Bowhead whales, auxiliary oceanographers
Bowhead whales are crossing iced regions in spring. They dive along their path and the environmental parameters are recorded and transmitted if they are equipped with Argos satellite telemetry tags. Two different tags have been tested and their records analyzed for both oceanographic and ecological studies.
Photo: A bowhead whale (cropped from Kit Kovacs/Norwegian Polar Institute)
In situ oceanographic data collection over larger spatial scales are difficult and time consuming to conduct at best, and even more so in iced regions. However, at the same time, those regions are the most affected by climate change, and the oceanography would benefit from a closer monitoring of the water column.
On the other side, a number of marine mammal studies are done in the polar regions using satellite telemetry Conductivity-Temperature-Depth (CTD) tags. Marine mammals such as elephant seals in the Southern Ocean are the best-known examples. They can provide temperature-salinity depth profiles at high spatial resolution (since they are diving and surfacing frequently compared to automated systems like Argo floats).
Whales can also be equipped, even if this is challenging due to their short time at the surface (usually a few seconds, at most). Batteries life is also a limitation. The Argos system allows collection of low-power transmissions with concatenated data from oceanographic tags. Working in polar regions offer the advantage of more satellite-fixes than when operating closer to the Equator.
Disko Bay, in West Greenland (69°N 53°W) hosts about 1500 wintering bowhead whales (Balaena mysticetus) feeding on copepods. Late May, when much of the ocean in the area is still iced, the whales leave the Bay, and cross Baffin Bay to Canada. When the tagged whales follow their migration, it is possible to collect oceanographic data on the ice-covered route across Baffin Bay, where traditional methods would be difficult and expensive. A new satellite Conductivity-Temperature-Depth tag from Wildlife Computers, Seattle was tested and compared to another model from SMRU, University of St. Andrews.
During 7-13 May 2017, nine bowhead whales were tagged with CTD tags in Disko Bay. Transmissions lasted between 6 and 155 days and the tags provided between 9 and 393 CTD profiles. The feasibility of CTD tags on large whales, the importance of tag position on the whales, and their usefulness in collecting oceanographic data in an ice-covered and data sparse region are demonstrated in this study. Last, but not least, it enables a better understanding of whale ecology with respect to their environment in otherwise poorly sampled regions and seasons [Teilmann et al. 2020].
References & links
- Teilmann, J., Agersted, M.D., Heide-Jørgensen, M.P., A comparison of CTD satellite-linked tags for large cetaceans – bowhead whales as real-time autonomous sampling platforms Deep-Sea Research Part I, https://doi.org/10.1016/j.dsr.2020.103213.