Well to make it quick the answer is YOU DON'T. You cannot profit from something when it is falling down, but it is when it is recovering is the time you will profit. That is why a lot of people short (sell) their holdings when they know it is time to jump and stay in fiat currency, they will then buy their shares/holdings back when it has settled in or is recovering, with this method they have increased their holdings as they bought their cryptocurrencies at a cheaper price resulting into a profit when they sell at a higher price.
"Shark" is a term used to refer to traders with huge assets in the cryptocurrency market. Because of strong potential, sharks can increase the price of a coin a dozen times, but can also cause price to fall dramatically, costing a dozen times. So we can take advantage of opportunity to make money under "Shark".
Well, even though they are in the same categories, they are actually referred to as whales literally and not as sharks. Taking advantage of the market requires great deal of knowledge and experience and it is not something that can be achieved in a very short term for those who want to really do it well.
Whales are like the market controllers since they are holding a lot of the market, and in that case, you simply want to be knowledgeable enough to know which direction they want to gear towards or not.