The UniversiTy of AlAskAoregon sTATe UniversiTy

The UniversiTy of BriTish ColUmBiAThe UniversiTy of WAshingTon

AnnUAl reporT 2006-2007

NORTH PACIFIC UNIVERSITIES

MARINE MAMMALR E S E A R C H C O N S O R T I U M

Marine Mammal Research UnitUniversity of British ColumbiaRoom 247, AERL, 2202 Main MallVancouver, B.C. Canada V6T 1Z4

Tel.: (604) 822-8181Fax: (604) 822-8180consortium@zoology.ubc.cawww.marinemammal.org

The work of the Consortium has been greatly aided by the U.S. National Marine Fisheries Service, the Alaska Department of Fish and Game (ADF&G), and Fisheries and Oceans Canada.

We are particularly grateful to ADF&G for field support and to Miller & Miller, P.S. for auditing the financial and compliance aspects of our grant-funded research programs.

We extend our thanks to the Vancouver Aquarium for providing us with research space and expertise in Steller sea lion training and husbandry.

We are particulalry grateful to Petro-Canada for their ongoing assistance and donations to support the Open Water Research Station.

We are also grateful to members of the Consortium’s Research and Scientific Advisory Committees for the many hours they have spent preparing and reviewing the Consortium’s research plans.

We thank and acknowledge our volunteers and our many and varied donors for their support and continued interest in our research.

We particularly appreciate the support of the North Pacific Marine Science Foundation and its Board members, and the in-kind donations of fish, field equipment, services, and logistic support.

We also gratefully acknowledge the financial support and helpful assistance of the National Oceanic and Atmospheric Administration.

Finally, we thank and acknowledge the Development team at the UBC College for Interdisciplinary Studies for their ongoing assistance and support.

Donations

Alaska Fisheries Development FoundationAlaskan ObserversAlec BrindleAleutian Pribilof Island Community Development Association (APICDA)Aleutians East BoroughAt-Sea Processors AssociationAvil K. ScullBristol Bay Native Corp.City of UnalaskaCoastal Villages Region FundDelta WesternFarrell Born, CPAFoss MaritimeGlacier Fish Marine Conservation AllianceM/V Savage, Inc.Northwest Fisheries AssociationPacific Seafood Processors AssociationRadtke Marine, Inc.Sea Dog FisheriesSouthwest Alaska Municipal Conf.Top Dog PublishingUnited Catcher BoatsWells Fargo

other support

Alaska Marine LinesAt-Sea Processors AssociationFish ExpoMiller & MillerMundt MacGregor LLPNOAA NMFS North Pacific Research BoardPacific Seafood Processors AssociationPetro-CanadaPollock Conservation CooperativeReed Point Marina Ltd.

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NORTH PACIFICUNIVERSITIESM A R I N EMAMMALR E S E A R C HCONSORTIUM

ACknoWledgemenTssUpporTing mArine sCienCe

ConTenTsthe North Pacific oceaN is unlike anywhere else on Earth. Wild and unpredictable, it is a place of extremes: light and darkness, tempest and calm, feast and famine, birth and death.

The coastal regions of the North Pacific are home to an unparalleled richness of marine life – thousands of known species with more still to be discovered – which collectively make an unfathomable contribution to global biodiversity.

But survival here is never guaranteed, even for the strong. Alarming and unexplained shifts in key predator populations in recent decades have snapped into focus the fragile nature of life in the North Pacific.

co N t e N t s – a N N U a l r e P o r t 2006–2007 • page �

foreWord

Can entire populations of Steller sea lions, one of the ocean’s most formidable predators, virtually disappear in less than 40 years? And if so, which of nature’s mechanisms determine the success or failure of these populations? Is human activity to blame, or are they simply casualties of the ocean around them?

Dozens of scientists, working collaboratively under the North Pacific Universities Marine Mammal Research Consortium, are seeking the answers to these questions and many more.

This report represents a year of their work.

ackNowledgeMeNts 2foreword 3overview 4orgaNizatioN & PersoNNel 5aNalysis & MatheMatical Models 6field stUdies 10caPtive stUdies 15sUMMary 17PUblicatioNs 18

Change is Constant in the North Pacific Ocean, but the past 40 years have seen major shifts in the abundance of seals, sea lions, whales and seabirds. In Alaska, harbor seal populations are greatly reduced, northern fur seals are depleted, and Steller sea lions have been declared endangered in parts of their range. Similar declines have been reported in some seabird breeding colonies.

