You need local knowledge mate, and that would be me, the sark, like the esk, liddle, lyne, kirtle, annan, eden was one of those rivers back in the 1970's that would have the british record chub swimming in it, in the 60's a guy called jack cairns, who, was my english teacher at school caught 2 7lb chub in the kirtle which is next door to the sark and similar in size etc, like the other local rivers around here it suffered some problems in the 80's and 90's and the chub and dace almost dissapeared, personally i think a lot were electro fished out to please the posh trout angler, silly move as the trout havent done too well without them, the natural ecology and all that.
There are chub and dace in the sark and its making a recovery
I know the lyne better, ive lived beside it most of my life, in the 70's it was brilliant, brown trout, sea trout, salmon, chub, dace, eels , flounders and the odd grayling, it was match fished in the 70's, the lyne today is a shadow of its former self, being marketed off as a posh trout fishery, granted there a few good ones in there, but not as many as when the chub and dace were there, and believe it or not there was roach at the old railway bridge near westlinton on the lyne, i know guys that caught them, that was back in the day, you can make a fair comparison between the sark and the lyne to what has happened over the last 25 years.
I saw a site with a map at westlinton it said chub,grayling,perch and gudgeon, i dont know where he got that info from,chub - yes, grayling - possible, perch and gudgeon, no chance.
The sooner the ea restocks it with chub and dace the better, and mabye some grayling too and that goes for the other rivers around here