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Avoiding bias in estimates of population size for translocation management

Bickerton, Katherine T., Ewen, John G., Canessa, Stefano, Cole, Nik C., Frost, Fay, Mootoocurpen, Rouben, McCrea, Rachel (2023) Avoiding bias in estimates of population size for translocation management. Ecological Applications, 33 (8). Article Number e2918. ISSN 1939-5582. (doi:10.1002/eap.2918) (KAR id:103062)


Mark–recapture surveys are commonly used to monitor translocated populations globally. Data gathered are then used to estimate demographic parameters, such as abundance and survival, using Jolly–Seber (JS) models. However, in translocated populations initial population size is known and failure to account for this may bias parameter estimates, which are important for informing conservation decisions during population establishment. Here, we provide methods to account for known initial population size in JS models by incorporating a separate component likelihood for translocated individuals, using a maximum‐likelihood estimation, with models that can be fitted using either R or MATLAB. We use simulated data and a case study of a threatened lizard species with low capture probability to demonstrate that unconstrained JS models may overestimate the size of translocated populations, especially in the early stages of post‐release monitoring. Our approach corrects this bias; we use our simulations to demonstrate that overestimates of population size between 78% and 130% can occur in the unconstrained JS models when the detection probability is below 0.3 compared to 1%–8.9% for our constrained model. Our case study did not show an overestimate; however accounting for the initial population size greatly reduced error in all parameter estimates and prevented boundary estimates. Adopting the corrected JS model for translocations will help managers to obtain more robust estimates of the population sizes of translocated animals, better informing future management including reinforcement decisions, and ultimately improving translocation success.

Item Type: Article
DOI/Identification number: 10.1002/eap.2918
Additional information: For the purpose of open access, the author(s) has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising.
Uncontrolled keywords: lesser night gecko, conservation translocation, mark–recapture, reintroduction, Nactus coindemirensis, capture–recapture
Subjects: Q Science > QA Mathematics (inc Computing science)
Divisions: Divisions > Division of Computing, Engineering and Mathematical Sciences > School of Mathematics, Statistics and Actuarial Science
Funders: Engineering and Physical Sciences Research Council (
Natural Environment Research Council (
SWORD Depositor: JISC Publications Router
Depositing User: JISC Publications Router
Date Deposited: 04 Oct 2023 14:19 UTC
Last Modified: 25 Mar 2024 11:42 UTC
Resource URI: (The current URI for this page, for reference purposes)

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