Research finds bull shark in Hooghly River for first time
Kolkata: Research recently published by the Wildlife Institute of India in the ‘Journal of Wildlife Science’ has reported the “first occurrence” of bull shark from inland water of River Hooghly, West Bengal based on molecular and morphometric investigations.
According to the report, the global decline in the bull shark population, primarily due to overfishing, has led to its classification as Vulnerable on the International Union for Conservation of Nature (IUCN) Red List. “Globally, the shark populations are under severe threat due to direct and indirect human activities and concerns are being voiced in response to reports of declining numbers due to destructive fishing, industrial activities and habitat degradation,” the report claimed. The specimen of a potential bull shark (C. leucas) was captured near Chandni Ghat, Hooghly, situated 180 km upstream from the mouth of the Hooghly River.
It was captured in a fishing net during a moderate tidal phase from a meandering river channel with a width of 420 meters and a depth of 8.8 meters.
Both morphological and molecular assessments strongly supported the identification of the specimen, as a juvenile bull shark. The identification was confirmed through distinct morphological features, including a blunt snout, large dorsal fin, crescent-shaped mouth with sharp triangular teeth and a muscular asymmetrical upturned tail. The research utilized a combination of morphometric and molecular assessments because accurate identification of the bull shark remains a persistent challenge due to their close resemblance to other shark species, particularly the Ganges shark.
Research said that bull sharks’ remarkable tolerance to both freshwater and marine environments, allows them to migrate hundreds of kilometres upstream in large river systems like the Ganga and its tributaries, including the Hooghly River. One of the primary drivers of their inland movement is the fluctuation of salinity levels in riverine systems.
“The inland record of the juvenile bull shark in the present study also supports the findings that young individuals utilize riverine habitats preferably guided by predator avoidance and prey distribution,” it read.
The study said that due to the limited knowledge of the long-term migration patterns of bull sharks in riverine and estuarine habitats, the report of bull shark in Hooghly River provides valuable insights crucial for conservation and management.
