Publication date: January 2020
Source: Fisheries Research, Volume 221
Author(s): Hiroshi AshidaAbstract
The reproductive traits of skipjack tuna (Katsuwonus pelamis) in the subtropical (10–25°N) and temperate (25–42°N) western Pacific Ocean were investigated to examine the geographical differences in spawning potential. In total, 91% of spawning capable female specimens appeared in waters with sea surface temperatures (SSTs) of over 24 °C. The length of the spawning season for females varied among sampling areas according to the seasonal fluctuations in SSTs, with shorter spawning seasons in the high latitudinal areas (north of 25°N). Mature males were observed during almost all sampling months in all sampling areas. The total spawning fraction during the spawning season in each sampling area ranged from 0.23 to 0.46. Seasonal fluctuations in the spawning fraction were observed in the temperate western Pacific Ocean. The mean relative batch fecundity differed significantly between sampling areas (p < 0.05) and ranged from 67.2 to 106.1 oocytes per gram of body less the ovary weight. The estimated mean relative batch fecundity tended to be lower in the temperate western Pacific Ocean than in the subtropical western Pacific Ocean and the tropical western and central Pacific Ocean. The reproductive traits observed in the present study indicated that the spawning grounds of skipjack tuna in the western Pacific Ocean were expanded in the temperate western Pacific Ocean in the boreal summer, and that the spawning potential per individual in these areas was inferior to those in the subtropical western Pacific Ocean and tropical western and central Pacific Ocean.