Haul-out patterns of the Baltic grey seal (Halichoerus grypus) in the suburbs of a metropolis

In this study, we investigated the haul-out patterns of the Baltic grey seal in the coastal area adjacent to the metropolitan city, Saint Petersburg, during the ice-free seasons of 2017-2022. Grey seals occupied stony banks near Kotlin Island, in the easternmost part of the Gulf of Finland. The censuses were carried out from the island shore during evening hours. The number of seals reached 70 during the survey. Contrary to the common trend reported in similar studies, the annual minimum in seal abundance (May and June) coincided with the peak of moulting. Active use of the haul-out site was observed between July and November, implying that eastward movements of the grey seals take place in the Gulf of Finland in the post-moulting period. Wind speed and sea state interfered with the seal hauling out throughout the year, whereas the relationship with air temperature varied seasonally. Cloud cover, atmospheric pressure, wind direction and sea level had no impact on the seal number, though the fluctuations in sea level reduced the haul-out space. The tendency of the seals to haul out towards and after the sunset was determined. The most frequent sources of human disturbance were light planes (0.45 & PLUSMN; 0.12 confidence interval, per count) and powerboats (0.41 & PLUSMN; 0.14 confidence interval, per count), but only the powerboats significantly decreased the seal number. We found that the seals used the banks concurrently with seabirds. The area of Kotlin Island presumably attracts the seals by the diversity of prey items in the estuary of the Neva River. Establishing of a marine protected area and physical marking of the water space around the haul-out site are recommended. & COPY; 2023 Elsevier B.V. All rights reserved.

Automated summary

In this study, the haul-out patterns of the Baltic grey seal in the coastal area near Saint Petersburg were investigated. The seals were found to occupy stony banks near Kotlin Island and were most active from July to November. Human disturbances, particularly powerboats, significantly decreased the seal population. The seals coexisted with seabirds and were attracted to the area by a diverse range of prey items in the estuary of the Neva River.