To cite the Petersen package in publications use:

  Schwarz, C. J (2023). The Petersen-Estimator (and many more) for
  Two-Sample Capture-Recapture Studies with Applications to Fisheries
  Management. R Package.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {The Petersen-Estimator (and many more) for Two-Sample Capture-Recapture
                  Studies with Applications to Fisheries Management {R} {Petersen} Package},
    author = {Carl James Schwarz},
    year = {2023},
  }