William Yarrell (1784 - 1856) was an English zoologist and writer on natural history, particularly birds and fish.
This two-volume work was first published in 1836, though the Newfoundland anecdote below was not in that early edition, but was added for the 2nd edition, published in 1841 (London: John Van Voorst), from which the text here is taken.
The Newf anecdote is included in a lengthy letter to the author, quoted verbatim by Yarrell, that was written by the Earl of Home, who was prompted to send some fish-related anecdotes to Yarrell after reading the first edition of A History of British Fishes. The Earl's letter was dated January 10, 1837.
"My uncle, the same who caught the seventy pound Salmon, had a Newfoundland dog which was celebrated for catching Salmon. He knew the Monday mornings as well as the fishermen themselves, and used to go to the cauld or mill-dam at Fireburn mill on those mornings. He there took his station at the cauld slap, or opening in the dam, to allow the Salmon to pass, and has been known to kill from twelve to twenty Salmon in a morning. The fish he took to the side. The then Lord Tankerville instituted a process against the dog. I had a copy of the proceedings, but I regret to say it was lost when the old library was altered. This case was brought before the Court of Session, and the process was entitled, the Earl of Tankerville, versus a Dog, the property of the Earl of Home. Judgment was given in favour of the dog." (69 - 70)
This anecdote shows up in several subsequent publications, including The Local Historian's Table Book of Remarkable Occurrences by Moses Aaron Richardson (1841 - 1846) as well as a revised version of that book by Richardson, The Borderer's Table Book (1846). The story also appears, almost verbatim, in A Treatise on Fly-Fishing by G. W. Soltan (1847); a review of Soltan's book in the August, 1847, issue of Sporting Magazine, and the identical review in the August 1847 issue of The Sporting Review, also quotes the passage about the salmon-fishing Newf. I have read that the story is also to be found in The Domesday Book of Giant Salmon by Fred Buller (2007).