When i went to school, i remember the teacher telling us about past mass extinctions, and all sounded so far from us. But many scientists believe that we are already in the middle of the sixth mass extinction of the species on earth, and that cannot be stopped! We, as humans, can change our way of living and interacting with the environment only to slow down the irreversible extinction procedure that has already began. Most probably, 25% of the species will not exist after 100 years from now.
Maybe this explains the mysterious mass fish deaths and the multiple mysterious mass animal deaths that happened some time ago. Or maybe those animals died because of pollution or due to an unknown accident or a top-secret chemical/nuclear test.
No matter what, news are bad.