I don't know what herrings are like in their natural state, but I'm guessing their taste isn't usually much to be savoured, because otherwise why should herrings be so often soused? Sousing involves soaking the things in vinegar or brine, perhaps with the addition of cider, wine, tea, sugar, herbs, spices and chopped onion until they taste of...
...actually, sorry, I've never had the courage to try one.
I couldn't recommend being soused in vinegar (though vinegar is said to be a cure for verrucae) but a soak in salt water is supposed to be good for skin complaints and easing inflammation, so that can't do no harm.
Otherwise, someone who's described as soused may have been caught out in a sharp shower, but is much more likely to have been soaked in alcohol. From the inside outwards, naturally.
A sousing hawk is different, because it isn't wet at all: a sousing hawk one that's swooping down on its prey. This sort of sousing is, happily, quite easy: just keep an eye out for dropped coins, or visit a cut-price sale.
Word To Use Today. Souse as in soak comes from the Old French sous and is related to the Old High German sulza, which means brine.
The hawk type of souse may be connected in some way with the word source.