The meaning of two not-so-easy phrases

The meaning of two not-so-easy phrases

The passage below is from Fathoms: The World in the Whale Hardcover by Rebecca Giggs.

A kill-shot, hand-flung at close proximity, must only have been feasible in the case of porpoises, beluga, and calves, up to a certain measure. If bigger whales were pursued along the coast—or, less often, hunted from an ice shelf—it was necessary to harangue the animals over days and nights. Hunters in boats struck at their quarry from above using lances and bludgeons, and whales were sometimes strung with ‘drogues’, buoyancy devices that slowed their escape and impeded diving (a whale’s plunge is a ‘sounding’). The Inuit are known to have gutted and inflated seals for this purpose, having stitched up the creatures’ eyes and orifices to make, in a rudimentary sense, seal balloons. Their harrying technique relied on exhaustion and serial injury to enfeeble and eventually kill an animal, after which snarling it in floats prevented it from sinking.

In this passage I cannot understand the bold-faced parts.

First, “a whale’s plunge is a ‘sounding’”.

‘Plunge’ means ‘a sudden decline.’

‘Sounding’ in this context seems to mean ‘the act or process of measuring depth of water.’

Does the author try to refer to using the sound of a whale’s plunge to measure depth of water in a humorous sense?

If my wild guess is wide out of mark, could you tell me what it is that hits the mark?

On the second phrase ‘snarling it in floats.’

‘Float’ seems to mean ‘a raft.’ (Am I right?)

‘Snarl’ is not easy one for me.

In the sense of context, it seems to mean ‘to float.’

But dictionary doesn’t show the meaning that meets the contextual meaning.

Can you tell me what I miss in the meaning of ‘snarl’?

Thanks in advance.