Intergenerational Collaboration on Crab-Assisting Corridor (CAC) for Native Mitten Crabs' Home Return

Abstract

The native mitten crab in western Taiwan, can be traced back to indigenous peoples and the Qing Dynasty. During the Japanese occupation, it was named the Japanese mitten crab (Eriocheir japonica). With socio-economic development in the 1970s, river pollution and numerous weirs and dams’ construction, destroying its habitat corridors. In recent years, river pollution has been gradually controlled, and traces of the crab have been found in tidal regions. However, the used-called mitten crab's homeland is still declared extinct. In 2022, the mitten crabs were spotted at the Bitan Weir construction site. After three years of observation, it was confirmed that the main reason for the extinction of mitten crabs in the Xindian River middle and upper reaches was the lack of upstream migration corridors provided by weirs and dams, thus blocking their return journey.

Over the past three years, our team has tested several Crab-Assisting Corridors (CAC), assisting 30,000 (2023), 120,000 (2024), and 200,000 (2025) mitten crabs to successfully climb over the Bitan Weir. To achieve the healthy habitat threshold of over 3 million mitten crabs crossing the weir annually, this application proposes a two-year phased action plan for 2026-2027:
1. Monitoring of mitten crabs migrating upstream to the weir,
2. Basic preparation of CAC,
3. Intergenerational collaborative construction of CAC
4. Promotion of crab-assisting experience education.
It is hoped that through intergenerational collaboration, both the spatial corridors can be unblocked, and the 40 years interruption of residential common memories can be reconnected. This action is expected to approach the following goals: Facilitate the migration of over 3 million mitten crabs across the weir annually. Construct a stable habitat for mitten crabs to support local research. Provide a benchmark case for mitten crab restoration in western Taiwan.

Methodology and Implementation Steps

Currently, most upstream mitten crabs are trapped on the bottom side of the left bank of the Bitan Weir. Therefore, our team has tested CAC 1.0, 2.0, and 3.0, assisting 30,000 (2023), 120,000 (2024), and 200,000 (2025) crabs to successfully cross the Bitan Weir and migrate upstream along the Xindian River. To increase the number of crabs crossing the weir, this conservation effort will implement the following operations:

Monitoring of Upstream Migratory Crabs Reaching the Weir
To understand the timing and distribution of newly arrived juvenile crabs under the weir each year, and to provide a basis for selecting crab-crossing pathway locations, preparing materials, and determining the construction sequence. Work consists of on-site sampling (at least twice a month), physiological statistics (including sex, weight, and carapace width), and climbing ability tests.
Preparation of Crab-Assisting Corridors (2026-2027)
All the units include: netting under the weir, overflow channels above the weir, water level control in the stilling basin, and slope siphon conducting channels. In conjunction with river management, all materials suitable for natural biodegradation were used for preparation, including: halved bamboo tubes, recycled burlap sacks, and hemp rope netting. Tools such as mobile water pumping pipes, crab protection shelters, and stationery monitoring windows were also employed.
Intergenerational Collaborated Construction of CAC
This practices encouraging cooperation from various groups, including businesses included activities such as drawing auspicious messages on burlap sacks, weaving nets, attaching the sacks, and transporting equipment, allowing volunteers from different generations to participate in the construction of the crab relief trail according to their abilities. Promotion of Crab-Assisting Experience Education
To coincide with the construction of CAC and the upstream migration of mitten crabs, educational activities were held for volunteers and the public, allowing everyone to personally experience the joy of successfully migrating mitten crabs upstream.

Innovation and Cross-Disciplinary Collaboration

This project draws inspiration from the planning recommendations of New Taipei City's overall water environment improvement development blueprint. From the initial stages of the crab migration upstream movement, under the guidance of Professor Jhy-Yun Shy of National Penghu University of Science and Technology and Professor Tin-Yam Chan of National Taiwan Ocean University, the team gradually mastered professional knowledge about hairy crab migration. The addition of Professor Ta-Ken Huang from Tamkang University represents young scholars utilizing the Bitan Weir's crab migration site to develop a hydrological mechanism for controlling mitten crab movement, providing a theoretical foundation for wider future applications. Several parent association presidents from New Taipei City's elementary and middle schools have personally participated from the beginning, acting as catalysts for teachers and students from various schools along the Xindian River to join the protection effort. Through their efforts, they have now connected teachers and students from 10 high schools, junior high schools, and elementary schools to participate in this mitten crab protection movement. The Taiwan West Coast Development Association focuses on learning from experience and exploring the feasibility of its application and promotion in western coast of Taiwan. Taiwan Good Fish is a social enterprise brand dedicated to promoting environmentally friendly aquaculture and sustainability. It has received numerous accolades for its social innovation and B-type social enterprise initiatives. Because its core business philosophy aligns with this plan, its corporate network has been leveraged to facilitate the implementation of this initiative across public, private, industrial, academic, and research sectors.

Expected Results and Contributions

1. From stable species conservation to ecological foundations conducive to local research
2. Restoring shared emotional memories across generations
3. Providing practical case studies for river restoration in western Taiwan
4. Becoming a pioneering retrofit model for nature-based solutions to weirs and dams internationally