Crab-catching at Sungei Mandai Kechil Mangroves
(27th June 2002: 0900-1200)

 

This morning, we (Ann, Siva, Joelle, Yunwee and myself) set off from foot of NUS 'Raffles Museum to the Mandai Kechil mangroves in search of the forceps crab (Epixanthus dentatus, family Eriphiidae). Ann, an NUS honours student is doing her research project on the crab, and investigating how the structure of its claws enables the crab to open up gastropods like a can-opener.

Initially, Yunwee and I had no idea how the crab looked like or had any experience in catching crabs. In short, we had no idea what we were in for. But we were very interested and excited about the trip. This was going to be our first experience in catching crabs.

When we alighted along Woodlands Road, we took a short walk along Mandai Kechil Road towards our destination. Along the way, we passed by the railway track. Before long, we reached our destination, Mandai Kechil mangrove. According to Siva, this deserted area used to be Kampong Mandai Kechil. We could still see remnants of the kampong.

We were then told to orientate ourselves around the area. Siva drew a map indicating our exact location with respect to the Sungei Mandai Besar and Sungei Mandai Kechil. Then we moved to the sandbank to look for our target crabs.

Siva mentioned that the crabs are not fast-moving and they will usually remain stationary when found. The crabs are usually found hiding in crevices and under dead logs. They also have characteristic orange spots on their carapace and their average adult size is about 8cm.

We started scavenging around for the crabs. Yunwee found the first crab hiding between crevices of a log. Siva then came round to rip apart logs to catch the crab. I looked around and saw a crab hiding inside crevices of a mangrove tree trunk.

I got Joelle to identify the crab and also to help get the crab out of the crevice. However, it turned out to be a case of mistaken identity. The crab I spotted was not Epixanthus but Episesarma.

The task of catching the right crab was not as easy as I thought. Basic knowledge to identify the right crab was required. As I searched around for crabs, I found some other species. It was pretty fun watching the crabs move about. I also saw a sick flower crab and collected it. Siva mentioned I could make a specimen out of it. The flower crab was rather weak and did not move about much. It was about 6cm wide. A healthy flower crab is pretty aggresive and hard to catch, because it is agile and fast in sinking its claws into you.

I later went on the search together with Yunwee. He spotted an Epixanthus and hurried me to the spot. Together we forced the crab out of its hideout and caught hold of it. Before we knew it, time was running out, it was already 11.30am.

As I hurried back to our starting search point, I looked around and noticed a crab motionless on the ground. I hurried to it and was thinking to myself if it is a moult. It did not look like a moult because the eyes were black and not transparent. I believed the crab was about to move off to look for its prey when I caught sight of it. Because the Epixanthus is active at relatively high tide in the inter-tidal zone. The crab was still at the same spot staring at me. I took a stick and pointed towards it. It then pointed its claws at me.

At the same time, Siva looked at me and asked what I was doing. I told him there was this crab staring at me. Siva came over and told me that this is the Epixanthus I was looking for. I was then directed to catch the crab by grabbing it from the back at its hind appendages. Before that I had to juggle it around to get it off its best defensive position. With Siva's help and after a struggle, I finally got hold of it.

We then grabbed hold of our prized posessions and left the place as it was going to be twelve noon and the tide was coming in.

On the way back, I was brief by Siva on our locations and the various landmarks that could help me orientate my way.

Back to the lab, I ran through the specimens we collected. There was also a pair of the Epixanthus. The male was mating with the recently moulted female when it was found by Siva, Ann and Joelle. However, he had no idea they were mating until he saw the female in the crevice. Sadly as they tried to dig out the female, one of its claws was ripped off.

Neritas were also collected by Ann to experiment the crab's feeding behaviour.

At the Raffles Museum, we were asked to draw a map on our location at the Mandai Kechil mangrove. This helped to orientate myself and also to refresh my memory. Next I went back to the lab to label my specimen.

I was so glad as this was the first specimen that I collected and labelled. I have also gained the extra knowledge of how to label and preserve the specimen. Firstly, I labelled the name of the specimen followed by the location, date and the collector. Next the specimen was to be placed in the freezer before soaking it in alcohol. This was to prevent its appendages from dropping off.

At the end of the day, this was truly a worthy experience. I had learnt a couple of lessons from the field trip - from being mindful about orientating myself to preserving a specimen.