Answer: The decision to migrate to the new coastal area would be driven by a combination of factors that make living difficult in their current location (push factors) and the perceived benefits of the new location (pull factors).
Step-by-step explanation:
The decision of the clan to migrate to a new coastal area can be described as a "push-pull" factor.
The "push" factors would be the difficulties of living inland, such as limited resources and harsh climate. These factors would make it difficult for the clan to sustain themselves and would motivate them to seek out a better living situation.
The "pull" factors would be the abundance of shellfish and the warmer climate in the new coastal area. These factors would attract the clan to the new area, as they would provide a reliable source of food and a more comfortable living environment.