Narwhal (Monodon monoceros) sightings and population estimates for the Canadian High Arctic 2002-2004

Aerial surveys of narwhals (Monodon monoceros) were conducted in the Canadian High Arctic during the month of August from 2002 to 2004. The surveys covered the waters of Barrow Strait, Prince Regent Inlet, the Gulf of Boothia, Admiralty Inlet, Eclipse Sound, and the eastern coast of Baffin Island, using systematic sampling methods. Fiords were flown along a single transect down the middle. Near-surface population estimates increased by 1.9%-8.7% when corrected for perception bias. The estimates were further increased by a factor of approximately 3, to account for individuals not seen because they were diving when the survey plane flew over (availability bias). These corrections resulted in estimates of 27 656 (SE = 14 939) for the Prince Regent and Gulf of Boothia area, 20 225 (SE = 7285) for the Eclipse Sound area, and 10 073 (SE = 3123) for the East Baffin Island fiord area. The estimate for the Admiralty Inlet area was 5362 (SE = 2681) but is thought to be biased. Surveys could not be done in other known areas of occupation, such as the waters of the Cumberland Peninsula of East Baffin, and channels farther west of the areas surveyed (Peel Sound, Viscount Melville Sound, Smith Sound and Jones Sound, and other channels of the Canadian Arctic archipelago). Despite these probable biases and the incomplete coverage, results of these surveys show that the summering range of narwhals in the Canadian High Arctic is vast. If narwhals are philopatric to their summering areas, as they appear to be, the total population of that range could number more than 60 000 animals. The largest numbers are in the western portion of their summer range, around Somerset Island, and also in the Eclipse Sound area. However, these survey estimates have large variances due to narwhal aggregation in some parts of the surveyed areas.

2002年至2004年8月，研究团队于加拿大高北极地区开展了独角鲸（Monodon monoceros）的航空调查。本次调查采用系统抽样（systematic sampling）方法，覆盖水域涵盖巴罗海峡、雷根特王子湾、布西亚湾、阿德默勒尔蒂湾、日食湾以及巴芬岛东海岸；峡湾调查则沿中部单条样线飞行开展。经感知偏差（perception bias）校正后，近水面种群估计值提升1.9%~8.7%；为弥补因调查飞机飞越时个体潜水未被观测到的可用性偏差（availability bias），估计值需再乘以约3的系数。经上述校正后，雷根特王子湾与布西亚湾区域的种群估计值为27656（标准误SE=14939），日食湾区域为20225（SE=7285），巴芬岛东峡湾区域为10073（SE=3123）；阿德默勒尔蒂湾区域的估计值为5362（SE=2681），但该结果被认为存在偏差。
由于无法在其他已知的独角鲸栖息区域开展调查，例如东巴芬坎伯兰半岛水域，以及本次调查区域以西的航道（皮尔海峡、梅尔维尔子爵海峡、史密斯海峡、琼斯海峡及加拿大北极群岛其他航道）。尽管存在上述潜在偏差且调查覆盖范围不全，本次调查结果表明，加拿大高北极地区独角鲸的夏季栖息范围极为广阔。若如观测所示，独角鲸对夏季栖息区域具有恋栖地习性（philopatric），那么该栖息范围内的种群总数可超过60000头。夏季种群数量最多的区域位于其栖息范围西部的萨默塞特岛周边，以及日食湾区域。不过由于独角鲸在调查区域的部分区域集群分布，本次调查估计值存在较大的方差。