Spatiotemporal variation in the size structure of the chub mackerel, Scomber japonicus, over half a century in the East Asian Marginal Seas

• Published in: Regional studies in marine science Vol. 68; p. 103263
• Main Authors: Kunimatsu, Shota, Ohshimo, Seiji, Muko, Soyoka, Kurota, Hiroyuki, Tomiyama, Takeshi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30-12-2023
• Subjects: Age reduction; Age truncation; Global warming; Size reduction; Size-dependent distribution; Small pelagic fish; EAMS; Age truncation; NSJ; WKY; Age reduction; FL; WSJ; Size reduction; ECS; Small pelagic fish; SJ; Size-dependent distribution; YS; Global warming
• ISSN: 2352-4855; 2352-4855
• DOI: 10.1016/j.rsma.2023.103263

The size and age structure of a population are crucial aspects for understanding population dynamics. Many marine fish species have experienced long-term reductions in size and age owing to overfishing and/or global warming; however, these aspects remain unexplored. The present study elucidated the spatiotemporal variations in chub mackerel size and age structure based on the operational reports of large- and medium-sized Japanese purse seine fisheries for nearly half a century. Our results revealed size- and age-dependent segregation at a fine spatial scale, which may indicate ontogenetic niche shifts in response to thermal and feeding conditions or intercohort competition. On a long-term temporal scale, a significant reduction in size and age was observed in the East China Sea, whereas a contrasting increase in size and age was observed in the northern Sea of Japan. This may indicate that large fish have greater sensitivity to global warming and shift their distribution more rapidly northward than do small fish. In addition, the reduction in size and age during the spawning season in the East China Sea may result in a bias towards younger spawners, potentially rendering population dynamics more unstable. This study highlights the importance of investigating the spatiotemporal variation in the size structure of exploited fish stocks.