Mechanisms of coexistence between Scomber australasicus and Scomber japonicus from the perspective of feeding ecology

Scomber australasicus and Scomber japonicus are species of considerable economic importance in the Northwest Pacific Ocean, playing crucial roles in local food webs and energy flow. We combined stable isotope analysis of muscle tissue with fatty acid profiling to investigate their feeding ecology and interspecific relationship. The results showed significant differences in δ¹³C (P < 0.01) and δ¹⁵N (P = 0.05) values between S. australasicus and S. japonicus. Although the two species exhibited similar ranges in δ¹³C values, S. japonicus displayed a broader δ¹⁵N range compared to S. australasicus, suggesting a wider trophic niche and greater variability in trophic resource use. Although niche overlap analysis revealed considerable overlap between the two species at various growth stages, particularly within the 120-170 mm and 220-270 mm fork length groups, S. japonicus exhibited a greater overall niche breadth than S. australasicus. A total of 29 fatty acids were identified, including 10 saturated fatty acids (SFAs), 8 monounsaturated fatty acids (MUFAs), and 11 polyunsaturated fatty acids (PUFAs). The contents of SFAs, MUFAs, and PUFAs differed significantly between the two species (P < 0.01). Palmitic acid (C16:0), oleic acid (C18:1n-9), and docosahexaenoic acid (DHA, C22:6n-3) were the most abundant fatty acids within the SFAs, MUFAs, and PUFAs categories, respectively. Fatty acid composition analysis indicated that S. australasicus primarily feeds on plankton throughout its life cycle, whereas S. japonicus mainly consumes plankton during its juvenile stage and shifts toward small fish as it grows. Our study demonstrated that although both species share similar basal food sources, their coexistence is facilitated by trophic niche partitioning and dietary shifts at specific developmental stages. These findings enhanced the understanding of the mechanisms underlying the coexistence of S. australasicus and S. japonicus, providing a scientific basis for the sustainable management and conservation of their resources.