mumbai

Updated: Jan 06, 2019 15:24 IST

In a first along the Indian coastline, an octopus species was recently spotted in the estuarine zone of Narmada river, said scientists. Marine biologists confirmed that there were no previous reports of octopuses being spotted in inland waters along the Indian coastline.

Octopus is a marine species that is spotted up to the depth of 50m and is known to inhabit coastal sea waters. It is rarely observed in the estuarine brackish waters.

Seventeen specimens of the Cistopus indicus, commonly known as the old woman octopus, were identified by scientists from the Central Inland Fisheries Research Institute (CIFRI) Vadodra, Gujarat, under the Indian Council of Agricultural Research (ICAR). The octopuses were spotted during CIFRI’s routine survey as a part of a fish catch at Bhadbhut village, 35kms off the Gulf of Khambhat on December 16. CIFRI scientists declared their findings on Friday. “According to data collated by us since 1988, in India, octopuses are caught mainly as by-catch in trawl nets used for shrimp trawling, shore seines, boat seines, hooks, lines and stake nets, but they have never been caught within brackish estuarine water bodies,” said Dr Dibakar Bhakta, scientist, CIFRI Vadodra.

The 17 specimens, which are 190-320mm in length, are about the size of a human arm. The maximum length of the species was 325mm with a weight of 56.2g. The maximum length of this species along the Indian coastline was 600mm from the Bay of Bengal, said Bhatka. There are around 200 species of Octopus reported across the world and 38 species reported from Indian seas.

According to Bhakta and his team, the salinity of the Bhadbhut and adjacent Mahegam region was in the range of 18-20 parts per thousand (ppt) during December. The salinity of water in the ocean is around 35 ppt. The mixture of seawater and fresh water in estuaries has salinity ranging between 0.5 and 35 ppt.

“Initial analysis and high salinity show that ingress of high tide water may have allowed this marine species into the estuary. However, considering the low quantity of marine fish catch in these brackish waters between 2017 and 2018, environmental disturbances and anthropogenic alterations to their habitat can be another cause for their displacement,” said Bhakta.

Deepak Apte, director, Bombay Natural History Society, said marine species, mostly fish, are known to move into brackish waters for breeding mostly around winter months. “However, there are no previous records of octopuses depicting such behaviour.”

Independent experts who have carried out research on octopuses also said high tide water had most probably brought the species to the estuary. “It is extremely rare to spot such a find and further studies need to ascertain the level of water during low and high tide and species diversity in both phases,” said Vinay Deshmukh, marine biologist and former scientist, Central Marine Fisheries Research Institute (CMFRI).

Octopus made up merely 0.72% of the total molluscan resource (61688 tonnes) that landed in Gujarat during 2017. “This is clearly the first documentation of an octopus found along inland waters in India. It is unusual for such marine benthic species, irrespective of their size to survive in salinity ranging between 18-20 ppt. We need to study whether similar reports have occurred from other parts of the country to ascertain habitat changes,” said E Vivekanandan, former principal scientist and national consultant, Central Marine Fisheries Research Institute and currently heading the Bay of Bengal project on biodiversity conservation.