The number of dolphins in Darwin Harbor in Australia's Northern Territory (NT) has been halved since 2011, according to a leading expert.
Carol Palmer, a senior scientist for the NT Environment Department, has observed a steady decline in the number of dolphins in Darwin harbor since 2011.
The harbor is home to three species of small tropical coast hugging-dolphins; the near-threatened Australian snubfin, Australian humpback and coastal bottlenose.
"For the Australian humpback dolphin, where we've got the best data, they've been the most seen within Darwin Harbor, and the populations have dropped from about the mid 40s, down to in the 20s," Palmer told the Australian Broadcasting Corporation (ABC) on Friday.
In the wider Darwin region, the humpback population has fallen from 88 in 2011 to 50 in 2017.
The bottlenose dolphin population has fallen from 28 to 23 and snubfin dolphin population from 32 to 24.
Palmer identified climate change and increased underwater sound, which the dolphins have a high sensitivity to, as the likely causes.
"Potentially increasing underwater sound, prey availability, and a number of issues to do with climate change (are causing it)," she said.
"In 2016 we had the highest-recorded sea surface temperatures in Darwin Harbor, and across Northern Australia, and we know from work done overseas that can affect fish breeding and prey availability."
"And we don't really understand the influence of shipping and a whole range of things."
