When a pod of dolphins swam up a river near Falmouth in Cornwall on Monday, it became one of the worst cases of mass stranding in the U.K. It's thought something may have panicked them into their fatal journey. Having first denied it, the Ministry of Defense has now confirmed a submarine and survey ship have been in the area. It's been suggested that this could have caused confusion.

If, if that did occur in this case, we might not find anything the animals to tell us that that's the case, it would just be, perhaps that the animals would avoid something like a sound source.

The MOD says it's extremely unlikely sonar from its vessels affected the dolphins. However, marine experts argue that as the mammals have no fish in their stomach, this adds weight to the theory that they were panicked by an underwater disturbance whilst looking for food. Phil Greed says he saw huge numbers of fish in the area.

It was quite a large show, I would say, and maybe, you know, that's what they were interested in.

And the dolphins came up this far,is that true?

Yeah, right into this area, yeah, you know, I didn't see it before.

Other than chasing fish, the dolphins were well fed and showed no other signs of ill health. Detailed test results are not expected to be back for weeks. Today, conservationists are continuing to keep an eye on the few remaining dolphins, as they try to untangle what caused their companions to get lost in the shallows.