The Project Gutenberg EBook of Conservation of marine birds of northern North America: papers from the international symposium held at the Seattle Hyatt House, by Various This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org/license Title: Conservation of marine birds of northern North America: papers from the international symposium held at the Seattle Hyatt House Author: Various Editor: James C. Bartonek David N. Nettleship Release Date: June 30, 2015 [EBook #49335] Language: English Character set encoding: ASCII *** START OF THIS PROJECT GUTENBERG EBOOK CONSERVATION OF MARINE BIRDS *** Produced by Richard Tonsing, Bryan Ness and the Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.) WILDLIFE RESEARCH REPORTS This series comprises reports of research relating to birds, mammals, and other wildlife and their ecology, and specialized bibliographies on these, issued for wildlife research and management specialists. The Service distributes these reports to official agencies, to libraries, and to researchers in fields related to the Service's work. Library of Congress Cataloging in Publication Data Conservation of marine birds of northern North America. (Wildlife research report: 11) Supt. of Docs. no.: I 49.47/4:11 1. Sea birds—North America—Congresses. 2. Sea birds—Northwest, Pacific—Congresses. 3. Birds, Protection of— North America—Congresses. 4. Birds, Protection of—Northwest, Pacific—Congresses. 5. Birds—North America— Congresses. 6. Birds—Northwest, Pacific—Congresses. I. Bartonek, James C. II. Natural Resources Council of America. III. United States. Fish and Wildlife Service. IV. Series. QL681.C59 333.9'5 79-607005 Use of trade names does not imply U.S. Government endorsement of commercial products. CONSERVATION OF MARINE BIRDS OF NORTHERN NORTH AMERICA CONSERVATION OF MARINE BIRDS OF NORTHERN NORTH AMERICA Papers from the International Symposium held at the Seattle Hyatt House, Seattle, Washington, 13-15 May 1975 Edited by James C. Bartonek and David N. Nettleship Sponsored by Natural Resources Council of America National Audubon Society National Wildlife Federation U.S. Department of the Interior, Fish and Wildlife Service UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE Wildlife Research Report 11 Washington, D.C. • 1979 Dedicated to the Memory of Robert D. Bergman, Leonard A. Boughton, and J. Larry Haddock, Wildlife Biologists of the Fish and Wildlife Service, and Robert Johnson, Pilot of the Office of Aircraft Services, all of the U.S. Department of the Interior, who perished in the Gulf of Alaska on 30 September 1974 while conducting aerial surveys of marine birds, and to Einar Brun, Professor of Zoology in Tromsø University and a contributor to these proceedings, who perished in the Vega Sea on 13 July 1976 when returning from making aerial surveys of marine birds. Contents Page Foreword, by Harvey K. Nelson vii Introduction, by Lynn A. Greenwalt ix Marine Environment of Birds 1 Long-term Climatic and Oceanographic Cycles Regulating Seabird Distributions and Numbers, by M. T. Myres 3 Sea Ice as a Factor in Seabird Distribution and Ecology in the Beaufort, Chukchi, and Bering Seas, by George J. Divoky 9 Status of Marine Bird Populations 19 Distribution and Status of Marine Birds Breeding Along the Coasts of the Chukchi and Bering Seas, by James C. Bartonek and Spencer G. Sealy 21 Breeding Distribution and Status of Marine Birds in the Aleutian Islands, Alaska, by Palmer C. Sekora, G. Vernon Byrd, and Daniel D. Gibson 33 The Historical Status of Nesting Seabirds of the Northern and Western Gulf of Alaska, by LeRoy W. Sowl 47 Status and Distribution of Breeding Seabirds of Southeastern Alaska, British Columbia, and Washington, by David A. Manuwal and R. Wayne Campbell 73 The Biology and Ecology of Marine Birds in the North 93 Trophic Relations of Seabirds in the Northeastern Pacific Ocean and Bering Sea, by David G. Ainley and Gerald A. Sanger 95 Population Dynamics in Northern Marine Birds, by William H. Drury 123 Time-energy Use and Life History Strategies of Northern Seabirds, by Erica H. Dunn 141 Zoogeography and Taxonomic Relationships of Seabirds in Northern North America, by M. D. F. Udvardy 167 Conflicts Between the Conservation of Marine Birds and Uses of Other Resources 171 Social and Economic Values of Marine Birds, by David R. Cline, Cynthia Wentworth, and Thomas W. Barry 173 Resource Development Along Coasts and on the Ocean Floor: Potential Conflicts with Marine Bird Conservation, by Donald E. McKnight and C. Eugene Knoder 183 Mortality to Marine Birds Through Commercial Fishing, by Warren B. King, R. G. B. Brown, and Gerald A. Sanger 195 Interactions Among Marine Birds and Commercial Fish in the Eastern Bering Sea, by Richard R. Straty and Richard E. Haight 201 Interrelations Between Seabirds and Introduced Animals, by Robert D. Jones, Jr., and G. Vernon Byrd 221 Oil Vulnerability Index for Marine Oriented Birds, by James G. King and Gerald A. Sanger 227 Programs and Authorities Related to Marine Bird Conservation 241 Programs and Authorities