Let's try to look at this from the "laws of nature" perspective.....
(1) Little guys get out of the way of big guys 'cause the big guys can hurt you more.
(2) Fast, agile little guys can harass the big guys and rule 'cause the big guys can't catch 'em.
(3) Generally, predators rule the turf over prey 'cause the predators can eat you.
(4) The one with the most formidable presentation rules over the wimps.
(5) Survival of the fittest.
Now, let's look at this from the "ethics of man" perspective...
(1) Equal rights for all
(2) First come, first served
(3) "Grandfathered" privileges come into play 'cause the others guys have been there longer
(4) Don't bully, but respect others
(5) Treat others as you would like to be treated.
Hmmmm..... So.... SUP-pers are the biggest (rhinos of the surf zone crowd... only the outrigger canoes are bigger than them, and outriggers are rare in most waters...) Kiters are the fastest and most agile (we're the dinosaurs compared to the slow, lumbering reptiles). Surfers are the Grandfathers 'cuz they started this whole "fun in the surf" thing.... and swimmers and body surfers are tolerated in deference to the "Equal rigths for all" ethic.... (being an ex-avid body surfer, I actually think body surfers are more towards the small, "ultra agile" early mammal crowd, whereas the swimmers are just flotsam...)
Given this categorization, and the rules of nature versus the ethics of man, it would seem that the dominant rules are probably those most enforceable at the local site. "Whoever has the most effective enforcers present wins!" ("Gang theory") They get to develop their microclime social structure and rule.
Why can't we all just get along????? ('Cause there isn't enough supply to meet the demand.... which introduces competition.... and is the basis for the laws of nature.... which introduces the notion of social norms in civilization... which is why we are even talking about it in the first place...).