Final answer:
The Northern Elephant Seal population would most likely remain unchanged with a decrease in Horn Shark population, unless indirect ecological interactions, such as changes in carrying capacity or shared resources, significantly affect the seals.
Step-by-step explanation:
When considering the relationship between the Northern Elephant Seal population and the Horn Shark population, it is essential to understand their ecological interactions. Typically, the direct impact of a decrease in Horn Shark population due to disease on Northern Elephant Seals would likely be minimal because they do not share a predator-prey relationship, and their diets do not notably overlap.
However, if we consider broader ecosystem dynamics, we could hypothesize that the removal of a species such as the Horn Shark might indirectly affect the Elephant Seal population. For instance, this could occur through changes in species competition or the availability of prey items if Horn Sharks and Elephant Seals share some common prey, or if their roles in the ecosystem are interdependent in some other way.
In the absence of direct competition or prey relationship, the most likely answer to the given scenario would be Option 3: Population would remain unchanged. However, this assessment doesn't account for complex ecological interactions that may exist within the marine environment. Factors such as changes in the carrying capacity or available resources due to the absence of Horn Sharks, could potentially lead to an increase, decrease, or no change in the Elephant Seal population, highlighting the interconnected nature of ecosystems.