Related to Marine Bird Conservation in Washington State, by Ralph W. Larson 243 Programs and Authorities of the Province of British Columbia Related to Marine Bird Conservation, by W. T. Munro and R. Wayne Campbell 247 Petroleum Industry's Role in Marine Bird Conservation, by Keith G. Hay 251 Conservation of Marine Birds in Other Lands 259 Conservation of Marine Birds in New Zealand, by Gordon R. Williams 261 Marine Birds in the Danish Monarchy and Their Conservation, by Finn Salomonsen 267 Present Status and Trends in Population of Seabirds in Norway, by Einar Brun 289 Symposium Summary 303 Conservation of Marine Birds of Northern North America—a Summary, by Ian C. T. Nisbet 305 Appendix. Papers and oral summaries presented at the symposium but which do not appear in this publication 319 Foreword The international symposium "Conservation of Marine Birds of Northern North America" was convened because of a growing awareness that not all was well with our marine birds. The symposium provided a forum for scientists, governmental administrators, conservationists, and laypeople to discuss the diverse topics and issues that we must all understand if we are to act both responsively and responsibly to assure that marine birds will not be lost through our neglect. The symposium was cosponsored by the Natural Resources Council of America, National Audubon Society, National Wildlife Federation, and the U.S. Department of the Interior, Fish and Wildlife Service; additional support was provided by the Canadian Wildlife Service, the International Association of Game, Fish, and Conservation Commissioners, the Pacific Seabird Group, the Sierra Club, the Smithsonian Institution, the Wildlife Management Institute, and the Wildlife Society. Persons interested and knowledgeable in the many and varied aspects of marine bird conservation were invited to participate in this symposium. There were 139 registered and several score of unregistered participants in attendance. Major topics treated were: (1) socioeconomic considerations and conservation of marine birds; (2) the marine environment of birds; (3) status of marine bird populations on land and sea; (4) the biology and ecology of marine birds in the North; (5) conflicts between the conservation of marine birds and uses of other resources; (6) programs and authorities related to the conservation of marine birds; and (7) conservation of marine birds in other lands. The objective of the symposium was to identify problems and the needed information and programs necessary for the conservation of marine birds of northern North America. For the purpose of this symposium the term "northern North America" referred to the coasts of Washington, British Columbia, Alaska, Yukon Territory, and Northwest Territories and the adjacent North Pacific and Arctic Oceans. "Marine bird" was defined as being any bird using marine or estuarine waters. Speakers were asked to describe the status of information or the state of the art as it pertained to their topic within the limitations set by the objective of the symposium. Examples from other regions and of bird species not found in the regions of concern were to be used for comparative purposes when little pertinent information was known for regions or species of concern. Speakers were asked to identify the gaps in the knowledge and methodology that are most critical to their topic. I believe that this symposium was particularly successful in that it provided a timely forum for many scientists who were about to embark on studies of marine birds in those areas of Alaska and California being considered for outer continental shelf oil and gas exploration and development. These published proceedings may be of lesser importance from that standpoint because some data, particularly those on populations, are out of date. However, I believe that the proceedings will long be of importance to biologists and administrators alike in charting their respective courses to ultimately assure conservation of this valuable avian resource. Many people from many organizations and agencies worked hard to put together the symposium in the relatively short time of about 8 months. Nathaniel P. Reed was the person primarily responsible for bringing this symposium to fruition. The Steering Committee was composed of Daniel A. Poole, John S. Gottschalk, David N. Nettleship, Amos S. Eno, C. Eugene Knoder, Warren G. King, Louis Clapper, Robert Hughes, Fred G. Evenden, James C. Bartonek, and me. James C. Bartonek, Warren G. King, David N. Nettleship (Co-chairmen), C. Eugene Knoder, David A. Manuwal, William H. Drury, and Spencer G. Sealy served on the Program Committee. David A. Manuwal and Terence R. Wahl arranged trips for persons to observe pelagic birds off the Washington coast and other birds on Skagit Flats. C. Eugene Knoder handled financial matters. John A. Sayre and Richard Bauer made arrangements for facilities and entertainment. Elaine Rhode prepared the program and abstracts for printing. John Pitcher kindly contributed the artwork used