Answer: Observational Study
Natalie is observing the people who step on the seal, and counting each one through a tally system or frequency table. By frequency table, I mean that she may have each row represent a different day, and at the very bottom is the total count (the sum of everything in the frequency column).
Natalie is not conducting an experiment because she doesn't have two groups (treatment vs control) and she's not directly interacting with the people she's observing. This also means she's not conducting a survey either. That would involve her having to ask each student to fill out a form, or answer questions.