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.

(Table 1) Krill (Euphausia superba) biomass estimates at South Georgia Island from 2001-2005

The South Georgia region supports a large biomass of krill that is subject to high interannual variability. The apparent lack of a locally self-maintaining krill population at South Georgia means that understanding the mechanism underlying these observed population characteristics is essential to successful ecosystem-based management of krill fishery in the region. Krill acoustic-density data from surveys conducted in the early, middle and late period of the summers of 2001 to 2005, together with krill population size structure over the same period from predator diet data, were used with a krill population dynamics model to evaluate potential mechanisms behind the observed changes in krill biomass. Krill abundance was highest during the middle of the summer in 3 years and in the late period in 2 years; in the latter there was evidence that krill recruitment was delayed by several months. A model scenario that included empirically derived estimates of both the magnitude and timing of recruitment in each year showed the greatest correlation with the acoustic series. The results are consistent with a krill population with allochthonous recruitment entering a retained adult population; i.e. oceanic transport of adult krill does not appear to be the major factor determining the dynamics of the adult population. The results highlight the importance of the timing of recruitment, especially where this could introduce a mismatch between the peak of krill abundance and the peak demand from predators, which may exacerbate the effects of changes in krill populations arising from commercial harvesting and/or climate change.