This study investigated the relationship of the catch rates (CRs) of Spanish mackerel (Scomberomorus commerson) with oceanographic factors in the waters around Taiwan by using high-resolution fishery and environmental data for the period 2011–2016. The investigation results revealed that trammel nets accounted for 69.79% of the total catch of S. commerson and were operated mostly in the Taiwan Strait (TS). We noted seasonal variations in the distribution of high CRs. These CRs were observed in the southwestern TS, including the waters along the southwestern coast of Taiwan and around the Penghu Islands, and extended to the Taiwan Bank during autumn; they increased in winter. To predict the spatial and temporal patterns of Spanish mackerel density and their relationship with oceanographic and spatiotemporal variables, generalized additive models were used. These models explained 48.4% of the total deviance, which was consistent with the assumed Gaussian distribution. Moreover, all variables examined were significant CR predictors (p < 0.05). Latitude and longitude were the key factors influencing the spatiotemporal distribution of S. commerson, and sea surface chlorophyll a concentration was a key oceanographic factor. Observing projected changes in El Niño/Southern Oscillation events for S. commerson revealed that CRs were higher and distributed further southward during La Niña events than during other events. We inferred that the S. commerson distribution gradually moved toward the southwest with the northeast monsoon, which was enhanced during La Niña in winter.
The Taiwan Strait (TS) connects the East China Sea (ECS) and South China Sea (SCS). Flow circulation in the TS exhibits complicated patterns during winter. The cold China Coastal Current (CCC) flows southward into the northwestern side of the strait as the warm Kuroshio Branch (KB) enters the strait along the southeastern side. In addition to the control that the northeasterly monsoon exerts over the CCC intrusion strength, the complex topography modifies the circulation. The winter temperature gradient in the TS is nearly horizontal. The sea surface temperature (SST) data reveal the main circulation features, including a distinct SST front in the middle of the strait. A rotated empirical orthogonal function (REOF) analysis is applied to the advanced very-high-resolution radiometer data to define four SST regions: the CCC and KB sources as well as the regions influenced by the Taiwan Banks and the Chang-Yun Rise. The Mann-Kendall trend detection method indicated that the SST in the TS (except in the KB region) abruptly increased during 1992 -1994. The warming tendency in the KB region was slower compared with that of the other regions. The relationship between the El Niño-Southern Oscillation phase and SST variation in the TS exhibited spatial and decadal variations. The SST in the northern TS tended to be warmer (cooler) during El Niño (La Niña) years compared with normal years. However, the opposite relationship was found in the southern TS: SST cooling (warming) occurred during El Niño (La Niña) years and this phenomenon existed only after the SST warming regime shift (1992 -1994).
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