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PLoS Comput Biol. 2019 Mar 14;15(3):e1006425. doi: 10.1371/journal.pcbi.1006425. eCollection 2019 Mar.

Understanding narwhal diving behaviour using Hidden Markov Models with dependent state distributions and long range dependence.

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Greenland Institute of Natural Resources, Nuuk, Greenland.
Department of Mathematical Sciences, University of Copenhagen, Copenhagen, Denmark.
Greenland Institute of Natural Resources, c/o Greenland Representation, Copenhagen, Denmark.


Diving behaviour of narwhals is still largely unknown. We use Hidden Markov models (HMMs) to describe the diving behaviour of a narwhal and fit the models to a three-dimensional response vector of maximum dive depth, duration of dives and post-dive surface time of 8,609 dives measured in East Greenland over 83 days, an extraordinarily long and rich data set. Narwhal diving patterns have not been analysed like this before, but in studies of other whale species, response variables have been assumed independent. We extend the existing models to allow for dependence between state distributions, and show that the dependence has an impact on the conclusions drawn about the diving behaviour. We try several HMMs with 2, 3 or 4 states, and with independent and dependent log-normal and gamma distributions, respectively, and different covariates to characterize dive patterns. In particular, diurnal patterns in diving behaviour is inferred, by using periodic B-splines with boundary knots in 0 and 24 hours.

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