• Introduction - Seabirds and oil in Atlantic Canada waters
• Surveys of beached birds in Atlantic Canada
• Birds killed by oil at sea
• Assessing the numbers of seabirds killed by oil at sea
• The estimated number of Thick-billed Murres killed by oil
• The impact of these losses on Thick-billed Murre populations
• Mortality of other seabird species
• Overall numbers of seabirds killed each year

A. Introduction - Seabirds and oil in Atlantic Canada waters

Oil released at sea, whether from chronic operational discharges or accidental spills, can directly kill any seabird that it touches on the sea surface. This oiling causes severe distress for individual birds and can have significant impacts at the population level. Marine oil pollution from chronic operational discharges is both illegal and preventable. The costs of taking appropriate action to prevent such discharges make it important to quantify, to the degree possible, the severe ecological consequences of continuing to release oil into the sea.

Atlantic Canada is an important crossroads for seabirds, where productive marine waters support the tens of millions of birds¹. Huge numbers of birds from Newfoundland breeding colonies overlap with millions of seasonal visitors - wintering birds from colonies in Arctic Canada and Europe and from the south Atlantic. The same waters serve as commercial fishing grounds and major shipping lanes linking Europe and North America. Operational discharges of oil from the huge numbers of vessels present throughout the year continue to put millions of Atlantic Canada's seabirds at risk.

B. Surveys of beached birds in Atlantic Canada

Assessing the impact of this oil on seabird populations requires a knowledge of the number of birds of each species that are killed by oil at sea. This information is difficult to obtain in Atlantic Canada, where major currents and winds usually carry oiled birds away from land, and where there may be little direct evidence of large offshore kills of seabirds. However, some dead seabirds do wash ashore along the southern coast of the Avalon Peninsula in southeastern Newfoundland. Regular beached-bird surveys conducted there monthly since 1984, and almost weekly from 1998 to 2001, provide the best indication in Atlantic Canada of the numbers of seabirds killed by oil at sea.

These surveys indicate that the incidence of chronic oil pollution along the coast of southeastern Newfoundland is among the highest in world². More than 60% of all dead birds found over from 1984-1999 had oil on their feathers - 74% during the most recent five years³. However, there was no overall upward or downward trend over this period in the number of oiled birds, or the oiling rate, which is most reliably indicated by the number of oiled birds found each year per kilometer of beach that was surveyed. Most oil on the seabirds' feathers was heavy fuel oil mixed with lubricants, typical of the mixture found in the engine room bilges of large vessels⁴.

The proportion of beached birds found during these surveys with oiled feathers varied substantially from year-to-year, ranging from 31% to 80%³.

The population impacts considered in this scientific assessment are based largely on the results of these surveys, considered in the context of other information on seabird numbers, the incidence and location of oil spills, the numbers of birds killed by specific oiling incidents, and the ecology and population dynamics of the seabird species affected.

C. Birds killed by oil at sea

Based on the Avalon beached-bird survey results, other short-term beached-bird surveys in Atlantic Canada, and observations of birds directly killed by known oiling incidents, we can make the following general statements about the impacts of chronic operational oil discharges:

• Most seabirds are killed during the winter months, particularly November to March, when marine waters are cold and severe winter weather puts added stress on seabirds, and when large numbers of several seabird species that are vulnerable to oil over-winter in the waters of Atlantic Canada⁶.
• Although at least twenty seabird species are known to be killed by oil in waters of Atlantic Canada⁷, the species most commonly found oiled on surveys are (in decreasing order) Thick-billed Murres, Common Murres and Dovekies⁸. Together, these made up over 80% of the oiled birds recorded on the Avalon beached bird survey during the winter months⁸.
• Other oiled birds regularly encountered on that survey include Herring and Great Black-backed Gulls, Black Guillemots, Common Eiders, Atlantic Puffins, Northern Gannets and Long-tailed Ducks (or Oldsquaw)⁸. Common and Red-throated Loons, Double-crested Cormorants, Black-legged Kittiwakes and Greater Shearwaters are also regularly killed by oil in Atlantic Canada⁷.