Meanwhile, populations of Steller sea lions and harbor seals have increased in British Columbia. Further south, striking increases are also being observed in the range and abundance of elephant seals and California sea lions.

Are these large-scale changes a natural phenomenon? Or are they connected to similar changes occurring simultaneously in a number of commercial fisheries? While their causes may remain unclear, their effects on key marine mammal species are evident: in 1990, the Steller sea lion was classified as a threatened species under the U.S. Endangered Species Act.

Then, in 1997, the Steller sea lion was divided into two distinct populations: those east of Prince William Sound were declared threatened, while those to the west were classified as endangered. These classifications forbid commercial or industrial activity that could imperil the species.

The question of why Steller sea lions have declined in Western Alaska continues to puzzle biologists. Possible causes include: increased incidence of parasites and disease; predation by killer whales; nutritional stress resulting from competition with humans or other species for food; or nutritional stress caused by natural and/or human-induced changes in the abundance, quality, and distribution of prey. Pollution and toxic substances,

entanglement in marine debris, and incidental and intentional catch by fishermen may also play significant roles.

Whether the decline is caused by a single factor or a combination of the above is a matter of scientific debate: limited data has so far prevented the resolution of this question. However, research investigating the leading hypotheses of killer whale predation and nutritional stress is receiving ever-increasing attention. The interactions between fisheries and marine mammals are the subject of intensive research in many parts of the world and will continue to be a major focus of research in the North Pacific.

The North Pacific Universities Marine Mammal Research Consortium was formed in 1992 with four participating institutions: the University of Alaska, Oregon State University, the University of British Columbia and the University of Washington. Its mission is to undertake a long-term program of research on marine mammals and their interactions with fisheries, other species and oceanographic conditions in the North Pacific Ocean and Eastern Bering Sea.

The research program balances short-term and long-term studies designed to test the various hypotheses that have been put forward to explain the decline of Steller sea lions.

The integrated studies draw on the expertise of university-based physiologists, engineers, ecologists, marine mammalogists, fisheries specialists, oceanographers, and mathematical modelers. Only through a concerted effort and a commitment to long-term research can we hope to determine the causes of changes in the North Pacific.

Consortium researchers have completed their fourteenth full year of research. This report reviews their accomplishments from April 2006 to March 2007 and synthesizes some of the findings published during this period.

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overvieWsTUdying ChAnge in The norTh pACifiC oCeAn

The Consortium’s research program consists of four components:

1. Field studies contrasting healthy sea lion populations in Southeast Alaska, British Columbia and Oregon with declining populations in the Gulf of Alaska;

2. Captive studies on Steller sea lions to enable the development and testing of new techniques and technologies for studying sea lions in the wild; and to provide information that field studies cannot, including physiological data, nutritional requirements and how they use energy derived from food;

3. Developing new measurement techniques for processing biological samples; and

4. Analyzing historical data sets, constructing mathematical models and conducting laboratory studies.

The Consortium’s research program is overseen by a Scientific Advisory Committee made up of representatives from universities, industry, and government agencies.

A Research Committee, composed of research leaders from the four universities and three government institutions, is responsible for preparing a proposal for research each year and for reporting on progress to the Scientific Advisory Committee.

The Consortium is administered by the Marine Mammal Research Unit of the Fisheries Center at the University of British Columbia. Core staff consists of a Research Director, Dr. Andrew W. Trites, and an Administrative Manager, Pamela Rosenbaum.

Implementing sound management policies governing human activities requires decision-makers to have a better understanding of the relationship between such activities and the surrounding ecosystems.

The North Pacific Marine Science Foundation, which funds the research program of the Consortium, was formed specifically for this purpose.

Contributions to the Foundation have come from other foundations, federal grants, coastal communities and a wide spectrum of donors representative of the fishing industry.

