Sharks can sense the electric field perturbation?

[HomogenousCow]

Sharks use an organ known has the ampullae of Lorenzini to sense electric fields, they can sense fields as weak as 5*10^-9 V/m.
Which got me thinking, they should in principle be able to detect vacuum perturbation in the field, interesting?

 

[Jano L.]

How did they found out such value?

 

[HomogenousCow]

Not sure, but that's what I read on a bunch of websites.
I would assume they had a source at a long distance away?