Sandy,
The Cowie is a far more productive river over all and it has some properly deep holes (I'll let senior show you the secret one that he had dug out years back 😜). Through ury estate is the best of the fishing imo. What we used to do back when I fished it was to fish in pairs, park one car up at the inkbottle bridge and then drive the other down stream to mineralwell and pool hop each other until you got back to the first car. That way you cover an awful lot of water and don't have to walk all the way back again 👍
Now the bervie is another beast altogether. It astonishes me the number of fish that sit off the foreshore early on (I highly doubt they are all destined to run the bervie) but I've seen fish come in from march onwards with every half decent spate. I walk my dog over the two bridges at bervie numerous times per day and also stop for a look over and there's usually a fish or two there for the length of the season. Getting them to take can be a whole other story but it's nice to know that they are there 👍 I plan to have the bervie ac, arbuthnot stretch and Laurencekirk ac tickets next season which will cover almost the entirety of the river for £100. I've had seatrout to 6 1/4lb and salmon to a smidgen over 13 in the past couple of years. Ot really is a hidden wee gem imo and I never saw another angler other than thr one day a dad was out with his two young kids spinning in the estuary and whilst I doubt they had permits I didn't have the heart to tell him no as they really weren't doing any harm where they were and the last thing I wanted to do was put wee ones off of fishing...
Cheers,
Steven.