Importance of outer reef slopes for commercially important fishes: implications for designing a marine protected area in the Philippines

Abstract

A passive acoustic telemetry survey was conducted to determine occurrence patterns of commercially important fishes on a steep reef slope along a marine protected area (MPA) in the southern Philippines, where the outer reef edge is often set as an offshore MPA boundary. Based on 4-61 days of tracking data from 21 detected individuals from five species (Lutjanus argentimaculatus, Lutjanus monostigma, Lethrinus atkinsoni, Lethrinus obsoletus, and Siganus guttatus; 20.7-69.2 cm fork length) caught near the reef slope of the MPA, S. guttatus occurred most frequently on the reef flat of the MPA, whereas all individuals of the four lutjanid and lethrinid species were primarily (99.4-100%) detected near the reef slope, and nine individuals (56.3% of the four species) belonging to three species (other than L. obsoletus) most likely used the shallow (≤10 m) and deep (≥20 m) layers and thus, those middle layer of the slope. These findings indicate that commercially important lutjanid and lethrinid species predominantly and vertically used the areas near the reef slope, suggesting the importance of fully including reef slopes in MPAs to enhance their effectiveness by conserving such fishes.