S c i e n t i f i c A d v i S o r y co m m i t t e eDr. David Hanson, Chair Pacific States Marine Fisheries Commission Dr. Lee Alverson Natural Resources Consultants Dr. Doug DeMaster National Marine Fisheries ServiceDr. David Armstrong University of WashingtonMs. Marilyn Joyce Fisheries and Oceans CanadaDr. Ole Mathisen (Deceased) University of AlaskaDr. Villy Christensen University of British ColumbiaDr. Bruce Mate Oregon State University

r e S e A r c h co m m i t t e eDr. Markus Horning Oregon State UniversityDr. Alan Springer University of AlaskaDr. Andrew W. Trites University of British ColumbiaDr. Glenn Van Blaricom University of Washington

A S S o c i At e m e m b e r SDr. Lorrie Rea Alaska Department of Fish and GameDr. Tom Gelatt National Marine Fisheries ServiceMr. Jake Schweigert Fisheries and Oceans Canada

The Consortium received startup funding in late 199� and full-year funding beginning in 199�. In 199�, our fiscal schedule changed from the calendar year to April 1 – March �1. As of the 1999–�000 year, federal grants were recorded in the year expenditures were made.

Pe r s o N N e l – a N N U a l r e P o r t 2006–2007 • page �

orgAnizATion & personnel

b o A r d o f d i r e c t o r S

Dr. David L. Hanson, President Pacific States Marine Fisheries CommissionMr. Glenn Reed, Vice President Pacific Seafood Processors Association Mr. James Brenner, Treasurer Wells Fargo Bank, AlaskaMr. Dave Benton Marine Conservation AllianceMr. Larry Cotter Aleutian Pribilof Island community Development AssociationMr. Douglas C. Forsyth Premier Pacific Seafoods, Inc.Mr. Simon Kinneen Norton Sound Economic Development CorporationMr. Paul MacGregor At-Sea Processors AssociationMr. Jim McManus Trident SeafoodsMr. Eric A. Olson Bristol Bay Economic Development CorporationMr. Brent Paine United Catcher Boats

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AnAlysis & MAtheMAticAl Models

Researchers are increasingly turning to mathematical models to help them understand

the past dynamics of Steller sea lion populations and to project future trends.

Consortium models of the western Aleutian Islands and Southeast Alaska ecosystems have shown that a combination of factors, including

killer whale predation and competitive interactions with fish, can explain the changes in sea lion numbers. The models suggest that ocean climate (i.e., a regime shift) has been a

major force driving these changes.

Another study undertaken in 2006–07 used computer modeling to explore ecosystem

changes by simultaneously evaluating four hypotheses explaining the rise and

fall of Steller sea lions: fishing, predation, competition, and ocean productivity. A

separate study also reviewed the ecological consequences of fisheries – specifically, “fishing

down the food web” – as fundamentally different from other predatory impacts.

nearly 30 years ago, an abrupt change in ocean conditions swept through the North Pacific Ocean, affecting everything from sea-surface temperatures to fisheries. The so-called regime shift of 1976-77 was a natural event in the ocean’s climate cycle, but its impacts on Alaska’s marine ecosystems are still felt today.

This single climate event may be the missing link that ties together the various theories behind the decline in western Alaska’s Steller sea lion populations, and the curious success of populations to the east.

How can a change in ocean climate unify these seemingly unrelated theories of epidemic disease, killer whale predation and shifts in prey abundance? To find out, researchers considered sea lion diets, examined the region’s physical oceanography and marine ecosystems, and combed through archaeological data spanning 5,000 years. In the process they unraveled a tale of shifting fortunes with not one, but two endings.

Dietary Dilemma

The nutritional stress hypothesis – also referred to as the junk food hypothesis – is a leading ‘best guess’ at why western Alaska’s sea lions have declined. Simply put, it suggests that sea lions in declining populations shifted from a high-energy diet dominated by fatty fishes, to one dominated by lower-energy fish following the regime shift. This would require young sea lions to eat more low-quality food to meet their daily energy needs.

To use a human analogy, switching to a diet of popcorn would require one to eat more in order to feel full, and even more to meet basic nutritional requirements. The small stomach of a young sea lion cannot hold and process enough low-quality

food to satisfy hunger, thereby requiring that they stay with their mothers and consume energy-rich milk for an extra year or two.

Nutritional stress from low-quality prey affects the reproductive health of adults and lowers birth rates because mothers continue to nurse their pups beyond the first year of life. In contrast, areas of increasing populations saw sea lions consume a higher diversity of prey and enjoy a more energy-rich diet.

