Sea creatures that give birth to live young and those that lay eggs are all permissible to eat
Question

I know that all seafood is halal, but someone said that it is not permissible to eat whales (al-hut), because they give birth to live young and do not lay eggs, unlike other fish. He quoted as evidence for that the fact that seals, turtles and elephant seals, et cetera, are not permissible to eat, because they give birth to live young and do not lay eggs. Is it true that it is not permissible to eat these animals? Is there anything in the Qur’an or sahih Sunnah that refers specifically to this issue? Another question: how can we tell whether a particular sea creature is halal or haram? The shark, for example, lives in the sea, meaning that it is halal in that regard, but it is a predator that kills and eats other animals, so it becomes haram in that regard, because it is not permissible to eat animals that kill and eat others. I hope that you can explain.
Praise be to Allah.Firstly:
We have noted previously that all sea creatures that only live in the water are halal, whether they are caught alive or they are found dead (maytah, “dead meat”), because of the general meaning of the verse in which Allah, may He be exalted, says (interpretation of the meaning):
{Lawful to you is game from the sea and its food} [al-Ma’idah 5:96].
Abu Dawud (83) narrated from Abu Hurayrah that the Messenger of Allah (blessings and peace of Allah be upon him) said about the sea: “Its water is a means of purification and its animals that are found dead are permissible.” Classed as sahih by al-Albani in Sahih Abi Dawud.
The scholars of the Standing Committee said: The basic principle regarding sea creatures that usually only live in the water is that they are halal."(Fatawa al-Lajnah al-Da’imah  22 /312).
The guideline regarding sea creatures is that it is not haram to eat any of them if they only live in the water.
As for amphibious animals [those that live both in the water and on land], they are not all halal.
Secondly:
Eating al-hut [large fish; sometimes translated as whale] is permissible, because they are a type of fish.
It says in Lisan al-‘Arab [a famous Arabic-language dictionary] (2/26):
Al-hut means fish, and it was said that it refers to large fish. End quote.
Ibn Majah (3218) narrated from ‘Abdullah ibn ‘Umar that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Two types of ‘dead meat’ have been made permissible for us: fish and locusts.” Classed as sahih by al-Albani in Sahih Ibn Majah.
And we have noted above that all sea creatures are halal.
In Sahih al-Bukhari (4362) and Sahih Muslim (1935) it is narrated that Jabir (may Allah be pleased with him) said: We went out on campaign with the ‘army of the leaves’ [so called because they were so hungry that they ate leaves from trees], and Abu ‘Ubaydah was appointed as our commander. We were stricken with severe hunger, then the sea threw out a dead fish, the like of which we had never seen, which was called al-‘anbar (sperm whale) and we ate from it for half a month. Abu ‘Ubaydah took one of its bones and a rider passed under it. Abu’z-Zubayr told me that he heard Jabir say: Abu ‘Ubaydah said: Eat. When we came to Madinah, we told the Prophet (blessings and peace of Allah be upon him) about that, and he said: “Eat, for it is provision that Allah has given you, and give us some, if you have any of it with you.” So some of them gave him [some of that fish] and he ate it.
As for the fact that it gives birth to live young and does not lay eggs, that has nothing to do with the shar‘i ruling and does not affect it. There is nothing in the religious text to suggest that sea creatures that give birth to live young and do not lay eggs are haram and cannot be eaten; rather the general meaning of the evidence indicates that they are all halal. This is quite clear, and there is no argument about it.
Thirdly:
Sharks are halal, because of what is mentioned above and because of the general meaning of the words of the Prophet (blessings and peace of Allah be upon him): “Two kinds of ‘dead meat’ and two kinds of blood have been permitted to you. The two kinds of ‘dead meat’ are fish and locusts, and the two kinds of blood are the liver and spleen.”  Narrated by Ibn Majah (3314); classed as sahih by al-Albani.
The fact that the shark is a predator does not cancel that. The prohibition on every predator that has fangs applies only to land animals that are predators. As for the predators of the sea, this ruling does not apply to them.
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said:
It cannot be said that for whatever land animal is haram, its counterpart in the sea is also haram, because the sea is something separate, even though there are animals in it which have fangs with which they attack other animals, such as sharks… The point is that there are animals [in the sea] that kill and eat others, yet despite that they are halal. End quote from ash-Sharh al-Mumti‘ (15.34).
The scholars of the Standing Committee were asked:
Are sharks halal or haram?
They replied: All fish are halal, sharks and others, because of the general meaning of the verse in which Allah, may He be exalted, says (interpretation of the meaning): { Lawful to you is game from the sea and its food } [al-Ma’idah 5:96] and the words of the Prophet (blessings and peace of Allah be upon him): “Its water is a means of purification and its ‘dead meat’ [animals that died without being slaughtered in the prescribed manner] is permissible.”"(Fatawa al-Lajnah ad-Da’imah 22/320).
See also the answer to question no. 1919 .
And Allah knows best.