By: Charmain D Hamilton, Christian Lydersen, Jon Aars and Kit M Kovacs // Norwegian Polar Institute. Martin Biuw, Tore Haug and Nils Øien // Institute of Marine Research. Andrei N Boltunov and Varvara Semenova // Marine Mammal Research and Expedition Centre, Moscow. Erik W Born, Mads Peter Heide-Jørgensen, Kristin L Laidre[1], Aqqalu Rosing-Asvid and Fernando Ugarte // Greenland Institute of Natural Resources, Nuuk. Rune Dietz and Signe Sveegaard // Aarhus University. Lars P Folkow, Lisa E Kettemer, Erling S Nordøy and Audun H Rikardsen[2] // UiT The Arctic University of Norway. Dmitri M Glazov and Olga V Shpak // AN Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow. Øystein Wiig // Natural History Museum, University of Oslo

[1] Also affiliated with the Applied Physics Lab, University of Washington, Seattle
[2] Also affiliated with the Norwegian Institute of Nature Research

Large-scale ongoing environmental change and increasing levels of human activity in the northeast Atlantic Arctic has created a special need to identify marine mammal “hotspots” to help guide management and conservation efforts. Observational data from this area are limited because there are few human settlements, and logistical difficulties such as large expanses of sea ice and low levels of light up to six months of the year limit traditional surveys at sea. Additionally, the cryptic, dispersed nature of most Arctic marine mammal populations limits their detectability.

Thus, we collated all available data from biotelemetry instruments deployed on marine mammals in the Greenland Sea and Barents Sea between 2005 and 2019 to investigate the occurrence of marine mammal hotspots and areas of high species richness. In addition, the gap analysis implicit in such a hotspot analysis serves to identify regions and species on which more research is needed. The resulting dataset consisted of tracking information from 585 individuals from 13 different species (73 ringed seals Pusa hispida, 22 bearded seals Erignathus barbatus, 60 harbour seals Phoca vitulina, 51 walruses Odobenus rosmarus, 20 harp seals Pagophilus groenlandicus, 20 hooded seals Cystophora cristata, 235 polar bears Ursus maritimus, 23 bowhead whales Balaena mysticetus, 39 narwhals Monodon monoceros, 18 white whales Delphinapterus leucas, 10 blue whales Balaenoptera musculus, 6 fin whales Balaenoptera physalus, 10 humpback whales Megaptera novaeanglidae), collected by scientists from 11 different institutions including three partners within the Fram Centre.

Various hotspot identification methods were explored, but the Getis-Ord Gi* method was chosen as the best to analyse and display the results. Getis-Ord Gi* hotspots were calculated for each species as well as for all species combined, and areas of high species richness were identified for summer/autumn (Jun-Dec), winter/spring (Jan-May), and the entire year.

Locations were plotted within a 10 × 10 km grid, and the number of individuals of each species (individual hotspots analysis), the number of locations for each species (location hotspots analysis) and the number of species (species richness) were calculated for each grid cell. The 10 × 10 km grid was chosen as a compromise between showing large-scale patterns across the Greenland and Barents Seas and showing patterns within small fjords in Svalbard and Greenland.

Getis-Ord Gi* individual hotspots (a, c, e) and location hotspots (b, d, f) for the 13 species tagged around Svalbard and northeast Greenland over the entire year (a, b), during the summer/autumn (c, d) and during the winter/spring (e, f). Increasing intensities of red indicate hotspots of different levels of statistical significance. Figure from Hamilton et al (2021) Marine Ecology Progress Series

Hotspots (both individual and location) for all 13 marine mammal species were identified around the Svalbard archipelago, in coastal areas of northeast Greenland and in the marginal ice zone (MIZ) of the Greenland and northern Barents Seas. Similarities and differences among hotspot locations for each species highlight the ecological niches the animals occupy.

For example, bearded seals and walruses are both benthic foragers that feed in shallow, coastal regions and thus they would be expected to have similar hotspots in regions where both species occur. Similarities would also be expected among species with tightly coastal distributions, such as adult ringed seals and white whales in Svalbard, or for species that are heavily dependent on specific environmental features, such as sea ice in the case of subadult ringed seals and polar bears in the MIZ. Likewise, species that dive to intermediate depths in open ocean areas (harp seals and hooded seals) would be expected to have similar distributions.

However, it must be kept in mind that a species can have quite different habitat and movement patterns in different areas within its overall range. For example, species such as ringed seals, bearded seals, and white whales have limited seasonal movements in the Svalbard region, while these same species display quite pronounced seasonal movements, as they follow the advance and retreat of the sea ice in the Bering–Chukchi–Beaufort region. Fjords and coastal areas around the Svalbard archipelago and northeast Greenland were identified as hotspots for most of the marine mammals included in our analyses and these same areas were also identified as having the highest species richness in the northeast Atlantic Arctic.

It is important to note that areas with little tagging effort can be underrepresented in this kind of hotspot analysis, which is likely the case for northeast Greenland and certainly the case for the area around Franz Josef Land. Despite this bias, the results of our marine mammal hotspot analyses clearly show that the MIZ of the Greenland Sea and northern Barents Sea, and the coastal regions and fjords of Svalbard and northeast Greenland are very important areas for Arctic marine mammals.

Protection in these areas is needed to help guard against a myriad of threats posed by climate change and expanding human activities in the northeast Atlantic Arctic. Because the location and extent of the MIZ varies considerably both within and between years, conservation and management plans targeting this important marine mammal habitat will need to be flexible in both space and time in order to protect the many species that use this dynamic zone. It is noteworthy that many seabird and fish species are also found in the MIZ, due to its high summer pulse of biological productivity, as well as in coastal regions of Svalbard and East Greenland. Thus, conservation measures targeting these regions will positively benefit many groups of Arctic biota.

Further reading:

Hamilton CD, Lydersen C, Aars J, Biuw M, Boltunov AN, Born EW, Dietz R, Folkow LP, Glazov DM, Haug T, Heide-Jørgensen MP, Kettemer LE, Laidre KL, Øien N, Nordøy ES, Rikardsen AH, Rosing-Asvid A, Semenova V, Shpak OV, Svegaard S, Ugarte F, Wiig Ø, Kovacs KM (2021) Marine mammal hotspots in the Greenland and Barents Seas. Marine Ecology Progress Series 659: 3-28