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A new study conducted by the Palau International Coral Reef Center (PICRC) in partnership with the Ministry of Agriculture, Fisheries and Environment (MAFE) has found a significant decline in the number of horseshoe snails, locally known as Semum, in Palau. The survey was conducted from December 2023 to March 2024 and covered 57 sites from Kayangol to Peleliu Island, covering both reef crest and fore-reef areas.
Horseshoe snails are a mollusk that is important to Palauan culture, used for food and in a variety of products. Over the years, the snails have been overfished, causing their numbers to decline. The horseshoe snail fishing season is determined by the Palau National Council (Olbiil er a Kelulau) based on an assessment of the health of the horseshoe snail population.
From 2016 to 2019, the good news continued: the horse snail population grew from just over 1,000,000 to nearly 4,000,000. In addition, the average size of the horse snails increased significantly, by 38% in the fore-reef area and 72% on the reef crest. The increase in size means that more horse snails have matured and reached legal catch size, indicating a healthy population. In 2016, about 57% of the surveyed horse snails were above mature size, and this number rose to 83% in 2019.
However, the most recent survey painted a different picture: only 428 horseshoe snails were found at selected sites, with a total estimated population of 1,653,067, a significant decrease from 2019. The highest number of horseshoe snails was found in the southeast, while the lowest was found in the southwest, consistent with past surveys. The fore-reef area had a slight increase in horseshoe snails (4%), while the reef crest area had a 28% decrease in numbers.
Overall, 73% of surveyed horseshoe snails were above maturity, but there were only about 267 per hectare on the fore reef and 223 per hectare on the reef crest. This is well below the 600 per hectare threshold recommended for sustainable fishing, indicating that current populations are insufficient to support a fishing season.
Since 2016, the season for horse snail harvesting has only been open once, in 2021, for about three weeks. While it is unclear how much was harvested during this short period, the results of this survey suggest that stress is high and recovery is slow. Opening the season again could severely harm horse snail populations.
To help the horseshoe snails recover, the study suggests several measures: increasing size limits for harvesting to protect mature individuals so they can reproduce after closure, limiting the number of horseshoe snails that can be harvested by each individual, and restricting harvesting to certain areas.
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