Abstract
Mackerel scad Decapterus macarellus is a highly valuable species in the Philippines municipal and commercial fishing industry, particularly in northern Philippine waters in the Babuyan Channel fishing ground. The study assesses reproductive characteristics, including the sex ratio, catch seasonality, fecundity, gonadosomatic index (GSI), gonad and sexual maturity (Lm and L95), and length range distribution by gear. Samples were collected in the Babuyan Channel fishing ground from April 2018 to March 2020. The results showed that D. macarellus is present throughout the year in the fishing ground, with noted peaks from April to July. An unbalanced sex ratio was found between the females (1:18) and males (1). The mean fecundity was 25,546 eggs. The gonadosomatic index revealed that the spawning season of D. macarellus occurs throughout the year, with an observed prolonged spawning and a notable peak during the northeast monsoon. The length at maturity (Lm) was 14.15 cm, and L95 was 17.60 cm. Of all the fishing gear for catching the species, beach seines catch most of the juveniles. Management options such as establishing additional Marine Protected Areas to support fish populations and productivity of the species, and reducing fishing effort are recommended to protect and conserve the stock.