Long-term effects of land use on perinatal mortality in the Endangered Saimaa ringed seal population

Abstract

Human disturbance can affect the viability of wildlife populations partly through its effects on breeding success. Land use as a form of disturbance may do so by fragmenting the key environments of certain species. We used statistical pattern recognition methods to estimate the long-term effects of human disturbance on the Endangered, landlocked population of the Saimaa ringed seal Pusa hispida saimensis by examining how various densities of buildings on lake shores have altered the survival of juveniles and the persistence of the population. In addition, we examined whether disturbance caused by different intensities of land use would further reduce the long-term persistence of the population. We also provide estimates of the quality of Lake Saimaa shorelines as breeding habitat in relation to building density. Our results show that at present, the lairs of Saimaa ringed seals are located closer to potential sources of human disturbance than they were in the past and that land use intensity has an effect on juvenile mortality. Perinatal mortality increases significantly in more densely developed areas, where the nearest building is within 800 m of a birth lair. In addition, 29% of the shoreline of Lake Saimaa is no longer suitable for ringed seals due to intensive land use. Our results illustrate how human disturbances can significantly compromise juvenile survival and therefore the long-term existence of this Endangered population.

Winter behavior of Saimaa ringed seals: Non-overlapping core areas as indicators of avoidance in breeding females

“…The ringed seals spent an average of almost six hours during every second day hauled out on subnivean snow/ice structures, which is similar to duration of the haul out patterns in the summer [20]. Most conservation efforts have been typically focused on the seal birth sites on Lake Saimaa (e.g., [21, 37, 40, 54]), but our findings also highlight the conservation needs of winter time haul out sites in general.…”

“…The core area sizes of all tagged seals (1.7 km 2 ) found in this study, which equates ca. 700 m radius, supports the discovery of 800 m buffer zones in studies on the home range size of the nursed pup [21] and the link between human induced disturbances and an increased perinatal pup mortality [40]. The minimum magnitude of the buffer zones around birth lairs should be taken into account during land usage planning to mitigate the effects of disturbances caused by humans.…”

“…Although the seal population has slowly increased during the last decade [68], the current population, at less than 400 seals, is far from the potential population level. When calculating the theoretical carrying capacity of Lake Saimaa by regarding the core areas and accounting for the avoidance of females, and the fact that already almost third of the lake area is no longer suitable for seal lair sites due to intensive land usage [40], over 4 000 Saimaa ringed seals (sex ratio 1:1 [37]) could occupy the lake. According to Liukkonen et al [40], the Saimaa ringed seals lairs are currently located closer to the sources of anthropogenic disturbances than they were in earlier times, and the land use intensity has a negative effect on neonate survival.…”

“…The ice thickness and the snow cover of the subnivean lair have direct implications for the survival of ringed seal pups. Changing climate conditions with cumulative effects of varied anthropogenic factors (e.g., [40]) may have drastic influences on the breeding habitats and long-term survival of the population. Seals may be able to cope with the changing environments due to behavioral plasticity, such as the timing of reproduction and a shortened nursing period [13, 26, 69, 70].…”

“…To date, fishing restrictions have been established (e.g., [8]), and the negative effects of mild winters have been mitigated by a unique method in which volunteers pile snow along the shorelines, and the ringed seals adopt these drifts as their breeding and haul out sites [39]. Recent findings on the negative effects of land usage and other human activities on the Saimaa ringed seal population [40] suggest urgent spatial conservation needs during the breeding season, when the ringed seal is suggested to be the most sensitive to disturbance.…”