Following on from last month's CoTS blog post , Coral Cay Conservation (CCC) were invited by the honourable Ma'am Eva of the Provincial Environment and Natural Resources Management Office (PENRMO) to undertake Crown-of-Thorns Seastar (CoTS) density assessments throughout Sogod Bay. The aim of the report is to provide data on the densities of CoTS in the municipalities of Liloan and San Francisco. Although we had intended to conduct assays from Barangay Napantao to Liloan Proper, we experienced mechanical issues with our survey boat (an unfortunate reality of conservation work), and so, we were not able to conduct these assays but the data collected from our other surveys throughout 2019 provide good evidence of the current distributions of CoTS.
The densities of CoTS were estimated in the municipalities of Liloan and San Francisco in Sogod Bay and Cabalian Bay, Southern Leyte with data collected in 2019 using the Reef Check methodology. At each site, six to eight 100m transects were laid along the substrate parallel to the shoreline at depths of 6 and 12m. Each transect was segmented into four 20m sections, separated by a 5m gap, where no data were collected. Each transect was separated by 100m at each side. Two SCUBA divers recorded the number of CoTS found 2.5m either side of the transect line whilst swimming in a U-shaped pattern. A total of 400m2 was thus surveyed for each transect and GPS coordinates were taken for all sampling efforts.
In comparison, the Southern Leyte State University (SLSU) researches adopted the Manta Tow Technique with some modifications. This technique was employed for the detection of the presence of CoTS by towing a snorkel diver (observer) at a constant speed (4km/hr) behind a boat. The observer made a visual assessment of specific variables, along the span of a 10m band, during each manta tow. The towing proceeded in a continuous manner along the shore line and GPS coordinates were also taken at the start of each tow. After the manta tow, the researchers then identified the areas for extraction based on the number of CoTS sightings and scarring.
All the surveyed areas, except for Magallanes in Limasawa, were classified as reaching the Outbreak threshold (0.25CoTS/100m²).
A total of 8 sites were surveyed by CCC in 2019, and the number of CoTS counted at each site ranged from 0-25, equating to densities of 0.144 CoTS/100m² (Table 1). Five out of the eight sites sampled (Cagbungalon and Gudan in Liloan; Anislagon, Napantao and Santa Paz Norte in San Francisco) were over the Outbreak threshold of 0.25 CoTS/100m². However, densities in the CCC surveyed sites were much lower compared to densities recorded by the SLSU (which ranged from 1.80 - 50.00 CoTS/100m²) (Table 1).
We recommend that further density assays that quantify life-history of CoTS individuals, whilst establishing baseline densities, are undertaken. Further monitoring efforts should be deployed in areas that present densities above the threshold level (0.25 CoTS/100m²). Following further monitoring, and once criteria for an Outbreak are satisfied, efforts should be placed into areas with the highest recorded densities (municipalities Malitbog, Libagon, Padre Burgos and Limasawa). Without temporal monitoring and baselines, a precautionary approach should be practised to avoid further detrimental impacts to the bay's systems, as no comparative studies are available. If any resources are available subsequent to that, extraction efforts can be concentrated in the municipalities of San Francisco and Liloan.
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