There is a curious case with small male salmons: From https://www.fishingwithrod.com/articles/fish_biology/whats_u...

> Size obviously matters when it comes to mating for salmon. However, being a small male can also succeed when it comes to scoring a female. The so-called "jacks" that are found in chinook and coho salmon are male individuals that return to their natal streams a couple of years earlier than expected.

> Although they are much smaller than a fully grown male, they are also sexually matured when they reach the spawning ground. What advantages do these smaller fish have? It is obvious that they will not win when confronted by a fully grown male. Behavioural biologists believe that these jacks are "sneaker males". Their duty is to simply stand by when larger males are fighting for territory, and sneak in while unnoticed to mate with the females that are also waiting for the fights to end. As you can see, being big does not always have all the advantages, sometimes being small can be very beneficial too.

IIRC the female already laid the eggs, and the big males start to fight. During the fight the small one sneaks a fertilice them. "Waiting" and "Mate" are misleading.