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Our research has shown that the Baltic Sea is an ecosystem in transition. Chicks were weighted during the ringing procedure in the 70ths and from 1989 onwards. A gradual decrease in weights were observed during the 90ths. This can be explained by the following chain of events. The Common Murre fledgling weight has been decreasing
despite the fact that the Sprat (Sprattus sprattus) population,
the Common Murre source of food, has been significantly increasing.
The Sprat eats zooplankton; therefore as the Sprat population increased
there has been a rapid decline in the plankton population. This
meant that although there was more Sprat in the Baltic Sea, they
were smaller and provided less nutrition as they contained less
calories. Before the end of the 1980's the Sprat population had
been limited by the Cod (Gadus morhua). However, after the end of
the 1980's, the Cod was suffering from a severe case of over-fishing. After the year 2000, there was a decline in
the number of Sprat, but with an increase in the average nutritional
value of the Sprat. As expected the Common Murre chick weight increased
again. The link between the young bird's weights and the condition
of the Sprat is an example of how monitoring the birds help us understand
the ecosystem changes in the Baltic Sea. |
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In swedish 
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