© 2006 International Council for the Exploration of the Sea
Seabird numbers and prey consumption in the North Atlantic
a Tromsø University Museum, Department of Zoology NO-9037 Tromsø, Norway
b Canadian Wildlife Service 1141 Route de l'Eglise, PO Box 10100, 9th Floor, Ste-Foy, Quebec G1V 4H5, Canada
c Norwegian Institute for Nature Research NO-7485 Trondheim, Norway
d Department of Arctic Environment, National Environmental Research Institute Frederiksborgvej 399, PO Box 358, DK-4000 Roskilde, Denmark
e Cognitive and Behavioural Ecology Programme, Memorial University of Newfoundland, St John's Newfoundland A1B 3X9, Canada
f JNCC Dunnet House, 7 Thistle Place, Aberdeen AB10 1UZ, Scotland, UK
g Biology Department, College of Staten Island 2800 Victory Boulevard, Staten Island, NY 10314, USA
*Correspondence to R. T. Barrett: tel: +47 7 764 5013; fax: +47 7 764 5520. e-mail: robb{at}tmu.uit.no.
We compared seasonal composition, abundance, and biomass of seabirds between the Northeast (ICES region) and Northwest (NAFO region) Atlantic fisheries regions to identify differences in community assemblage and prey consumption. Seabirds were more abundant in the Northwest Atlantic, but biomass was greater in the Northeast. This disparity resulted from enormous numbers of little auks Alle alle breeding in West Greenland and of Leach's storm-petrels Oceanodroma leucorhoa breeding in Newfoundland, plus large numbers of non-breeding shearwaters Puffinus spp. entering southern NAFO areas in summer. The Northeast Atlantic communities were dominated numerically by northern fulmars Fulmarus glacialis, large auks Uria spp., and the Atlantic puffin Fratercula arctica. Seabirds occupying the North Atlantic consume approximately 11 x 106 t of food annually. Overall consumption rates peak during summer as a result of increased breeding activity and seasonal movements of birds into the North Atlantic. Because of the greater biomass of birds in the northeast, consumption (mainly by piscivores) in ICES areas was approximately 20% higher than that in NAFO areas, where planktivores dominate. NAFO areas had, however, a much greater consumption rate per unit area than ICES areas. Comparative studies such as these could prove informative in assessing large predator responses to the influence of fishing and ocean-scale climate change.
Keywords: community, consumption, North Atlantic, predators, seabirds
Received 27 September 2005; accepted 9 April 2006.
 |
Introduction |
|---|
 Top Introduction MethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
There is increasing need to integrate energy consumption by seabirds and other predators into management policies in both ICES and NAFO convention areas of the North Atlantic (ICES, 2001, 2002a; Garcia et al., 2003; O'Boyle et al., 2005). The need for such an ecosystem approach is amplified by increasing pressures from fisheries, mariculture, and climate change on species upon which seabirds and mammals feed (Arnott and Ruxton, 2002; Davoren and Montevecchi, 2003; Pauly et al., 2003; Hjermann et al., 2004; Miller and Sydeman, 2004; Wanless et al., 2004).
Incorporating endothermic predators into large-scale ecosystem and foodweb approaches is an integral aspect of these initiatives (Bundy et al., 2000; Camphuysen, 2005). Seabirds, in particular, being the most conspicuous and easily accessed of large marine predators, often provide useful insights into ecosystem conditions and processes (Montevecchi et al., 2006). This work was initiated by the ICES Working Group on Seabird Ecology (WGSE) to collate information on North Atlantic seabird communities, to compare the seabird communities, and to estimate their prey consumption throughout the ICES (north of 36°N, east of 42°W) and NAFO (Northwest Atlantic Fisheries Organization; north of 35°N, west of 42°W) convention areas of the North Atlantic.
The boreal and low Arctic coastal regions of the North Atlantic are highly productive and support large numbers of breeding seabirds belonging to nine families and 21 genera (Newton, 2003; Gaston, 2004). The North Atlantic seabird community is also diverse in form and feeding behaviour, and includes pelagic surface-feeders (e.g. petrels, Procellariiformes), coastal surface-feeders (e.g. terns, Sternidae), coastal omnivores (gulls, Laridae), benthic-feeders (cormorants, Phalacrocoracidae), and specialized, wing-propelled pursuit-divers (auks, Alcidae). The distribution of the last group is restricted to the northern hemisphere.
On an annual basis, many of these species exhibit varying periods of residence in different oceanographic regions and areas. Some migrate into breeding areas in spring and summer, and out of them during autumn and winter. Other visitors move into regions after breeding elsewhere. For example, in the Northwest Atlantic, trans-equatorial migrant shearwaters (Puffinus spp.) move onto the Grand Banks following austral summer breeding seasons in the South Atlantic. In comparison, some species do not exhibit regular migratory patterns, but rather a more diffuse dispersal (e.g. gulls and Atlantic puffin Fratercula arctica; Wernham et al., 2002; Bakken et al., 2003; Harris et al., 2005).
Recent models of prey consumption have shown that seabirds consume considerable quantities of small pelagic fish and crustaceans (Montevecchi, 2002, and references therein). These levels of consumption tend to be less than those of commercial fisheries at both regional and global scales, and they are vastly exceeded by consumption by marine mammals and predatory fish (Bundy et al., 2000; Barrett et al., 2002; Montevecchi, 2002; Brooke, 2004).
