THIRUVANANTHAPURAM: Here's proof of how rich and varied the marine biodiversity of our coastal waters is. Over the past one week, fishermen in coastal Thiruvananthapuram trapped three rare species of shark, all three listed as 'Vulnerable' and 'Near Threatened' in the IUCN Red List. A local marine biodiversity group identified the sharks as the 'Common Thresher' (Alopius vulpinus or 'Maanasraavu' in Malayalam), the Shortfin Mako Shark (Isurus oxyrinchus, 'Pannisraavu' in Malayalam) and the Tiger Shark (Galeocerdo cuvier, or, in Malayalam, 'Kaduva Sraavu').
The sharks were identified by the Friends of Marine Life (FML), a marine biodiversity group based in Valiyathura. "The sharks were identified as part of a documentation of marine biodiversity we are conducting. The fishermen said the sharks were caught 300 kms off Thiruvananthapuram at depths of 200 metres," marine researcher and FML convener Robert Panipilla said. Both these species are listed 'Vulnerable' in the IUCN list owing to their massive commercial exploitation by humans.
The Common Thresher can reach upto six metres in length, while the Shortfin Mako Shark can grow over three metres in length and weigh over 60 kgs. Also called the 'Sea Tiger,' the Tiger Shark, listed as 'Near Threatened' was trapped at a distance 100 kms off the Thiruvananthapuram coast. This shark species was first identified in 1822.
The Common Thresher and the Shortfin Mako Shark usually inhabit troughs between underwater sand dunes. It is sad that such discoveries usually go unreported by government agencies on time although various government-level institutions are active in the state. ''Also, it is sad that the knowledge of traditional fishermen in these matters is not properly documented,'' Panipilla said.
In July, as part of its study, FML had discovered four new species of sea slugs in the coastal waters off Thiruvananthapuram. These species were recorded for the first time in the country, and discovery was confirmed at the just-concluded World Congress of Malacology 2016 held at Penang, Malaysia. In early August, fishermen in the district had accidentally trapped an adult finless porpoise and a calf (Little Indian Porpoise - Neophocaena phocaenoides).