Spatial distribution patterns of sandfish juveniles released in a sea ranch area in Maliwaliw Island, Philippines

Abstract

Biophysical characteristics that affect the distribution of sandfish in the sea ranch were investigated to determine indicators for a suitable habitat for sandfish sea ranching. These include sediment grain size, organic matter (OM), chlorophyll a, pheophytin, penetrability, depth and seagrass cover. A total of 5864 hatchery-produced sandfish juveniles were released in seven batches in a 5-ha ranching site in Maliwaliw Island over a period of three years. The 5-ha ranch was divided into three zones, with Zone A (50 × 50 m) being the juvenile release site. Survey of the released sandfish was done quarterly from February 2016 until May 2017 and sediment collection done twice. A total of 750 sandfish weighing 10–600 g were recorded; 23% were <150 g, 59% were 151–350 g, 17% were 351–550 g, and 2% were >550 g. Distribution of substrate parameters between the different sea ranch zones showed no significant differences (p > 0.05). Visualized sediment grain-size data showed multiple cohorts of sandfish with varying sizes in different zones with predominantly medium and fine grains with relatively higher total OM and labile OM. Sandfish >351 g were found in deeper waters (>70 cm at low tide) with lower concentrations of labile OM and chlorophyll a, and higher pheophytin. Sandfish <350 g were found in areas with higher labile OM, higher chlorophyll a and lower pheophytin. Results of this study indicate the need for a sandfish sea ranch site with water depth >30 cm at low tide, and varying sediment particle size and composition to support the different stages of growth and development of sandfish.