Molting phenology of a lacustrine ringed seal, Pusa hispida saimensis

Abstract

The timing and effect of a range of environmental variables on the annual molt of ringed seals (Pusa hispida saimensis) in Lake Saimaa were studied in 2013–2019. Molting patterns were investigated by mixed models run on photoidentification data collected by camera trapping and digital camera surveys. Photoperiod was the predominant environmental variable affecting the molt but molting of females was also linked to air temperature and ice thickness. The cumulative proportion of molting seals peaked around the 18th–20th May, when day length reached 18 h. The main molting season, when most of the seals were hauled out at the same time, lasted on average for 16 days with considerable inter-annual differences in the duration (range 11–22 days). The results provide important baseline information on Saimaa ringed seal molt. Continued monitoring is important as the molt is an energetically demanding period for the seals, and any changes in molting behavior may indicate changes in habitat or in environmental conditions.