Answer:
Due to more production of melanin.
Step-by-step explanation:
Areas with more sunlight, the skin of the whale darkens in color because of more production of melanin. When the skin is exposed to the sun, it makes more melanin in order to protect the skin's lower layers from damage. When the skin becomes damaged due to sunburn, it produces more melanin. The extra melanin causes whales to become a darker color but it only occurs in those regions where sunlight intensity is higher.