Impact of Fishing Pressure on Reproductive Biology of Mackerel Scad, Decapterus macarellus (Cuvier, 1833)in Sulawesi Sea and Maluku Sea, Indonesia

The high fishing pressure may cause species evolutionary changes toward smaller maturation sizes. In this context, the fishing practices of mackerel scad, Decapterus macarellus (Cuvier, 1833), in tropical eastern Indonesia provide an excellent opportunity to examine this hypothesis. Two distinct fishing grounds, the Sulawesi Sea and Maluku Sea, were selected to explore this phenomenon. Samples of D. macarellus caught by purse seine fishers operating were sourced from the two fishing grounds. Analysing the total length and maturity stage of each D. macarellus specimen from the two stocks were made to estimate key parameters such as the length at first maturity (Lm) and total mortality (Z). The results revealed that total mortality, used as an indicator of fishing pressure, was higher in the Maluku Sea (5.3 year-1) than in the Sulawesi Sea (3.7 year-1) and other areas. Additionally, the Lm of D. macarellus in the Maluku Sea was remarkably lower (22.9 cm) than in the Sulawesi Sea (23.9 cm), which can be attributed to the higher fishing pressure. These findings support the fisheries-induced evolution hypothesis, particularly within Indonesian tropical fish stocks and their respective regions, adding new growing evidence that fishing pressure affects fish reproductive biology. The length at first maturity may serve as a valuable proxy for assessing the intensity of fishing pressure on fish stocks.