Focal forage species (e.g. sandeels Ammodytes spp. in the Northeast Atlantic and capelin Mallotus villosus in the Northwest Atlantic) provide primary food bases for marine birds, mammals, and fish (Lavigne, 1996; Camphuysen, 2005). These fish are important as prey for many commercial fish species targeted by industrial and commercial fisheries on both sides of the Atlantic (Aikman, 1997; Carscadden and Nakashima, 1997). Owing to their pivotal roles in marine foodwebs, we pay particular attention to their consumption by different seabird communities in different oceanographic regions.
Here we draw together information on the marine bird communities and generate model estimates of their consumption throughout the North Atlantic. We make comparisons between avian communities in different oceanographic regions, and compare different feeding guilds of avian predators and their changing spatial and temporal distributions throughout an annual cycle. These comparisons aid in assessments of ocean-scale variation in seabird communities and their associated foodwebs.
|
Methods |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
Population estimates
Breeding birds
The population estimates are primarily of birds nesting in coastal regions and feeding wholly or partially at sea, but the numbers of gulls may also include a small fraction of non-marine, inland-breeding segments of the populations. Of the many species of divers (Gaviidae), ducks, and geese (Anatidae) that could also be classified as seabirds, only the common eider (Somateria mollissima) is included here as a breeding species owing to its total dependence on marine food, and to its very large numbers in some areas of the North Atlantic. Rare species whose numbers do not total more than a few hundred pairs (e.g. gull-billed tern Gelochelidon nilotica and Sabine's gull Xema sabini) are not included in the calculations.
Members of the WGSE provided the best estimates of the numbers of seabirds currently breeding in their respective countries and regions; these data are presented in WGSE reports (ICES, 2002a, 2003 – available at http://www.ices.dk/reports/occ/). Data from the huge colonies of northern fulmars (Fulmarus glacialis), guillemots (Uria spp.), and little auks (Alle alle) in Canada, Greenland, Iceland, Svalbard, and the Barents Sea, and of black-legged kittiwakes (Rissa tridactyla) and Atlantic puffins in some areas are less precise owing to the vast numbers involved as well as difficulty of access. Moreover, while data for many species were presented to the nearest hundred, ten, or even individual pairs, others were presented as ranges, some as large as 100 000–1 000 000 pairs. For the sake of simplicity, all such ranges were entered as midpoints between the two extremes.
To simplify comparison across the Atlantic, many of the ICES and some of the NAFO areas were combined to form larger biogeographically similar regions (Figure 1, Tables 1 and 2).
|
|
|
Immature and non-breeding birds
Whereas the numbers of breeding adults were generally based on field data, numbers of nestlings and pre-breeders were estimated based on a classification of whether the species laid single- or multiple-egg clutches, and calculations based on numbers of breeding pairs (bp) plus the numbers of immature birds (Cairns et al., 1991). Estimates of the numbers of non-breeding birds were made separately for single-egg species (= (bp x 0.7) + (bp x 0.7)) and for multi-egg species (= (bp x 0.6) + (bp x 1)). These estimates assumed that the numbers of non-breeding birds (immature birds and deferred breeders) were equivalent to 35% or 30% of the breeding population, and that the fledging success of single-egg and multi-egg clutch species was 0.7 and 1.0 chicks per pair, respectively.
These calculations are, however, very coarse, and do not take into consideration population trends of the different species. In the calculations of seasonal changes in total numbers (and hence biomass and food consumption) of birds in a population (i.e. breeding pairs + immatures), the resulting figures were used over the entire year, and no correction was made to account for the fact that reproduction takes place in summer whereas mortality occurs during all seasons. As a result, the autumn population sizes are likely to be underestimated and the spring population sizes overestimated. For single-egg species, these under- and overestimates will each be about 10%, and for multi-egg species about 20%, based on normal survival rates of adult and immature birds.
Seasonal movements of birds into and between areas
In addition to those populations that breed in NAFO and ICES areas, there are large numbers of seabirds and waterfowl that breed outside these areas (including inland), but enter them at certain times of the year as migratory or wintering populations. The most abundant species were accounted for in the appropriate season in the model through rough estimates of the numbers of birds likely to have entered the respective areas along known migration and dispersal routes, based on the experience of the authors, consultation with experienced researchers who have worked at sea, published at-sea distribution atlases (Huettmann and Diamond, 2000; Stone et al., 1995), and published consumption models (Montevecchi, 2000; Appendices 1 and 2).
Furthermore, birds breeding in a given ICES and NAFO area may also move through or to other areas during migration or to spend the winter (Merkel et al., 2002; Wernham et al., 2002; Bakken et al., 2003). We attempted to account for these movements by estimating the numbers of each species present in each area each season (Appendices 3 and 4). These attempts were limited to the most abundant species breeding within a given area, i.e. species whose biomass constituted >2% of an exploratory estimate of the total biomass of seabirds breeding in that area (based on Tables 2.1–2.5 of ICES, 2002a and Table 3.1 of ICES, 2003).
No attempt was made, however, to quantify attendance in the large, central North Atlantic ICES XII area. No useful (in this context) estimates of bird numbers have been published for that area but, while extensive, these deep waters are relatively poor in nutrients (Shealer, 2002) and therefore probably also in seabird numbers. It is consequently unlikely that any estimates of seabird consumption in ICES XII will substantially affect the total. Moreover, being in the middle of the North Atlantic, this caveat will not preclude any east–west comparison of results.
Owing to differences in ocean climate regimes in the eastern and western North Atlantic, the seasons were defined differently, i.e. for NAFO areas, spring = April–June, summer = July–September, autumn = October–December, and winter = January–March; for ICES areas, spring = February–April, summer = May–July, autumn = August–October, and winter = November–January.