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seA of ChAngeoCeAn ClimATe And sTeller seA lions

Figure 1. Conceptual model showing how sea lion numbers might be affected by ocean climate through bottom-up processes. This hypothesis suggests that water temperatures, ocean currents and other climatic factors determine the relative abundances of fish available to eat, which in turn affects sea lion health (proportion of body fat, rates of growth and at a cellular level – oxidative stress). These three primary measures of individual health ultimately determine pregnancy rates, birth rates, and death rates (through disease and predation). Also shown are the effects of human activities that could have directly or indirectly affected sea lion numbers.

But while a change in ocean conditions could indeed force an entirely new diet upon sea lions, the nutritional stress hypothesis does not explain how a regime shift affecting the entire Gulf of Alaska could produce different responses in the eastern and western portions of the basin. In order to answer that question, the researchers had to delve deeper into the Gulf’s physical composition.

The Dividing Line

Recent field research has uncovered the significance of Samalga Pass (169°W), an unassuming geographical feature just west of Unmak Island on the Aleutian chain. The pass is a transition point between the eastern waters of the continental shelf and the western waters of the open ocean. The shelf waters east of the pass are governed by the Alaska Coastal Current, while the open waters further west are at the mercy of the Alaskan Stream.

The Alaskan Stream is the continuation of the Alaska Current (a relatively warm, counter-clockwise gyre in the Gulf of Alaska) as it moves west along the southern side of the Aleutian Islands. Mathematical models of sea-surface temperatures (SST) – the most complete set of oceanographic data available – show a strengthening of the Alaskan Stream following the 1976-77 regime shift.

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The strengthening of the Alaskan Stream was likely due to a shift in atmospheric circulation patterns over the Aleutian Islands, and may have impacted large ocean eddies that transport nutrients across the Aleutians.

While these mechanisms are not fully understood, they suggest that the stronger Alaskan Stream could have fundamentally altered the distribution of energy through the waters of western Alaska, resulting in an increased abundance of low-quality prey such as cod and pollock.

Conversely, in the eastern Gulf of Alaska, the models show nearly unchanged flows in the Alaska Current after the regime shift. The fundamental difference in source waters between the eastern and western portions of the basin – and the degree to which the strengthened Aleutian Low impacted the western waters – set the stage for a dramatic contrast in habitat on either side of Samalga Pass. Sea lions were among the many winners and losers of this ecological shakedown.

While eastern populations of sea lions may appear to have avoided the climate-induced poverty of their western counterparts, archaeological data suggests that their good fortune may be temporary. Sea lion populations have varied significantly in Alaska over

the past 5,000 years, and historic accounts tell of at least one other collapse within the last few centuries. Hunting and fishing did not significantly contribute to any of the historical declines. Thus, ocean climate may very well underpin ecosystem restructurings that manifest as large, regional changes in Steller sea lion abundance.

The enigmatic ‘black box’ of ocean climate perhaps more closely resembles a Pandora’s Box: a cascade of ecosystem impacts triggered by key events such as the 1976-77 regime shift. By fundamentally reconfiguring the marine environment, these episodes of sea change act as harbingers of feast or famine for sea lions.

One event, one ocean, two outcomes: portions of western Alaska’s Steller sea lions face extinction while eastern populations thrive. Each is at the mercy of the ocean’s changing fortunes, and whether their fates will reverse is not so much a question of if, but when.

Trites, A. W., A. J. Miller, H. D. G. Maschner, M. A. Alexander, S. J. Bograd, J. A. Calder, A. Capotondi, K. O. Coyle, E. D. Lorenzo, B. P. Finney, E. J. Gregr, C. E. Grosch, S. R. Hare, G. L. Hunt, J. Jahncke, N. B. Kachel, H.-J. Kim, C. Ladd, N. J. Mantua, C. Marzban, W. Maslowski, R. Mendelssohn, D. J. Neilson, S. R. Okkonen, J. E. Overland, K. L. Reedy-Maschner, T. C. Royer, F. B. Schwing, J. X. L. Wang and A. J. Winship. 2007. Bottom-up forcing and the decline of Steller sea lions (Eumetopias jubatus) in Alaska: assessing the ocean climate hypothesis. Fisheries Oceanography 16:46-67.

in the latter half of the twentieth century, the seemingly timeless coast of Alaska saw a revolution in everything from ocean climate to populations of some of its smallest – and largest – marine inhabitants. Some changes were due to natural cycles; others were the result of increased human activity. By the 1980s, two contrasting trends had emerged among Steller sea lion populations: a sharp and severe decline in Western Aleutian populations, and a concurrent increase in Southeast Alaska.

