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Summer at-sea distribution of seabirds and marine mammals in polar ecosystems: a comparison between the European Arctic seas and the Weddell Sea, Antarctica
Journal of Marine Systems 27 Ž2000. 267–276 www.elsevier.nlrlocaterjmarsys
Summer at-sea distribution of seabirds and marine mammals in polar ecosystems: a comparison between the European Arctic seas and the Weddell Sea, Antarctica Claude R. Joiris ) Laboratory for Polar Ecology, Free UniÕersity of Brussels (VUB), Pleinlaan 2, B-1050 Brussels, Belgium Received 16 November 1998; accepted 28 February 2000
Abstract The summer at-sea distribution of seabirds and marine mammals was quantitatively established both in Antarctica ŽWeddell Sea. and in the European Arctic: Greenland, Norwegian and Barents seas. Data can directly be compared, since the same transect counts were applied by the same team from the same icebreaking ship in both regions. The main conclusion is that densities of seabirds and marine mammals are similar in open water and at the ice edge from both polar regions, while the presence of Adelie ´ penguins, minke whales and crabeater seals in densities more than one order of magnitude higher in Antarctic pack-ice must reflect a major ecological difference between both polar systems. The ecological implications of these observations are discussed, especially concerning important primary and secondary Žkrill. productions under the Weddell Sea pack-ice. q 2000 Elsevier Science B.V. All rights reserved. Keywords: seabirds; cetaceans; pinnipeds; European Arctic; Antarctica
1. Introduction The quantitative analysis of the at-sea distribution of seabirds and marine mammals provides useful information on the ecological structure of the ecosystems they belong to, since they integrate and reflect the availability of food, i.e. from primary production to herbivores, carnivores, microbial loop and sedimentation, both qualitatively and quantitatively. Data
)
Tel.: q32-2-629-3414; fax: q32-2-629-3438. E-mail address: [email protected] ŽC.R. Joiris..
collected in the North Sea showed that seabird distribution is bound to the main water masses, as recognised by water temperature and salinity characteristics ŽJoiris, 1978.. Such differences are to be explained by differences in the ecological structure of the water column, with a classical herbivorous food chain leading to high zooplankton and pelagic fish production in Atlantic water, but a short-cut of primary production to microbial loop and sedimentation in North Sea water ŽJoiris et al., 1982.. In the Antarctic, a known paradox concerns the pelagic production by phytoplankton, namely that actual primary production is lower than expected
0924-7963r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 7 9 6 3 Ž 0 0 . 0 0 0 7 2 - 5
268 Table 1 Total numbers of seabirds and marine mammals encountered in the Greenland, Norwegian and Barents seas, 1974–1993 Žselected species; mean number per half-an-hour count. Species
S cetaceans S pinnipeds
F. glacialis Sula bassana Pagophila eburnea Larus hyperboreus R. tridactyla Rhodostethia rosea U. aalge U. lomÕia A. alle Fratercula arctica
1
2
3
4
5
6
7
8 a
6 and 7 1974 y 54
8 and 9 1979 y 444
5 and 6 1980 y 66
7 and 8 1985 y 492
6 1988 q 380
7 1988 q 360
6 and 7 1989 q 116
67.2 0.833
13.7 2.65
45.7 0.924
38.2 0.033
0.385 5.17
12.2
0.614 10.1
132 0.008 0.361 0.131 1.02
10.8 0.009 0.310 0.086 3.53
3.89
2.33
12.7
0.677
9.81 0.037 0.950 0.213 11.5 0.003 2.41
0.463
2.55
4.94
11.0
1.91
4.65
1.68
40.2 1.30 79.6
1.95 0.428 139
8.19 0.526 28.4
2.17 0.069 16.3
0.031 1.53
0.069 0.207
0.154 0.217
11.7
5.74 92.6 nq nq
6.58 2.14 37.7 0.162
0.136 23.4 107 0.015
14.7 5.9 75.8 0.248 1.19
0.032 1.62
0.500
6 1991 q 852
9 EPOS 2 6 and 7 1991 q 52
7.35 0.016 0.408 0.176 4.05
7.37 0.346 2.65 22.1
0.019
0.058
10 Barents 8 1991, 92, 93 y 554
11 NEW a 5 and 6 1993 q 144
12 NEW a 6, 7 and 8 1993 q 308
All a
3822
11.5 0.002 0.114 0.273 12.4 0.004 0.256
6.35
2.27
1.20 0.410 5.28 0.257
0.412 0.071 1.73 0.276 0.003
29.4 0.501 0.513 0.501 8.40 0.094 2.10
11.5
16.2
9.23
0.416
5.88
24.8 0.02 71.9
16.0 0.49 60.2
2.53 0.097 26.3
2.68 0.175 8.22
10.9 3.49 61.9
0.076 0.410
0.049 0.224
0.962
0.045 0.875
0.088 0.804
References: 1: Joiris, 1976; 5: Joiris, 1992; 6: Joiris and Tahon, 1992; 9: Joiris, 1996; 10: Joiris et al., 1996; 11 and 12: Joiris et al., 1997; others: Joiris et al., unpublished results. a Excluding data collected in the North East Water polynya; nq: not quantified.