Consumption and energy expenditure
The annual consumption by seabirds in a given area was estimated using calculated species-specific energy demands, numbers of individuals of that species within that area, number of days present, and a mean energy density of food (see below). Consumption was modelled separately for each season, then summed to give an annual total.
Field metabolic rates during the breeding season were estimated using Ellis and Gabrielsen's (2002) allometric equations for different orders of seabirds. For seaducks, the equations for "all seabirds" were used. The length of the breeding season was set as the incubation period plus the fledging period (in days, as given in Cramp and Simmons, 1977, 1983; Cramp, 1985) plus 20 days (see Barrett et al., 2002, for examples from ICES I and II).
For the non-breeding component of the breeding population (chicks, immatures, and deferred breeders) during the breeding season and for all birds outside the breeding season, FMR (field metabolic rate) was set as 2.5 x BMR (basal metabolic rate; Gales and Green, 1990; G. W. Gabrielsen, pers. comm.). BMR was calculated using Ellis and Gabrielsen's (2002) allometric equations. FMR values for breeders and non-breeders were summed to give the overall energy expenditure for a given species within a given season.
Because diet composition is largely unknown in many species in most of the ICES and NAFO areas, a fixed energy density of prey of 5.5 kJ g–1 wet mass was chosen after an exploratory study comparing a model using fixed densities with one using species-specific diet composition and energy densities (fatty fish, lean fish, or invertebrates) from the Norwegian and Barents Seas (Barrett et al., 2002). Digestion efficiency was set at 75% (Hilton et al., 2000).
|
Results |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
Breeding populations
Approximately 68 x 106 pairs of seabirds breed in the North Atlantic, with approximately 60% (41 x 106 pairs, equivalent to ca. 141 x 106 seabirds) in the NAFO areas and ca. 40% (26 x 106 pairs, or 91 x 106 seabirds) in the ICES areas (Tables 1 and 2). Note that these totals do not include the ca. 3.5 x 106–4 x 106 pairs (mostly Brünnich's guillemots, Uria lomvia) that breed in the eastern Canadian Arctic, west of NAFO 0 (Nettleship and Evans, 1985; Gaston and Jones, 1998).
In terms of total biomass, however, the balance is reversed, with seabirds breeding in the western North Atlantic (ca. 31 000 t) weighing approximately 60% of those breeding in the eastern North Atlantic (ca. 59 000 t; Tables 1 and 2). This difference is due to the huge numbers of small little auks (>100 x 106 birds, body mass 
160 g) and Leach's storm-petrels Oceanodroma leucorhoa (>15 x 106 birds, body mass 50 g) that dominate the breeding communities in NAFO 1 and NAFO 2 + 3, respectively.
Auks dominate the communities breeding in the northern regions on both sides of the Atlantic, constituting 80% and 99% of those breeding along eastern Baffin Island and western Greenland, respectively, in the NAFO areas, and about 70% of those breeding in the Barents and Norwegian Seas, eastern Greenland, and Iceland in the ICES areas (Tables 1 and 2). In western Greenland, 33 x 106 pairs of little auks comprise ca. 80% by number and ca. 60% of total biomass of the total NAFO summer population. Atlantic puffins, little auks, common guillemots (Uria aalge), and Brünnich's guillemots make up, respectively, 22%, 18%, 9%, and 9% (by number) of the total ICES populations. In biomass, the contribution by little auks falls to 5%, whereas that of the larger species is between 13% and 16%.
The petrels are also very unevenly distributed and numerically dominate the Newfoundland and Labrador community (80% by number, but just 20% by biomass because of the small size of Leach's storm-petrel), and the southern ICES areas (60–65% by number and biomass in region E6, mostly Cory's shearwaters, Calonectris diomedea). Northern fulmars and Manx shearwaters (Puffinus puffinus) also make up large proportions by number (41%) and biomass (30%) of the seabirds breeding in the Faroes and along the western borders of the UK. Northern fulmars are also numerous at Iceland (estimated to be 1.5 x 106 pairs).
The Pelecaniformes (great cormorants, Phalacrocorax carbo, European shags, P. aristotelis, and northern gannets, Morus bassanus) constitute more of the seabird community in the three southern NAFO areas (10–20% by number, 20–46% by biomass, Table 1) than in any other NAFO area or any ICES region. In the eastern North Atlantic, they attain only 5–7% by number and 13–22% by biomass in regions around the UK and in the Baltic Sea (Table 2).
The shallow, inland Baltic Sea and its approaches are dominated by common eiders and gulls, constituting 40% and 41% by number and 67% and 18% by biomass of the total breeding population, respectively. Approximately 45% of ca. 1 x 106 pairs of common eiders that nest in all ICES areas breed in the Baltic. Common eiders also attain their highest proportions (7–10% by number, 14% by biomass) in the inshore NAFO areas 4–6.
The only subarea in the NAFO and ICES areas where gulls dominate the seabird breeding community is NAFO 5 and 6. Of the approximately 380 000 pairs of seabirds breeding in that subarea, 60% are gulls (mainly laughing gulls, Larus atricilla and herring gulls, L. argentatus). Together with terns (Sternidae), they make up a large majority of the community (65% of the total biomass). In the ICES areas, breeding gulls are more evenly spread (except in eastern Greenland and Iceland, where they are relatively few), and constitute 14–40% by number and 12–36% of the biomass in the different regions, and nowhere do terns constitute >10% by number or >1% of the biomass.
