International Journal of Marine Science, 2025, Vol.15, No.2, 75-91 http://www.aquapublisher.com/index.php/ijms 81 times, and fishermen from coastal countries often chase migrating Spanish mackerel populations according to seasons (Pan et al., 2020). There are also a wide variety of Spanish mackerels in the Indian Ocean region. For example, the famous narrow-band Spanish mackerels are widely distributed in the Red Sea, Arabian Sea, Gulf of Bengal and East Africa coasts, and are the center of local fishery species. The annual monsoon conversion drives its migration along the East Coast of Africa and the Indian subcontinent, following the bait fish in the upward high-yield areas (Sougueh et al., 2023). In the tropical waters of Southeast Asia, spotted Spanish mackerels, Queensland mackerels (northeast coast of Australia), Indian mackerels (population of S. guttatus in the Indian Ocean), etc. are living. Most of these fish are active along the coast and near island reefs, and are of considerable scale. For example, the Bay of Bengal and the Andaman Sea have huge spotted Spanish mackerel fisheries that support local livelihoods. 5.2 The transmission channel into the Atlantic Ocean and the mediterranean There are relatively few Spanish mackerels in the Atlantic Ocean and mostly belong to the "New World" genealogy, which is believed to be the result of independent evolution in the Atlantic Ocean after migrating through sea routes. The main species include: Spanish mackerels (S. maculatus) and king Spanish mackerels (S. cavalla) distributed in the northern part of the Western Atlantic Ocean, cero Spanish mackerels (S. regalis) distributed in the Caribbean Sea and the Gulf of Mexico, and three-tooth Spanish mackerels (S. tritor) distributed along the eastern Atlantic Ocean and West Africa. These species have a close relationship and together form the "Atlantic mackerel species group" (i.e., the S. regalis population), which has a slightly larger genetic distance from the Indo-Pacific population. There may be two ways to appear at the Atlantic mackerel: one is to enter the Atlantic coast from the Indian Ocean through the southern tip of Africa (Cape of Good Hope). The current model shows that from the end of the Miocene to the early Pliocene, the warm currents in the western Indian Ocean could transport organisms along the coast of West Africa through the then warmer South Atlantic. The second is to enter the Western Atlantic Ocean from the Eastern Pacific Ocean through the Central American waterway (before the closing of the Isthmus of Panama). However, the Panama Isthmus was completely closed about 3 million years ago, and the main differentiation of the genus Spanish mackerel may be slightly later, so more evidence supports the first pathway. After entering the Atlantic Ocean, Spanish mackerel successfully settled on the nearshores of North and South America and formed a trend of expansion toward temperate zones (Rohde and Hayward, 2000). The Mediterranean Spanish mackerels are likely to originate from the "invaders" of the Red Sea. Since the opening of the Suez Canal in 1869, more than 300 Red Sea species have migrated to the eastern Mediterranean Sea, and narrow-band Spanish mackerel is one of the representative large migratory fish. Narrow-band Spanish mackerel was recorded along the Palestine coast as early as the 1930s, and by the end of the 20th century the species had established populations in the Eastern Mediterranean. In recent years, reports have also pointed out that narrow-band Spanish mackerels have been found in the western Mediterranean Sea, such as Tunisia (Figure 2) (Weng et al., 2021). This indicates that it is continuing to spread into the Mediterranean, which may have an impact on local ecology and fisheries. Figure 2 Photomicrograph of a sagittal section of S. commerson aged 7.08 years (142 cm FL; female). The arrows show the position of opaque zones. The otolith was photo-graphed at Figure 40 × magnification (Adopted from Weng et al., 2021)
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