It's been brought up a couple of times.
I've been looking at shrimp populations on niwa and have found a few dune lakes (No sea connection) contain shrimp.
If they have enough food they should breed and grow.
Mine just get what they can scavenge that the fish have missed. Yes it should be back to normal after a couple of moults.
Give it time, one day they'll all be floating plants
Edit: just checked the website, there aren't any surveys in you specific area, have you tried just typing in "wellington" ?
Looking at wellington your best spot to start would be porirua stream, they have bullies (unidentified) and giant kokopu.