Abstract
The Japanese Whale Research Program under Special Permit in the Antarctic(JARPA) and in the Northwest Pacific Ocean (JARPN) has been conducted by the Institute of Cetacean Research(ICR). The lethal component of the JARPA and JARPN was an explosive harpoon used as the primary method of killing whales. In order to improve the method of whale killing, ICR and Kyodo Senpaku made improvements to the explosive harpoon. The newly developed Norwegian grenade and the improved Japanese grenade were compared to the traditional Japanese grenade. Trial firing using cubic target objects and practical experiments were conducted from 2000 to 2004. The new Norwegian grenade and the improved Japanese grenade decreased the time to death(TTD; the time from the first harpoon strike to death of the whale) and increased the instantaneous death rate(IDR) significantly compared to the traditional Japanese grenade. Both the improved Japanese and new Norwegian grenades have common features of low rate of misfire and short explosive distance (the distance from a hit point of the harpoon to point of the grenade explosion), which increased a rate of the explosion of the grenade inside the whale's body. Comparing the two types of grenades, the Norwegian grenade had a higher IDR for smaller whales. It was also easy to handle and load because of its integrated structure. The improved Japanese grenade had the shortest TTD and the lowest rate of misfire. As there is not much difference in actual performance between the two, the lower price of the Japanese grenade may be an important factor in selecting future whaling devices.
