SINGAPORE - Thirteen blacktip reef sharks and more than 30 crabs of various species were found in three fishing nets on Lazarus Island, located south of the Republic, on Sunday morning.

Unfortunately, all the sharks caught in the gillnets were dead, although a number of crabs managed to survive after they were disentangled and released by the people who found them.

The St John's Island Marine Laboratory said in a Facebook post on Sunday morning that the shark carcasses are being stored in its freezer and will be passed to the Lee Kong Chian Natural History Museum for analysis.

The lab, which is part of the National University of Singapore's Tropical Marine Science Institute, also called for responsible fishing.

Replying to one of the comments on the post, the institute said that the fishermen who laid the nets "were remorseful and not defensive when talked to about the destructive effects of (the) nets".

The page also noted in a comment: "They (the fishermen) even helped to bring the nets to land. Nobody want this to happen. Let's continue to remind each other on using our nature areas responsibly."

Gillnets are nets typically made of monofilament or multifilament nylon that hang in the water column. According to the United States National Oceanic and Atmospheric Administration, the mesh sizes are designed to allow fish to get only their head through the netting, but not their body. The fish's gills then get caught in the mesh as the fish tries to back out of the net.

Dr Tan Heok Hui, a fish expert from the Lee Kong Chian Natural History Museum, told The Straits Times that some sharks need to move in order to respire. "Blacktip reef sharks are one of those that need to move constantly," he said.

"From the photo, (the dead sharks) all appear to be of the same cohort as they are all around the same size. Some could even be siblings," he said.

The sharks that were found dead are likely to have been juveniles.

audreyt@sph.com.sg