Claude R. JOIRIS

Very low biodiversity of top predators—seabirds and marine mammals—in the high Arctic Ocean

Claude R. JOIRIS1, 2*

1Laboratory for Polar Ecology (PolE), 26130 Saint-Restitut, France;2Conservation Biology Unit, Royal Belgian Institute for Natural Sciences (RBINS), 1000 Brussels, Belgium

During the ARK-XXIII/3 expedition of icebreaking RVin the high Arctic Ocean (north of 73°N) from 25 August to 10 October 2008, 550 transect counts lasting 30 min were devoted to seabird and marine mammal counts from the bridge. In the whole area, the three most numerous species, kittiwake, fulmarand Brünnich’s guillemotrepresented 90% of the total of 12000 individuals registered, followed by ivory gull, black guillemotand Ross’s gull. Four geographical zones were recognized on the basis of number of species and density. Both were especially low in the deeper areas (mean depth of 3000 m), both ice-free and heavily ice-covered: 0.3 birds per 30 min count belonging to three and four species respectively. The most numerous species was kittiwake with 0.25 per count (50 individuals) in the ice-covered area. Pinniped numbers were very low as well, the most numerous of the four species tallied being 20 harp sealsand 10 ringed seal. Seven polar bearswere encountered. These observations were basically confirmed during 12 helicopter flights lasting one hour each with very low numbers: 50 kittiwakes and 13 harp seals, almost none in the ice-covered deep zone. A comparison between data obtained from ship and from helicopter seems however to reflect the importance of seabird followers including for long distances. The only cetaceans were two adult belugastallied from helicopter.

seabirds, marine mammals, at-sea distribution, high Arctic Ocean

1 Introduction

At-sea observations of marine “top predators” are essential to understanding the ecological drivers of many species. Although technologies like the Global Positioning System and Geolocator tags are helping to identify environmental parameters that might affect their behaviour, only a limited number of individuals can be targeted. At-sea transects can better identify assemblage areas, and combined with on-board sensors which measure spatially and temporally fine-scale information, we are able to detect the events or features which lead to these accumulations of marine life. This is particularly helpful in remote areas like the high Arctic Ocean, which have generally poor satellite coverage. The area is very poorly studied, being accessible by icebreakers only. The importance of hydrographic features such as water masses and fronts, pack ice and ice edge on seabird distribution was detected decades ago (Joiris, 1978; Pocklington, 1979). The relationship of seabirds and marine mammals to such frontal regions has been previously examined (e.g. Ainley et al., 1998; Hyrenbach et al., 2007; Joiris and Falck, 2011; Ribic et al., 2011; Force et al., 2015; Joiris, 2018; Yurkowski et al., 2018).

2 Materials and methods

In the frame of our long-term study on the at-sea distribution of “top predators”—seabirds and marine mammals—in polar ecosystems, our main aims are to study the environmental factors explaining their distribution at sea, as well as to detect possible temporal and spatial evolutions, with special attention to global climatic changes. Seabird and marine mammal quantitative at-sea distribution was studied during the high Arctic circumpolar expedition ARK-XXIII/3 of icebreaking RVfrom the eastern end of the North-West Passage (130°W) on 25 August, to 10 October 2008 off Northern Norway (29°E). Data selected for this article were all collected north of 73°N. Transect counts were conducted from the bridge (18 m above sea level) without width limitation during 30 min periods, on a continuous basis as ship operations, light and visibility conditions allowed. When detected, followers were included as far as possible only once per count. More details on our counting method have been described and discussed previously (Joiris, 2011, 2018a; Joiris and Falck, 2011; Joiris et al., 2014). Taking into account the importance of followers and the great heterogeneity in the distribution of top predators, basic data are presented in this article, without correction e.g.for the diving pattern of the animals. Nor are calculations such as density presented. Counts were also run during helicopter flights, lasting between 40 and 90 min along return transects (mean: duration 60 min, speed 100 n mile·h?1, height 200 feet).

3 Results

During the northern part of theexpedition in the high Arctic Ocean (north of 73°N), totals of 12135 seabirds, 36 identified pinnipeds and 7 polar bears were encountered during 550counts. This represented a mean value of 22 birds per count. Most numerous species were 5000 kittiwakes, 4000 fulmarsand 2000 Brünnich’s guillemots. Together, these three species represented thus 90% of the total, followed by 400 ivory gulls, 340 black guillemotsand 170 Ross’s gulls. Among the pinnipeds, 20 harp sealsand 13 ringed sealwere the most numerous of the four species tallied. Seven polar bearswere registered (Table 1).

