Read the article again. The largest amount of dead dolphins happened in the 2 months of the year before the spill.
Let's not forget that there are many times more people looking for any dead or sick animals/sealife than before the spill. Basic logic says that if you look twice as much, you find twice as much.
As for corexit, it is 0-1-1-0 on hazmat. You can put it on your skin and it doesn't do anything to you but strip the oils out of your skin. You can drink it, but I wouldn't.
It was the same dispersant used on the largest oil spill in the Gulf, Ixtoc in 1979. Yes, check it out - BP spill isn't the largest in the Gulf of Mexico. Just 2 years after Ixtoc, researchers could not document any negative effects.
Just like with these dolphins - that they cannot link to the spill through any evidence.
Commercial fishermen are getting excellent harvests from the Gulf. The 6 - 9 month break from fishing has done more benefit than the BP spill did in damage.