WHY don't they know the impact?
When I was in this man's Navy (US) out on the Big Pond, we used practice depth charges all the time, and that was way back when Moby Dick was a minnow.
We killed 30,000 shrimp one time and, I'm sorry ... they deserved it for doing performance art where their echo pattern looked like a submarine. They weren't "a" submarine, but they were submarine.
Anyway, if we can construct punny remarks that amuse the author, I'm certain we could test this idea with small underwater sonic booms and do a surface body count charted against Db to see if we can eliminate, " [Scientists] ...aren't sure how the cannons will affect fish and other sea creatures or how any physiological effects on them may impact the fishing industries of the U.S."