The carrying capacity of the Baltic Sea could withstand a seal population twice its current size, but hunting quotas and Baltic herring mean weight greatly impact the future of the seals. A recent study provides a new estimate for the carrying capacity of the Baltic grey seal population and accurate guidelines for decision-makers when determining hunting quotas.
The Baltic grey seal population took a historic dive in the 1970s to just some 3,000 individuals following excessive hunting and proliferation of organochlorines (such as DDT and PCB) used in pesticides and paint. At the same time, the population size of the Baltic Sea’s other seal species, the Baltic ringed seal, dropped dramatically to 5,000 individuals.
After these setbacks, seal hunting was banned in the Baltic Sea in the 1980s and the use of substances harmful to seals was regulated. Thanks to these measures, seal populations began to grow.
A study led by the University of Helsinki examines developments in Baltic grey seal populations. Since the 1970s, the Baltic grey seal population has grown to 57,000 individuals. A University of Helsinki –led study revealed the impact of herring weight on seal population growth. As the average weight of herring continues to increase, the number of seal pups could grow by as much as 10% every year.
The researchers estimate that the carrying capacity of the Baltic Sea could withstand double the current number of seals, in other words, some 120,000 individuals in total. This new carrying capacity estimate is 30% larger than a previous estimate based on early 20th century hunting statistics.
The researchers applied the same statistical model that they used in their study on the Baltic ringed seal population , published in spring 2025.
Modern techniques enable digital population modelling, which allows estimation of how the population changes in response to external factors such as hunting pressure. The model combines several long-term datasets, including aerial counts and hunting statistics as well as samples collected from dead seals. Together, they provide a more accurate picture of the seal population than any single dataset on its own.
In the same study, the researchers assessed the effects of different potential hunting quotas on the Baltic grey seal population.
"Our model predicts that the Baltic grey seal population can remain viable under the current combined yearly hunting quota of approximately 3,050 individuals in Finland, Sweden and the Åland Islands. However, with the yearly hunting quota raised to 3,600 individuals, the probability of extinction would grow considerably. With a yearly harvest of 4,800 seals, the population is predicted to go extinct by 2070 at the latest," estimates Professor of Statistics Jarno Vanhatalo from the University of Helsinki.
At the same time, hunting selectivity also has a significant impact on population dynamics. Should hunting become selective so that more females would be harvested, in all likelihood the population would take a downward turn already under the current hunting quotas.
The results support decision-making in setting hunting quotas for the Baltic grey seal and back up conservation efforts in the Baltic Sea and the work of the Baltic Marine Environment Protection Commission (HELCOM).
The study was carried out with Natural Resources Institute Finland, the University of Eastern Finland, the Turku University of Applied Sciences and the Swedish Museum of Natural History.
Ecological Modelling
10.1016/j.ecolmodel.2026.111666
Bayesian integrated population model of Baltic grey seals (Halichoerus grypus grypus) informs on population carrying capacity and the impact of Baltic herring (Clupea harengus membras) on reproduction
26-May-2026