in this publication as well as that used in the program and abstracts. George Reiger made general introductions to the symposium; Spencer G. Sealy, Daniel W. Anderson, and I served as Session Chairmen; and James C. Bartonek served as General Chairman. Elvis J. Stahr was guest speaker at the symposium banquet. Most credit for the success of this symposium goes to the 52 persons who as authors, coauthors, or summarizers of sessions presented much meaningful information in their presentations, during recorded discussions, and during many informal occasions. I wish to make special recognition of Ian C. T. Nisbet for his skillful summary of the symposium. Editorial assistance in preparing the proceedings was provided by Judith Brogan. Harvey K. Nelson Chairman of Symposium and Director of Wildlife Resources Introduction Migratory birds make up a resource that is shared by many people of many nations. Public awareness of marine birds— their manifold values, ecological requirements, and problems—is prerequisite to their protection. I am proud that the Fish and Wildlife Service can further this needed awareness by publishing these proceedings of the international symposium "Conservation of Marine Birds of Northern North America." Lynn A. Greenwalt, Director Fish and Wildlife Service MARINE ENVIRONMENT OF BIRDS Long-term Climatic and Oceanographic Cycles Regulating Seabird Distributions and Numbers by M. T. Myres Department of Biology, University of Calgary Calgary, Alberta, Canada T2N 1N4 Abstract Seabird ornithologists have generally paid little attention to the possible roles played by long-term climatic cycles or air-ocean interactions on population changes at established colonies or on the processes of colony establishment or extinction. Yet, a rapidly expanding literature in the physical sciences suggests that seabird numbers are not naturally stable at particular colonies for any great length of time. It is suggested that the establishment of new colonies at one end of the range may counter the decline of colonies at the other end. Perhaps these changes in small marginal colonies are important, and they may be more indicative and significant (when detected and explained) than are much larger changes in numbers in bigger reproductive units in the center of a species' range. Fluctuations in seabird numbers must in future be first considered as possible responses either to short-term, or turnarounds in longer term, natural climatic or oceanographic cycles, or to trends ranging in length from a few years to at least several decades. During the last 30 years extensive literature in the fields of physical and biological oceanography has accumulated that is not readily accessible to the nonprofessional student of seabirds and not as widely understood by career seabird ornithologists as it should be. This literature in oceanography and marine fisheries is as extensive in Russian and Japanese together as in the main languages of Western Europe combined; this abundance compounds the problem of becoming familiar with it if, as a student of seabirds, one's interest in the literature is initially somewhat marginal. Nevertheless, to achieve the best possible appreciation of the oceanographic influences affecting seabirds, particularly in the north Pacific Ocean and its adjacent embayment seas, it is necessary to make the effort. Because of the rigor of carrying out their primary duties while at sea, only a very few North American and European oceanographers or fishery biologists have found time to interest themselves in seabirds and then, with a few notable individual exceptions, only as an off-duty pastime. The reason is not far to seek. It is far less important to examine the ecology of organisms at the next highest level of the food chain to the ones that are the primary concern than it is to examine the next lowest level (the food of the fishes or, in the case of phytoplankton, the physical and chemical environment in which the organisms grow best). Seabirds are at the very top of the marine food chain, and they are not wholly aquatic in any case since they mainly travel through the air rather than the water and reproduce on land rather than in the sea. Only with the relatively recent recognition that seabirds contribute to the recycling of nutrients back into the ocean to an important degree, have seabirds gained a new scientific constituency. At about the same time, governments have begun to recognize that seabirds are relatively easily examined indicators of the presence of unseen chemical pollutants in coastal seas, perhaps primarily for the very same reasons that they were previously so largely ignored; namely, that they are at the top of the food chains (and so accumulate the most-persistent and least-degradable pollutants) and that the on-land failures in their reproductive biology are readily visible. During the last 10 years, it has become evident that yet another fundamental science is even more basic to the achievement of a balanced and in-depth understanding of the influence of