[pensador (OP)]

I am currently in the Azores islands, middle of the Atlantic Ocean for those not good at Geography.

This year huge numbers of Portuguese men of war have appeared around the Azores. Very few Whales have been observed and there are not as many Dolphins as are usual. Could the Whales and Dolphins be being forced away by plagues of Portuguese men of war. The other thing noted is the sea temperature here is 4C higher than seasonal norms ie 23C as opposed to 19C. Could the water temperature be causing the Whales and Dolphins to go elsewhere, and could it also be supporting the bloom of Portuguese men of war.

Edit https://en.wikipedia.org/wiki/Portuguese_man_o%27_war

Edit 2 Photos
https://www.google.pt/search?q=Caravelas+Azores+warning&tbm=isch&source=univ&sa=X&ved=2ahUKEwj0keSC2PXjAhWQDxQKHYOaC88QsAR6BAgIEAE&biw=1366&bih=619

Edit 3 I am guessing since Dolphins and Humans are mammals and Portuguese men o war are toxic to humans, and can be lethal if too many stings are received. A similar effect likely will be observed with dolphins, as they are approx. the same size as a human depending on species. How about a big whale a Blue, Sperm or Hump back, perhaps a sting in the eye when it is the size of a dinner plate might be a painful deterrent.

[alancalverd]

More likely that the mammals are pursuing their usual prey, which prefers colder water. I'd be surprised if a PMOW sting penetrated dolphin skin as easily as human.

[evan_au]

There is certainly a predator-prey relationship between jellyfish and fish:
- Some fish eat smaller jellyfish
- Many jellyfish will eat small fish

If you deplete the fish stocks (eg around Japan), the jellyfish population will increase
- The jellyfish will eat more fish larvae and more algae, so fish stocks will be further depleted
- The jellyfish will grow very large, so they can kill even large fish
- Japan is suffering a plague of jellyfish up to a meter across; sometimes fishing nets only catch masses of jellyfish goo

With fewer fish around, the toothed dolphins and whales will go elsewhere (or starve).
With less algae and zooplankton around, the baleen whales will go elsewhere (or starve).

I think we should all look up some Korean jellyfish recipes (I found it a bit chewy, and rather tasteless...)

[pensador (OP)]

I guess dried korean chilies might have spiced it up a bit.