D. Assessing the numbers of seabirds killed by oil at sea

Only a small proportion of birds killed by oil are actually found on shore, because many never reach land, instead being carried offshore or sinking. Others may reach the shore but are never found, instead becoming buried in the beach, decomposing or being carried off by scavengers. Estimates of the actual number of birds dying at sea are derived using an approach that sequentially builds in the following information:

• the number of oiled birds found washed ashore on beaches,
• the length of time that carcasses of oiled birds remain on a beach,
• the length of time that an oiled bird carcass floats at sea before sinking,
• the proportion of those birds that die at sea which drift towards shore, and
• the size of the ocean area being considered, where ship-source oil pollution and seabirds overlap, resulting in the risk of oiling to seabirds.

For the waters off southeastern Newfoundland, the many variables that must be considered to complete these complicated calculations have been assembled for the species most commonly found oiled - the Thick-billed Murre, or turr. This species breeds in colonies in the eastern Canadian Arctic and western Greenland, and is one of the most numerous wintering seabirds in waters off Newfoundland and northern Nova Scotia. It is regionally important as the most common species taken in the Newfound-land turr hunt.

E. The estimated number of Thick-billed Murres killed by oil

Estimates were derived using this approach by Francis Wiese of Memorial University of Newfoundland, from data collected in 1998-99 to 2000-01. He estimated that between 180,000 and 250,000 Thick-billed Murres were killed each winter from chronic oil pollution in waters off southeastern Newfoundland, within an area encompassing the adjacent Grand Banks directly south of Newfoundland⁹. However, recognizing the degree of uncertainty in several of the factors used in these calculations, he advises using an conservative estimate of about 200,000 Thick-billed Murres¹⁰.

F. The impact of these losses on Thick-billed Murre populations

The effect of this level of mortality on Thick-billed Murre populations can be calculated, based on our estimates of the size of the population breeding in Canada's eastern Arctic - about 2,000,000 breeding pairs11 - and our knowledge of murre life history and survival from detailed studies at Canadian colonies, particularly in northern Hudson Bay¹².

• Wiese estimated that in the absence of any oil-related mortality, the Canadian Thick-billed Murre population could grow appreciably, at an average rate of about 3.5%/year, even with present levels of hunting in Newfoundland1³.
• He estimated that oil-related mortality reduces the growth rate of harvested murre populations to about 1%/year, removing most of its growth potential¹². The population thus has little buffer to withstand the effects of occasional high mortality. This includes natural losses, as may occur when stormy winters or heavy pack-ice make feeding difficult, or the impact of occasional large accidental oil spills of the type that occurred following the wrecks of the Arrow¹⁴ and the Kuridistan¹⁵, when tens of thousands of birds may die.

G. Mortality of other seabird species

Wiese also estimated that about 25,000 to 40,000 Common Murres and 60-80,000 Dovekies may have been killed each winter by oil off southeastern Newfoundland, during 1998-99 to 2000-01⁹. Because it is so difficult to quantify the numbers of other species killed off southeastern Newfoundland, and to assess oil-related mortality off the Maritime provinces, estimates cannot be made for other species.

However, it is clear that death by oiling at sea can significantly depress population numbers and population growth for long-lived seabird species, particularly when mortality levels are sustained, adults are impacted or species with small populations are affected.

H. Overall numbers of seabirds killed each year

Given the uncertainties in assessing numbers of birds killed by oil when based on the results of beached-bird surveys, and the annual variation in the numbers of birds that succumb to oil, it is prudent to use a conservative but realistic estimate of the minimum number killed. A scientifically-defensible minimum estimate of this type can be derived by using minimum values of Wiese's estimates for murres and dovekies killed off Newfoundland, expanding the area considered to include other areas of Atlantic Canada where ship-source oil pollution and wintering populations of seabirds overlap, and extrapolating to include other species of seabirds present during the winter.

Such an approach results in a conservative estimate that about 300,000 seabirds are killed each winter in the waters of Atlantic Canada, by chronic operational discharges of oil at sea¹⁶. This minimum estimate confirms concerns that huge numbers of birds are killed needlessly and illegally in our waters, with appreciable effects on populations of commonly-oiled species such as Thick-billed Murres.

