The correct answer is option 3, Whales.

Let`s dissect each option to have a better understanding.

Option 1: Fish

Fish can be found in both shallow and deep waters, so they are not exclusively deep-sea animals. They can adapt to different depths depending on their species.

Option 2: Dolphins

Dolphins are marine mammals, and while they are known to swim in deep waters, they are not considered predominantly deep-sea animals. They are commonly found in coastal areas and open oceans.

Option 3: Whales

Whales are the predominantly deep-sea animals. They are well-adapted to live in the depths of the ocean and have specific characteristics, such as their large size and ability to dive to great depths. Whales can often be found in the open ocean, away from coastal areas.

Option 4: Turtles

Turtles, like fish, can also be found in both shallow and deep waters. While some species of turtles may venture into deep waters for certain periods, they are not exclusively deep-sea animals.

In conclusion, out of the options given, whales are considered the predominantly deep-sea animals due to their unique adaptations and preference for deep ocean habitats.