Also, Thinking a bit, you can use occupancy modelling but still you will have to split the transect in several sub-units but still need to define thewith of the belt. If your tapir is rare or have low density or detectability it could perform. Search for some papers about tigers and some references about using occupancy as a surrogate for rare or elusive species. You can get some feedback about it suitability for your project in:
https://www.researchgate.net/publication/26410981_Occupancy_as_a_surrogate_for_abundance_estimationConn, P. B., L. L. Bailey, and J. R. Sauer. 2004. Indexes as surrogates to abundance for low abundance species. Pages 59–74 in W. L. Thompson, editor. Sampling rare and elusive species: concepts, designs, and techniques for estimating population parameters. Island Press, Washington, D.C., USA