the environment upon seabirds—the combined field of astrophysics, geophysics, and climatology. New developments in this field (when they are not published in Nature or Science) appear in journals that are less familiar to seabird ornithologists than those in which the fishery biologists and biological oceanographers publish their findings. Unfortunately, important advances in understanding the dynamics and energy transport mechanisms of both the atmosphere and the water masses of the oceans are not being picked up by students of seabirds because of the natural lag in communication that occurs between disparate disciplines. Only in the last few years have oceanographers and climatologists been invited to address gatherings of ornithologists, and the modesty with which they have sometimes done so has limited the impact of their offerings. At this symposium, it was left to a biologist with no pretentions in either physics or mathematics to demonstrate the need for seabird ornithologists to understand basic environmental processes well beyond their usual range of interests. I did so with a series of slides taken from this "other" literature, and I had intended to include in the published version of this paper an extensive bibliography, subdivided into category groupings, so that seabird ornithologists could make their own selection of the points in the spectrum at which they most needed information. Unfortunately, limitations upon space in this volume, daily additions to the exploding literature, and my own inability to keep up with understanding this have forced me to omit any references and not to attempt to expound detailed specific physical mechanisms. Thus unencumbered here, I shall briefly outline instead what I perceive to be some of the significance for seabird ornithology and conservation of the rapidly expanding understanding of the oceans, the air-sea interface, atmospheric dynamics, and influences upon the world's climate of extraterrestrial events. Small-scale or Short-term Influences There is no need to dwell on the well-known events that could be mentioned under this heading. Seabird ornithologists are familiar with the fact that the atmosphere is the medium of seabirds both when searching the ocean for feeding areas and when on migration, and also a violent enemy, as when particular storms cause occasional "wrecks" of seabirds inland from coastlines. As a refinement of the former, Manikowski of Poland suggests that seabirds respond to the passage of weather systems, so that their distribution over the open ocean may be constantly changing. Whereas some species may attempt to avoid the stormy conditions of low-pressure areas (cyclonic conditions), others more highly specialized for exploiting the aerodynamic properties of wind over a moving water surface may possibly, instead, try to avoid large high-pressure regions (anticyclonic conditions with little or no wind). My student, Juan Guzman, is attempting to determine whether this may be so; if it is, it might be possible, for example, to predict some things about the distribution patterns and population structure of southern hemisphere shearwaters while they are visiting the oceans of the northern hemisphere during the nonbreeding season. In comparison with the "wrecks" brought about by storms, which are of short duration and not usually very serious, seabird ornithologists are also familiar with relatively brief and localized disasters caused by changes in the ocean itself. The best- known example is a slight change in the boundary of an ocean current (or other shift in the position of a distinctive water mass) that results in the failure of food fishes to appear as they normally would, close to breeding sites of conspicuous colonial seabirds, such as the periodic shift in the El Niño off the west coast of South America. A scarcely studied refinement of this type of event would be the effects of less-pronounced oceanic changes that might reduce the planktonic food supply of nocturnally active, burrow-nesting seabirds. In such instances, the effects might also be a breeding failure for only one or two seasons; in all probability such events occur, but whether they are as likely to be detected by us is problematical. However, the populations of most seabirds are probably already adapted to survive short-term crises of this type because, having long adult life spans, reproductive adults that fail to raise young one year may mostly live to succeed in doing so in the next or succeeding year, when the oceanic "anomaly" has disappeared. What constitutes an "anomaly" will be considered again shortly. A third critical condition for seabirds may be local or widespread, temporary or final, or some combination of these. A single local spill, or outfall, of a chemical pollutant will be short term if we can take steps to alleviate the consequences or stem the flow. Alternately, we may consider it to be long term if we take the view that it is one additional act of violence resulting from the "progress" of Industrial Man, and that