Final answer:
Decline in food sources due to pollution or overfishing leads to a decrease in the carrying capacity for seals and a consequent decrease in the seal population.
Step-by-step explanation:
If the major food source of seals declines due to pollution or overfishing, the carrying capacity of seals would decrease, as would the seal population. This is because carrying capacity is defined as the maximum population size of a species that an environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment. When the food source for seals is diminished, there is less energy available to support the seals, thus the environment can sustain fewer individuals.
Answer choice (a) the carrying capacity of seals would decrease, as would the seal population, is the most likely scenario if the major food source of the seals declines.