Background
Fishermen who catch mud crabs are catching crabs in a variety of ways mainly using crab traps or crab hook. In comparison to data collected four decades ago, mud crab production has sharply declined according to data collected by fishermen from the Gulf of Mottama (Figure 1).Due to the declining capture rate of mud crab, it is necessary for the fishermen to know and follow the mud crab catching method and the freshwater fishery law for sustainable development in order to prevent the extinction of the mud crab species. In addition, deforestation has damaged the mud crab environment. Fishermen need to be aware the threats to mud crabs such as capture of larvae, capture of juvenile crab, capture of females with eggs.
Objective
To be able to sustainably cultivate mud crabs in the mangrove forest without harming the environment and to increase income.
The reason for the decline of mud crabs
- Development of more efficient crab trapping equipment and techniques.
- Use of illegal mud crabbing nets.
- Population growth.
- Deforestation.
- Catching under size mud crab and female with eggs.
- Limited awareness raising activities on mud crab production and mud crab cultivation.
About Mud crab in Gulf of Mottama
There are four species Mud crab in South-East Asia but Myanmar has only two species. They are the black mud crab Scylla olivacea and the white mud crab Scylla paramosain (Figure 2); Mud crab fishers in Gulf of Mottama capture only Scylla olivaea. (Figure 3)
Features of Mud crab
The shape of the mud crab is round. It is wide at the top and narrow at the bottom. The back and abdomen are covered with hard shells; the back is smooth and has sharp slopes from the eye-stalk to the second leg. The carapace's color is green or black or reddish. It has a pair of eyes with stalks. Mud crabs have three pairs of walking legs and a pair of swimming legs (Figure 4).
Mud crabs go through many molts in their life time. Mud crabs have to molt in order to grow and compete with other crabs for resources. During the molting process, the crabs remove their shell making them vulnerable predators. But it is the only way they can grow and survive. The time it takes for a crab to complete a molt varies. As a general rule, the larger the crab, the longer the whole process will take. It is not unusual for an average-sized crab to spend about four to eight weeks going through the whole process, during which time it may stay completely buried in the sand.
(https://www.thesprucepets.com/duration-of-hermit-crab-molting-1239079)
Living Habit of Mud crab
The Mud crabs mainly live in streams, canals and marshes which receive salt water though regular tidal flooding. Mud crabs live by digging holes in the marshes on the shore. Although Mud crabs find food on the shore at the night time; they stay in the deep water during the day time. Mud crabs dig holes on the marshes on the shore. Mangrove and marshes are most suitable living areas for Mud crabs.
Cultivation System
There are three Mud crab cultivation system. 1). Earth pond mud crab cultivation system, 2). Cage mud crab cultivation system and 3). Mangrove friendly mud crab cultivation system. The GoMP promotes Mud crab fishers to cultivate mangrove friendly mud crab productionsystem to develop their long-term sustainable harvest of mud crabs.
Mangrove friendly mud crab cultivation system
Site selection: Site selection is important for healthy mud crab cultivation. The selected land must be even at neap (lowest) tide. The site should exist among the mangrove.
Mud crab pond construction: Various steps in mud crab cultivation are illustrated in Figures 5-7. Mud crab farmers should dig a trench 50 meters from edge of the river. The mud crab pond should be covered with bamboo screen or nylon screen to prevent mud crabs escape form pond. Mud crab farmer should do only 2000 m² to 4000 m² for small scale mud crab cultivation. A feeding trench of ten feet width and two feet depth should be dug on the edge of the pond.
To install the blue net screen and bamboo slat screen, the bamboo poles should be 5 feet apart and tied in three rows with long bamboo row. The blue net screen and bamboo slat screen should be raised one and half feet above the maximum high tide level. Blue screen and bamboo slat screen should be put in the ground 1.5 feet depth to prevent mud crab from penetrating the ground. The trench should be dug about 2 feet deep to allow water to low tide. Mangroves should not be cut down unnecessarily.
This is important so the mud crabs will be able to hide in the water during low tide. The feeding bridge and feeding tray must be installed on the side of the pond depending on the pond size. Feeding trays can be used not only for feeding but also for collecting data samples. Mud crab farmers should install a three feet width sluice gate at the lowest water level of the pond. There must be inflow
and outflow of water in the mud crab pond depending on low tide and high tide. The sluice gate can control pond water level. Mud crabs can hide in the middle of pond among the mangrove during molting period.
POND PREPARING
Mud crab farmer should prepare pond like a fish pond preparation method such as applying lime, and monitoring the water quality or managing.
Stocking mud crablet (baby crab)
There are two types of mud crablet stocking into the pond. The first type mud crab farmers can stock directly from natural water resources during high tide. The mud crablet and various fish species will enter the pond by the high tide. And farmers can add mud crablet from mud crab finder. It is not able to count for number of mud crab, number of various fish. Farmers could not choose the desired size of mud crab. The second type mud crab farmers stock mud crablets after they prepare the pond and perform water quality management. Farmers can get mud crablets from individual mud crab finder. They can select size of the mud crab and the number of mud crabs for stocking into their pond. Farmers should stock not more than 2 pc/m mud crablet in their pond for low stocking rate system.
Feeding
Mud crabs are omnivores who will eat just about anything they encounter, including bivalves, worms, fish, plant material and smaller crabs. Mud crabs use many senses to locate their food. Shellfish and mollusks are the mud crab's favorite foods.
(https://www.ras-aquaculture.com/post/what-to-feed-mud-crabs)
Therefore, mud crab farmers can get trash fish from fishermen who used stow net and bag net. Mud crabs can get natural food from pond water depending on natural water which entered by tide. Mud crab farmers should feed mud crab once or twice per day depending on stocking rate and feed consumption. Farmers must use feeding tray and feeding bridge.
Sampling for growth rate and feeding rate (Monitoring)
Farmers should collect sampling data for growth rate and feeding rate twice per month. Only by knowing the estimated growth rate, we calculated the feeding rate. Farmers must use weight scale, ruler and recording book for sampling data collection.
HARVESTING
Farmers should harvest partially after three month of cultivation period. Farmers have to use mud crab trap for partial harvest. After farmers have already harvested partially 75% of stocking, they should re-stock mud crablets. Farmers must sell mud crabs who weigh above 150g when they partially harvest.