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
Fulmar Gannet Ivory gull Glaucous gull Kittiwake Ross’s gull Common guillemot Brunnich’s ¨ guillemot Little auk Puffin S birds
Expedition no. Remark Month Year Pack-ice included Number of counts
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
269
Table 2 Numbers of seabirds and marine mammals encountered in the Weddell Sea, Antarctica Žnumbers per half-an-hour count; EPOS I, leg 1, October–November 1988; see legend Table 1; from Joiris, 1991. Species
Zone Ice cover Žtenths. Water temperature Ž8C. Number of counts
Open water 0 0.2 40
OMIZ -3 y1.4 30
IMIZ 3 to 8 y1.5 51
Chinstrap penguin Chinstrap penguina Adelie ´ penguin Cape pigeon S birds Crabeater seal Leopard seal Fur seal S pinnipeds Minke whale S cetaceans
P. antarctica P. antarctica P. adeliae Daption capense
2.40 238
27.5 258 1.03 32.7 336 0.100 0.067 3.43 3.63 0.100 0.167
26.5 23.9 18.8 63.2 155 0.627 0.235 1.88 2.75 0.078 0.078
L. carcinophagus Hydrurga leptonyx Arctocephalus gazella
74.9 344
0.125 0.125
Balaenoptera acurostrata
CPI )8 y1.7 170 2.92 109 0.88 120 8.4 0.341 8.78 0.200 0.206
Total
291 9.52 63.5 67.2 25.3 179 5.04 0.247 0.701 6.00 0.141 0.151
OMIZ: outer marginal ice zone; IMIZ: Intermediate marginal ice zone; CPI: closed pack-ice. a On icebergs.
from light conditions and nutrients concentration Že.g. Heywood and Whitaker in Laws, 1984; Treguer and ´ Jacques, 1992; Knox, 1994.. The second paradox is
that production of the higher trophic levels, on the contrary, is higher than the one of northern polar regions Že.g. Knox, 1994..
Table 3 Calculated daily food intake by seabirds and marine mammals in polar regions: synopsis A. European Arctic seas: n
Polar open water 6
Ice edge 3
Closed pack-ice 3
Fulmar Kittiwake Brunnich’s guillemot ¨ Little auk
0.53 Ž0.36–0.88. 0.34 Ž0.12–0.84. 0.78 Ž0.57–1.17. 0.28 Ž0.03–0.46.
0.21 Ž0.13–0.28. 0.06 Ž0.04–0.07. 0.62 Ž0.18–1.1. 0.78 Ž0.11–1.46.
0.32 Ž0.10–0.53. 0.03 Ž0.01–0.05. 0.10 Ž0.09–0.12. 0.54 Ž0.03–1.05.
S birds S cetaceans S pinnipeds Total
2.0 Ž1.4–3.0. 0.35 Ž0–0.85. 0.24 Ž0–0.51. 2.6
1.8 Ž0.73–2.9. 0.17 Ž0.15–0.21. 1.45 Ž0.55–2.5. 3.4
1.1 Ž0.25–1.9. 0 0.25 Ž0.10–0.42. 1.3
B. Weddell Sea, Antarctica Polar open water
Ice edge
Closed pack-ice
Adelie ´ penguin S penguins S tubenoses
0 0.85 0.90
0.05 3.1 0.60
23.6 25.2 0.40
S birds S cetaceans S pinnipeds Total
1.8 0 0.01 1.8
3.8 1.0 0.70 5.5
26.0 4.3 12.0 42.3
Kg fw kmy2 .dayy1 ; mean; Žmin.y max. per expedition.; n s number of expeditions.
270
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
This paper deals with a quantitative comparison of seabirds and marine mammals at-sea distribution in both polar regions, with emphasis on the importance of the less studied ice-covered zones.
2. Methods Seabirds and marine mammals Žpinnipeds and cetaceans. at-sea distribution was determined by
Fig. 1. Distribution map for selected seabird species during RV Meteor expedition 71 Žpartim., 30 June–16 August 1985; from C.R. Joiris and J. Tahon, unpublished results; numbers per half-an-hour count; each symbol corresponds to one count; dotted line: limit of the pack-ice. Ža. Dark morph of the fulmar F. glacialis; four classes: nihil, 1–5, 6–25, 26–125. Žb. Common guillemot U. aalge; four classes: nihil, 1–5, 6–25, 26–125. Žc. Brunnich’s guillemot U. lomÕia; four classes: nihil, 1–10, 11–100, 101–1000. Žd. Little auk A. alle; four classes: nihil, ¨ 1–20, 21–400, 401–8000.
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
271
Fig. 1 Ž continued ..
transect counts mainly carried out on board the German icebreaking RV Polarstern. Taking into account the large size range of animals concerned: from very small petrels to albatrosses and whales, we decided not to apply the AusualB method with a transect width limited to 300 m, as proposed by Tasker et al. Ž1984. for the North Sea, but on the contrary, without width limitation. In order to convert actual numbers counted into densities, the sur-
face covered during the count was calculated, taking into account the transect length and a different width for each species, using specific conversion factors depending on the conspicuousness of the animals Žsee description and discussion in Joiris, 1991; Joiris et al., 1997.. This conversion factor was determined during various exercises, where experienced observers ŽCJ, J. Tahon and others. evaluated the distance at which seabirds and marine mammals were
272
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
Fig. 1 Ž continued ..
detectable, separately and together Žsee Joiris et al., 1997.; the density per square kilometer is obtained by multiplying the number of birds per kilometer by this factor. A comparison of data obtained by both methods shows that the results are similar ŽJoiris et al., 1997.. In order to make sure that results are comparable, however, this paper will mainly involve our own data, being collected by the same team with
the same methodology and basically from the same ship. The reproducibility of the counting method is illustrated by counts in the eastern Barents Sea collected during three similar transects in 1991, 1992 and 1993 ŽJoiris et al., 1996., during 75, 60 and 129 half-an-hour counts, respectively. Median counts in the polar water zone for the main species were: 1.50,
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
273
Fig. 1 Ž continued ..
