This is correct. Water has an extremely high heat capacity, meaning that it takes a lot of energy to warm or cool it by any noticable amount. Land does not. So while the different amount of sunlight in summer/winter changes the land temperature by a large amount, the ocean barely changes. Most of the land on Earth is in the northern hemisphere and therefore we get those temperature swings.
If it lurks on a reef and has two sets of teeth, that’s a moray!