A Computer System for Mark-Recapture Analysis of Open Populations

Abstract

A computer system is described for mark-recapture obtained from animal populations subject to dilution (new additions) and losses, and where marked animals are individually identifiable and classified according to various attributes (age, sex, species, etc.). The system edits and displays the data, provides general statistics-gathering capabilities, and provides a comprehensive set of analyses based on the Jolly-Seber models. The analyses include pooling methods to increase precision by combining information among sample times. A general capability for splitting off subgroups of attribute classes, sample times, or both, is provided. A simulation capability that can help in planning experiments and exploring sources of bias is provided. J. WILDL. MANAGE. 44(2):325-332 Mark-recapture experiments on open populations involve sampling a well-defined population at a set of discrete sample times. Unmarked animals from the samples or deliberate additions (injections) to the population are given marks that identify each animal uniquely and are then returned to the population. The time of recapture of all previously marked animals is recorded and any such animal may be removed (lost-on-capture) or returned to the population. When an animal is first seen, certain fixed attributes also can be recorded (year class, sex, species, etc.). An open population is one that is subject to dilution (recruitment of new animals into the catchable population by birth, growth, immigration), losses (by handling, death, or permanent emigration), or both. The most adaptable and widely used methods for obtaining estimates of population size, dilution rates, and/or loss rates are based on methods first proposed by Jolly (1965) and Seber (1965). The Jolly-Seber analyses have proved to b remarkably adaptable. They can allow for recovery data (such as band returns, where marked animals are recapture once at most) and recaptures sampling (where no marking is done but only sightings of marked animals are recorded). They can be modified to allow for heterogeneity in survival rate (Manly 1969). They can allow for partial closure (loss but no dilution, or vice versa; see Seber 1973, chapter 5, for discussion of all of these). Moreover, the properties of the estimates have come to be well understood. The precision of the estimates can be estimated (Jolly 1965), the sampling intensity needed to avoid small sample bias and poor precision can be anticipated (Gilbert 1973, Kreger 1973), and the robustness or bias of the estimates when catchability and survivorship are not constant is well documented (Cormack 1972, 1973; Carothers 1973). Adding to their usefulness is a large battery of tests of the assumptions that also are applicable to mark-recapture data: tests for closure or partial closure (Pollock et al. 1974), tests of unequal catch1 The computer system was developed during 1975-78 with financial support provided by an operating grant to A. N. Arnason and a postgraduate scholarship (1976-77) to L. Baniuk, both from the National Research Council of Canada.