Reproductive Biology of Indo-Pacific King Mackerel (Scomberomorus guttatus Bloch & Schneider, 1801) in Bantul Waters

Abstract

This study investigated the reproductive biology of Indo-Pacific king mackerel (Scomberomorus guttatus) in Bantul waters, Yogyakarta, Indonesia, to provide baseline data for sustainable fisheries management. We collected 96 specimens (51 females, 45 males) from October 2021 to February 2022 using gillnets (3.5-inch mesh) and hook-and-line (size 12) along the Pantai Baru, Kuwaru, and Depok coasts. The sex ratio was 1:0.8 (female: male), showing no significant differences from 1:1 (chi2 = 0.75, p > 0.05). Gonad maturity level (GML) distribution showed that 58.8% of females were immature (GML I), while males were more advanced, with 42.2% at GML II and 13.3% at GML III. Gonadosomatic index (GSL) increased progressively from GML II to GML IV in both sexes, with females reaching 2.3±0.97% and males 0.42±0.08% at GML IV. Length and weight distributions were similar between sexes, with a modal length of 38 cm (31.4% females, 33.3% males) and a modal weight of 400 g (45.1% females, 48.9% males). Egg diameter analysis revealed two distinct populations: pre-spawning eggs (0.2-0.5 mm, 52.9%) and mature eggs (0.6-0.8 mm, 47.1%), indicating partial spawning behavior. Fecundity ranged from 60,000 to 352,000 eggs for fish measuring 45.8-55.1 cm, following a power relationship with body length. Length at first capture (Lc) was approximately 37 cm for both sexes, while length at first maturity (Lm) was estimated at 45 cm for females and 41 cm for males. These findings indicate that current fishing practices in Bantul waters capture a substantial proportion of immature individuals, particularly females, suggesting the need for management interventions including minimum size regulations and seasonal closures during peak spawning periods to ensure sustainable exploitation of this commercially important species