1.83 and 0.99, respectively for the fulmar Fulmarus glacialis; 1.26, 3.27 and 1.28 for the kittiwake Rissa tridactyla; and 16.7, 28.1 and 24.5 for all birds Ž S birds.. For other species, differences registered in the same type of water mass are much more important, and can be attributed to actual heterogeneities Žpatchiness. in the animals’ distribution; this is obviously the case for little auk Alle alle, seals and cetaceans Žsee further, Table 3..
The density data were expressed as daily food intake by using allometric equations from the literature, as described and discussed in Joiris Ž1991, 1992. and Joiris and Tahon Ž1992., namely: I s 0.191 = W 0.723 = N where I is the daily ingestion in kg fw kmy2 , W the average individual biomass in kg and N the density in numbers per km2 .
274
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
3. Results and discussion A summary of the data collected during different spring and summer expeditions is presented in Table 1 for the Greenland, Norwegian and Barents seas, and in Table 2 for the Weddell Sea, in order to show the basic recorded data and the effort involved in this study. In the Arctic, 27 seabird species were encountered, of which four species represent 95% and more of the total numbers: fulmar F. glacialis, little auk A. alle, kittiwake R. tridactyla, and Brunnich’s ¨ guillemot Uria lomÕia. In the Weddell Sea, the density of flying birds is of the same order of magnitude as in the Arctic, but they are represented by a lower number of species Ž20, mainly tubenoses.. They are however outnumbered by penguins, mainly Adelies Pygoscelis adeliae, by more than one order ´ of magnitude. Marine mammals also are present in 10 times higher densities Žmainly crabeater seal Lobodon carcinophagus among the pinnipeds, and minke whale Balaenoptera acutorostrata among the cetaceans.. The presence of a lower number of species, of which a few represented by very large numbers of individuals, obviously reflects a lower biodiversity in the Weddell Sea than in European Arctic seas. Our spring observations in the Weddell Sea were confirmed during the following summer expedition by van Franeker Ž1992.. The data, as presented, e.g. in Table 1, show however a great heterogeneity leading to an apparent onreproducibility of the counts. This is in fact to be explained by differences in the spatial distribution of the various species. In order to avoid the utilization of somehow artificial geographical zones, the results were submitted to a cluster analysis aiming at an objective identification of the main factors influencing the at-sea distribution of seabirds and marine mammals. As an example of treatment of the results, data collected in the Norwegian and Greenland seas in 1985 ŽJoiris and Tahon, unpublished results. are presented and discussed here. Basic data, expressed as numbers per count Ži.e. per half-hour., are presented as distribution map for some species: dark morph of the fulmar and alcids: common guillemot Uria aalge, Brunnich’s guillemot and little auk ŽFig. ¨ . 1 . A cluster analysis was also performed ŽSPSS, see Wildi and Orloci, 1980.. Results of the clustering of the stations on the base of all counts from this
expedition allow to recognise the existence of four clusters ŽFig. 2., to be explained by environmental factors such as water temperature and salinity, i.e. corresponding to different water masses: cluster 1 to Atlantic water, cluster 4 to polar water, cluster 3 to coastal Norwegian water, and cluster 2 to some unidentified characteristics, possibly some mixed water areas between Atlantic and polar water ŽFig. 3.. Taking these environmental factors into account, this separation into water masses Žs clusters. allows to explain up to 90% of the variability in the counting results. A synopsis of the results is presented in Table 3, expressed as calculated daily food intake, and grouped as a function of the main hydrological features affecting the at-sea distribution of warmblooded vertebrates: main water masses, ice edge, type of pack-ice Žice coverage. in order to simplify and facilitate discussion. The most obvious conclusion is that densities are of the same order of magnitude in the Arctic and the Weddell Sea in polar water, ice edge or marginal ice zone, while differences in closed pack-ice reach one to two orders of magnitude: calculated daily food intake by seabirds is 1 in Arctic closed pack-ice, and 25 in Antarctic closed pack-ice; for cetaceans, the figures are 0 Ž- 0.005. and 4; for pinnipeds, 0.2 and 11; for the sum of all warm-blooded predators, 1 and 40. Recent
Fig. 2. Cluster analysis of the seabirds and marine mammals data collected in 1985: dendrogramme.
