IOMRC and The UWA Oceans Institute, School of Animal Biology and Centre for Marine Futures , University of Western Australia (M470) , 35 Stirling Highway, Crawley, Western Australia 6009 , Australia.
School of Civil, Environmental and Mining Engineering and UWA Oceans Institute, University of Western Australia (M470), 35 Stirling Highway, Crawley, Western Australia 6009, Australia; Australian Institute of Marine Science, c/o UWA Oceans Institute (MO96), 35 Stirling Highway, Crawley, Western Australia 6009, Australia.
R Soc Open Sci. 2016 Mar 23;3(3):150668. doi: 10.1098/rsos.150668. eCollection 2016 Mar.
Body size and age at maturity are indicative of the vulnerability of a species to extinction. However, they are both difficult to estimate for large animals that cannot be restrained for measurement. For very large species such as whale sharks, body size is commonly estimated visually, potentially resulting in the addition of errors and bias. Here, we investigate the errors and bias associated with total lengths of whale sharks estimated visually by comparing them with measurements collected using a stereo-video camera system at Ningaloo Reef, Western Australia. Using linear mixed-effects models, we found that visual lengths were biased towards underestimation with increasing size of the shark. When using the stereo-video camera, the number of larger individuals that were possibly mature (or close to maturity) that were detected increased by approximately 10%. Mean lengths calculated by each method were, however, comparable (5.002 ± 1.194 and 6.128 ± 1.609 m, s.d.), confirming that the population at Ningaloo is mostly composed of immature sharks based on published lengths at maturity. We then collated data sets of total lengths sampled from aggregations of whale sharks worldwide between 1995 and 2013. Except for locations in the East Pacific where large females have been reported, these aggregations also largely consisted of juveniles (mean lengths less than 7 m). Sightings of the largest individuals were limited and occurred mostly prior to 2006. This result highlights the urgent need to locate and quantify the numbers of mature male and female whale sharks in order to ascertain the conservation status and ensure persistence of the species.
体型大小和成熟年龄是衡量一个物种灭绝脆弱性的指标。然而，对于那些无法被束缚进行测量的大型动物来说，这两个指标都很难估计。对于像鲸鲨这样的大型物种，体型大小通常是通过目测来估算的，这可能会导致误差和偏差的产生。在这里，我们通过将西澳大利亚宁格鲁珊瑚礁使用立体视频摄像机系统收集的测量数据与目测数据进行比较，研究了与目测鲸鲨体长相关的误差和偏差。使用线性混合效应模型，我们发现随着鲨鱼体型的增大，目测体长存在低估的偏差。使用立体视频摄像机时，可能成熟（或接近成熟）的较大个体的检测数量增加了约 10%。然而，两种方法计算的平均体长是可比的（5.002 ± 1.194 和 6.128 ± 1.609 m，标准差），这证实了宁格鲁种群主要由未成熟的鲨鱼组成，这是基于已发表的成熟体长得出的结论。然后，我们整理了 1995 年至 2013 年期间在全球鲸鲨聚集区采集的总长度数据集。除了东太平洋有报道称存在大型雌性鲸鲨的地点外，这些聚集区也主要由幼鲨组成（平均长度小于 7 米）。最大个体的目击记录有限，主要发生在 2006 年之前。这一结果强调了迫切需要定位和量化成熟雄性和雌性鲸鲨的数量，以确定该物种的保护状况并确保其持续存在。
