title: Behavioral responses of Atlantic cod to sea temperature changes.
abstract: Understanding responses of marine species to temperature variability is essential to predict impacts of future climate change in the oceans. Most ectotherms are expected to adjust their behavior to avoid extreme temperatures and minimize acute changes in body temperature. However, measuring such behavioral plasticity in the wild is challenging. Combining 4 years of telemetry-derived behavioral data on juvenile and adult (30-80 cm) Atlantic cod (Gadus morhua), and in situ ocean temperature measurements, we found a significant effect of sea temperature on cod depth use and activity level in coastal Skagerrak. During summer, cod were found in deeper waters when sea surface temperature increased. Further, this effect of temperature was stronger on larger cod. Diel vertical migration, which consists in a nighttime rise to shallow feeding habitats, was stronger among smaller cod. As surface temperature increased beyond ∼15°C, their vertical migration was limited to deeper waters. In addition to larger diel vertical migrations, smaller cod were more active and travelled larger distances compared to larger specimens. Cold temperatures during winter tended, however, to reduce the magnitude of diel vertical migrations, as well as the activity level and distance moved by those smaller individuals. Our findings suggest that future and ongoing rises in sea surface temperature may increasingly deprive cod in this region from shallow feeding areas during summer, which may be detrimental for local populations of the species.
authors.affiliation: Department of Natural Sciences, Faculty of Engineering and Science, University of Agder Post Box 422, 4604, Kristiansand, Norway ; Institute of Marine Research Flødevigen, 4817, His, Norway ; Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto 4050-123, Porto, Portugal.
authors.forename: Carla
authors.initials: C
authors.lastname: Freitas
authors.affiliation: Department of Natural Sciences, Faculty of Engineering and Science, University of Agder Post Box 422, 4604, Kristiansand, Norway ; Institute of Marine Research Flødevigen, 4817, His, Norway ; Department of Biosciences, Centre for Ecological and Evolutionary Syntheses (CEES), University of Oslo PO Box 1066, Blindern, 0316, Oslo, Norway.
authors.forename: Esben Moland
authors.initials: EM
authors.lastname: Olsen
authors.affiliation: Department of Natural Sciences, Faculty of Engineering and Science, University of Agder Post Box 422, 4604, Kristiansand, Norway ; Institute of Marine Research Flødevigen, 4817, His, Norway.
authors.forename: Even
authors.initials: E
authors.lastname: Moland
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University 104 CEOAS Administration Building, Corvallis, Oregon, 97331-5503.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Ciannelli
authors.affiliation: Department of Natural Sciences, Faculty of Engineering and Science, University of Agder Post Box 422, 4604, Kristiansand, Norway ; Institute of Marine Research Flødevigen, 4817, His, Norway ; Department of Biosciences, Centre for Ecological and Evolutionary Syntheses (CEES), University of Oslo PO Box 1066, Blindern, 0316, Oslo, Norway.
authors.forename: Halvor
authors.initials: H
authors.lastname: Knutsen
keywords: Acoustic telemetry; Gadus morhua; climate change; diel vertical migration; sea surface temperature