I am convinced this is due to Aucustic experiemnts,or Scalar weapons,most people say scalar weapons don't exist,think about the wild fires in Russia last year.As we know these animals have very fragile ears.Wich would either kill them either disorientate them,and when they get lost they die off eventually.Sound travels much faster in water than in air,thus explaining all the dead sea life.It might be due to some other reason like polution or climate changes,but due to recent events I think these two are most plausable.
"Sometimes the most unbeliavable suggestions,are most plausable."
Edit:Maylene,the event you described is going to happen aproximetly after 5 milion years,when the sun runs out of Hydrogen,thus egniting the carbonite,and mutliplying its size by a factor of 8.
(Also know as a "Red Giant")