Changes in haul-out use by spotted seals (Phoca largha) on Rebun Island, Hokkado, Japan, in response to controls on harmful animals

Abstract

Harmful animal controls on spotted seals on Rebun Island have been conducted each spring since 2010 due to an increase in the number of seals and damage to local fisheries. To evaluate the influences of controls on seals, we used the numbers of haul-out sites and hauled-out seals, and photo-identification to study differences in the usage patterns of haul-out sites by seals before and after controls. As a result, two major changes were confirmed. Firstly, in spring after controls, the numbers of hauled-out seals at Northern Rebun (NR) greatly decreased, while at Bensashi (Ben) on the southern side of Rebun they greatly increased, compared to spring prior to controls. Secondly, the number of identified seals observed at both NR and Ben (NR-Ben) increased after controls, while most of the seals that changed to NR-Ben after controls were observed only at NR (NR-NR) before controls. Additionally, most of the seals using NR-Ben were observed year-round. The controls had a direct influence on reducing the numbers of seals in the controls area mainly during the period of controls. However, many seals that avoided the controls area used other haul-out sites, and the numbers of year-round-seals on Rebun increased after controls.