ABSTRACT
The ringed seal (Phoca hispida) is an ice-dependent pinniped of Arctic origin. There are up to five subspecies of the ringed seal, one of which is the endangered Saimaa ringed seal (P. h. saimensis). This endemic freshwater subspecies inhabits Lake Saimaa, where it was isolated about 9 500 years ago after the glacial period. During the most recent centuries, the population declined from thousands of individuals to a little over 100 seals at the lowest point in the 1980s. The decline occurred mainly due to anthropogenic factors, such as bounty hunting, bycatch in gill nets, environmental toxins and water-level fluctuations. Today, the population size is around 400 seals, and its growth is slow despite the various conservation efforts. The main threats currently include incidental bycatch mortality from gill-net fishing as well as human-induced disturbances and poor breeding conditions as a result of warming climate. The small population is recovering from the historic bottlenecks, but the majority of its genetic diversity has been lost due to the isolation. To aid the growth of the population and thus its ability to adapt to environmental changes, more data are needed on the spatial ecology of the subspecies. Understanding the ecological factors behind the usage of various areas is essential for developing more effective conservation measures and improving existing measures.
In this study, we collected novel spatial data on the behaviour patterns of the Saimaa ringed seal during the ice-covered period, which is one of the most critical periods for seal conservation as breeding occurs during the ice- and snow-covered winter. Despite the importance of the winter months for the seal life cycle, the knowledge about this period has remained relatively limited. In addition to the traditional telemetry tracking methods, multidisciplinary approaches combining ecological data and computational tools were utilised. We applied computer learning to data on the locations of seal lair sites and shoreline buildings to study the effect of human disturbance on seal breeding success as there has been an increasing quantity of leisure activities taking place on the lake during the breeding season. Finally, we utilised the existing telemetry data on seal movements during the open-water season and developed an individual-based movement model to aid in the evaluation and development of effective conservation measures.
The present study showed that seal movements are highly constricted during the ice-covered period. Consequently, our findings highlight that the local conditions around the lair sites during the breeding season (mid-February to mid-March) significantly affect seal breeding success. The data on telemetry-tracked individuals revealed that home ranges during the ice-covered period are, on average, more than ten times smaller than those during the open-water season. Interestingly, female wintertime home range core areas did not overlap, which may indicate some degree of territoriality among mature females. We also observed that adult seals tend to inhabit the main breeding areas, while juveniles are mainly found in lower quality habitats. The small-scale habitat usage and potential territoriality of the philopatric females highlights the importance of breeding habitat conservation. In addition, edge areas that are mainly occupied by juveniles should also be taken into account in the development of conservation measures.
We also investigated the quality of current and potential seal breeding areas in Lake Saimaa. This study shows that almost one-third of the Lake Saimaa shoreline is already unsuitable for seal breeding due to intensive land use. Analysis of the shoreline buildings and lair locations showed that the proximity and density of buildings increases the risk of perinatal mortality, which further supports the need for lair site protection. There are approximately 70 000 buildings on the shoreline of Lake Saimaa, and an increasing proportion of the cottages are used throughout the year, including in the winter during the seal breeding season. Consequently, the possible disturbance can cause negative effects on population viability as a result of the trade-off between parental investment and survival at the individual level.
An individual-based movement model capable of predicting seal movement patterns and home range formation was developed to aid evaluation of the efficiency of conservation measures. As environmental change occurs at a fast pace, we must be able to foresee its possible effects on seal population dynamics to develop and modify effective conservation measures. The model showed that individual variation in home range formation is very large and complex process; greater knowledge of the mechanisms of individual behaviour are needed for model calibration. Therefore, further model development that includes the recent data on seal wintertime behaviour and the effects of human disturbance would help us to detect the key habitats that could be protected.
This study highlights the importance of conservation measures that take place during the most sensitive periods of the seal’s life cycle. The breeding season and the first months of pups’ independent lives are the periods when mortality is at its highest. Constricted movements during the ice-covered period, together with the impairing effects of human disturbance on seal breeding, call for protection of the breeding areas. In addition, edge areas outside the main breeding areas should also be considered for protection, as they are utilised by juvenile individuals who are in the greatest danger of becoming bycatch during the first months of the open-water season. Moreover, disturbance-free zones around the lair sites should be implemented to aid pup survival. Lake Saimaa shoreline development, in terms of new buildings, should be directed to areas that are already densely built, while the most suitable areas for seal breeding should be left undeveloped and unoccupied. In general, we should look deeply into the combined effects of climate change, human disturbance and spatial behaviour on the population dynamics of the Lake Saimaa seal.
The doctoral dissertation of MSc Lauri Liukkonen, entitled Linking spatial ecology to conservation of the endangered Saimaa ringed seal will be examined at the Faculty of Science and Forestry. The opponent in the public examination will be Docent Nina Peuhkuri, Natural Resources Institute Finland, and the custos will be Professor Raine Kortet, University of Eastern Finland.
Photo available for download at https://kuvapankki.uef.fi/A/UEF+kuvahakemisto/18500?encoding=UTF-8
