The preliminary analysis of carbon and nitrogen stable isotope composition of skipjack(Katsuwonus pelamis) gathering around fish aggregation devices in the Western and Central Pacific Ocean

Abstract:

The distribution of stable carbon and nitrogen isotope composition(δ¹³C and δ¹⁵N) and ratios of carbon to nitrogen(C:N) with fork length were studied to investigate the characteristics of stable isotope of skipjack, Katsuwonus pelamis, collected from Fish Aggregating Devices(FAD), based on the survey data of purse-seine fishery in the Western and Central Pacific Ocean from February to March 2013. The results showed that the mean value of fork length was(44.30±7.85) cm, ranged from 31.0 to 65.0 cm in fork length, with the dominant fork length of 40.1 to 50.0 cm accounting for 45.12% of the total samples. The mean value of δ¹³C was(-15.94±0.59)‰, and it was significantly influenced by fork length(F=10.92, P<0.05). The differences among the mean values of δ¹³C from each fork length class were very small and it indicated that the sources of initial diets were similar for all samples. The δ¹⁵N was significantly influenced by fork length(F=16.72, P<0.05). The mean value of δ¹⁵N was(17.50±1.81)‰ and it was greater in small skipjacks, which indicted that the trophic position of skipjack is higher in small scale than in larger scale. The mean value of C:N ratios was(3.06±0.05)‰, and it was significantly influenced by fork length(F=4.21, P<0.05). The mean value of C:N ratios decreases with the increase of the fork length, which indicated that nutritional status of skipjack reduced by fork length class.