Abstract
Multistate capture-recapture data comprise individual-specific sighting histories, together with information on individuals’ states related, for example, to breeding status, infection level, or geographical location. Such data are often analysed using the Arnason–Schwarz model, where transitions between states are modelled using a discrete-time Markov chain, making the model most easily applicable to regular time series. When time intervals between capture occasions are not of equal length, more complex time-dependent constructions may be required, increasing the number of parameters to estimate, decreasing interpretability, and potentially leading to reduced precision. Here we develop a multi-state model based on a state process operating in continuous time, which can be regarded as an analogue of the discrete-time Arnason–Schwarz model for irregularly sampled data. Statistical inference is carried out by regarding the capture-recapture data as realisations from a continuous-time hidden Markov model, which allows the associated efficient algorithms to be used for maximum likelihood estimation and state decoding. To illustrate the feasibility of the modelling framework, we use a long-term survey of bottlenose dolphins where capture occasions are not regularly spaced through time. Here, we are particularly interested in seasonal effects on the movement rates of the dolphins along the Scottish east coast. The results reveal seasonal movement patterns between two core areas of their range, providing information that will inform conservation management.
Funding Statement
This research was funded by the German Research Foundation (DFG) as part of the SFB TRR 212 (NC)—Projektnummer 316099922. RK was supported by the Leverhulme research fellowship RF-2019-299.
Acknowledgments
We thank Paul Thompson and Barbara Cheney from the University of Aberdeen Lighthouse Field Station and Phil Hammond and Monica Arso-Civil from the Sea Mammal Research Unit, University of St Andrews for provision of the dolphin data used in this study. We also thank all organisations who have provided funding over the three decades of research that has contributed to the individual based bottlenose dolphin project. All photo-identification surveys were conducted under Scottish Natural Heritage Animal Scientific Licences. We also thank Julia Schemm and Irina Janzen for their contributions to a preliminary analysis of the dolphin data which motivated the present paper. Finally, we are grateful to David Borchers, to the Associate Editor and to an anonymous reviewer for their insightful and very useful feedback that helped us to improve this article.
Citation
Sina Mews. Roland Langrock. Ruth King. Nicola Quick. "Multistate capture–recapture models for irregularly sampled data." Ann. Appl. Stat. 16 (2) 982 - 998, June 2022. https://doi.org/10.1214/21-AOAS1528
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