T. Gaston, G. Gilchrist
Environment Canada, National Wildlife Research Centre, Carleton University, Ottawa, Canada K1A 0H3
The two species of murres (N. America)/guillemots (Europe), Uria lomvia (Thick-billed Murre) and U. aalge (Common Murre), both have circumpolar distributions, the former breeding in Arctic and Subarctic regions, from northern Norway, Iceland, Newfoundland and the Aleutian Islands to the High Arctic, while the latter is predominantly a Subarctic and Boreal species breeding from California, the Gulf of St. Lawrence and northern Spain to the northern Bering Sea, Labrador and Bjornoya (Bear Island). In winter, U. lomvia occurs mostly in Arctic waters, while U. aalge, although overlapping extensively with U. lomvia, is found predominantly in subarctic and temperate waters (Figs. 1 and 2). They are among the most abundant seabirds in the northern hemisphere, with both species exceeding 10 million adults (Gaston and Jones 1998).
Murres feed from coastal to pelagic waters, taking a wide range of small fish (<50 g) and invertebrates, including annelids, pteropod and cephalopod molluscs, and mysid, euphausiid, amphipod and decapod crustacea. Common Murres generally feed more on fish than Thick-billed Murres (Gaston and Jones 1998, Anker-Nilssen et al. 2000). Adults of both species weigh about 1 kg, can remain under water for up to 4 min and dive regularly to depths >100 m, reaching a maximum depth of ~150 m. Their diving capacity, when combined to their typical foraging radius of up to100 km from the colony, means that murres sample a relatively large volume of the marine environment around their colonies (Falk et al. 2000, Elliott et al. 2008).
Murres have proven useful indicators of environmental change in studies of population trends (Gaston et al. 2009), nestling growth (Barrett 2002, Gaston et al. 2005) and nestling diet (Osterblom et al. 2001). They breed in very large colonies of up to 1 million birds on mainland cliffs or offshore islands. In most places, they lay their eggs in the open, making breeding adults simple to count. Consequently, their population trends are relatively easy to assess and this, allied to their abundance and widespread distribution, makes them ideal subjects for circumpolar environmental monitoring. In addition, being robust birds and returning annually to the same breeding sites, they are useful platforms on which to deploy depth and temperature recorders, GPS and geolocator tags. These devices have greatly amplified the value of the birds for environmental monitoring.
Status and Trends
The sensitivity of murre populations to changes in environmental conditions has been demonstrated on a hemispheric scale in recent studies by the Seabird Working Group of CAFF (C-Bird). Irons et al. (2008) combined population trend data from around the Arctic with information on surface sea temperature (SST) and decadal-scale oscillations, to show that both species of murre showed negative population trends where there was a large change in SST, either warmer or cooler. Colony growth was most often positive where conditions remained relatively stable (Fig. 3). More specifically, the northern species, U. lomvia, exhibited highest population growth where conditions warmed moderately. U. aalge showed highest rates of increase where things cooled moderately. In the context of global warming, this result suggests that not only the direction but the magnitude of change may be important in determining outcomes and that Common and Thick-billed Murres may not necessarily react in the same way to a given temperature change.
Both species have shown substantial variation in regional population trends since the 1970s. A comparison of the period from 1977-1989, when Sea Surface Temperatures (SST) in the North Pacific were generally above normal and those in the North East Atlantic generally below normal, with the period from 1989-1999 when the situation reversed, showed that populations in the North Pacific were generally decreasing during the earlier decade and increasing subsequently (Fig. 4, Irons et al. 2008). Conversely, those in the eastern Atlantic showed more variable trends. However, several European colonies were affected by widespread collapse of fish stocks in the 1980s (Vader et al. 1990). Those European colonies not affected by fish-stock collapses mostly increased up to 1989, but increases were less general between 1989-1999. Only a few colonies, principally those in the eastern Canadian Arctic, have shown consistent increases in population and no colonies have shown persistent downward trends (C-bird unpubl. data). Subsequent to 1999, regional trends have been less clear. Populations of both species in the Barents Sea have begun to recover from earlier declines related to fish stock collapse (Barrett et al. 2006). Those in Alaska and in the Canadian Arctic have been stable overall since the 1990s (Dragoo et al. 2008, Gaston et al. in press).
