Black spot disease is associated with the breakdown of chitin by chitinolytic bacteria resulting in extensive black lesions across the body of crustaceans. Black spot is prevalent across most fished crustaceans worldwide. Severely infected individuals are rejected from the fishery resulting in financial loss to both fisher’s and seafood export and processing companies. Ecologically, populations with high infection rates may have increased mortalities resulting in fewer individuals surviving the population. The prevalence and severity of shell disease in the edible crab, Cancer pagurus, of various size classes, was assessed via scaled images taken from crabs sampled within the Berwickshire Marine Reserve, UK. A total of 22.4% of individuals across all size groups were found to contain black spot lesions. Male crabs were more commonly affected (26.21%), with more body parts showing lesions and a greater overall blackspot coverage (1.75%) than females (16.43% and 1% respectively). Crabs under the MLS (140mm) showed a significantly higher black spot coverage, but size did not significantly affect infection rates. Carapace and chelae were the most commonly affected areas. Compared to previous studies the Berwickshire Marine Reserve has a relatively low prevalence of black spot disease in Cancer pagurus.