Seasonal changes in numbers and biomass of seabirds
Overall, the seabird community in the NAFO areas is dominated by huge numbers of individual birds feeding at low trophic levels, including three small planktivorous species (little auk in NAFO 1, Leach's storm-petrel in NAFO 2 + 3, and Wilson's storm-petrel, Oceanites oceanicus, migrating into and through NAFO 4–6).
Owing to temporary movements of birds from the southern Atlantic into northwestern waters, and the migration of North Atlantic seabirds across fishing areas, there are, however, considerable seasonal changes in numbers and biomasses of seabirds occupying the various parts of the North Atlantic (Tables 3 and 4). Such movements include those of large numbers of birds migrating south out of Arctic Canada and the northernmost NAFO areas, and those moving southwestward from the northern ICES areas into the southern NAFO areas in autumn and winter (Appendices 1–4). For example, the large increase in numbers and biomass off eastern Newfoundland and Labrador in autumn and winter is due to the influx of millions of common eiders, auks (including probably >10 x 106 Brünnich's guillemots and >100 x 106 little auks), and black-legged kittiwakes (Rissa tridactyla) from colonies northwest of the NAFO areas (in the eastern Canadian Arctic), Baffin Island, and western Greenland, and from ICES regions (the Barents Sea, Norwegian Sea, and Iceland; Appendices 1 and 3). Farther south, 4.5 x 106–5 x 106 non-breeding birds (mostly greater shearwaters, Puffinus gravis, sooty shearwaters, P. griseus, and Wilson's storm-petrels) enter southern NAFO areas from the southern oceans in summer, and 1.5 x 106 inland-breeding ring-billed gulls (L. delawarensis) move out to the coast in the same areas in winter (Appendix 1). Similarly, in the eastern North Atlantic, nearly 7 x 106 seaducks winter in the Baltic Sea, but leave again in spring to breed inland. These include 4.3 x 106 long-tailed ducks (Clangula hyemalis), 1.2 x 106 common scoters (Melanitta nigra), and 1 x 106 velvet scoters (M. fusca; Appendix 2).
|
|
It should be noted, however, that our quantifications of these movements of seabirds across the fishing areas were based on few data collected in the 1970s and 1980s, such that very little is known about the actual numbers of the different species in the various areas during a given period. Many of the values used here are based on best guesses fitting the estimated population numbers, known migration routes, and at-sea distributions gleaned from the literature.
The total biomasses of seabirds occupying NAFO and ICES waters (Table 4) in different seasons vary little (39 000–48 000 t in NAFO waters, 54 000–64 000 t in ICES waters). This low variability in overall numbers and biomass in NAFO waters is due to the large influx of non-breeding birds from the South Atlantic compensating for the large numbers of birds returning to their breeding colonies in Arctic Canada and the eastern North Atlantic. Similarly, the numbers and biomass of ducks entering and leaving the Baltic nearly compensate for the birds moving westward from the northern ICES to winter in NAFO areas.
Our calculations are based only on estimates of the maximum number for any given species and season, and do not consider how long individual birds stay within each area. Thus, short stays in two or more areas, e.g. during migration in spring and autumn, will result in a slight over-representation of those species in the total numbers and biomasses across those areas.
Consumption estimates
Seabirds occupying the NAFO and ICES areas of the North Atlantic consume an estimated 11 x 106 t of food annually, with 46% being taken in the western sector and 54% in the east (Table 5).
|
While numbers (Table 3) and biomass (Table 4) of seabirds in a given area in a given season are based on maximum numbers in that season (see above), the food consumption of seabirds occupying the NAFO and ICES areas (Table 5) is based on the number of days each species stays in a given subarea and therefore does not correspond directly with the numbers and biomass in Tables 3 and 4.
Of the 11 x 106 t consumed, about 2 x 106 t was eaten annually in each of areas W2 (West Greenland), W3 (East Newfoundland and Labrador), and E2 (East Greenland and Iceland), and 1.5 x 106 t in E1 (Barents and Norwegian Seas). Consumption in these four areas accounts for 70% of the annual total consumption of food in the northern North Atlantic (Table 5).
There are also large seasonal differences, especially in the northern NAFO regions. In West Greenland, consumption is four times greater in summer than in winter, whereas in eastern Newfoundland and Labrador, winter consumption is five times greater than in summer (Table 5). In the Northeast Atlantic (E1 and E2), consumption increases by a factor of two from winter to summer, whereas in the Baltic Sea it increases by the same factor from summer to winter (Table 5).
|
Discussion |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
Seabird numbers
Considering the large oceanographic differences between the cold low Arctic waters of the Northwest Atlantic and the warmer boreal waters of the Northeast Atlantic, there are significant differences in the avian communities and foodwebs across the North Atlantic (ICES, 2002b, 2003, 2004).
Most strikingly, planktivores dominate the breeding community in the Northwest Atlantic, especially in areas W2 and W3, whereas piscivores play dominant trophic roles in the Northeast Atlantic. The dominance by planktivorous species in the Northwest Atlantic is almost entirely a consequence of the vast number (>30 x 106 pairs) of little auks nesting in northwestern Greenland. In Newfoundland, the community of breeding seabirds is dominated numerically, but not in terms of biomass, by Leach's storm-petrels. In the Northeast Atlantic, the avian communities are dominated by large alcids (mainly guillemots and Atlantic puffins), which feed primarily on small schooling fish (sandeels, capelin, young herring (Clupea harengus), young gadoids). The Northwest Atlantic community is further supplemented by high numbers and a large biomass of trans-equatorial migrant shearwaters that are predominantly planktivorous and breed in the south Atlantic Ocean (Brown et al., 1981; Cairns et al., 1991). These shearwaters also occur in the Northeast Atlantic, but not nearly in the numbers that move into the Northwest Atlantic. Non-breeding seabirds play a more dominant role in the Northwest than in the Northeast Atlantic, and even with the uncertainties associated with these estimates, the relative differences between the two areas appear striking and robust.
