Mangrove crab sustainability is vital for fishers in Indonesia’s Aru Islands

  • Mud crab fishing in Lorang village, Aru Islands, has been a vital livelihood since 2014, but a recent survey suggests signs of depletion, raising concerns among local fishers.
  • The boom in crab fisheries began after a government moratorium on various commodities.
  • Despite high economic value, a rapid assessment by Indonesian researchers reveals a decline in mud crab abundance, possibly due to overfishing exceeding natural regeneration.
  • To address this, there’s a call for conservation efforts, including a wildlife protection reserve and agreements with neighboring villages to establish a “crab bank” for sustainable crab populations.

CENTRAL ARU, Indonesia — One afternoon last November, Natanel Ginobal, 67, drove his motorboat to check the mud crabs caught by the traps he had installed earlier the day. He had to move quickly before the tide started receding and made it much more difficult for him to harvest his catch of the day.

Natanel had set 15 traps between the roots of mangrove plants (Rhizophora) in a narrow river inlet that required him to switch from the motorboat and use a smaller boat to maneuver through the mangrove gaps. This is a common practice among the many mud crab fishers, like Natanel, in Lorang village of Aru Islands district in Maluku province.

The crab traps were placed between 30 and 50 centimeters (12 and 20 inches) below the water surface, specifically designed to lure the creature with a small fish and close shut once it took the bait. After checking the traps one by one, Natanel found seven of them containing crabs.

“The karaka [crab] catch is good. I estimate the total price at over 1 million rupiah [$63],” he told Mongabay-Indonesia with a big smile across his face.

A recent rapid survey in Lorang village by Indonesian researchers, however, has indicated signs of depletion in the abundance of mud crabs, sparking new concerns among local fishers who depend on the marine creature for their livelihoods.

Natanel, a mud crab fisher from Indonesia’s Aru Islands, on his wooden boat, maneuvers through the thick riverine mangrove forest. Image by Ridzki R. Sigit/Mongabay-Indonesia.
A traditional trap for mud crabs. Image by Ridzki R. Sigit/Mongabay-Indonesia.

What happened to the crabs?

The boom in mud crab fisheries in the Aru Islands started in 2014 when the Indonesian government imposed a moratorium on various fisheries commodities, including shrimp and fish.

“In the late 1990s, some people in Lorang were hunting for crabs in the mangroves,” said Natanel, who was also one of the first generation of crab catchers in the village. “But it started to flourish from 2015 until now.”

The Indonesian government has estimated the potential for crab resources in the fisheries management area that includes the Aru Islands at 1,498 tons with a total allowable catch of 1,198 tons. Fishers in Lorang village, for example, don’t need to go far to sell their mud crabs, as buyers from elsewhere in the district would travel there themselves.

Typically, crabs weighing 300-700 grams (10-25 ounces) are sold for 90,000 rupiah ($5.70), and those weighing more than that, up to 1 kilogram (2.2 pounds), are priced at 180,000 rupiah ($11.40). Crabs larger than 1 kg can be sold for up to 300,000 rupiah ($19).

“In Lorang, on average each family head has 15-20 fish traps,” Natanel said, indicating that crabs are an important source of income for the households in the village.

However, an assessment carried out in November by researchers from the School of People’s Empowerment (SPR) at the Bogor Agricultural University (IPB) indicated that the mud crab abundance was already depleting.

Based on interviews with mud crab fishers, the researchers found that large crabs were becoming more difficult to find compared with the previous 3-5 years even though the mangrove habitats and the surroundings were seemingly undamaged. A 2020 study showed that the orange mangrove crab (Scylla olivacea) in the Aru Islands is larger than those in Thailand, Malaysia, India and even when compared with those in other regions of Indonesia such as Tapanuli, Semarang and Merauke regions. In Aru, it reaches 110-185 millimeters (4.3-7.3 inches), with an average of 135 mm (5.3 in).

The most reasonable explanation for the abundance decline is likely that in the field, there is a rate of crab catching that is faster than the natural regeneration rate, according to Mustaghfirin, a socioeconomic researcher and founder of the SPR, which carried out the rapid assessment of socioeconomic potential in Lorang Village.