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
275
Fig. 3. Cluster analysis of the seabird and marine mammal data collected in 1985: geographic distribution of the stations belonging to the four main clusters Žsee text and Fig. 2..
review papers on seabird distribution ŽHunt et al., 1994. and on krill consumption by seabirds ŽCooper and Whoeler, 1994. in the Antarctic provide similar values for seabird density and food intake in open water, i.e. mainly for flying birds. Within a broader ecological interpretation, one can consider that the at-sea distribution of seabirds and marine mammals is mainly depending on the
availability of prey. In close pack-ice, the main prey of the most abundant Antarctic seabirds and marine mammals is krill Ž Euphausia spp., mainly superba., in proportions varying for Adelie ´ penguin between 30% ŽGreen and Johnstone, 1988; Puddicombe and Johnstone, 1988, both in Cooper and Whoeler, 1994. and 100% ŽEmison, 1968; Volkman et al., 1981, both in Croxall, 1984. to ApredominantB prey for
276
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
crabeater seal ŽKooyman, 1981. and for minke whale ŽStewart and Leatherwood, 1985.. For the baleen whales, our data must be considered as underestimates, since daily food intake was calculated on a year basis, while they are known to consume much more food during summer in polar regions than during winter in tropical waters. The same is true for the crabeater seal, since no correction was applied for taking their daily hauling out rhythm into account: our values obviously underestimate the actual seal populations in pack-ice. The high density on seabirds and marine mammals in close pack-ice must reflect the abundance of krill, and thus its high production, under the pack-ice. The existence of significant phytoplankton and krill biomasses under the pack-ice was already detected, e.g. by under water pictures, but remain very difficult to quantify, due to the difficulty of in situ determination of biomass, not to mention production. The data on warm-blooded predators provide a minimum evaluation of these productions Žobviously, predators cannot consume more that what is produced at the lower trophic levels., and thus reflect the existence of much higher primary and secondary productions under the Antarctic pack-ice than under the Arctic one. Acknowledgements I am very grateful to Dirk Van Speybroeck, APNA, VUB, for support in applying the cluster analysis. References Cooper, J., Whoeler, E.J., 1994. Consumption of Antarctic krill Ž Euphausia superba. by seabirds during summer in the Prydz Bay region, Antarctica. In: El-Sayed, Z. ŽEd.., Southern Ocean Ecology: The Biomass Perspective. Cambridge Univ. Press, pp. 247–260. Croxall, J.P., 1984. Seabirds. In: Laws, R.M. ŽEd.., Antarctic Ecology vol. 2, pp. 533–620. Hunt, G.L. Jr., Croxall, J.P., Trathan, P.N., 1994. Marine ornithology in the southern Drake Passage and Bransfield Starit during the BIOMASS Programme. In: El-Sayed, Z. ŽEd.., Southern Ocean Ecology: The Biomass Perspective. Cambridge Univ. Press, pp. 231–246.
Joiris, C., 1976. Seabirds seen during a return voyage from Belgium to Greenland in July. Gerfaut 66, 419–440. Joiris, C., 1978. Seabirds recorded in the North Sea in July: the ecological implications of their distribution. Gerfaut 68, 419– 440. Joiris, C.R., 1991. Spring distribution and ecological role of seabirds and marine mammals in the Weddell Sea, Antarctica. Polar Biol. 11, 415–424. Joiris, C.R., 1992. Summer distribution and ecological role of seabirds and marine mammals in the Norwegian and Greenland seas ŽJune 1988.. J. Mar. Syst. 3, 73–89. Joiris, C., 1996. At-sea distribution of seabirds and marine mammals around Svalbard, summer 1991. Polar Biol. 16, 423–429. Joiris, C., Tahon, R., 1992. Distribution and food intake of seabirds and marine mammals in the Norwegian and Greenland seas ŽJuly 1988.. R. Acad. Overseas Sci. ŽBrussels., 113–133. Joiris, C., Billen, G., Lancelot, C., Daro, M.H., Mommaerts, J.P., Bertels, A., Bossicart, M., Nijs, J., Hecq, J.H., 1982. A budget of carbon cycling in the Belgian coastal zone: relative roles of zooplankton, bacterioplankton and benthos in the utilization of primary production. Neth. J. Sea Res. 16, 260–275. Joiris, C.R., Tahon, J., Holsbeek, L., Vancauwenberghe, M., 1996. Seabirds and marine mammals in the eastern Barents Sea: late summer at-sea distribution and calculated food intake. Polar Biol. 16, 245–256. Joiris, C.R., Kampp, K., Tahon, J., Møbjerg Kristensen, R., 1997. Summer distribution of seabirds in the North–East Water polynya, Greenland. J. Mar. Syst. 13, 51–59. Knox, G.A., 1994. The Biology of the Southern Ocean. Cambridge Univ. Press, 444 pp. Kooyman, G.L., 1981. Crabeater seal. In: Ridgway, S.H., Harrison, R. ŽEds.., Handbook of Marine Mammals, vol. 2, pp. 221–236. Laws, R.M. ŽEd.., Antarctic Ecology, vol. 2, Academic Press, New York, 850 pp. Stewart, B.S., Leatherwood, S., 1985. Minke whale. In: Ridgway, S.H., Harrison, R. ŽEds.., Handbook of Marine Mammals, vol. 3, pp. 91–136. Tasker, M.L., Jones, P.H., Dixon, T.J., Blake, B.F., 1984. Counting seabirds at sea from ships: a review of methods employed and a suggestion for a standardised approach. Auk 101, 567– 577. Treguer, P., Jacques, G., 1992. Dynamics of nutrients and phyto´ plankton, and fluxes of carbon, nitrogen and silicon in the Antarctic Ocean. Polar Biol. 12, 149–162. van Franeker, J.A., 1992. Top predators as indicators for ecosystem events in the confluence zone and marginal ice zone of the Weddell and Scotia seas, Antarctica, November 1988 to January 1989 ŽEPOS Leg 2.. Polar Biol. 12, 93–102. Wildi, O., Orloci, L., 1980. Management and multivarite analysis of vegetation data. Swiss Fed. Inst. of Forestry Res., Report No. 215, 68 pp.
