high or low gonadal index values depending on the region and season. The highest gonadal indices were observed mostly in areas having Sea Surface Temperature (SST) ranging between 24°-29°C. However, the reproductive activity of females appears to be mainly restricted to the warmer epipelagic layers of the western regions with a deeper thermocline. The size at first maturity of females (LJFL₅₀) was estimated at 146.5 cm LJFL and the maturity function was pm= 1 / (1 + e^{(-0.1398 (LJFL-146.5))}). Qualitative maturity indicators of females support the results obtained using gonadal indices. According to catch rate data by size, sex and region, the presence of males 125-165 cm LJFL would account for the high prevalence of males in regions where the most intense reproductive processes were observed. The characteristic ‘spawning’ related sex-ratio at size patterns are explained by this positive anomaly in these regions favouring males in a ratio up to 9 or 11 times greater than the abundance of females within the same medium size range. The complex reproductive process of this species would point to the practice of courting rituals, which would explain the migratory pattern of this species and its stratification by area-size-sex.

Key words:  Swordfish, reproduction, gonadal index, maturity stages