Scientists warn that a high number of harbour porpoises are killed annually in fishing nets.
The population of harbour porpoises in Danish coastal waters and the western part of the Baltic, known as the Belt Sea population, is facing a critical decline, as highlighted by researchers from Denmark, Germany, and Sweden. The population has significantly decreased from approximately 40,000 individuals in 2012 and 2016 to only 14,000 by 2022. This decline is a cause for concern as the population is shrinking by 2.7% annually.
Various factors contribute to this decline, including by-catch due to net fishing, deoxygenation, pollution, and a lack of fish. By-catch, where porpoises become entangled in fishing nets and drown, is a significant issue. To address this, researchers recommend limiting net usage in commercial fishing or mandating the use of acoustic alarms on all nets to reduce porpoise mortality.
Researchers have been conducting aerial surveys since 2005 to count harbour porpoises. These surveys involve systematically flying over ocean segments to spot porpoises on the surface. By extrapolating the number of spotted porpoises in the studied areas, researchers estimate the entire population. Despite the method's uncertainties, data from 2005 to the present show a clear decline in the harbour porpoise population, with a noticeable decrease observed since 2016.
The Belt Sea, where approximately 14,000 harbour porpoises reside, is a coastal area shared by Denmark, Sweden, and Germany. Although considered one population, these porpoises are genetically distinct from those in the North Sea and the Baltic Sea. Harbour porpoises in the Belt Sea migrate in search of food and tend to congregate in areas with abundant food sources, such as the Femern Belt, Øresund, Storebælt, Lillebælt, and Kattegat along the Swedish west coast.
While various factors impact the harbour porpoise population, the researchers are particularly concerned about the threat posed by commercial fishing, as by-catch remains a significant issue. They emphasize the urgent need for policymakers to address this threat by limiting net fishing to reduce porpoise mortality and allow the population to recover.
Unlike their counterparts in the Belt Sea, harbour porpoises in the North Sea have maintained a stable population between 300,000 and 400,000 from 1994 to 2022. The North Sea porpoises have more space to move and follow fish shoals, leading to their better survival compared to the Belt Sea population. These differences in population dynamics are attributed to the distinct environmental adaptations of the two groups, as evidenced by variations in skull morphology linked to their feeding habits.
The worries about the decline of the Belt Sea population are compounded by the inability of North Sea porpoises to repopulate the area if the local population disappears. Hence, urgent conservation measures are needed to protect and stabilize the Belt Sea harbour porpoises. Failure to act promptly may result in irreversible consequences for this unique population.
Overall, the research underscores the pressing need for immediate conservation efforts to mitigate the threats facing harbour porpoises in the Belt Sea and ensure the long-term viability of this vital marine mammal population.
Source: https://www.eurekalert.org/news-releases/1036882
Various factors contribute to this decline, including by-catch due to net fishing, deoxygenation, pollution, and a lack of fish. By-catch, where porpoises become entangled in fishing nets and drown, is a significant issue. To address this, researchers recommend limiting net usage in commercial fishing or mandating the use of acoustic alarms on all nets to reduce porpoise mortality.
Researchers have been conducting aerial surveys since 2005 to count harbour porpoises. These surveys involve systematically flying over ocean segments to spot porpoises on the surface. By extrapolating the number of spotted porpoises in the studied areas, researchers estimate the entire population. Despite the method's uncertainties, data from 2005 to the present show a clear decline in the harbour porpoise population, with a noticeable decrease observed since 2016.
The Belt Sea, where approximately 14,000 harbour porpoises reside, is a coastal area shared by Denmark, Sweden, and Germany. Although considered one population, these porpoises are genetically distinct from those in the North Sea and the Baltic Sea. Harbour porpoises in the Belt Sea migrate in search of food and tend to congregate in areas with abundant food sources, such as the Femern Belt, Øresund, Storebælt, Lillebælt, and Kattegat along the Swedish west coast.
While various factors impact the harbour porpoise population, the researchers are particularly concerned about the threat posed by commercial fishing, as by-catch remains a significant issue. They emphasize the urgent need for policymakers to address this threat by limiting net fishing to reduce porpoise mortality and allow the population to recover.
Unlike their counterparts in the Belt Sea, harbour porpoises in the North Sea have maintained a stable population between 300,000 and 400,000 from 1994 to 2022. The North Sea porpoises have more space to move and follow fish shoals, leading to their better survival compared to the Belt Sea population. These differences in population dynamics are attributed to the distinct environmental adaptations of the two groups, as evidenced by variations in skull morphology linked to their feeding habits.
The worries about the decline of the Belt Sea population are compounded by the inability of North Sea porpoises to repopulate the area if the local population disappears. Hence, urgent conservation measures are needed to protect and stabilize the Belt Sea harbour porpoises. Failure to act promptly may result in irreversible consequences for this unique population.
Overall, the research underscores the pressing need for immediate conservation efforts to mitigate the threats facing harbour porpoises in the Belt Sea and ensure the long-term viability of this vital marine mammal population.
Source: https://www.eurekalert.org/news-releases/1036882
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