Summer at-sea distribution of seabirds and marine mammals in polar ecosystems: a comparison between the European Arctic seas and the Weddell Sea, Antarctica Claude R. Joiris ) Laboratory for Polar Ecology, Free UniÕersity of Brussels (VUB), Pleinlaan 2, B-1050 Brussels, Belgium Received 16 November 1998; accepted 28 February 2000
Abstract The summer at-sea distribution of seabirds and marine mammals was quantitatively established both in Antarctica ŽWeddell Sea. and in the European Arctic: Greenland, Norwegian and Barents seas. Data can directly be compared, since the same transect counts were applied by the same team from the same icebreaking ship in both regions. The main conclusion is that densities of seabirds and marine mammals are similar in open water and at the ice edge from both polar regions, while the presence of Adelie ´ penguins, minke whales and crabeater seals in densities more than one order of magnitude higher in Antarctic pack-ice must reflect a major ecological difference between both polar systems. The ecological implications of these observations are discussed, especially concerning important primary and secondary Žkrill. productions under the Weddell Sea pack-ice. q 2000 Elsevier Science B.V. All rights reserved. Keywords: seabirds; cetaceans; pinnipeds; European Arctic; Antarctica
1. Introduction The quantitative analysis of the at-sea distribution of seabirds and marine mammals provides useful information on the ecological structure of the ecosystems they belong to, since they integrate and reflect the availability of food, i.e. from primary production to herbivores, carnivores, microbial loop and sedimentation, both qualitatively and quantitatively. Data
)
Tel.: q32-2-629-3414; fax: q32-2-629-3438. E-mail address: [email protected] ŽC.R. Joiris..
collected in the North Sea showed that seabird distribution is bound to the main water masses, as recognised by water temperature and salinity characteristics ŽJoiris, 1978.. Such differences are to be explained by differences in the ecological structure of the water column, with a classical herbivorous food chain leading to high zooplankton and pelagic fish production in Atlantic water, but a short-cut of primary production to microbial loop and sedimentation in North Sea water ŽJoiris et al., 1982.. In the Antarctic, a known paradox concerns the pelagic production by phytoplankton, namely that actual primary production is lower than expected
0924-7963r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 7 9 6 3 Ž 0 0 . 0 0 0 7 2 - 5
268 Table 1 Total numbers of seabirds and marine mammals encountered in the Greenland, Norwegian and Barents seas, 1974–1993 Žselected species; mean number per half-an-hour count. Species
S cetaceans S pinnipeds
F. glacialis Sula bassana Pagophila eburnea Larus hyperboreus R. tridactyla Rhodostethia rosea U. aalge U. lomÕia A. alle Fratercula arctica
1
2
3
4
5
6
7
8 a
6 and 7 1974 y 54
8 and 9 1979 y 444
5 and 6 1980 y 66
7 and 8 1985 y 492
6 1988 q 380
7 1988 q 360
6 and 7 1989 q 116
67.2 0.833
13.7 2.65
45.7 0.924
38.2 0.033
0.385 5.17
12.2
0.614 10.1
132 0.008 0.361 0.131 1.02
10.8 0.009 0.310 0.086 3.53
3.89
2.33
12.7
0.677
9.81 0.037 0.950 0.213 11.5 0.003 2.41
0.463
2.55
4.94
11.0
1.91
4.65
1.68
40.2 1.30 79.6
1.95 0.428 139
8.19 0.526 28.4
2.17 0.069 16.3
0.031 1.53
0.069 0.207
0.154 0.217
11.7
5.74 92.6 nq nq
6.58 2.14 37.7 0.162
0.136 23.4 107 0.015
14.7 5.9 75.8 0.248 1.19
0.032 1.62
0.500
6 1991 q 852
9 EPOS 2 6 and 7 1991 q 52
7.35 0.016 0.408 0.176 4.05
7.37 0.346 2.65 22.1
0.019
0.058
10 Barents 8 1991, 92, 93 y 554
11 NEW a 5 and 6 1993 q 144
12 NEW a 6, 7 and 8 1993 q 308
All a
3822
11.5 0.002 0.114 0.273 12.4 0.004 0.256
6.35
2.27
1.20 0.410 5.28 0.257
0.412 0.071 1.73 0.276 0.003
29.4 0.501 0.513 0.501 8.40 0.094 2.10
11.5
16.2
9.23
0.416
5.88
24.8 0.02 71.9
16.0 0.49 60.2
2.53 0.097 26.3
2.68 0.175 8.22
10.9 3.49 61.9
0.076 0.410
0.049 0.224
0.962
0.045 0.875
0.088 0.804
References: 1: Joiris, 1976; 5: Joiris, 1992; 6: Joiris and Tahon, 1992; 9: Joiris, 1996; 10: Joiris et al., 1996; 11 and 12: Joiris et al., 1997; others: Joiris et al., unpublished results. a Excluding data collected in the North East Water polynya; nq: not quantified.
