Harbor porpoises once inhabited a much larger area of the Baltic Sea, including regions where they are now rare or absent. This finding comes from a new study that analyzed centuries-old Swedish newspapers. Researchers reconstructed past distribution patterns of the Baltic Proper harbor porpoise.
Scientists from the Swedish Museum of Natural History, Lund University, and the Natural History Museum of Denmark conducted the study. They analyzed digitized Swedish newspapers dating from the late 1700s to the early 1900s. Their findings, published in the journal *Ecology and Evolution*, show how the distribution of *Phocoena phocoena* has changed over time.
The newspapers indicate that porpoises historically lived along the entire Swedish coastline. This included the northernmost parts and the Gulf of Bothnia, where the species is seldom seen today. Reports from the Baltic Sea were less frequent but still suggested a wider historical distribution. Many northern Baltic reports were from spring and summer. This suggests these areas may have served as feeding grounds for porpoises migrating from the southern Baltic or Belt Sea.
The research team searched the National Library of Sweden's digitized newspaper archive. They used keywords related to harbor porpoises. Over 100,000 search results were screened, yielding about 1,500 relevant newspaper reports. More than 1,400 individual porpoise sightings were extracted and verified. The team then examined changes in reported porpoise distribution based on recorded locations and publication dates.
Today, porpoises are largely absent from parts of the northern Baltic Sea. This represents a loss of approximately one-third of their historical range. The Baltic Proper population is critically endangered, with only about 500 individuals remaining. Current surveys also show a dramatically shrinking distribution. Historical information helps establish a baseline for understanding species range changes, preventing present conditions from becoming the sole reference point for what is considered normal.
This study is part of a growing scientific effort to use historical sources like tax records, fishing logs, and newspapers. This approach, known as Marine Historical Ecology, helps reconstruct past marine ecosystems. The findings identify areas where porpoises once thrived. These areas could potentially support their return if environmental conditions improve. Historical records provide crucial data for guiding future conservation efforts.
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