ABSTRACT

Measurements of body length play an important role in the assessment of size and population structure of whales, allowing estimation of population parameters such as age at sexual and physical maturity. Uniquely, sperm whales can be measured from the interpulse interval (IPI) of their echolocation clicks, which contain information on the length of the head, which is allometrically related to body length. Measurements of IPI were taken from 424 acoustic recordings made between 1996 and 2019 at Kaikōura, New Zealand. Extrapolation to total length, using a new regression equation calculated from this population, revealed a significant increase in the mean length of whales visiting Kaikōura during summer in recent years (2014–2019), with no trend in the mean length for those visiting in winter. Increasing size during summer months appears to be driven by the growth of the same individuals returning summer after summer, combined with declining recruitment of new, smaller individuals. Thus, we hypothesise that the whales that visit in summer may represent an aging population. This is significant as sperm whales are a taonga [Of special significance to NZ Māori] species, top predators in the Kaikōura ecosystem, and the primary focus of the tourism industry at Kaikōura.

摘要

体长测量在评估鲸鱼的大小和种群结构方面发挥着重要作用，可以估计性年龄和身体成熟度等种群参数。独特的是，抹香鲸可以通过回声定位点击的脉冲间间隔 (IPI) 进行测量，其中包含有关头部长度的信息，头部长度与体长异速生长有关。IPI 的测量值取自 1996 年至 2019 年在新西兰凯库拉制作的 424 份录音。使用根据该种群计算的新回归方程外推到总长度，显示近年来（2014-2019 年）夏季访问凯库拉的鲸鱼的平均长度显着增加，而冬季访问的鲸鱼的平均长度没有趋势. 夏季月份体型的增加似乎是由于相同个体的生长在一个又一个夏季返回，同时新的、较小的个体的招募减少。因此，我们假设夏季来访的鲸鱼可能代表人口老龄化。这一点意义重大，因为抹香鲸是一种 taonga [对新西兰毛利人具有特殊意义] 物种，是凯库拉生态系统中的顶级掠食者，也是凯库拉旅游业的主要焦点。