title: Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator.
abstract: Investigating the factors regulating fish condition is crucial in ecology and the management of exploited fish populations. The body condition of cod (Gadus morhua) in the Baltic Sea has dramatically decreased during the past two decades, with large implications for the fishery relying on this resource. Here, we statistically investigated the potential drivers of the Baltic cod condition during the past 40 years using newly compiled fishery-independent biological data and hydrological observations. We evidenced a combination of different factors operating before and after the ecological regime shift that occurred in the Baltic Sea in the early 1990s. The changes in cod condition related to feeding opportunities, driven either by density-dependence or food limitation, along the whole period investigated and to the fivefold increase in the extent of hypoxic areas in the most recent 20 years. Hypoxic areas can act on cod condition through different mechanisms related directly to species physiology, or indirectly to behaviour and trophic interactions. Our analyses found statistical evidence for an effect of the hypoxia-induced habitat compression on cod condition possibly operating via crowding and density-dependent processes. These results furnish novel insights into the population dynamics of Baltic Sea cod that can aid the management of this currently threatened population.
authors.affiliation: Department of Aquatic Resources, Institute of Marine Research , Swedish University of Agricultural Sciences , Turistgatan 5, 45330 Lysekil , Sweden.
authors.forename: Michele
authors.identifier: 0000-0003-4910-5236
authors.initials: M
authors.lastname: Casini
authors.affiliation: Department of Aquatic Resources, Institute of Marine Research , Swedish University of Agricultural Sciences , Turistgatan 5, 45330 Lysekil , Sweden.
authors.forename: Filip
authors.initials: F
authors.lastname: Käll
authors.affiliation: Swedish Meteorological and Hydrological Institute , Sven Källfelts gatan 15, 42671 Gothenburg , Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Hansson
authors.affiliation: Fish Resources Research Department , Institute of Food Safety, Animal Health and Environment , Daugavgrivas 8, 1048 Riga , Latvia.
authors.forename: Maris
authors.identifier: 0000-0002-7733-2148
authors.initials: M
authors.lastname: Plikshs
authors.affiliation: Fish Resources Research Department , Institute of Food Safety, Animal Health and Environment , Daugavgrivas 8, 1048 Riga , Latvia.
authors.forename: Tatjana
authors.initials: T
authors.lastname: Baranova
authors.affiliation: Department of Environmental Research and Monitoring , Swedish Museum of Natural History , Box 50007, 10405 Stockholm , Sweden.
authors.forename: Olle
authors.initials: O
authors.lastname: Karlsson
authors.affiliation: Department of Aquatic Resources , Swedish University of Agricultural Sciences, Institute of Coastal Research , Skolgatan 6, 74242 Öregrund , Sweden.
authors.forename: Karl
authors.initials: K
authors.lastname: Lundström
authors.affiliation: National Institute of Aquatic Resources , Technical University of Denmark , 2920 Charlottenlund , Denmark.
authors.forename: Stefan
authors.initials: S
authors.lastname: Neuenfeldt
authors.affiliation: Department of Aquatic Resources , Swedish University of Agricultural Sciences, Institute of Coastal Research , Skolgatan 6, 74242 Öregrund , Sweden.
authors.forename: Anna
authors.identifier: 0000-0003-1803-0622
authors.initials: A
authors.lastname: Gårdmark
authors.affiliation: Department of Aquatic Resources, Institute of Marine Research , Swedish University of Agricultural Sciences , Turistgatan 5, 45330 Lysekil , Sweden.
authors.forename: Joakim
authors.initials: J
authors.lastname: Hjelm
keywords: Baltic Sea; cod (Gadus morhua); density-dependence; hypoxia; prey availability; suitable habitat