Here are some possible reasons listed in the article.
- This year's unusually warm winter. As Discovery News recently reported, the unusually warm temperatures are affecting animal reproductive cycles, hibernation patterns and more. The change could also somehow be impacting dolphins.
- Geography. Moore said the hooked shape of Cape Cod appears to be trapping the dolphins and confusing them. But the question still remains, why are the dolphins going in that direction in the first place?
- Movement of prey. Climate cycles could be altering the course of fish and other dolphin prey, the AP report suggests. Dolphins following the prey could then become stranded. That might help to explain why both sardines and dolphins washed up in Peru.
- Disease. This is an obvious reason, but workers at the IFAW are tagging and taking blood samples of the stranded animals, AP has reported. Researchers have also conducted necropsies on dead dolphins, and yet still there are no clear answers. A Congressional briefing was even held earlier this month in the push to resolve the problem.
- Decompression. I would be curious to know if the dolphins have internal air bubbles that can cause decompression sickness, more commonly known as "the bends" in humans. That might seem far fetched, but scientists have determined that the blood and tissues of some deceased beaked whales stranded near naval sonar exercises are riddled with bubbles.
In the comments people are also mentioning that chemicals in the water might cause intoxication of the dolphins, which might cause them to act differently than normally.
In whichever case, it might not affect only dolphins but all sea life.