Murres, both adults and eggs (especially lomvia), are harvested by aboriginal people and by local communities in many Arctic jurisdictions. These activities are not thought to have much impact on populations except in West Greenland, where some colonies have been substantially reduced by harvesting of adults while breeding (CAFF). Both species are highly susceptible to oiling and they are often the most numerous species killed by oil spills. They are frequently drowned in gill-nets, especially when these are set overnight (Melvin et al. 1999): hundreds of thousands were killed in salmon gill-nets off West Greenland in the 1960s (Tull et al. 1972). Although currently abundant, with few populations showing cause for alarm, climate change will pose a future problem and range contraction appears likely in the longer-term.
Despite substantial research and monitoring on the two species, information is generally inadequate to quantify changes in murre feeding ecology and food availability, or changes in mortality due to oil pollution, commercial fisheries, and hunting. In 1996, the Circumpolar Seabird Group reviewed conservation issues affecting murres, and produced an International Murre Conservation Strategy and Action Plan to guide future international conservation efforts. The plan proposed action to assess the threats to murres from harvests, and commercial and industrial activities. The Plan also recommended further research to address the potential effects of global climate change on murre populations.
* Note: On "murres" vs "guillemots". We think the use of murres is preferable because guillemot does not exclude Cepphus spp. when used as a collective noun.
Anker-Nilssen, T., Bakken, V., Ström, H., Golovkin, A.N., Bianki, V.V. and Tatarinkova, I.P. 2000. The status of marine birds breeding in the Barents Sea region.
Barrett, R.T. 2002. Atlantic Puffin Fratercula arctica and Common Guillemot Uria aalge chick diet and growth as indicators of fish stocks in the Barents Sea. Marine Ecology Progress Series 230: 275-287.
Barrett, R.T., Lorentsen, S.H. and Anker-Nilssen, T. 2006. The status of breeding seabirds in mainland Norway. Atlantic Seabirds 8: 97-126.
Circumpolar Seabird Working Group. 1996. International Murre Conservation Streategy and Actiona Plan. CAFF International Secretariat. Environment Canada, Ottawa. 11pp.
Dragoo, D. E., Byrd, G.V. and Irons, D.B. 2008. Breeding status, population trends and diets of seabirds in Alaska, 2005. U.S. Fish and Wildl. Serv. Report AMNWR 08/03. Homer, Alaska.
Elliott, K., Woo, K., Gaston, A.J., Benvenuti, S., Dall'Antonia, and Davoren, G. 2008. Foraging behaviour of an arctic seabird indicates prey type. Marine Ecology Progress Series 354: 289-303.
Falk, K., Benvenuti, S., Dall'antonia, L., Kampp, K., Ribolini, A. 2000. Time allocation and foraging behaviour of chick-rearing Brunnich's Guillemots Uria lomvia in high-arctic Greenland. Ibis 142: 82-92.
Gaston, A.J. and Jones, I.L. 1998. The Auks – Alcidae. Oxford University Press, Oxford, UK.
Gaston, A.J., H.G. Gilchrist and J.M. Hipfner. 2005. Climate change, ice conditions and reproduction in an Arctic nesting marine bird: the thick-billed murre (Uria lomvia, L.). J. Animal Ecology 74: 832-841.
Gaston, A.J., Bertram, D.F., Boyne, A.W., Chardine, J.C., Davoren, G., Hedd, A., Hipfner, J.M., Lemon, M.J.F., Mallory, M.L., Montevecchi, W.A., Rail, J.F. and Robertson, G.W. 2009. Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs. Environmental reviews in press.
Irons, D.B., Anker-Nilssen, T., Gaston, A.J., Byrd, G.V., Falk, K., Gilchrist, G., Hario, M., Hjernquist, M., Krasnov, Y.V., Mosbech, A., Olsen, B., Petersen, A., Reid, J., Robertson, G., Strom, H. and Wohl, K.D. 2008. Magnitude of climate shift determines direction of circumpolar seabird population trends. Global Change Biology 14: 1455-1463.
Melvin, E. F., Parrish, J.K. and Conquest, L.L. 1999. Novel tools to reduce seabird bycatch in coastal gillnet fisheries. Conservation Biology 13: 1386-1397.
Osterblom, H., Bignert, A., Fransson, T. and Olsson, O. 2001. A decrease in fledging body mass in Common Guillemot Uria aalge chicks in the Baltic Sea. Marine Ecology Progress Series 224: 305-309.
Tull, C.E., Germain, P. and May, A.W. 1972. Mortality of Thick-billed Murres in the Greenland salmon fishery. Nature, Lond. 237: 42-44.
Vader W., Barrett R.T., Erikstad K.E. and Strann K.-B. 1990. Differential responses of Common and Thick-billed Murres to a crash in the Capelin stock in the southern Barents Sea. Studies in Avian Biology 14: 175-180.