Size Distribution and Growth Pattern of Mackerel Scad (Decapterus Sp.) Caught by Boat Lift Nets in Doreri Bay Waters, Manokwari Regency, West Papua, Indonesia and Its Management Implications

Aims: The present study aims to explore some of biological characteristics of mackerel scad, such as size structures and length and weight relationship in which that information is important for the management of the fish resources.

Place and Duration of Study: The data collection was conducted from April to June 2019 in the waters of Doreri Bay, Manokwari Regency.

Methodology: The data were collected from 6 boat lift nets during their fishing operation, 7 days every month for 3 months of research. The data collected was the catch of mackerel scad fish and the size of total length and weight the individual fish samples. The data were then descriptively analyzed to explore the fish size structures. Simple regression analyses was used to estimate the length weight relationship (LWR) of fish.

Results: The production of mackerel scad caught in the waters of Doreri Bay from April to June was around 68.5 tonnes which was dominated by the species Decapterus macerellus. The individual size structure of each species varies. D. macerellus has a size range of 17.8 cm to 25.7 cm, Decapterus macrosoma measures 10.5 cm to 12.7 cm, Decapterus akaadsi measures 7.9 cm to 19.0 cm, Decapterus kuroides measures 9.4 cm to 14.9 cm, and Decapterus scrombinus measures 10.3 cm to 18.0 cm. On average, the size of the individuals caught is smaller than the size at first smaturity (Lm). The growth pattern of mackerel scad fish varies between species. Fore example species D. macrosoma tend to follow a positive allometric growth pattern, while D akaadsi and D. macerellus tend to follow a negative allometric growth pattern.

Conclusion: Mackerel scad caught on average were dominated by individuals with a size less than the size of the first maturity (Lm); Growth pattern of Mackerel scad varied among different species and among different months; and Mackerel scad fish caught using boat lift nets in Doreri Bay, Manokwari Regency need to be managed properly by considering the minimum legal sizes and the aspect of carrying capacity.