NARRATOR：

Now listen to part of a lecture on the topic you just read about.

FEMALE PROFESSOR：

Quackers are certainly a very strange phenomenon.

Experts still debate what the source of the sounds was.

No one can be sure exactly what caused them, but these experts cite certain problems with all of the theories that you just read about.

Here are a few of the arguments that they make.

First, the idea that the sounds were caused by orca whales seems plausible at first, but is ultimately highly unlikely.

It’s true there were orca populations in the general areas that the Russian submarines were patrolling, but orca whales mostly live near the surface of the water.

The submarines typically remained deep in the ocean and should not have been able to hear the whale sounds from near the surface.

Also, the orca whales would have been detected by the Russian sonar if they were nearby.

Giant squid may be a better candidate, but one critical fact speaks against the squid theory as well: Russian submarines first detected quacker sounds in the 1960s, and reports of them continued for about two decades, but the sounds disappeared entirely by the 1980s.

However, as far as we know, squid have always lived in the ocean where the submarines were patrolling, and continue to live there today.

If these were squid sounds, there would be no reason to suddenly start hearing them in one decade and then suddenly stop hearing them twenty years later.

Third, the idea that the quackers were caused by a secret submarine from another country does not hold up.

The sources of the sounds appeared to move around and change direction very quickly.

Submarines cannot move or change direction that quickly.

Also, all submarines make some engine noise, but no such noise accompanied the quackers.

Even today, we don’t have technology to build submarines that are that fast and have engines that are that silent.