Evidence for the continued use of river dolphin oil for bait fishing and traditional medicine: implications for conservation

Populations of the Ganges river dolphin (Platanista gangetica gangetica) are endangered, with ~3500 individuals
estimated worldwide. Threats to this precarious population is exacerbated by accidental entanglement and illegal
hunting for oil, which is used in bait fisheries and traditional medicine. Alternatives to dolphin oil have been
proposed and extensively promoted in India, to curb the immediate threat to dolphin populations. However, it is
not known whether dolphins are still being poached for oil, despite the proposal of aforementioned alternatives.
Herein, a molecular protocol to monitor the presence of Dolphin DNA, using species identification of DNA
extracted from bait oils obtained from fishermen is presented. This is coupled with information from social
surveys to understand the current status of use of dolphin oil. Results indicate that molecular tools provide an
accurate technique for detecting the presence of dolphin DNA, and can be used by enforcement agencies to
monitor and identify points of threat to dolphins. Social survey results indicate the preference of fishermen to
continue the use of dolphin oil for bait, despite knowing the legal implications. It is found that alternate oils do
not provide an effective solution to curb dolphin oil use, and only shifts the threats of endangerment from one
species to another, in the long run. The ban of bait fishing, effective enforcement combined with monitoring
through molecular tools, continued community engagement and livelihood skill development are the most viable
solutions for a holistic conservation approach.

PINGERS: can be the eyes of blind ganges dolphins (Platanista Gangetica Gangetica, Roxburgh 1801)

The growing need for fish extraction for livelihood is resulting in the by-catch mortality and injury of the aquatic
mammals through fishing gear entanglement. It is one of the most significant issue of conservation of Ganges Dolphin.
The inability of Ganges dolphins to identify the presence of monofilament gill nets results in entanglement and death
due to suffocation. In this study, the interactions of Ganges dolphin with fishing gear (Gill net) by attaching Pingers
have been investigated. It was assumed that the proximity zone around the fishing gear is the risk zone for the Ganges
dolphin. A visual observation was made in an experimental set up of: Control Net (Without reflectors or Pingers), Net
with reflectors (used locally to attract fish), Pinger with frequency and source level lower than what is used by Ganges
dolphins (10KHz and 132 decibel) and Pingers with Ganges dolphin frequency (70KHz and 145 decibel). A significant
difference in mean sighting distance of Ganges dolphins from different experimental set upss has been estimated.
Nearest proximity in control net was <1m with a sighting rate of 1.41 sightings/hr whereas for Dolphin Pingers it was
5 to 10m with a sighting rate of 0.12 sightings/hr. Dolphins seem to avoid fishing gear with active Pingers and hence
the experiment was to be carried forward to the next level of estimation for determining whether there was any
attraction or change in catch per unit effort (CPUE) of fish or habituation of dolphin. Popularising the efficiency of
Pingers among management stakeholders and introducing it to the fisher communities can be the next significant step
to conserve the species.