National Research Institute of Fisheries Engineering, Fisheries Research Agency, Kamisu, Hasaki, Kashima, Ibaraki 314-0408, Japan.
J Exp Biol. 2010 Jan 1;213(1):146-52. doi: 10.1242/jeb.037655.
Dolphins and porpoises have excellent biosonar ability, which they use for navigation, ranging and foraging. However, the role of biosonar in free-ranging small cetaceans has not been fully investigated. The biosonar behaviour and body movements of 15 free-ranging finless porpoises (Neophocaena phocaenoides) were observed using electronic tags attached to the animals. The porpoises often rotated their bodies more than 60 deg., on average, around the body axis in a dive bout. This behaviour occupied 31% of the dive duration during 186 h of effective observation time. Rolling dives were associated with extensive searching effort, and 23% of the rolling dive time was phonated, almost twice the phonation ratio of upright dives. Porpoises used short inter-click interval sonar 4.3 times more frequently during rolling dives than during upright dives. Sudden speed drops, which indicated that an individual turned around, occurred 4.5 times more frequently during rolling dives than during upright dives. Together, these data suggest that the porpoises searched extensively for targets and rolled their bodies to enlarge the search area by changing the narrow beam axis of the biosonar. Once a possible target was detected, porpoises frequently produced short-range sonar sounds. Continuous searching for prey and frequent capture trials appeared to occur during rolling dives of finless porpoises. In contrast, head movements ranging +/-2 cm, which can also change the beam axis, were regularly observed during both dives. Head movements might assist in instant assessment of the arbitrary direction by changing the beam axis rather than prey searching and pursuit.
海豚和鼠海豚具有出色的生物声纳能力，它们利用这种能力进行导航、测距和觅食。然而，生物声纳在自由游动的小型鲸类中的作用尚未得到充分研究。我们使用附着在动物身上的电子标签观察了 15 只自由游动的江豚（Neophocaena phocaenoides）的生物声纳行为和身体运动。海豚在潜水过程中，身体通常会绕着身体轴旋转超过 60 度，平均每次潜水持续 186 小时的有效观察时间中，这种行为占潜水持续时间的 31%。滚动潜水与广泛的搜索努力有关，滚动潜水时间的 23%用于发声，几乎是垂直潜水发声比例的两倍。海豚在滚动潜水时比在垂直潜水时更频繁地使用短间隔点击声纳，频率是后者的 4.3 倍。突然的速度下降表明个体进行了转身，这种情况在滚动潜水时比在垂直潜水时发生的频率高 4.5 倍。这些数据表明，海豚通过改变生物声纳的狭窄波束轴来广泛搜索目标并滚动身体以扩大搜索区域。一旦发现了可能的目标，海豚就会频繁地发出短距离声纳声。连续搜索猎物和频繁的捕获尝试似乎发生在江豚的滚动潜水期间。相比之下，头部上下移动 2 厘米，也可以改变波束轴，这种运动在两种潜水时都经常观察到。头部运动可能通过改变波束轴而不是搜索和追逐猎物来帮助即时评估任意方向。
