Thanks for all the feedback. I should have mentioned that I was fishing the faster water about 200m below the old bridge so abrasion could have played a part. I had started out just below the bridge but went further down to where the birds were working and got a fish on my first cast. I always re tie my knots after each fish but there could have been stone bruising to the line. Not sure but I will try some 10lb line next time and if my hit rate drops go back to what I was using.