“In the past, you just needed to give pieces of coconut or salted fish [as bait]. Now it’s different, you won’t necessarily be able to attract [the crabs] using pieces of fresh fish such as grouper or snapper,” Mustaghfirin said.

Fishers in Lorang village show their caught mud crabs. Image by Ridzki R. Sigit/Mongabay-Indonesia.
Even though the mangroves in Lorang village seemingly are undamaged, a concern has emerged over the declining abundance of mangrove crabs. Image by Ridzki R. Sigit/Mongabay-Indonesia.

Mangroves: A crab refuge

Mud or mangrove crabs, scientifically known as Scylla serrata, inhabit muddy environments within mangrove ecosystems. The Aru Islands, with 156,524 hectares (386,779 acres) of mangrove habitat, as reported in 2018 by the nongovernmental organization Forest Watch Indonesia (FWI), provide significant opportunities for the cultivation of mangrove crabs in the Maluku region, subsequently driving the local economy.

Indeed the mangrove crab fishery has much potential for local economic growth. A 2017 analysis estimated the profit margin for crab fishers in Aru was 11.85-12.5 million rupiah ($750-790).

“Buyers from Dobo [the capital of Aru Islands] collect the crabs from fishermen and then send them to other cities. Some of them even continue to be exported,” said A.L.O. Tabela, the head of the Aru Islands fisheries agency.

Mangrove forests are therefore a key to sustainability for the survival of local residents in the Aru Islands, which spread across 800 islets. Lorang village is located on Maekor Island, which can only be reached by sea and is not connected to any mainland. To get to this village, boats have to go through narrow straits, which are thickly overgrown with mangroves on both sides.

According to FWI’s spatial map of Indigenous land, Lorang village with its population of 233 people spans 40,000 hectares (98,800 acres) and much of its marine ecosystem is densely covered with natural mangroves, rendering it ideal for crab habitat.

The high economic value of the mud crabs has prompted awareness and an urge among the people of Lorang village to conserve the remaining mangrove forest. Therefore, they created a local custom in Lorang that prohibits crab seekers from taking egg-carrying females and from taking crabs that are smaller than 300 grams. Should they catch any such crabs, the fishers are required to release them back into the wild immediately.

“The karaka lives between mangrove roots, [so] we [must] protect the forest,” said Zakarias Gaetedi, 75, the customary chief in Lorang.

Mangrove crab regeneration also must be maintained, especially pertaining to the fishing gear. Traditional traps are believed to help maintain crab population levels when the size of the trap net is large enough to allow juvenile crabs to escape from the trap.

“Actually, fishermen will make more profits and get higher purchasing prices if they get crabs that weigh more than 1 kg,” Mustaghfirin said.

He suggested the establishment of a wildlife protection reserve area that could sustain the wild population of crabs. He noted a mutual agreement with neighboring villages was also important for fishers in Lorang in their effort to conserve the crabs’ population.

“From a cultural sociology perspective, this is a challenge. There needs to be an agreement to find and build a crab sanctuary location, which in the future can be agreed to become a ‘crab bank’ so that the population is guaranteed in nature,” Mustaghfirin said.

The high economic value of the mud crabs has prompted awareness and an urge among the people of Lorang village to conserve the remaining mangrove forest. Image by Ridzki R. Sigit/Mongabay-Indonesia.

This story was reported by Mongabay’s Indonesia team and first published here on our Indonesian site on Jan. 12, 2024.

See related:

Saving Aru: The epic battle to save the islands that inspired the theory of evolution


William G, B. & Ediyanto. (2017). Analisis Rantai Pemasaran dan Pola Distribusi Kepiting Bakau (Scylla serrata) di Dobo, Kabupaten Kepulauan Aru, Provinsi Maluku. Jurnal Ilmiah Satya Minabahari, 2(2), 127-137. doi:10.53676/jism.v2i2.35

Pane, A. R. P., Alnanda, R., Herlisman, & Suman, A. The exploitations status of the orange mud crub (Scylla olivacea Herbst, 1796) in Aru Islands and adjacent waters, Maluku, Indonesia. IOP Conference Series: Earth and Environmental Science, 584. doi:10.1088/1755-1315/584/1/012008

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