Studies on harbour porpoise Phocoena phocoena incidentally caught by fishing gears around Japan and the mechanism of bycatch

分析了鲸目动物研究所收集的黑线江豚搁浅记录，4、5月份报告的搁浅比例较高。报告最多的搁浅地点是Usujiri(36人)，其次是Shiraoi(7人)。本次调查确认的副渔获个体数为16只，从卵巢观察来看，均为未成熟个体。在小田鱼水族馆的池塘中对个体进行了通过性实验，发现50%通过孔的宽度为39 cm，并随着习惯性的增加而变窄。进行了tau点分析，找出了接近目标的速度控制。Tau呈线性增加，Tau-Dot估计为0.772。在靶前2秒和0.7秒有两个tau的拐点。从行为学观察，在2ms和5ms处有两个Crick间期峰值，这意味着回声定位的目标是1.5m和4m。这些结果表明，利用回波定位技术对江豚目标的识别发生在目标前4m和1.5m处。

The stranding records of Harbour porpoise Phocena phocoena collected by Institute of Cetacean Research was analyzed and the high proportion of the stranding was reported on April and May. The most frequently reported stranding place was Usujiri (36 individuals) and the next was Shiraoi (7 individuals). The number of bycatch individuals confirmed by our survey was 16. From the observation of ovary, they were immature. The passability experiment was conducted in the pool of Otaru Aquarium for an individual and found that the 50% passable aperture width was 39cm and become narrower as the habituation. The tau dot analysis was conducted to find the approach speed control to the target. Tau was increased linearly and tau-dot was estimated as 0.772. There were two inflection points of tau at 2sec and 0.7sec before the target. From the behaviour observation, there were two peaks of inter crick intervals at 2ms and 5ms, which means the target of the echo-location was 1.5m and 4m. These result suggest that the target recognitions of harbour porpoise was occurred at 4m and 1.5m before the target using echo-location.