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
Fulmar Gannet Ivory gull Glaucous gull Kittiwake Ross’s gull Common guillemot Brunnich’s ¨ guillemot Little auk Puffin S birds
Expedition no. Remark Month Year Pack-ice included Number of counts
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
269
Table 2 Numbers of seabirds and marine mammals encountered in the Weddell Sea, Antarctica Žnumbers per half-an-hour count; EPOS I, leg 1, October–November 1988; see legend Table 1; from Joiris, 1991. Species
Zone Ice cover Žtenths. Water temperature Ž8C. Number of counts
Open water 0 0.2 40
OMIZ -3 y1.4 30
IMIZ 3 to 8 y1.5 51
Chinstrap penguin Chinstrap penguina Adelie ´ penguin Cape pigeon S birds Crabeater seal Leopard seal Fur seal S pinnipeds Minke whale S cetaceans
P. antarctica P. antarctica P. adeliae Daption capense
2.40 238
27.5 258 1.03 32.7 336 0.100 0.067 3.43 3.63 0.100 0.167
26.5 23.9 18.8 63.2 155 0.627 0.235 1.88 2.75 0.078 0.078
L. carcinophagus Hydrurga leptonyx Arctocephalus gazella
74.9 344
0.125 0.125
Balaenoptera acurostrata
CPI )8 y1.7 170 2.92 109 0.88 120 8.4 0.341 8.78 0.200 0.206
Total
291 9.52 63.5 67.2 25.3 179 5.04 0.247 0.701 6.00 0.141 0.151
OMIZ: outer marginal ice zone; IMIZ: Intermediate marginal ice zone; CPI: closed pack-ice. a On icebergs.
from light conditions and nutrients concentration Že.g. Heywood and Whitaker in Laws, 1984; Treguer and ´ Jacques, 1992; Knox, 1994.. The second paradox is
that production of the higher trophic levels, on the contrary, is higher than the one of northern polar regions Že.g. Knox, 1994..
Table 3 Calculated daily food intake by seabirds and marine mammals in polar regions: synopsis A. European Arctic seas: n
Polar open water 6
Ice edge 3
Closed pack-ice 3
Fulmar Kittiwake Brunnich’s guillemot ¨ Little auk
0.53 Ž0.36–0.88. 0.34 Ž0.12–0.84. 0.78 Ž0.57–1.17. 0.28 Ž0.03–0.46.
0.21 Ž0.13–0.28. 0.06 Ž0.04–0.07. 0.62 Ž0.18–1.1. 0.78 Ž0.11–1.46.
0.32 Ž0.10–0.53. 0.03 Ž0.01–0.05. 0.10 Ž0.09–0.12. 0.54 Ž0.03–1.05.
S birds S cetaceans S pinnipeds Total
2.0 Ž1.4–3.0. 0.35 Ž0–0.85. 0.24 Ž0–0.51. 2.6
1.8 Ž0.73–2.9. 0.17 Ž0.15–0.21. 1.45 Ž0.55–2.5. 3.4
1.1 Ž0.25–1.9. 0 0.25 Ž0.10–0.42. 1.3
B. Weddell Sea, Antarctica Polar open water
Ice edge
Closed pack-ice
Adelie ´ penguin S penguins S tubenoses
0 0.85 0.90
0.05 3.1 0.60
23.6 25.2 0.40
S birds S cetaceans S pinnipeds Total
1.8 0 0.01 1.8
3.8 1.0 0.70 5.5
26.0 4.3 12.0 42.3
Kg fw kmy2 .dayy1 ; mean; Žmin.y max. per expedition.; n s number of expeditions.
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This paper deals with a quantitative comparison of seabirds and marine mammals at-sea distribution in both polar regions, with emphasis on the importance of the less studied ice-covered zones.
2. Methods Seabirds and marine mammals Žpinnipeds and cetaceans. at-sea distribution was determined by
Fig. 1. Distribution map for selected seabird species during RV Meteor expedition 71 Žpartim., 30 June–16 August 1985; from C.R. Joiris and J. Tahon, unpublished results; numbers per half-an-hour count; each symbol corresponds to one count; dotted line: limit of the pack-ice. Ža. Dark morph of the fulmar F. glacialis; four classes: nihil, 1–5, 6–25, 26–125. Žb. Common guillemot U. aalge; four classes: nihil, 1–5, 6–25, 26–125. Žc. Brunnich’s guillemot U. lomÕia; four classes: nihil, 1–10, 11–100, 101–1000. Žd. Little auk A. alle; four classes: nihil, ¨ 1–20, 21–400, 401–8000.
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271
Fig. 1 Ž continued ..
transect counts mainly carried out on board the German icebreaking RV Polarstern. Taking into account the large size range of animals concerned: from very small petrels to albatrosses and whales, we decided not to apply the AusualB method with a transect width limited to 300 m, as proposed by Tasker et al. Ž1984. for the North Sea, but on the contrary, without width limitation. In order to convert actual numbers counted into densities, the sur-
face covered during the count was calculated, taking into account the transect length and a different width for each species, using specific conversion factors depending on the conspicuousness of the animals Žsee description and discussion in Joiris, 1991; Joiris et al., 1997.. This conversion factor was determined during various exercises, where experienced observers ŽCJ, J. Tahon and others. evaluated the distance at which seabirds and marine mammals were
272
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Fig. 1 Ž continued ..
detectable, separately and together Žsee Joiris et al., 1997.; the density per square kilometer is obtained by multiplying the number of birds per kilometer by this factor. A comparison of data obtained by both methods shows that the results are similar ŽJoiris et al., 1997.. In order to make sure that results are comparable, however, this paper will mainly involve our own data, being collected by the same team with
the same methodology and basically from the same ship. The reproducibility of the counting method is illustrated by counts in the eastern Barents Sea collected during three similar transects in 1991, 1992 and 1993 ŽJoiris et al., 1996., during 75, 60 and 129 half-an-hour counts, respectively. Median counts in the polar water zone for the main species were: 1.50,
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273
Fig. 1 Ž continued ..
