Accurate spatial ecology of endangered Saimaa ringed seals as a base for fishing closure determination

Abstract

Saimaa ringed seal (Phoca hispida saimensis) is an endangered subspecies living landlocked in Lake Saimaa, southeastern Finland. One of the major threats of this small population (ca 370 seals) is by-catch due to mainly recreational gill net fishing. For mitigating by-catch mortality varied fishing closures and restrictions have been established in the lake over time. The fishing restrictions cover year round ban of the most dangerous fishing methods and springtime (15.4.-30.6.) gill net ban to protect especially the pups. In this study, we describe the usage of accurate spatial ecology data of the Saimaa ringed seals as a base for conservation measures. Telemetry tracking data of both; juveniles and adults (N= 41) together with the lair and haul out locations were used to determine the key distribution area for conservation measures. Radius of average home range (5.2 km) is buffered over known lair and haul out sites, to create overall occurrence area of the seals. The distribution area usage of the seals indicate that the seals occur almost all of lake surface area. This method approach was already utilized by government Decree (259/2016), and now closures are covering spatially ca. 60% of the lake surface area (4 400 km2). However, bycatch mortality still exists, which indicate that closures are inadequate and whole distribution area would need more fishing closures. Furthermore, the temporal gill net ban is underestimated as nowadays the by-catch mortality takes place outside the temporal ban.