As autumn is the season for eating Chinese mitten crabs, also known as Dazha crabs (大閘蟹), legislators and academics in the field of ecology yesterday warned that the aquaculture of these crabs in Taiwan may cause a local environmental crisis.
At a joint press conference, Chinese Nationalist Party (KMT) Legislator Chiu Wen-yen (邱文彥), Democratic Progressive Party Legislator Tien Chiu-chin (田秋堇) and People First Party Legislator Chang Show-foong (張曉風) urged the government to tighten its controls on the increasing development of Chinese mitten crabs aquaculture.
Chiu said the Chinese mitten crab is a non-native invasive species, and its improper management may cause an environmental crisis similar to that caused by the imports of ampullariidae (apple snails) many years ago.
Although apple snails may have been profitable in the short term, their pervasive impact on Taiwan’s ecology has caused even greater economic costs controlling it, he added.
National Chung Hsing University life science professor Shih His-te (施習德) said the spread of such crabs has already raised concerns in Europe and North America about their damage to local ecology — competing with local species and clogging drainage systems.
He said the species has already been listed by the Union for Conservation of Nature’s as one of the world’s worst 100 invasive alien species, and if the crabs escape from the more than 250 crab aquaculture farms in Taiwan, they may threaten the survival of local crabs and other plants and animals.
Allen Chen (陳昭倫), an associate research fellow at the Biodiversity Research Center at Academia Sinica, said Taiwan has an isolated island ecosystem with many endemic species, and is more fragile to invasive alien species, so precautionary measures are more important to prevent situations like the negative environmental impacts caused by spreading Taiwanese tilapia (吳郭魚), or fire ants.
However, KMT Legislator Chen Chao-ming (陳超明) said that the survival rates of the Chinese mitten crab in aquaculture farms are low, only about 10 to 30 percent, and because prices are relatively high in the market, most aquaculture farmers have already taken strict measures to prevent their crabs from dying, escaping or even being stolen.
He suggested Taiwan should put more emphasis on developing the Chinese mitten crab aquaculture industry.
Fisheries Agency deputy director-general Tsay Tzu-yaw (蔡日耀) said the Chinese mitten crab aquaculture industry began importing the crabs in 2007, and while the farms have set up good anti-escape measures, the agency also held workshops to teach aquaculture farmers about the potential dangers of these crabs.
Coast Guard Administration senior executive officer Lee Hao (李皓) said his agency has seized many illegal imports of the crab in recent years, such as a cargo containing 2,200kg of crabs in September, but smugglers are changing tactics, making them more difficult to catch.
Tien suggested that the government should prohibit new Chinese mitten crab aquaculture farms from being set up in Taiwan, instruct the current farms located in areas more sensitive to mudslides and floods to move to safer places, and also inspect the anti-escape prevention measures at the farms.
In response, Tsay said the agency will try to find a balance between economic development and environmental protection.