1.83 and 0.99, respectively for the fulmar Fulmarus glacialis; 1.26, 3.27 and 1.28 for the kittiwake Rissa tridactyla; and 16.7, 28.1 and 24.5 for all birds Ž S birds.. For other species, differences registered in the same type of water mass are much more important, and can be attributed to actual heterogeneities Žpatchiness. in the animals’ distribution; this is obviously the case for little auk Alle alle, seals and cetaceans Žsee further, Table 3..
The density data were expressed as daily food intake by using allometric equations from the literature, as described and discussed in Joiris Ž1991, 1992. and Joiris and Tahon Ž1992., namely: I s 0.191 = W 0.723 = N where I is the daily ingestion in kg fw kmy2 , W the average individual biomass in kg and N the density in numbers per km2 .
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3. Results and discussion A summary of the data collected during different spring and summer expeditions is presented in Table 1 for the Greenland, Norwegian and Barents seas, and in Table 2 for the Weddell Sea, in order to show the basic recorded data and the effort involved in this study. In the Arctic, 27 seabird species were encountered, of which four species represent 95% and more of the total numbers: fulmar F. glacialis, little auk A. alle, kittiwake R. tridactyla, and Brunnich’s ¨ guillemot Uria lomÕia. In the Weddell Sea, the density of flying birds is of the same order of magnitude as in the Arctic, but they are represented by a lower number of species Ž20, mainly tubenoses.. They are however outnumbered by penguins, mainly Adelies Pygoscelis adeliae, by more than one order ´ of magnitude. Marine mammals also are present in 10 times higher densities Žmainly crabeater seal Lobodon carcinophagus among the pinnipeds, and minke whale Balaenoptera acutorostrata among the cetaceans.. The presence of a lower number of species, of which a few represented by very large numbers of individuals, obviously reflects a lower biodiversity in the Weddell Sea than in European Arctic seas. Our spring observations in the Weddell Sea were confirmed during the following summer expedition by van Franeker Ž1992.. The data, as presented, e.g. in Table 1, show however a great heterogeneity leading to an apparent onreproducibility of the counts. This is in fact to be explained by differences in the spatial distribution of the various species. In order to avoid the utilization of somehow artificial geographical zones, the results were submitted to a cluster analysis aiming at an objective identification of the main factors influencing the at-sea distribution of seabirds and marine mammals. As an example of treatment of the results, data collected in the Norwegian and Greenland seas in 1985 ŽJoiris and Tahon, unpublished results. are presented and discussed here. Basic data, expressed as numbers per count Ži.e. per half-hour., are presented as distribution map for some species: dark morph of the fulmar and alcids: common guillemot Uria aalge, Brunnich’s guillemot and little auk ŽFig. ¨ . 1 . A cluster analysis was also performed ŽSPSS, see Wildi and Orloci, 1980.. Results of the clustering of the stations on the base of all counts from this
expedition allow to recognise the existence of four clusters ŽFig. 2., to be explained by environmental factors such as water temperature and salinity, i.e. corresponding to different water masses: cluster 1 to Atlantic water, cluster 4 to polar water, cluster 3 to coastal Norwegian water, and cluster 2 to some unidentified characteristics, possibly some mixed water areas between Atlantic and polar water ŽFig. 3.. Taking these environmental factors into account, this separation into water masses Žs clusters. allows to explain up to 90% of the variability in the counting results. A synopsis of the results is presented in Table 3, expressed as calculated daily food intake, and grouped as a function of the main hydrological features affecting the at-sea distribution of warmblooded vertebrates: main water masses, ice edge, type of pack-ice Žice coverage. in order to simplify and facilitate discussion. The most obvious conclusion is that densities are of the same order of magnitude in the Arctic and the Weddell Sea in polar water, ice edge or marginal ice zone, while differences in closed pack-ice reach one to two orders of magnitude: calculated daily food intake by seabirds is 1 in Arctic closed pack-ice, and 25 in Antarctic closed pack-ice; for cetaceans, the figures are 0 Ž- 0.005. and 4; for pinnipeds, 0.2 and 11; for the sum of all warm-blooded predators, 1 and 40. Recent
Fig. 2. Cluster analysis of the seabirds and marine mammals data collected in 1985: dendrogramme.
C.R. Joiris r Journal of Marine Systems 27 (2000) 267–276
275
Fig. 3. Cluster analysis of the seabird and marine mammal data collected in 1985: geographic distribution of the stations belonging to the four main clusters Žsee text and Fig. 2..