This overall assessment exceeds estimates of the regulated harvest of murres in the Newfoundland turr hunt (about 170,000 to 290,000 birds annually¹⁷). It is also significantly higher than the highest estimates of the number of breeding seabirds killed in inshore fishing gear in Newfoundland waters, during peak years in the early 1980s (about 30,000 birds annually¹⁸).

I. Sources of information

The above results are based on the following publications, theses and reports, and the observations of biologists and research scientists from the Canadian Wildlife Service and Memorial University of Newfoundland:

1. Page 23 in: Chardine, J.W. 1995. The distribution and abundance of aquatic birds in Canada in relation to the threat of oil pollution. Pp. 23-36 in: L. Frink ed., Wildlife and Oil Spills: Response, Research, Contingency Planning. Tri-State Bird Rescue and Research, Newark, Delaware, 182 pp.

2. Page 47 in: Wiese, Francis K. 2002. Estimation and impacts of seabird mortality from chronic marine oil pollution off the coast of Newfoundland. Ph.D. Thesis (submitted September 2002), Dept. Biology, Memorial University of Newfoundland, St. John's, 321 pp.

3. Page 38 (Table 2.1) in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

4. Page ii in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

5. Page 49 in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

6. Page 45 (Figure 2.9) in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

7. several sources, including the authors' personal observations of beached birds, and: Pages 23-24 (Table 5) in: Piatt, J.F., R.D. Elliot, A. MacCharles. 1985. Marine Birds and Oil Pollution. Memorial University of Newfoundland. Nfld. Institute for Cold Oceans Science Report 105, 63 pp.

8. Page 46 (Table 2.2) in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

9. Page 226 in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

10. Page 243 in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

11. Page 257 (Table 8.1) in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland, and Page 151 in: Gaston. A. J. and I. L. Jones. 1998. The auks. Oxford University Press, Oxford, U.K.

12. The results of Canadian Wildlife Service studies at Coats Island, Nunavut, including: Gaston, A.J., L.N. de Forest, G. Donaldson and D.G. Noble. 1994. Population parameters of Thick-billed Murres at Coats Island, Northwest Territories, Canada. Condor 96: 935-948. Gaston, A.J. and J.M. Hipfner. 2000. The Thick-billed Murre Uria lomvia. In: A. Poole and F. Gill, eds. The Birds of North America No. 497. The Birds of North America, Inc., Philadelphia, Pennsylvania. Gaston, A.J. 2002. Studies of high-latitude seabirds. 5. Monitoring Thick-billed Murres in the eastern Canadian Arctic, 1976-2000. W. A. Montevecchi, ed. Canadian Wildlife Service Occasional Paper 106, 59 pp.

13. Page 268-269 (Table 8.2) in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

14. Described in: Brown, R.G.B., D.I. Gillespie, A.R. Lock, P.A. Pearce and G.H. Watson. 1973. Bird mortality from oil slicks off eastern Canada, February-April 1970. Can. Field-Naturalist. 87:225-234.

15. Described in: Brown, R.G.B. and B.C. Johnson. 1980. The effects of Kurdistan oil on seabirds. Pp. 203-208 In Scientific studies during the Kurdistan tanker incident: Proceedings of a workshop. June 26-27 1979. (J.H. Vandermeulen, ed.) B.I.O. Report series BI-R-80-3.

16. Page 239 in: Wiese, Francis K. 2002. Ph.D. Thesis, Memorial University of Newfoundland.

17. Page 13 in: Chardine, J.W., B.T. Collins, R.D. Elliot, H. Levesque and P.C. Ryan. 1999. Trends in the annual harvest of murres in Newfoundland and Labrador. Bird Trends 7:11-14.

18. Page 344 in: Piatt, J.F. and D.N. Nettleship. 1987. Incidental catch of marine birds and mammals in fishing nets off Newfoundland, Canada. Marine Pollution Bulletin. 18:344-349.