The evidence I offer you is a link to NOAA, the US Department of Commerce, National Oceanographic and Atmospheric Administration, Department of Fisheries. Mostly, marine mammal wash-ups are attributed to morbillivirus, a virus like measles and canine distemper. Here is the NOAA information page. Here is the FAQ. Besides disease, another common source of die-off is biotoxins (poisonous substances produced by a living organism).
The petroleum prospecting industry, not unlike the banking industry, the medical industry, the communications industry, etc, is well able to defend itself in congress (money). The compromise reached is this: When we seismologists first fire up our air guns we must begin with the volume low, only gradually working up to full power. The idea is to give the mammals plenty time to flee if they don't like the noise.
Still though, as a seismologist and a swimmer and diver, I wish I'd find myself an opportunity to swim during the acquisition of seismic data to listen for myself. I know it's pretty noisy for the workers on the shooting vessel but myself, I don't know what it sounds like in the water. Two friends of mine who do frequent the shooting ships say porpoises are curious. They have seen them approach active guns to look them over. I asked them to help me find a video of this. They also describe the job of the mandated MMOs (Marine Mammal Observers), often young ladies they are delighted to have aboard. The MMOs add to the cost of any survey, hence surveys of all companies, so nobody really pays for them but the final customer (you).
Museum caption: "More than forty whales were found beached along the Netherlands shores during the sixteenth and seventeenth centuries. At the time, many interpreted such recurrences as ominous warnings, but today we know that they were likely the result of murky waters' confusing the whales' sonar navigation systems." [We do?]
And my hypothesis? Any whale entering the Gulf of Mexico should be stranded within a week!