it is never going to shift into reverse gear. We may say that the effect on seabird populations of spills of oil products or chemical pollutants in coastal waters of a region will be a "final solution" for any that become wholly extinct before the oil wells go dry or the industries fail. On the other hand, the effect will have been merely a perturbation of the population if the species survives and outlives these activities. Recent upturns in populations of peregrine falcons (Falco peregrinus) and pelicans (Pelecanus sp.) in certain places where environmental controls have been enacted give us hope that crises of several years' duration can be withstood by at least those species that once were common in relation to their respective food sources or available safe breeding habitats. The really critical features to document are the means whereby abandoned breeding sites are reoccupied and the time it takes. It must never be forgotten that we know almost nothing about the ecology of subadult or nonreproductive adult seabirds during the years they are at sea unconfined by membership in a breeding unit and that we know almost nothing about the activities of pelagic seabirds in the nonbreeding season. These birds may be far from land and hard to study, but what happens during those phases of their lives is basic to the composition of the colony and condition of the birds when breeding. A start would be to learn everything that is known and is being discovered about the oceans by oceanographers and, thus forearmed, go looking for the seabirds with certain questions clearly in mind. Detecting the Effects of Long-term Cycles A scientist's working life lasts only a few decades, and few studies of seabirds by a single author or agency have been continued for longer than 5-10 years on any one problem. Further, while we as individuals may live to be equally active in a certain field of research 20 years hence, our collective conscience and collective muscle consist of several levels of government that tend to exhibit 4- or 5-year changes of direction and priorities. Certainly, the civil service may live on as an inertial recorder of collective experience. Certainly, too, those who live under one form or another of dictatorship or, as in some Canadian provinces, where conservative patterns of voting occur, may experience a continuity of research and development and conservation policies that exceed the 4- to 5-year turnaround pattern that is most common. Yet, even these more continuous systems may come to an end quite suddenly because of economic or political happenstance. The point of this digression is to show that seabird ornithologists must not rely on government programs to provide continuous data over a long period of years—not, at least, in most countries. Monitoring the biological circumstances of seabirds is not the same as recording the temperature regularly by machine at a weather station, since this activity is unlikely to be terminated unless the society collapses altogether. We may know that in some countries the amateur naturalist exists in such numbers that records of seabirds will continue to be made whatever the circumstances. Nevertheless, planning of censuses that will be repeated every 10 years is best assured if government and career biologists combine with the amateur element, so that any one of them can continue the work if any other element should be incapacitated. At any one time, either the amateur or the government or the university personnel may be the prime mover, and each of these forms now exists in various countries. What the scientific literature in the fields of the geophysical, atmospheric, and oceanographic disciplines demonstrates is that natural climatic oscillations probably range in length from the 11-year sunspot cycle through several decades (or a human lifetime) to several hundred years. So, when our children are the new trustees of seabird colonies 20 or 40 years hence, they must interpret their data using the full range of physical as well as biological data that we can leave for them. Indeed, the information is, I believe, already available over a long enough period (since 1940 at least) to allow some speculative interpretations of what may have been happening to our seabird populations, whether or not we knew or had any evidence of it. I have already suggested that extraterrestrial events, particularly the 11-year sunspot cycle, are increasingly believed to influence the atmosphere of this planet. The Chinese and Japanese have remarkably precise records of the northern limits of certain agricultural crops at particular times, the phenology of flowering, and the freezing of lakes. These demonstrate long- term trends in overall climate in eastern Asia that extend over hundreds of years. The climate of Japan is influenced by the high-pressure area in winter over mainland East Asia. There is evidence that severe ice conditions in the Bering Sea during the early 1970's may have been due to an eastward shifting of this high-pressure area. Again, the