Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.053.
Section : Zakah on Wealth Extracted from the Sea.
Most scholars stipulate that zakah is not payable on anything extracted from the sea, such as pearls, corals, chrysalite, cachalot ambergris, fish, and so on. There is, however, a report from Ahmad that if the amount extracted reaches a nisab, then zakah is due on it. Abu Yusuf agrees with him in the case of pearls and cachalot ambergris. Ibn ‘Abbas holds that there is no zakah of cachalot, because it is an object thrown out by the sea. Jabir said that there is no zakah on cachalot, but that it is a free spoil for anyone who finds it.