A number of scientific explanations have alternately implicated human fisheries, marauding killer whales, a shift in ocean climate, and inter-species competition for prey. Yet no single theory has to date successfully explained the conflicting rise and fall of Steller sea lion populations in each ecosystem, and most research to date could only test one hypothesis at a time.

With advances in computer modeling, ecosystem changes can now be explored by simulating ecological scenarios. Using such a model, researchers simultaneously evaluated four hypotheses explaining the rise and fall of Steller sea lions: fishing, predation, competition, and ocean productivity.

East vs. West

Researchers compared the Aleutian Islands and Southeast Alaska, two areas that differed by the trends of their respective sea lion populations, their fishing histories, and the characteristics of their ecosystems. They modeled each area between 1963 and 2002, a period that encompasses the 1976-77 ocean regime shift, the development of the major fisheries, and the major changes in Steller sea lion abundances.

The model identified the Pacific Decadal Oscillation (PDO) – an ocean climate system that warms or cools the Gulf of Alaska on a decadal basis – as a central player in the abundance of Steller sea lions and other marine life. In 1977, an abrupt shift in the PDO ushered in a new ocean climate regime, decreasing primary production (phytoplankton) and altering the quantity or quality of the marine food web. Climate appears to have impacted several species in both ecosystems, including Atka mackerel and Pacific herring, which form an important part of the Steller sea lion diet. Thus, a change in ocean productivity appears to have had a major, indirect effect on sea lions.

When modeled in a computer simulation, this shift in ocean productivity impacted the Aleutian model more than the Southeast Alaska model. According to the model’s predictions, the Steller sea lion decline in the Aleutians can largely be explained by the regime shift and by killer whale predation, although the model also suggests that fishing for Atka mackerel and competition between sea lions and large flatfish for prey also played a role.

In contrast, simulations of Southeast Alaska suggested that the rise in Steller sea lion populations was linked to change in ocean productivity and simultaneous increases in herring and salmon populations, which together overruled the effect of killer whale predation and competition for prey by flatfish.

Finally, the model showed that predation by killer whales was important when sea lions were less abundant (in the 1990s in the Aleutians and in the 1960s in southeast Alaska), but appear to have little effect when sea lion numbers were high.

Overall, the ecosystem modeling exercise succeeded in integrating climate, competition, fisheries, and predation as potential causes of change in each ecosystem. Like all ecosystems, the Alaskan coast is in constant flux, and this study provided valuable information that enables scientists to further explore the subtle changes and interactions beneath the surface of the North Pacific Ocean.

Guénette, S., S.J.J. Heymans, V. Christensen, and A.W. Trites. 2006. Ecosystem models show combined effects of fishing, predation, competition, and ocean productivity on Steller sea lions (Eumetopias jubatus) in Alaska. Canadian Journal of Fisheries and Aquatic Sciences 63:2495-2517.

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sCrATChing The sUrfACeeCosysTem models reveAl sUBTle inTerACTions

the apex predators, a class of marine heavyweights that includes pinnipeds (seals and sea lions), cetaceans (whales and dolphins), seabirds and sharks, have long enjoyed a unique position atop the marine food web. But after an uninterrupted reign lasting millions of years, apex predators in the 21st century are facing a new contender: humans.

It may be easy to dismiss human fisheries as “just another predator”, especially given a dearth of scientific data assessing the more subtle impacts of fisheries. However, the ecological consequences of fisheries are fundamentally different from other predatory impacts.

Fishing Down the Food Web

Fishing directly impacts ecosystems by removing large quantities of targeted and by-caught species and by physically damaging the ocean floor through activities such as bottom trawling. While these effects are obvious and relatively easy to document, the indirect effects of fishing pressure are far more nebulous and complex.