water mass of the Kuroshio Extension and the West Wind Drift takes several years to travel across the Pacific Ocean, and there is an established temperature variation that travels like a slow wave with it. Off Japan, the Kuroshio Current periodically develops meanders which slow the speed of the eastward flow. Cold and warm "pools" of water approach the west coast of Canada and the western United States from time to time. Ocean currents are driven by the atmospheric motion above them, which consists of several convective cells between the equator and each pole. The outcome is zonal winds, such as the trade winds and the westerlies. However, as the influence of the sun on the atmosphere is variable, the input of heat and the extent of the major high-pressure areas vary, as does the path of the jet stream. The recent droughts in northern Africa and unusually heavy rains in Australia are both linked to a southward shift of the Intertropical Convergence Zone in the atmosphere and a "corrugation" of the wind circulation from a more normal zonal (latitudinal) path. These shifts in the atmospheric circulation are almost certainly transmitted also to the ocean currents and the marine ecosystem, with the influence being felt for a long period of years. One of the oceanic domains of the North Pacific is the transitional domain, which lies east-west where the West Wind Drift impinges upon the coasts of British Columbia and Washington State. It is precisely in this sector that there was a well- documented "temperature anomaly" in 1957-58. Since an anomaly implies something completely out of the ordinary, I seriously question the appropriateness of the term for an event that may or may not be recurrent (at the time it was a pronounced variation from the oceanographic records accumulated up to that time, but the period had not been a very long one). It is no coincidence that the numbers of albatrosses recorded at Ocean Weather Station "Papa" was higher during this warm-water "anomaly" than subsequently (indeed, an 18-year record of the seabirds recorded at "Papa" also exhibits other interesting fluctuations from the base-line data in certain years). Recent analyses of sediments from off the coast of California have demonstrated long-term fluctuations in sardine populations extending back at least 1,800 years, with increases lasting 20-150 years and spaced 20-200 years apart. The number of anchovies declined steadily. Yet until now, El Niño events have been treated as anomalies in that region as well as off the coast of Peru. Just as we recognize that different species of fish follow the warm water north on such occasions, we must also recognize the rather distinct seabird species assemblage that is trapped, as it were, in the Gulf of California. Clearly, like the termination point of the West Wind Drift at about the 45-55° parallel, the coast of Baja California and southern California State, from the 25-35° parallel where the California Current begins to swing away from the coast to the west as the North Equatorial Current, is another zone of instability. I think that it is no accident that the southern limit of several northern species of North Pacific seabirds ends in southeastern Alaska or northern British Columbia, and that the northern limit of the ranges of several other species occurs in Washington State or southern British Columbia. Indeed, the west coast of Vancouver Island is not rich in species, and several of those that exist are not present in great numbers. This is a region of rather more variable conditions than elsewhere, and species evidently find that it is difficult to colonize and it quickly becomes unsuitable again. Since 1940, indeed, there has been a parallel decline in the annual mean sea-surface temperature at a number of coastal recording stations in British Columbia, and this seems to have been a rebound from a less well-documented rise in sea-surface temperatures during the 20 years before that, which culminated in a peak around 1940. Salinity has likewise trended downwards during the last 30 years. The seabird colony size data before 1960 are so nonquantitative that it is impossible to be sure what changes in seabird populations and breeding sites may have taken place in response to these physical changes. The lesson is that we must now examine all future census and distribution data with trends in sea-surface temperature and salinity in mind as two of several likely factors influencing them. We must no more ignore data outside our own field than a salmon ecologist might. Conclusions We know little of the accuracy of censuses of seabird numbers made between 1850 and 1950. There has been a tendency to assume that numbers of seabirds at long-established colonies have been relatively unchanging, even though the expansion of some species into previously unrecorded breeding sites in low numbers is well documented. Contraction of breeding ranges, likewise, has most commonly been attributed to the influence of man. Recent literature from the physical sciences, on the