The oceanographic rationales for these differences need to be explored. For example, what are the oceanographic conditions off western Greenland that support a vast abundance of plankton-eating seabirds (plus historically large numbers of fish-eating guillemots)? For seabirds, the presence of suitable nesting sites may limit population size (Ashmole, 1963; Olsthoorn and Nelson, 1990), and that limitation may be relevant here. Western Greenland may contain an especially large number of little auk nest sites, or perhaps the islands off Newfoundland provide especially abundant burrow sites for Leach's storm-petrels. More likely, however, is that differences in seabird species composition between regions reflect differences in the prey base. In terms of numbers, the little auks in northwest Greenland deserve special consideration. This is an Arctic community, located near a polynya system, where a high primary production, an extraordinarily long growth season, and a close coupling of primary and secondary production at the planktonic level translates across the regional foodweb to support the largest population of marine birds known in the Arctic (Deming et al., 2002; Hobson et al., 2002; Karnovsky and Hunt, 2002). Little auks in northwest Greenland eat copepods, amphipods, and small polar cod (Boreogadus saida; Nettleship and Birkhead, 1985; Gaston and Jones, 1998; Egevang and Falk, 2001; Karnovsky and Hunt, 2002; Montevecchi and Stenhouse, 2003).
The superabundance of Leach's storm-petrels in Newfoundland may be explained by a combination of nest-site and foraging opportunities. This species requires remote and mammal-free islands, suitable soil in which to dig nest burrows, and sufficient night-time in which to access burrows without being preyed upon by diurnal predators. Sufficient soil for burrowing disappears a short distance north of Newfoundland, and summer daylength increases too. Moreover, secondary productivity is considerably higher around Newfoundland and on the Grand Banks than it is a short distance to the south (Backus and Bourne, 1987).
The piscivorous birds that dominate the bird communities of the Northeast Atlantic are primarily guillemots and Atlantic puffins that feed almost exclusively on schooling forage fish such as sandeels, herring, pilchard (Sardina pilchardus), young gadoids, and sprat (Sprattus sprattus; Mitchell et al., 2004). These fish are found in shallow shelf waters (defined here as a depth < 200 m; Daan et al., 1990). The North Sea, for example, is 89% shelf waters (by comparison, the average proportion of shelf waters overall in the North Atlantic is about 20%). Therefore, part of the dominance by piscivores in the northeast (ICES I–VII) could be due to the high proportion of shelf waters there. However, a similar extent of the shelf waters of W3 not only supports large numbers of piscivorous auks, which breed in the area, but also larger numbers of planktivorous storm-petrels and shearwaters, many of which feed in deep water and along the shelf edge and consume an almost equal biomass of food.
Consumption
Total estimated consumption by seabirds in the North Atlantic of 11 x 106 t is approximately 10–20% of the total consumption by the world's seabirds (maximum CI range = 56–133 x 106 t) estimated by Brooke (2004). Although this percentage seems relatively high, it may reflect both the elevated consumption by seabirds at high latitudes and the conservative approach of Brooke's estimate.
Although still relatively crude in its construction (with regard to numbers of birds, the time they spend in each area, and estimates of energy requirements), we are confident that our consumption estimates are in the correct order of magnitude. This statement is, for example, corroborated by Lilliendahl and Solmundsson's (1997) estimate of summer consumption by six seabird species in Iceland (442 000 t), only 14% lower than that estimated using our model (513 000 t). In waters off eastern Canada, Diamond et al. (1993) estimated seabird food requirements to be 1.1 g m–2 (or 1.1 t km–2), similar to our figure of 0.8 t km–2 (Table 6). Our estimates also corroborate those of Diamond et al. (1993), who found a maximum food requirement off the coasts of Labrador and Newfoundland (W3, Figure 1). Similarly, while our estimate for the Northeast Atlantic (5.9 x 106 t y–1) is ca. 20% higher than Furness' (1994) 4.9 x 106 t y–1, and for the North Sea (680 000 t y–1) is 13% higher than Tasker and Furness' (1996) 600 000 t y–1, the lower figures were based on counts of breeding birds made in the early 1980s, since when the numbers of many species have increased considerably (Mitchell et al., 2004).
|
Taking seasonal movements of birds between and into NAFO and ICES areas into account increased the model output in the NAFO areas by 63% (from 2.9 x 106 to 5.0 x 106 t), and in the ICES areas by 15% (from 5.2 x 106 to 6.0 x 106 t; Table 7). In the ICES areas, this is most evident in the Baltic, Skagerrak, and Kattegat, where adding the population of wintering seaducks nearly doubled the annual consumption estimate for that subarea. The most striking differences in the NAFO areas are attributable to the huge seasonal influxes of birds to and from the southern oceans into NAFO 5 and 6, and the exchanges between northern ICES areas, the eastern Canadian Arctic, and NAFO 0, 1, 2, and 3.
|
The total food consumption estimate for NAFO areas is similar in summer and winter (Table 5), whereas in ICES areas consumption peaks in summer at levels about 50% higher than in winter. The elevated energy demand in summer is primarily due to increased reproductive activity, but also partly to a larger number of birds (and hence higher biomass) in summer than in winter in the northeastern Atlantic. In the ICES areas there are 37% more birds (and 11% higher biomass) as a result of large numbers moving out of the areas in winter and returning in summer. In the NAFO areas, the numbers and biomasses of seabirds are similar in summer and winter.
