Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator
2016
Investigating the factors regulating fish condition is crucial in ecology and the management of exploited fish populations. The body condition of cod (
Gadusmorhua ) in the
BalticSea 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
Balticcod condition during the past 40 years using newly compiled fishery-independent
biological dataand hydrological observations. We evidenced a combination of different factors operating before and after the ecological
regime shiftthat occurred in the
BalticSea in the early 1990s. The changes in cod condition related to feeding opportunities, driven either by
density-dependenceor 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-dependentprocesses. These results furnish novel insights into the population dynamics of
BalticSea cod that can aid the management of this currently threatened population.
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