contrary, suggests that seabird numbers at particular colonies are most unlikely to have been stable for any great length of time, at least at high or middle latitudes and particularly at points where boundaries between currents impinge on continental coasts. Indeed, some early estimates of colony sizes may not have been as much in error as we may have assumed, neither when apparently too large nor when apparently unlocated by previous visitors. The halving of a large colony over a period of 20 to 50 years in the middle of the range of a species and the establishment and disappearance of smaller breeding groups at opposite extremes of the range (both latitudinally and longitudinally), may equally reflect natural long-term climatic or oceanographic changes and may naturally be reversed at some time in the future, perhaps within half a century. The implication for conservation of seabird colonies that are at the contracting end of a species' range is that cultural rather than biological criteria may be the best determinants. Sea Ice as a Factor in Seabird Distribution and Ecology in the Beaufort, Chukchi, and Bering Seas by George J. Divoky[1] U.S. Fish and Wildlife Service Fairbanks, Alaska Abstract Arctic sea ice has a variety of effects on seabirds. Although the decrease in surface area available for feeding and roosting is probably the major restrictive effect, also important are productivity of water covered by ice and the reduced prey abundance in nearshore areas due to ice scour. The most important benefit that sea ice provides to seabirds is the plankton bloom that occurs in the ice in the spring. In the Beaufort and Chukchi seas this bloom supports an under-ice fauna that is an important food source for seabirds. Sea ice is a major factor in the distribution and ecology of many of the birds treated in this symposium. Sea ice is defined here as ice formed by the freezing of seawater and includes both free floating pack ice and the more stable shorefast ice. Since icebergs are composed of ice of land origin, they are not discussed. Before discussing the specific relationship of birds and sea ice in the Beaufort, Chukchi, and Bering seas, I list the general effects that arctic ice can have on seabirds. For purposes of discussion these effects can be divided into negative effects, or disadvantages, and positive effects, or advantages. General Effects of Ice on Birds Negative Effects Sea Ice Decreases the Surface Area of Water The decrease in the surface area of water is the simplest and most immediate effect that sea ice has on birds. Ice acts as a barrier that restricts the availability of food in the water. Surface feeders are the most severely affected since, in general, ice cover of 50% reduces the possible feeding area by half. The effect on diving species is not as severe since, if open water is scattered throughout the ice, diving species still have access to much of the prey in the water column and benthos. When open water is scarce, however, diving species can become concentrated in the available water, resulting in intense competition for available prey. In certain situations the open water is used only as a migratory pathway, but open water is necessary for birds that must roost or feed. Sea Ice Reduces Primary Productivity in the Water Column Ice inhibits phytoplankton blooms in the water column, thus decreasing the biological productivity of ice-covered waters. This inhibition occurs in two ways: • By decreasing light penetration of the water column.—Much of the sunlight reaching the ice is reflected by the ice and by snow on the ice. The amount of light reaching the water depends on the angle of the light, thickness of ice, and amount of snow cover. When the layer of under-ice algae forms, it absorbs light and further reduces the amount of light reaching the water (Bunt 1963). This reduction in light reduces the depth of the euphotic zone. • By increasing the stability of the water column.—Increased stability of the water column reduces the upwelling of nutrient-rich waters into the euphotic zone. Ice stabilizes the water column primarily by preventing wind-driven movement of surface waters and by forming a layer of meltwater at the surface in the spring and summer (Dunbar 1968). Sea Ice Reduces Benthic and Intertidal Biota Benthic flora and fauna can be reduced by the presence of ice in two ways: In shallow water ice can freeze to the bottom for much of the year and prevent the establishment of plant and animal populations; and when ice floes are pushed together, they form underwater ice keels that can scour the bottom when the ice moves. Both of these events not only act directly to decrease benthic populations but also disturb the sediment, making it less suitable for colonization. In areas with heavy ice scour, sessile benthic populations can be greatly reduced, although motile species may move into scoured areas during the ice-free period in summer. In addition to preventing the establishment of sessile benthic animal populations, ice scour also prevents the