Historically, fishing started at the top of most food chains by removing the larger, valuable and more easily caught species, and then moved down to the next-biggest species as those above were depleted and were no longer easy or economical to catch. The downward shift towards taking species from lower trophic levels is termed fishing down the food web.

Commercially valuable species in a number of ecosystems are reported to be smaller in size than they once were (at the same age) and appear to be reproducing earlier in life. This is a source of concern to biologists because smaller fish typically produce fewer eggs and have a higher mortality rate than larger fish of the same species. These long-

term reductions in size and fecundity (reproductive capacity) due to fishing pressure could translate to evolutionary changes in their genome that may be difficult to reverse.

Further, large-scale ecosystem models show that predators may be affected by fisheries targeting prey that is not part of their diet. Such food-web competition occurs when the primary producers at the base of the food web cannot support both the fishery and the apex predators (see Figure �).

Thus as catches increase, the primary production available to marine mammals appears to decline; this can translate to a reduction in prey that limits the predator’s survival and reproductive success. Human fisheries are not subject to the same biological controls limiting what and how much they take. Instead, fisheries are regulated solely by

economic incentives, which ironically often increase (rather than decrease) as a species becomes scarce.

The Human Advantage

Fisheries consume a size and volume of prey that is unmatched in the natural world. Yet humans lack the long history of co-evolution and natural selection with their prey that other predators have experienced. Apex predators have developed an arsenal of special adaptations including keen vision and hearing, specialized teeth, and physiological prowess such as diving or breath-holding. In response, fish and other prey have come to rely on camouflage, schooling, and prolific breeding to improve their chances of survival.

While such interactions have undoubtedly helped to maintain the integrity and stability of marine ecosystems, many of the features that have allowed prey to flourish in the face of apex predators now make fish more vulnerable to being caught by fisheries (e.g. schooling behavior, diurnal movement towards surface light, etc.).

By operating outside of the natural rules that govern populations and their ecosystems, fisheries may well be the ultimate apex predator. A relative latecomer to the evolutionary predator-prey game, fisheries represent an abrupt, knife-edged selective force that has potentially destabilizing consequences.

Will recent improvements in fisheries data and ecosystem modelling help to slow the dangerous trend of fishing down the food web?

Trites, A.W., V. Christensen and D. Pauly. 2006. Effects of fisheries on ecosystems: just another top predator? In I.L. Boyd, K. Camphuysen and S. Wanless (eds), Top predators in marine ecosystems: their role in monitoring and management. Cambridge University Press, Cambridge. pp. 11-27.

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i, predATorAre modern fisheries reshAping oCeAn eCosysTems?

Figure �. Schematic of food web competition. Marine mammals and fisheries may not directly compete (they consume different species), but could indirectly compete through the primary production required to sustain their respective prey populations.

Field studiesBy allowing scientists to observe wild animals

in their changing natural environment, field studies provide information that captive studies

often cannot. As such, field work is an essential component of the Consortium’s research

mandate. Field data is often compared, where appropriate, with data from captive studies;

together they present Consortium scientists with as holistic and realistic a picture as possible of the

North Pacific Ocean and its denizens.

In 2006–07, a legal dispute between the U.S. National Marine Fisheries Service and the

Humane Society of the United States significantly hindered the Consortium’s ongoing field

research in the North Pacific. However, this lawsuit did not affect Consortium research on the night-time foraging habits of killer whales in Southeast Alaska, the breeding behavior of

northern fur seals in the Pribilof Islands, and the highly specialized foraging behavior of

killer whales in Kodiak, Alaska.

Other Consortium research studied the effect of environmentally induced food shortages on

maternal attendance among South American sea lions in Peru’s Ballestas Islands. Researchers also analyzed data from previous field seasons

to determine how the timing of weaning in pups has influenced the decline and lack of recovery of

Steller sea lions in Western Alaska.

for a few short months eaCh year, winter relaxes its icy grip on the northernmost reaches of the Bering Sea, providing local wildlife with a fleeting window for mating and birthing the young of the year. On the far-flung Pribilof Islands, an obscure five-island chain in the eastern Bering Sea, a most unlikely event is occurring.

