Environmental use,population dynamics and abundance of harbour seals (Phoca vitulina) in a Swedish fjord
2024
Amariei Perez, Alexandru
Harbour seals (Phoca vitulina) are one of the most charismatic and controversial marine predators. Their wide distribution across the globe and their rising population numbers have been a matter of concern for fishermen and stakeholders. Fear that these animals may prey on almost depleted fish stocks and hinder the recovery of commercially valuable species populations have led the Swedish environmental protection agency to allow hunting in recent years. The hunt is carried out according to count and estimation data from the aerial August national survey, when most seals are at land. However, little is known for restored coastal environments like fjords, where such management could have adverse consequences or not deliver the desired effects. Through the use of novel non-invasive methods such as photo ID and camera traps I aimed at studying the ecology and movements of the seals in a highly valuable ecosystem: the Gullmarsfjorden on the Swedish West coast. I assessed population numbers with photo ID mark capture-recapture estimates. Pictures taken during spring and autumn 2022 and 2023, suggest there is a high variability in the seal seasonal habits and population numbers with high site fidelity and low exchange of individuals between areas. This suggests potentially lower predatory pressure on local stocks than what was previously thought. I discuss how seal predation may not be the real cause for the depletion and slow recovery of fish stocks and instead look at other most likely potential drivers, which need to be addressed. The limitations and large potential of this study are also discussed with suggestion of new strategies and methods for the monitoring of a highly dynamic predator.
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