Environmental Biology of Fishes

, Volume 21, Issue 4, pp 293–307

Petersen and removal population size estimates: combining methods to adjust and interpret results when assumptions are violated

  • A. John GatzJr.
  • James M. Loar
Full paper

DOI: 10.1007/BF00000377

Cite this article as:
Gatz, A.J. & Loar, J.M. Environ Biol Fish (1988) 21: 293. doi:10.1007/BF00000377


We present ways to test the assumptions of the Petersen and removal methods of population size estimation and ways to adjust the estimates if violations of the assumptions are found. We were motivated by the facts that (1) results of using both methods are commonly reported without any reference to the testing of assumptions, (2) violations of the assumptions are more likely to occur than not to occur in natural populations, and (3) the estimates can be grossly in error if assumptions are violated. We recognize that in many cases two days in the field is the most time fish biologists can spend in obtaining a population estimate, so the use of alternative models of population estimation that require fewer assumptions is precluded. Hence, for biologists operating with these constraints and only these biologists, we describe and recommend a two-day technique that combines aspects of both capture-recapture and removal methods. We indicate how to test: most of the assumptions of both methods and how to adjust the population estimates obtained if violations of the assumptions occur. We also illustrate the use of this combined method with data from a field study. The results of this application further emphasize the importance of testing the assumptions of whatever method is used and making appropriate adjustments to the population size estimates for any violations identified.

Key words

Capture-recapture Closed population Equal catchability Marked fish Catch-effort estimate 

Copyright information

© Kluwer Academic Publishers 1988

Authors and Affiliations

  • A. John GatzJr.
    • 1
  • James M. Loar
    • 1
  1. 1.Environmental Sciences DivisionOak Ridge National LaboratoryOak RidgeUSA
  2. 2.Department of Biological SciencesOhio Wesleyan UniversityDelawareUSA

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