Hundreds of thousands of northern fur seals (Callorhinus ursinus), once pushed to the brink of extinction, have converged on the Pribilofs in time for the breeding season. More than 57% of the world’s million-strong population of northern fur seals comes here to breed, providing a spectacular display of nature’s resilience. Few species on Earth have faced extinction and lived to tell the tale.

One look at the thick, luxurious coat of a northern fur seal makes the cause of their historic near-extinction immediately apparent: they were hunted into obscurity. Beginning in the 1780s and continuing unabated until 1911, northern fur seals were hunted for their thick pelts, on land and at sea, with an intensity that reduced the Pribilofs’ breeding population from 2.5 million to just 300,000 individuals.

The International North Pacific Fur Seal Treaty was ratified in 1911– which prohibited Japan, Russia, Canada and the United States from killing seals at sea in the North Pacific – and resulted in populations of northern fur seals recovering from this historic low. But their present population of about 600,000 is a far cry from the 1950s level of 2.1 million, and it continues to decline at a rate of 6% per year.

The causes of the current decline are unknown and are likely complex. Northern fur seals spend eight months of the year at sea, scattered throughout the North Pacific, only coming ashore in summer to mate. Their breeding distribution and behavior is well studied by scientists, but they remain an enigma for the rest of the year.

With hunting pressure almost entirely removed, save a small subsistence hunt on the Pribilof Islands, the ongoing decline of northern fur seal populations poses a puzzle to researchers. Are commercial fisheries influencing the availability of their key prey? Could disease or pollution be a factor? Are killer whales or natural variations in ocean climate affecting them?

Summer is brief in the Bering Sea, and quickly turns to autumn as the hundreds of thousands of breeding northern fur seals abandon the Pribilof Islands for the sanctuary of the open ocean. If winter is kind to them, they will return en masse next summer in an attempt to renew and reinvigorate their dwindling population. And Consortium scientists will be on hand, carefully studying their biology and ecology in an attempt to conserve these important denizens of the North Pacific Ocean.

pUzzle in The priBilofsreseArChers seT sighTs on norThern fUr seAls

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one of the main forCes controlling populations of Steller sea lions, northern fur seals, and other marine mammals in the North Pacific could be predation by mammal-eating killer whales. These active, warm-blooded animals have tremendous appetites, and each consumes the approximate equivalent of one harbor seal per day. Thus a killer whale population in the hundreds can exert a substantial predatory influence.

Understanding the effects of killer whale predation requires a sound understanding of how mammal-eating killer whales hunt and the types of prey they prefer, but studying killer whale predation in the wild is challenging. During the day, researchers rely on short glimpses into the lives of the animals when they break the surface to breathe; at night, researchers must frequently rely on best guesses.

The question of whether or not mammal-eating killer whales continue to hunt at night has important implications on the extent to which predators control prey populations, especially in high-latitude areas that experience perpetual twilight for parts of the year.

Unlike fish-eaters, mammal-eating killer whales do not emit echolocation clicks to search for prey. Instead, they may rely on visual cues to locate marine mammals, or listen for sounds generated by the prey. Hunting would have to stop after nightfall if killer whales only relied on their vision to find prey. However, if killer whales relied primarily on passive listening to detect the sounds of their prey, they might prefer to hunt under cover of darkness.

Researchers used DTAGs, a novel digital recording device, to better understand the nighttime predatory behavior of mammal-eating killer whales in Southeast Alaska. Developed at the Woods Hole

Oceanographic Institution, the tag is about the size of a cell phone and its four suction cups attach to the back of a killer whale using a seven-metre carbon fiber pole.

For durations of up to 16 hours, the tags record the precise movements of tagged whales and any sounds the animal makes or hears, including the ‘crunching’ sounds of feeding killer whales that indicate a successful predation event.

Over a 14-day research trip in July 2006, the team tagged 13 individual killer whales and obtained over 100 hours of on-animal data. Seven of the tags remained on the animals overnight. The four tags analyzed to date recorded predation events during the hours of darkness, which is surprising as nighttime lasts for only about four hours in Southeast Alaska in July.

The results show that killer whales have no problems finding marine mammal prey in the dark, suggesting that they rely primarily on acoustic, not visual cues. The whales worked with impressive efficiency and swiftness to capture and subdue challenging prey; a single group of four whales launched three successful attacks on Dall’s porpoises during a 12-hour tag deployment.