As for the numbers of seabirds, there is also considerable spatial variation in consumption rate across the ICES and NAFO areas. The apparent paradox of 20% greater total consumption by seabirds in the ICES areas despite the fact that 50–100% more birds occupy the NAFO areas (Table 3) is due to (i) the smaller size of NAFO birds and hence their lower total biomass (Table 4) and energy demand and (ii) the large numbers of planktivores in the NAFO areas. The seabird community of the Northwest Atlantic is dominated by planktivorous seabirds that breed there (Leach's storm-petrels), migrate into the region trans-equatorially in summer (shearwaters), or move into the region in winter (little auks; Brown, 1986; Montevecchi, 2000). Because the energy density of planktonic prey may be approximately 20% lower than the 5.5 kJ g–1 used in the present model, consumption by these planktivores will actually be slightly higher than that calculated here, so reducing this paradox. Moreover, when the surface areas of the NAFO and ICES regions are considered, the consumption rate per unit area in the eastern sector is only approximately half that in the west (Table 6). The greatest harvest rate (2.0 t km–2) was calculated for the area off western Greenland, where the planktivorous little auks dominate the community, and rates >1.0 t km–2 were also apparent off Labrador and Newfoundland, around Iceland, and in the North and Baltic Seas. The lowest rates (0.03 t km–2) were in the deep seas off France and Iberia, and around the Azores.
Many seabirds, however, forage over the rich, inshore shelf areas (Shealer, 2002), and an exploratory analysis taking only shelf areas (here defined as waters <200 m deep) into consideration showed intense feeding off west Greenland, Labrador and Newfoundland, and around Iceland, and a minimum in the deepwater southeastern sector of ICES (the Azores), and in the Gulf of St Lawrence and the Scotian Shelf (W4; Table 6). Such analyses taking into account physical (sea temperature, extent of frontal systems, length of coastline/continental shelf, etc.) and biological parameters (production, etc.) should, however, be investigated further.
|
Summary |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
The comparisons presented here are useful in increasing our understanding of mega-scale oceanic processes and fluxes. Such comparisons will be useful in assessing trends as well as more abrupt changes in oceanography and climate. Considerations of changing trophic interactions will facilitate assessments of shifts in coastal and pelagic foodwebs and how these might be related to the oceanography. It is these biophysical associations between marine birds, their prey, and physical oceanographic variation that are needed for comprehensive engagement of questions about the biological effects of climate change, and about upper trophic level consequences of human fishing practices.
|
Appendix 1 |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
|
|
Appendix 2 |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
|
|
Appendix 3 |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
|
|
Appendix 4 |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
|
|
Acknowledgements |
|---|
This paper is a product of contributions from, and constructive discussions within, the ICES Working Group on Seabird Ecology, for which we are most grateful. We thank also Geir W. Gabrielsen for his advice concerning the energetic equations, and Mardik Leopold and Bob Furness for helpful comments on an early draft. WAM's long-term seabird research programme has been supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and Fisheries and Oceans, Canada.
|
References |
|---|
|
TopIntroductionMethodsResultsDiscussionSummaryAppendix 1Appendix 2Appendix 3Appendix 4References |
|---|
-
Aikman P. (1997) Industrial "Hoover" Fishing: a Policy Vacuum(Greenpeace, Amsterdam) 75 pp.
In Anker-Nilssen T., Bakken V., Strøm H., Golovkin A.N., Bianki V.V., Tatarinkova I.P. (Eds.). The Status of Marine Birds Breeding in the Barents Sea Region. Norsk Polarinstitut Rapportserie, 113 (2000) (Norwegian Polar Institute, Tromsø) 213 pp.
Arnott S.A. and Ruxton G.D. (2002) Sandeel recruitment in the North Sea: demographic, climatic and trophic effects. Marine Ecology Progress Series 238:199–210.[ISI]
Ashmole N.P. (1963) The regulation of numbers of tropical oceanic birds. Ibis 103b:458–473.
Backus R.H. and Bourne D.W. (1987) Georges Bank(MIT Press, Cambridge, MA) 593 pp.
Bakken V., Runde O., Tjørve E. (2003) Norsk ringmerkingsatlas vol. 1. Norwegian bird ringing atlas, vol. 1(Stavanger Museum, Stavanger) 431 pp.
Barrett R.T., Anker-Nilssen T., Gabrielsen G.W., Chapdelaine G. (2002) Food consumption by seabirds in Norwegian waters. ICES Journal of Marine Science 59:43–57.
Brooke M.de.L. (2004) The food consumption of the world's seabirds. Proceedings of the Royal Society, London, Series B 271:S246–S248.
Brown R.G.B. (1986) Atlas of Eastern Canadian Seabirds(Canadian Wildlife Service, Ottawa) 110 pp.
Brown R.G.B., Barker S.P., Gaskin D.E., Sandeman M.R. (1981) The foods of great and sooty shearwaters Puffinus gravis and P. griseus in eastern Canadian waters. Ibis 123:19–30.
