Changes in population depth distribution and oxygen stratification are involved in the current low condition of the eastern Baltic Sea cod (<i>Gadus morhua</i>)
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Published:2021-02-22
Issue:4
Volume:18
Page:1321-1331
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Casini MicheleORCID, Hansson Martin, Orio AlessandroORCID, Limburg KarinORCID
Abstract
Abstract. During the past 20 years, hypoxic areas have expanded rapidly in the
Baltic Sea, which has become one of the largest marine “dead zones” in the
world. At the same time, the most important commercial fish population of
the region, the eastern Baltic cod, has experienced a drastic reduction in
mean body condition, but the processes behind the relation between
deoxygenation and condition remain elusive. Here we use extensive long-term
monitoring data on cod biology and distribution as well as on hydrological
variations to investigate the processes that relate deoxygenation and cod
condition during the autumn season. Our results show that the depth
distribution of cod has increased during the past 4 decades at the same
time of the expansion, and shallowing, of waters with oxygen concentrations
detrimental to cod performance. This has resulted in a progressively
increasing spatial overlap between the cod population and low-oxygenated
waters after the mid-1990s. This spatial overlap and the actual oxygen
concentration experienced by cod therein statistically explained a large
proportion of the changes in cod condition over the years. These results
complement previous analyses on fish otolith microchemistry that also
revealed that since the mid-1990s, cod individuals with low condition were
exposed to low-oxygen waters during their life. This study helps to shed
light on the processes that have led to a decline of the eastern Baltic cod
body condition, which can aid the management of this population currently in
distress. Further studies should focus on understanding why the cod
population has moved to deeper waters in autumn and on analyzing the overlap
with low-oxygen waters in other seasons to quantify the potential effects of
the variations in physical properties on cod biology throughout the year.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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