Improving the accuracy of estimations on natality and pre-weaning pup mortality of the endangered Saimaa ringed seal

Abstract

The Saimaa ringed seal (Phoca hispida saimensis) is the only endemic mammal in Finland. It inhabits fresh water Lake Saimaa, and its population size is around 370 individuals with 60-80 pups born annually. One of the most critical threats for the population is climate change. The ringed seal is dependent on sufficient ice and snow cover for a breeding habitat, and mild winters have a negative effect on pup survival. In addition, the reliability of the population estimates, which are based on annual lair censuses, suffers when there is no sufficient snow cover for subnivean lairs or when the lairs are not detectable during the census due to early melting. For improving the seal stock monitoring the underwater surveys at the seal’s lair sites were annually conducted soon after ice break up during 2014-2017. Divers were looking for placentas as a proof of born pups, and pup carcasses or other remains of dead pups. Altogether 584 lair sites were investigated by divers. The underwater surveys increased the number of born pups by 29, which is 10% of the total observed natality during the study years. In addition, 13 dead pups were found during the surveys, which is 32% of all pups observed dead before weaning during the study. The underwater surveys at the seal’s lair sites are effective method to improve the accuracy of the population estimations especially during mild winters. Reliable knowledge on natality and pre-weaning mortality of the Saimaa ringed seal is essential for the assessment of the conservation needs and effectiveness of conducted conservation acts.

References: Auttila, M. 2015. The endangered Saimaa ringed seal in a changing climate - challenges for conservation and monitoring. PhD thesis, University of Eastern Finland, Joensuu, Finland.

Auttila, M., M. Niemi, T. Skrzypczak, M. Viljanen & M. Kunnasranta. 2014. Estimating and mitigating perinatal mortality of the endangered Saimaa ringed seal (Phoca hispida saimensis). Annales Zoologici Fennici 51:526−534.