To cite Distance in publications use:

  Miller DL, Rexstad E, Thomas L, Marshall L, Laake JL (2019).
  “Distance Sampling in R.” _Journal of Statistical Software_, *89*(1),
  1-28. doi:10.18637/jss.v089.i01
  <https://doi.org/10.18637/jss.v089.i01>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Distance Sampling in {R}},
    author = {David L. Miller and Eric Rexstad and Len Thomas and Laura Marshall and Jeffrey L. Laake},
    journal = {Journal of Statistical Software},
    year = {2019},
    volume = {89},
    number = {1},
    pages = {1--28},
    doi = {10.18637/jss.v089.i01},
  }