establishment of beds of kelp and eelgrass (Zostera marina), thus decreasing the diversity and productivity of arctic inshore waters. Both kelp and eelgrass beds are important feeding sites for birds in areas south of the region affected by ice scour. Sea Ice Allows Terrestrial Predators Access to Breeding Sites The formation of ice between the mainland and offshore islands allows the arctic fox (Alopex lagopus) and other predators access to the islands used by breeding birds. Foxes can become permanently established on islands that have food sources during the period when birds are absent from the island. Often, however, there is little to attract foxes to the islands other than breeding birds. Because moats form around many islands before the breeding birds arrive, foxes are primarily a problem when moat formation is incomplete or when the breakup of ice is late. Arctic foxes are found on the pack ice throughout the summer and thus can visit islands that are separated from the mainland by open water but are adjacent to the pack ice. Advantages Sea Ice Provides a Matrix and Substrate for an Ice-associated Plankton Bloom and an Associated Under-ice Fauna The first detailed studies on the blooms of diatoms that occur in the lower levels of ice were done by Appollonio (1961). The importance of this bloom in the energy budgets of arctic and subarctic seas has only recently been realized (Alexander 1974; McRoy and Goering 1974). In areas where ice is present throughout the year, the plankton bloom supports a population of under-ice invertebrates. These populations have been little studied but apparently consist primarily of copepods and amphipods (Mohr and Geiger 1968). Feeding on the invertebrates associated with the ice are two species of fish, polar cod (Arctogadus glacialis) and arctic cod (Boreogadus saida). Andriashev (1968) used the term cryopelagic to describe such fish, which are found in the midwater zone but also are associated with ice during some part of their life cycle. The underside of multi-year ice has numerous ridges and pockets that provide a heterogeneous environment for the under- ice fauna. This environment is protected from disturbance from currents and wave action by ice keels acting as barriers, which also provide shelter from predators in the same manner as a coral reef. The overall effect of the under-ice flora and fauna is to increase the diversity of surface waters in arctic seas by creating an inverted benthic biota. Sea Ice Provides Hauling Out Space for Marine Mammals The mammals that inhabit the ice in the Chukchi and Bering seas and their adaptations to the pack ice environment were discussed by Fay (1974). Many of these species frequently haul out on the ice, where they provide food in the form of feces, placentas, and carcasses. Sea Ice Provides Roosting Sites Ice provides a hard substrate that allows seabirds to leave the water to roost. This allows such species as the Larus gulls, which typically roost on hard substrates, to occur in large numbers well offshore. Sea Ice Reduces Wind Chill The unevenness of the upper surface of the ice reduces the speed of winds directly over the ice, thus providing a microhabitat and reducing the amount of wind chill for birds sitting on and next to the ice. Sea Ice Decreases Wave Action Ice floating on the water reduces the surface disturbance of the water. Although swells pass through areas with much ice cover, waves do not. In addition, surface waters on the lee side of ice floes and cakes usually have little surface disturbance. Surface feeders may be able to locate prey more easily because of these reductions in surface disturbance. Specific Effects of Ice on Birds in the Western Arctic The retreat of the pack ice each spring and the formation of new ice each fall greatly affect a large area of the Arctic Ocean off the coast of Alaska and much of the Bering Sea. Specific ways in which birds are affected by ice in the western Arctic are discussed on a seasonal basis. All observations are my own, unless otherwise stated. Winter Chukchi and Beaufort Seas From late November to mid-April, ice cover of the Chukchi and Beaufort seas is almost complete. The only areas where birds can be expected to winter in these seas are the chronic lead systems. Such lead systems are found off Wainwright and Point Barrow and south of the Point Hope-Cape Thompson area (Shapiro and Burns 1975). Only the black guillemot (Cepphus grylle) is known to regularly winter offshore from Wainwright and Point Barrow (Gabrielson and Lincoln 1959; Nelson 1969). In the Point Hope-Cape Thompson area, glaucous gulls (Larus hyperboreus), the common murre (Uria aalge), and the thick-billed murre (U. lomvia) occur throughout the winter (Swartz 1967). It is likely that black guillemots are also found in this area. The lack of chronic lead systems in the Beaufort Sea precludes the presence of wintering seabirds. The one species that may be found wintering in the Beaufort is the Ross' gull (Rhodostethia rosea). Ross' gull is believed to winter primarily in