review papers on seabird distribution ŽHunt et al., 1994. and on krill consumption by seabirds ŽCooper and Whoeler, 1994. in the Antarctic provide similar values for seabird density and food intake in open water, i.e. mainly for flying birds. Within a broader ecological interpretation, one can consider that the at-sea distribution of seabirds and marine mammals is mainly depending on the
availability of prey. In close pack-ice, the main prey of the most abundant Antarctic seabirds and marine mammals is krill Ž Euphausia spp., mainly superba., in proportions varying for Adelie ´ penguin between 30% ŽGreen and Johnstone, 1988; Puddicombe and Johnstone, 1988, both in Cooper and Whoeler, 1994. and 100% ŽEmison, 1968; Volkman et al., 1981, both in Croxall, 1984. to ApredominantB prey for
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crabeater seal ŽKooyman, 1981. and for minke whale ŽStewart and Leatherwood, 1985.. For the baleen whales, our data must be considered as underestimates, since daily food intake was calculated on a year basis, while they are known to consume much more food during summer in polar regions than during winter in tropical waters. The same is true for the crabeater seal, since no correction was applied for taking their daily hauling out rhythm into account: our values obviously underestimate the actual seal populations in pack-ice. The high density on seabirds and marine mammals in close pack-ice must reflect the abundance of krill, and thus its high production, under the pack-ice. The existence of significant phytoplankton and krill biomasses under the pack-ice was already detected, e.g. by under water pictures, but remain very difficult to quantify, due to the difficulty of in situ determination of biomass, not to mention production. The data on warm-blooded predators provide a minimum evaluation of these productions Žobviously, predators cannot consume more that what is produced at the lower trophic levels., and thus reflect the existence of much higher primary and secondary productions under the Antarctic pack-ice than under the Arctic one. Acknowledgements I am very grateful to Dirk Van Speybroeck, APNA, VUB, for support in applying the cluster analysis. References Cooper, J., Whoeler, E.J., 1994. Consumption of Antarctic krill Ž Euphausia superba. by seabirds during summer in the Prydz Bay region, Antarctica. In: El-Sayed, Z. ŽEd.., Southern Ocean Ecology: The Biomass Perspective. Cambridge Univ. Press, pp. 247–260. Croxall, J.P., 1984. Seabirds. In: Laws, R.M. ŽEd.., Antarctic Ecology vol. 2, pp. 533–620. Hunt, G.L. Jr., Croxall, J.P., Trathan, P.N., 1994. Marine ornithology in the southern Drake Passage and Bransfield Starit during the BIOMASS Programme. In: El-Sayed, Z. ŽEd.., Southern Ocean Ecology: The Biomass Perspective. Cambridge Univ. Press, pp. 231–246.
Joiris, C., 1976. Seabirds seen during a return voyage from Belgium to Greenland in July. Gerfaut 66, 419–440. Joiris, C., 1978. Seabirds recorded in the North Sea in July: the ecological implications of their distribution. Gerfaut 68, 419– 440. Joiris, C.R., 1991. Spring distribution and ecological role of seabirds and marine mammals in the Weddell Sea, Antarctica. Polar Biol. 11, 415–424. Joiris, C.R., 1992. Summer distribution and ecological role of seabirds and marine mammals in the Norwegian and Greenland seas ŽJune 1988.. J. Mar. Syst. 3, 73–89. Joiris, C., 1996. At-sea distribution of seabirds and marine mammals around Svalbard, summer 1991. Polar Biol. 16, 423–429. Joiris, C., Tahon, R., 1992. Distribution and food intake of seabirds and marine mammals in the Norwegian and Greenland seas ŽJuly 1988.. R. Acad. Overseas Sci. ŽBrussels., 113–133. Joiris, C., Billen, G., Lancelot, C., Daro, M.H., Mommaerts, J.P., Bertels, A., Bossicart, M., Nijs, J., Hecq, J.H., 1982. A budget of carbon cycling in the Belgian coastal zone: relative roles of zooplankton, bacterioplankton and benthos in the utilization of primary production. Neth. J. Sea Res. 16, 260–275. Joiris, C.R., Tahon, J., Holsbeek, L., Vancauwenberghe, M., 1996. Seabirds and marine mammals in the eastern Barents Sea: late summer at-sea distribution and calculated food intake. Polar Biol. 16, 245–256. Joiris, C.R., Kampp, K., Tahon, J., Møbjerg Kristensen, R., 1997. Summer distribution of seabirds in the North–East Water polynya, Greenland. J. Mar. Syst. 13, 51–59. Knox, G.A., 1994. The Biology of the Southern Ocean. Cambridge Univ. Press, 444 pp. Kooyman, G.L., 1981. Crabeater seal. In: Ridgway, S.H., Harrison, R. ŽEds.., Handbook of Marine Mammals, vol. 2, pp. 221–236. Laws, R.M. ŽEd.., Antarctic Ecology, vol. 2, Academic Press, New York, 850 pp. Stewart, B.S., Leatherwood, S., 1985. Minke whale. In: Ridgway, S.H., Harrison, R. ŽEds.., Handbook of Marine Mammals, vol. 3, pp. 91–136. Tasker, M.L., Jones, P.H., Dixon, T.J., Blake, B.F., 1984. Counting seabirds at sea from ships: a review of methods employed and a suggestion for a standardised approach. Auk 101, 567– 577. Treguer, P., Jacques, G., 1992. Dynamics of nutrients and phyto´ plankton, and fluxes of carbon, nitrogen and silicon in the Antarctic Ocean. Polar Biol. 12, 149–162. van Franeker, J.A., 1992. Top predators as indicators for ecosystem events in the confluence zone and marginal ice zone of the Weddell and Scotia seas, Antarctica, November 1988 to January 1989 ŽEPOS Leg 2.. Polar Biol. 12, 93–102. Wildi, O., Orloci, L., 1980. Management and multivarite analysis of vegetation data. Swiss Fed. Inst. of Forestry Res., Report No. 215, 68 pp.