JUNE 11,
2019
The prime
predators of the Baltic Sea at the top of the food web are losing weight,
according to a new study that links the deteriorating health of gray seals and
cod with changes in bottom-living crustaceans, isopods and amphipods.
"It is
important that you understand how the food web works when managing a
fishery. It is not enough to manage how the fish and fisheries are changing.
The availability and quality of food is
at least as important," says Lena Bergström, researcher at the Department
of Aquatic Resources at the Swedish Agricultural University.
In a
collaboration between several universities, the authors of the study examined
how the health and abundance of certain species has changed over two decades in
the Bothnian Sea and the Baltic Proper. They investigated seal, cod, herring,
sprat, isopods, amphipods and zooplankton, species that all occur at different
levels in the Baltic Sea food web. The system is complex and several species
can be both predators and prey. For example, herring eats zooplankton and some
bottom fauna while the herring itself is eaten by cod and seal.
Shrinking
habitats for bottom-living animals
The study
primarily shows that there are links between the health of both cod and seal
with the availability of bottom-living animals. Regarding the seals, the
connection is indirect through that the herring it eats is influenced by the
availability of the bottom-living animals. In both cases, there is a link to
climate change and eutrophication.
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