SEASONAL VARIATION, POPULATION DYNAMICS AND MANAGEMENT OF MACKEREL SCAD, DECAPTERUS MACARELLUS (CUVIER, 1833) IN THE ILOCOS COAST FROM 2014-2023

Abstract

Mackerel scad (Decapterus macarellus), commonly known as “galunggong” or locally as “palapal,” is a key small pelagic fishery resource in the Ilocos Coast. This study presents a comprehensive length-based stock assessment of mackerel scad in the Ilocos Coast, covering the period from January 2014 to December 2023. The primary objective was to evaluate the sustainability of the stock and provide insights to inform future fisheries management strategies. Length-frequency data were collected using dominant fishing gears, including drive-in nets and ring nets, and analyzed to assess key indicators, such as fishing mortality (F/M), exploitation rates (E), percentage of mature fish, and biomass index (Bcurrent/B0). The results indicated fluctuating catch and catch-per-unit-effort (CPUE) trends for mackerel scad from 2014 to 2023, with seasonal peaks in catch observed from May to July. The majority of mackerel scad were caught using drive-in nets and ring nets, while other gears contributed minimal catch volumes. Growth parameters, estimated using the von Bertalanffy growth model, were found to be L∞ = 38.50 cm TL and k = 1.75. Annual fishing mortality rates exceeded natural mortality (F/M > 1), and the annual exploitation rates consistently surpassed the optimum rate (Eopt = 0.5). Maturity indicators also revealed that mackerel scad in the Ilocos Coast are subjected to high fishing pressure, resulting in a reduced number of mature fish available to reproduce and replenish the stock. The biomass index (Bcurrent/B0 = 0.23) was notably lower than the biomass associated with the biomass maximum sustainable yield (BMSY = 0.29), signifying significant stock depletion due to overfishing. Most performance indicators were found to exceed their respective limit reference points, suggesting that the mackerel scad population is at risk of further depletion and potential collapse if current fishing practices remain unregulated. To restore the stock to a healthy state, stricter law enforcement is essential to prevent active fishing gears, particularly drive-in nets, from operating within municipal waters. Additionally, implementing harvest control measures such as establishing minimum and maximum size limits, increasing mesh sizes, restricting illegal fishing gears, and enforcing seasonal closures are recommended to conserve, manage, and protect the mackerel scad stock in the Ilocos Coast.