Instead I'll share some supporting information:
-"Were-shark" is J. Eric Holmes' second A&E article in issue #13, July 1976, with Chris listed as a co-author. It's an early version of
Chapter 2 of the Maze of Peril.
-There are no stats in the article, which is written as a campaign story, but they are compared to were-tigers ("If there are were-tigers and sharks are tigers of the sea..."), implying similar strength (5 HD in OD&D). Update: After writing this I remembered that in the story a M-U puts 4 of 5 were-sharks in a group to sleep with a Sleep spell, meaning they must have a HD of 4 or less. The 1975 Warlock version of Sleep affects "one 6-sided die of 3rd or 4th level types". This differs from the OD&D Vol 1 version which affects 1d6 of 3 HD but only 1 of 4 HD.
-Gygax sent in letters published in A&E # 2, 8 and 15, and the last letter references issue #14, so it's likely he also read issue #13.
-Holmes next mentioned the were-shark in one sentence in the Basic manuscript: "Thus we find were-wolves in Europe, were-tigers in India, were-leopards in Africa and were-sharks in Polynesia". Per Gygax, "I reviewed Eric's manuscript" and "I was in charge of the manuscript when it was turned over", which means he would have encountered the idea of the were-shark here even if he didn't see them in the A&E story. Gygax left the sentence referring to the were-sharks unchanged in the published Basic rulebook, which is where most of us encountered and wondered about it. Update: I meant to also mention that the were-shark is also significant because it is the first non-mammalian lycanthrope in D&D.
-The Monster Manual then mentions, "There are some other forms of lycanthropes, but these are very rare in the extreme". This comes after Holmes mentioned the possibility of were-leopards and were-sharks. Eventually in 1983 the Monster Manual II would include a few more of these, including Gygax's take on the were-shark.
-Holmes' were-sharks surfaced again in the Maze of Peril (1986), where we learn more about them and the Dagonites they associate with. One detail from Maze of Peril I liked is that the Dagonites clad the hulls of their outriggers with silver to "ward off the were-sharks", suggesting an uneasy alliance.
See also: Part 28: "Thus We Find Were-Sharks in Polynesia"
Updates:
See all of the posts tagged WERESHARK in the Holmes Basic G+ Community Archive.
I wrote-up a version of the Were-Shark for inclusion in the Forgotten Smugglers' Cave adventure.