A mass balance model of the Newfoundland–Labrador shelf. In Bundy A., Lilly G.R., Shelton P.A. (Eds.). Canadian Technical Report of Fisheries and Aquatic Sciences (2000) 2310: pp. 1–157.
Cairns D.K., Chapdelaine G., Montevecchi W.A. (1991) Prey exploitation by seabirds in the Gulf of St Lawrence. Canadian Special Publication of Fisheries and Aquatic Sciences 113:277–291.
Camphuysen C.J. (2005) Seabirds at sea in summer in the NW North Sea. British Birds 98:2–19.
Carscadden J. E. and Nakashima B. S. (1997) Abundance and changes in distribution, biology and behavior of capelin in response to cooler waters of the 1990s. Proceedings of the International Symposium: Role of Forage Fishes in Marine Ecosystems pp. 457–468 Alaska Sea Grant College Program 97-01.
In Cramp S. (Ed.). The Birds of the Western Palearctic (1985) Oxford University Press vol. IV: 960 pp.
In Cramp S. and Simmons K.E.L. (Eds.). The Birds of the Western Palearctic (1977) Oxford University Press vol. I: 722 pp.
In Cramp S. and Simmons K.E.L. (Eds.). The Birds of the Western Palearctic (1983) Oxford University Press vol. III: 913 pp.
Daan N., Bromley P.J., Hislop J.R.G., Nielsen N.A. (1990) Ecology of North Sea fish. Netherlands Journal of Sea Research 26:343–386.
Davoren G.K. and Montevecchi W.A. (2003) Signals from seabirds indicate changing biology of capelin stocks. Marine Ecology Progress Series 258:253–261.[ISI]
Waterbird Population Estimates. In Delany S. and Scott D. (Eds.). Wetlands International Global Series (2002) 3rd edn (Wetlands International, Wageningen, Netherlands) 12: 226 pp.
Deming J.W., Fortier L., Fukuchi M. (2002) The international north water polynya study (NOW): a brief overview. Deep-Sea Research Part II 49:4887–4892.[CrossRef]
Diamond A.W., Gaston A.J., Brown R.G.B. (1993) A model of the energy demands of the seabirds of eastern and Arctic Canada. In Montevecchi W.A. (Ed.). Studies of High-latitude Seabirds vol. 3: pp. 1–39 Canadian Wildlife Service Occasional Paper, 77.
Durinck J., Skov H., Jensen F. P., Pihl S. (1994) Important marine areas for wintering birds in the Baltic Sea. EU DG XI research contract no. 2242/90-09-01. Ornis Consult Report. 110 pp.
Egevang C. and Falk K. (2001) Chick diet of dovekies Alle alle in Northwest Greenland. Polar Biology 24:53–58.[CrossRef][ISI]
Ellis H.I. and Gabrielsen G.W. (2002) Energetics of free-ranging seabirds. In Schreiber E.A. and Burger J. (Eds.). Biology of Marine Birds(CRC Press, Boca Raton, FL) pp. 359–407.
Furness R.W. (1994) An estimate of the quantity of squid consumed by seabirds in the eastern North Atlantic and adjoining seas. Fisheries Research 21:165–177.[CrossRef][ISI]
Gales R.P. and Green B. (1990) The annual energetics cycle of little penguins Eudyptula minor. Ecology 71:2297–2312.[CrossRef][ISI]
Garcia S.M., Zerbi A., Aliaume C., Do Chi T., Lassarre G. (2003) The ecosystem approach to fisheries. FAO Fisheries Report, 443 71 pp.
Gaston A.J. (2004) Seabirds: a Natural History(T & AD Poyser, London) 222 pp.
Gaston A.J. and Jones I.L. (1998) The Auks(Oxford University Press, Oxford) 349 pp.
In Hagemeijer W.J.M. and Blair M.J. (Eds.). The EBCC Atlas of European Breeding Birds (1997) (T & AD Poyser, London) 903 pp.
Harris M.P., Anker-Nilssen T., McCleery R.H., Erikstad K.E., Shaw D.N., Grobois V. (2005) Effect of wintering area and climate on the survival of adult Atlantic puffins (Fratercula arctica) in the eastern Atlantic. Marine Ecology Progress Series 297:283–296.[ISI]
Hilton G.M., Furness R.W., Houston D.C. (2000) A comparative study of digestion in North Atlantic seabirds. Journal of Avian Biology 31:36–46.[CrossRef][ISI]
Hjermann D., Stenseth N.C., Ottersen G. (2004) Indirect climate forcing of the Barents Sea capelin: a cohort effect. Marine Ecology Progress Series 273:229–238.[ISI]
Hobson K., Fisk A., Karnovsky N., Holst M., Gagnon J.-M., Fortier M. (2002) A stable isotope (
13C, 15N) model for the North Water foodweb: implications for evaluating trophodynamics and the flow of energy and contaminants. Deep-Sea Research Part II 49:5131–5150.[CrossRef]
Huettmann F. and Diamond A.W. (2000) Seabird migration in the Canadian northwest Atlantic Ocean: moulting locations and movement patterns of immature birds. Canadian Journal of Zoology 78:624–647.
ICES. (2001) Report of the Working Group on Ecosystem Effects. ICES Document CM 2001/ACME: 09. 102 pp.
ICES. (2002a) Report of the Working Group on Ecosystem Effects. ICES Document CM 2002/ACME: 03. 195 pp.
ICES. (2002b) Report of the Working Group on Seabird Ecology. ICES Document CM 2002/C: 04. 69 pp.
