TAIPEI (Taiwan News) — Taiwan’s Fisheries Research Institute on Tuesday said it has successfully tracked Spanish mackerel migration using ear stones, as catches have declined in recent years.
Spanish mackerel is a high-value coastal species. Taiwan’s annual catches have dropped significantly, from 6.6 million kilograms in 2002 to 578,000 kilograms in 2022, according to CNA.
International studies on the species’ migratory routes remain limited. Previous domestic attempts to track Spanish mackerel with satellite tags were unsuccessful due to technical constraints.
Researchers turned to otoliths, ear stones that record daily growth and chemical signals, to reconstruct the fish’s migration history. By analyzing growth rings and oxygen stable isotope sequences in juvenile otoliths, and combining the data with the global ocean numerical forecast model HYCOM, they mapped the fish’s early life and migration patterns.
Results indicate that Spanish mackerel primarily migrate in waters around Taiwan with temperatures between 23 C and 25 C. This shows that water temperature strongly influences the species’ movement.
The study provides a scientific basis for monitoring fishing grounds, assessing fishery resources, and supporting sustainable management of Taiwan’s coastal fisheries, the institute said. It plans to refine otolith and stable isotope techniques and expand their use to other high-value migratory species.
Combined with tagging, satellite tracking, and molecular markers, these methods aim to strengthen fisheries monitoring and promote sustainable development of Taiwan’s marine resources.