Where the question is as to the existence of any right or custom, the following facts are relevant:
(a) any transaction by which the right or custom in question was created, claimed, modified, recognized, asserted, or denied, or which was inconsistent with its existence;
(b) particular instances in which the right or custom was claimed, recognized, or exercised or in which its exercise was disputed, asserted or departed from.
The question is, whether A has a right to a fishery. A deed conferring the fishery on A's ancestors, a mortgage of the fishery by A's father, a subsequent grant of the fishery by A's father, irreconcilable with the mortgage, particular instances in which A's father exercised the right, or in which the exercise of the right was stopped by A's neighbours are relevant facts.