Dolphin strandings have more than tripled in the last few years, with more than 70 of them washed up dead or dying on Irish beaches since the start of the year.
Most are common dolphins and the majority of beachings occur between January and March, adding to the mystery of their deaths.
Dozens of corpses collected by the Irish Whale and Dolphin Group (IWDG) have been sent to the Marine Institute for tests as part of a joint investigation with the National Parks and Wildlife Service.
Mick O'Connell, strandings officer with the IWDG, said the sooner the analysis was complete the better, as the problem had been growing since 2011 and had escalated in the last few years.
"The collection scheme came to an end in December but the number of strandings has increased again this year so anything the analysis can tell us about what's going on would be important," he said.
"Animals die for all sorts of reasons - disease, old age, from plastic pollution, as accidental bycatch in fisheries.
"But something changed in 2011 and we're at a record number of strandings now.
"It's mainly one species and it's mainly one time of the year. Something's going on and it needs to be looked at."
On average up to 2011, there were about 130 reported strandings of whales, dolphins and porpoises a year.
The number doubled to 260 last year, with common dolphins accounting for most of the increase.
Numbers have grown again this year and already in just three and half months there have been 107 reported strandings.
Of those, 78 were dolphins of which 59 were confirmed as common dolphins, 11 were either common or striped dolphins, four were striped, three were bottlenose and one was a Risso's.
Before 2011, around 30 common dolphins would be stranded during an entire year.
Twenty whales have also been found so far this year, of which 12 were pilot whales, four were beaked whales, two were unidentified, one was a minke and one was a sperm whale. Thirteen harbour porpoises were also found.
The common dolphin is found all around Ireland but is most populous in the west, south-west and south.
It is our smallest dolphin, ranging from 1.5m to 2.7m and of slender build.
Details of strandings can be logged on the IWDG website.