International Journal of Marine Science, 2025, Vol.15, No.2, 75-91 http://www.aquapublisher.com/index.php/ijms 86 implementation coordination, because Spanish mackerel mainly operates in coastal waters and does not fall into the scope of high seas fisheries, and it is difficult to force countries to comply with unified quotas. Another manifestation of the transnational management dilemma is the inadequate monitoring and law enforcement. The fishing industry of Spanish mackerel fish are mostly small nearshore ships, and lacks VMS (ship monitoring system), etc., making it difficult to eliminate stealing and cross-border fishing. There is often a lack of information sharing channels among countries, and fishing catches and efforts cannot be exchanged in time, making resource assessments difficult to accurately carry out. 8 Ecological Risks in the Context of Climate Change 8.1 The impact of ocean warming on migration behavior Global warming is causing significant increases in ocean temperatures, with profound impacts on fish such as Spanish mackerels that rely on water temperature to trigger migration and breeding. The study predicts that as sea water warms, the geographical distribution of Spanish mackerels may undergo range transfer and timing changes. First, the trend of the distribution range extending to high latitudes. Temperature is one of the main environmental driving forces for Spanish mackerel migration. Every spring, when the water temperature along the coast rises to the appropriate range, Spanish mackerel begins to breed northward. As global warming, spring and summer temperatures in high-latitude waters will provide new habitat for Spanish mackerels. Some species that were originally limited to the tropical region may gradually spread to subtropical and even temperate waters. For example, Japanese Spanish mackerel in the North Pacific has observed signs of a spawning ground moving north. Simulation studies show that under the moderate emission scenario (RCP4.5), the appropriate habitat area of Japanese Spanish mackerel will be reduced by about 33% in the summer of 2050, while its distribution center will move northward, and the degree of northward migration will be more significant by 2100 under the high emission scenario (RCP8.5) (Figure 3) (Go et al., 2025). This means that the current temperate waters may become a new major gathering area for Spanish mackerels in the future, while some traditional tropical fishery may attract fewer fish schools due to the high water temperature. Second, warming will change the migration clock of Spanish mackerels. Increased water temperatures usually advance and extend the breeding season. In some areas, if winter becomes warmer, Spanish mackerels may no longer migrate southward to overwinter, but can overwinter at mid-latitude, thereby shortening the migration distance. This has been observed in Spanish mackerels in North America: As the nearshore winter temperatures become higher, its overwintering distribution has advanced. In addition, ocean warming may also lead to changes in Spanish mackerel migration paths, as temperature gradients affect ocean currents and food chain pattern. Figure 3 Predicted water temperature and salinity at 10 m depth for (a) the 2010s and (b) 2050s, and (c) their differences (Adopted from Go et al., 2025)
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