Moreover, striking very important geographical differences in seabird abundance were registered, allowing to identify four zones (A to D) with mean values of 0.3, 17, 0.3 and 93 birds per count respectively. The majority of counts did not provide any bird contact at all in zones A and C. These zones correspond to differences in hydrological features such as water depth, water temperature and salinity, and ice cover (Table 1, Figure 1). Zones A and C were characterized by their very deep bathymetry, 3000 m mean depth: They both correspond to the deep Arctic basin, zone A being almost ice free, zone C very closely ice-covered. Seabird numbers were extremely low in zone A: 12 individuals only representing 4 species. Zones B and C correspond to the ice-free and ice-covered parts south and north of 80°N, below and above the continental shelf respectively. In zone B ten species were tallied, mainly 4000 kittiwakes with numbers up to 100 to 150 per count, and a group of 250 out of effort close to count 379, 220 ivory gulls and 170 Ross’s gulls. In zone C the very low numbers correspond to one species mainly: 40 ivory gulls. Zone D corresponds to the Laptev, Kara and Barents seas off North Norway: 4000 fulmar, 2000 Brünnich’s guillemots and 1000 kittiwakes by far dominated in numbers. Number of species in zone D was 13 out of a total of 15 for the whole expedition (Table 1, Figure 2). Such data resemble the ones obtained in the Greenland Sea and Fram Strait. Some other seabird observations deserve special mention: three Steller’s eidersat count 476, two juvenile kittiwakes at counts 722 and 723 on 7 October, and two juvenile Brünnich’s guillemots at count 764 on 9 October (see Figure 1).

Figure 1 Seabirds recorded during Polarstern expedition ARK-XXIII/3 (partim north of 73°N) from 25 August to 10 October 2008; N = total number, mean per count. Four zones were recognised (A to D, see text); count numbers; positions and hydrological data from Jokat (2009).

Table 1 “Top predators”—seabirds and marine mammals—recorded during Polarstern expedition ARK-XXIII/3 (partim north of 73°N) from 25 August to 10 October 2008. N = total number of individuals, all seabirds; n = number of 30 min transect counts: mean per count; positions and hydrological data from Jokat (2009)

Figure 2 Seabirds and marine mammals recorded during Polarstern expedition ARK-XXIII/3 (partim North of 73°N) from 25 August to 10 October 2008. Numbers per 30 min count: a, fulmar Fulmarus glacialis; b, kittiwake Rissa tridctyla; c, ivory gull Pagophila eburnea; d, Ross’s gull Rhodostethia rosea; e, Sabine’s gull Xema sabini; f, polar bear Ursus maritimus.

Numbers of pinnipeds were very low as well, with none in zone A, 17 identified individuals in zone B of which ten harp sealsand six ringed seals, eight seals in zone C and 11 in zone D, mainly harp seals. One harp seal mother with pup was tallied at count 458. Seven polar bearswere observed in the Outer Marginal Ice Zone of zone B (Table 1, Figure 2) as well as two individuals out of effort close to counts 376 and 447.

No cetaceans at all were tallied from the ship. Two factors can explain this absence of data: or they are basically absent from this area, or they left already to their southern overwintering areas.

Countings were also realised during 12 return helicopter flights from 31 August to 4 October, i.e. six counts covering zone B and six zone C. Numbers were extremely low as well, with the exception of 48 kittiwakes, of which 47 in zone B (33 in one count) (Table 2). The main pinniped concentration consisted in 11 harp seals in zone B. Many ringed seals holes (15) were tallied in zone C during flight number seven. The same two adult belugasonly were encountered twice from helicopter during return flight number five (Table 2).

Table 2 “Top predators”—seabirds and marine mammals—recorded during 12 return helicopter flights during Polarstern expedition ARK-XXIII/3 (partim north of 73°N) between 31 August and 4 October 2008

4 Discussion

Densities of seabirds and pinnipeds were extremely low in zones A and C with a mean value of 0.30 birds per count. They were much higher in zone D with 90 birds per count. Numbers were intermediate in zone B with 17 birds per count, representing thus ratios of one and more than two orders of magnitude respectively. The main factor influencing these differences does not seem to be ice coverage since zone A was basically ice-free with a mean ice-coverage of 5%, while zone C was completely ice-covered with a mean coverage of 95%. Ice cover did thus not seem to play a major role. Visually the hydrological main factor seems to be water depth corresponding to the continental shelf, zones A and C showing mean depths of 3000 m, compared to 1300 m in zone B and 225 m in zone D (Table 1, Figures 1 and 3).

