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Sci Rep. 2019 Apr 4;9(1):5642. doi: 10.1038/s41598-019-42109-w.

Classifying grey seal behaviour in relation to environmental variability and commercial fishing activity - a multivariate hidden Markov model.

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Marine Mammal Research, Department of Bioscience, Aarhus University, Frederiksborgvej 399, DK-4000, Roskilde, Denmark.
Department of Business Administration and Economics, Bielefeld University, Universitätsstraße 25, 33615, Bielefeld, Germany.
Department of Aquatic Resources, Swedish University of Agricultural Sciences, Lysekil, SE-45321, Sweden.
National Institute for Aquatic Resources, Technical University of Denmark, Kemitorvet, Kgs. Lyngby, DK-2800, Denmark.
Marine Mammal Research, Department of Bioscience, Aarhus University, Frederiksborgvej 399, DK-4000, Roskilde, Denmark.
Thünen Institute of Baltic Sea Fisheries, Alter Hafen Süd 2, D-18069, Rostock, Germany.
Department of Environmental Research and Monitoring, Swedish Museum of Natural History, Box 50007, SE-104 05, Stockholm, Sweden.
Sea Mammal Research Unit, University of St Andrews, St Andrews, KY16 8LB, United Kingdom.
Evolutionary Genomics Section, Natural History Museum of Denmark, Department of Biology, University of Copenhagen, Øster Voldgade 5-7, DK-1350, Copenhagen K, Denmark.


Classifying movement behaviour of marine predators in relation to anthropogenic activity and environmental conditions is important to guide marine conservation. We studied the relationship between grey seal (Halichoerus grypus) behaviour and environmental variability in the southwestern Baltic Sea where seal-fishery conflicts are increasing. We used multiple environmental covariates and proximity to active fishing nets within a multivariate hidden Markov model (HMM) to quantify changes in movement behaviour of grey seals while at sea. Dive depth, dive duration, surface duration, horizontal displacement, and turning angle were used to identify travelling, resting and foraging states. The likelihood of seals foraging increased in deeper, colder, more saline waters, which are sites with increased primary productivity and possibly prey densities. Proximity to active fishing net also had a pronounced effect on state occupancy. The probability of seals foraging was highest <5 km from active fishing nets (51%) and decreased as distance to nets increased. However, seals used sites <5 km from active fishing nets only 3% of their time at sea highlighting an important temporal dimension in seal-fishery interactions. By coupling high-resolution oceanographic, fisheries, and grey seal movement data, our study provides a scientific basis for designing management strategies that satisfy ecological and socioeconomic demands on marine ecosystems.

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