ICES. (2003) Report of the Working Group on Seabird Ecology. ICES Document CM 2003/C: 03. 91 pp.
ICES. (2004) Report of the Working Group on Seabird Ecology. ICES Document CM 2004/C: 05. 53 pp.
Karnovsky N.J. and Hunt G.L. (2002) Estimation of carbon flux to dovekies (Alle alle) in the North Water. Deep-Sea Research Part II 49:5117–5130.[CrossRef]
Kershaw M. and Cranswick P.A. (2003) Numbers of wintering waterbirds in Great Britain, 1994/1995–1998/1999. 1. Waterfowl and selected waterbirds. Biological Conservation 111:91–104.[CrossRef][ISI]
Trophic Relationships and Energetics of Endotherms in Cold Ocean Systems, Studies of High-latitude Seabirds Lavigne D. M. (1996) Ecological interactions between marine mammals, commercial fisheries, and their prey: unravelling the tangled web. vol. 4:59–71 Canadian Wildlife Service Occasional Paper, 91.
Lilliendahl K. and Solmundsson J. (1997) An estimate of summer food consumption of six seabird species in Iceland. ICES Journal of Marine Science 54:624–630.
Lyngs P. (2003) Migration and winter ranges of birds in Greenland. Dansk Ornitologisk Forening Tidsskrift 97:1–165.
Merkel F.R., Mosbech A., Boertmann D.M., Grøndahl L. (2002) Winter seabird distribution and abundance off southwest Greenland, 1999. Polar Research 21:17–36.[CrossRef][ISI]
Miller A.K. and Sydeman W.J. (2004) Rockfish response to low-frequency ocean climate change as revealed by the diet of a marine bird over multiple time scales. Marine Ecology Progress Series 281:207–216.[ISI]
In Mitchell P.L., Newton S.F., Ratcliffe N., Dunn T.E. (Eds.). Seabird Populations of Britain and Ireland (2004) (Christopher Helm, London) 480 pp.
Montevecchi W.A. (2000) Seabirds. A Mass Balance Model of the Newfoundland–Labrador Shelf. In Bundy A., Lilly G.R., Shelton P.A. (Eds.). Canadian Technical Report of Fisheries and Aquatic Sciences 2310: pp.15–18.
Montevecchi W.A. (2002) Interactions between fisheries and seabirds. In Schreiber E.A. and Burger J. (Eds.). Biology of Marine Birds(CRC Press, Boca Raton, FL) pp. 527–557.
Montevecchi W.A., Garthe S., Davoren G.K. (2006) Biophysical influences on seabird trophic assessments. In Boyd I.L., Wanless S., Camphuysen C.J. (Eds.). Management of Marine Ecosystems(Cambridge University Press, UK) pp. 118–130.
Montevecchi W.A. and Stenhouse I.J. (2003) Dovekie (Alle alle). In Poole A. and Gill F. (Eds.). The Birds of North America, 701(American Ornithologists Union and Academy of Natural Sciences, Philadelphia).
In Nettleship D.N. and Birkhead T.R. (Eds.). The Atlantic Alcidae. The Evolution, Distribution and Biology of the Auks Inhabiting the Atlantic Ocean and Adjacent Water Areas (1985) (Academic Press, London) 574 pp.
Nettleship D.N. and Evans P.G.H. (1985) Distribution and status of the Atlantic Alcidae. In Nettleship D.N. and Birkhead T.R. (Eds.). The Atlantic Alcidae(Academic Press, London) pp. 53–154.
Newton I. (2003) The Speciation and Biogeography of Birds(Academic Press, Amsterdam) 668 pp.
Nygård T., Larsen B.H., Follestad A., Strann K.-B. (1988) Numbers and distribution of wintering waterfowl in Norway. Wildfowl 39:164–176.
O'Boyle R., Sinclair P., Keizer L.K., Ricard D., Yeats P. (2005) Indicators for ecosystem-based management on the Scotian Shelf: bridging the gap between theory and practice. ICES Journal of Marine Science 62:598–605.
Olsthoorn J.C.M. and Nelson J.B. (1990) The availability of nesting sites for some British birds. Bird Study 37:145–164.[ISI]
Pauly D., Alder J., Bennett E., Christensen V., Tyedmers P., Watson R. (2003) The future of fisheries. Science 302:1359–1361.
Shealer D.A. (2002) Foraging behavior and food of seabirds. In Schreiber E.A. and Burger J. (Eds.). Biology of Marine Birds(CRC Press, Boca Raton, FL) pp. 137–177.
Stone C.J., Webb A., Barton C., Ratcliffe N., Reed T.C., Tasker M.L., Camphuysen C.J., Pienkowski M.W. (1995) An Atlas of Seabird Distribution in North-West European Waters(Joint Nature Conservation Committee, Peterborough) 326 pp.
Tasker M. and Furness R.W. (1996) Estimation of food consumption by seabirds in the North Sea. 216: pp. 6–42 ICES Cooperative Research Report.
Wanless S., Wright P.J., Harris M.P., Elston D.A. (2004) Evidence for decrease in size of lesser sandeels Ammodyrtes marinus in a North Sea aggregation over a 30-yr period. Marine Ecology Progress Series 279:237–246.[ISI]
In Wernham C.V., Toms M.P., Marchant J.H., Clark J.A., Siriwardena G.M., Baillie S.R. (Eds.). The Migration Atlas: Movements of the Birds of Britain and Ireland (2002) (Poyser, London) 884 pp.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||