The comparison of data collected from the bridge ofand from helicopter flights in zone B are fitting very well for harp seal with mean values of 0.007 and 0.0065 per kilometer from ship and helicopter respectively (calculation based on duration and speed). They were however very different for kittiwake with 2.7 and 0.02 km respectively, i.e. two orders of magnitude (Tables 1 and 2). Such a huge discrepancy between ship and helicopter by one order of magnitude for seabird data does not seem to be due to differences in detection. The basic explanation might thus become that birds are mainly followers including on long distances (one to a few days). Table 3 presents such examples, the kittiwake numbers being grouped in successive counts; together these five groups of counts concern 3300 individuals, including 2035 in one group of 33 counts, i.e. by far the majority of the 4000 kittiwakes registered in zone B in 260 counts (Table 3, Table 1). The importance of following seabirds could always be the case in marine ornithology but becomes especially obvious in areas with extremely low ships density—e.g. during this expedition, no ship at all were encountered. This can be extrapolated and generalised to similar zones with very low ships density such as the high Arctic (Joiris et al., 2016; this paper) or the North-East Passage off Siberia (Joiris, in prep).

Figure 3 Ice conditions recorded during Polarstern expedition ARK-XXIII/3 (partim north of 73°N) from 25 August to 10 October 2008: a, situation on 22 September 2008; b, situation on 10 October 2008; zones: see Table 1 and Figure 1. From: Institute of Environmental Physics, University of Bremen, Germany.

Table 3 Numbers of kittiwakes Rissa tridactyla recorded from the bridge of Polarstern during expedition ARK-XXIII/3 (partim north of 73°N) during successive counts in zone B; starting count number; N = number of kittiwakes; n = number of counts; mean per count (see Table 1 and Figure 1)

On the other hand, such data also fit the general phenomenon of hotspots, the majority of observations being centralised in a limited surface of the study area (e.g. my synopsis in Joiris, 2018; Yurkowski et al., 2018).

Data were already collected by this team in the same area, in the ice-covered area mainly along the Lomonosov Ridge in July–September 2014 (Joiris et al., 2016). They basically fit the observations presented here, with very low numbers of species and of individuals. Both data sets show a full compatibility with the model predictions of Arctic seabird species distribution (Huettmann et al., 2011; Humphries and Huettmann, 2014), even if our data are lower than predicted. This might be due to temporal limitations or to the fact that many seabirds breeding on the coast actually don’t reach the open ocean and thus escape at-sea observations.

5 Conclusion

Data collected on board icebreaking RVfrom August till October 2008 reflect the very low numbers of seabird and marine mammal species and densities in the high Arctic Ocean, many 30 min counts from the ship showing no contact at all in some areas corresponding to the deep Arctic basin. In contrast, ice-coverage did not play a major role. A comparison between ship and helicopter observations seems to reflect the presence of many seabird followers, so that the densities registered from ships might provide an over-estimation of actual densities in areas with very low ships presence.

These data confirm previous results collected by this team in the same area (Joiris et al., 2016) and basically fit with the predictive model for number of seabird species by Huettmann et al. (2011).

They reflect an extremely low biodiversity with a few species only, of which one was dominating in numbers in each geographical zone, both for seabirds as for pinnipeds. Moreover, considering that top predators distribution follows their prey abundance, they also reflect very low bio-productivity in the deep Arctic basin.

I am very grateful to the Alfred Wegener Institute for Polar and Marine Research (AWI), Bremerhaven, Germany, to late coordinator E. Farhbach and to chief scientist W. Jokat for invitation on board RV. D. D’Hert and D. Nachtsheim (PolE) kindly helped prepare Figures 1 to 3.

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7 June 2019;

19 September 2019;

7 December 2019

: Joiris C R. Very low biodiversity of top predators—seabirds and marine mammals—in the high Arctic Ocean. Adv Polar Sci, 2019, 30(4): 375-381, doi:10.13679/j.advps.2019.0022

, E-mail: crjoiris@gmail.com

10.13679/j.advps.2019.0022