Further analysis of the data is underway to determine whether predation rates actually increase after nightfall or remain the same.

killers in The dArk The nighT-Time BehAvior of TrAnsienT killer WhAles

fi e l d s t U d i e s – a N N U a l r e P o r t 2006–2007 • page 11

population dynamiCs is an area of particular interest to Steller sea lion researchers. How far do young Steller sea lions disperse once they leave their natal rookery? How many survive to adulthood?

To investigate these and other questions, the National Marine Fisheries Service, the Oregon Department of Fish and Wildlife, and the Alaska Department of Fish and Game initiated a wide-ranging research program that involves capturing and branding sea lions at rookeries from northern California to Russia.

Hot-iron branding creates a permanent identifying mark and is currently the best and only available tool for long-term studies of dispersal, survival, reproduction rates, and age at sexual maturity. However, there are concerns that branding impacts pup mortality.

To determine dispersal patterns and the effects of branding on apparent post-branding survival rates, Consortium researchers monitored Steller sea lion pups that had been branded and tagged at Rogue Reef, Oregon and St. George Reef, California.

Adult males frequented Oregon and California during the breeding season from May to September, but dispersed to northern feeding grounds at other times of year. A high seasonal concentration of females, juveniles, and pups at Sea Lion Caves, Oregon during winter suggests that this area should be considered as critical habitat for Steller sea lions

of the eastern stock.

Using re-sighting data collected between northern California and Alaska, researchers found that most pups stayed close to their natal rookery, while 9-22% of individuals each year dispersed further than 500km. Each year, the percentage of females returning to their natal rookery increased to a maximum of 87% at age four, suggesting that this is the age of sexual maturity among females.

A monitoring study at Rogue Reef addressed concerns that branding may impact individual survival. Researchers observed the capture of 160 pups in one day, which were randomly assigned a treatment of flipper tag only (no branding) or a combination of flipper tag and hot-iron branding. Aside from the branding, all pups were handled and treated identically.

Over the following 73 days, Consortium researchers monitored the newly tagged and branded pups. They found lower apparent survival for branded pups over unbranded pups. However, apparent surivorship includes both mortality and emigration; thus, the observed differences may be due to differences in emigration rates between the two groups, or mortality rates, or both.

Scordino, J. 2006. Steller sea lions (Eumetopias jubatus) of Oregon and northern California: seasonal haulout abundance patterns, movements of marked juveniles, and effects of hot-Iron branding on apparent survival of pups at Rogue Reef. M.Sc. thesis, Oregon State University, Corvalis. 112 pp.

when assessing fish stoCks, managers typically use a conventional model that assumes a rate of natural mortality that is independent of time and age, and ignores the potentially significant effect of predator-prey interactions.

Consortium researchers have developed a new model that considers the impacts of multi-species predation on the population dynamics of a fish stock. The model was fitted to existing catch data for walleye pollock, Pacific cod, and Atka mackerel in the Aleutian Islands; indices of abundance for these species; and dietary data for each predator species.

When compared to a conventional model, the multi-species model generated a much higher estimate of age-zero abundance and total mortality for younger animals. Trends in spawning biomass were robust between both models for all species except Atka mackerel.

These and other results suggest that the quantities on which management reference points are currently based (e.g., spawning biomass) are not greatly improved by including predation in stock assessment models. However, basing assessments on multi-species models could substantially improve estimates of quantities needed to determine how much food is available to predators.

Punt, Andre E., 2007. Including trophic interactions in fish stock assessments in the Aleutian Islands. School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA.

sighTings And re-sighTingssTUdying dispersAl And sUrvivAl in BrAnded pUps

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TAking sToCkA mUlTi-speCies model

the birthing, nursing and weaning of a Steller sea lion pup requires an almost perfect set of conditions: a stable ocean climate, an abundant food supply and the good fortune to elude predators on land and at sea. Under the right circumstances, a mother’s hard work pays off and her pup survives its first year of life. This critical graduation phase, when the nursing pup begins to forage for itself, is known as the age at weaning.

Newly weaned pups are believed to be that age group that is most vulnerable to shortages in prey, which can lead to a physiological condition called nutritional stress. For much of the 1990s, researchers blamed nutritional stress for the widespread starvation of immature pups following weaning in western Alaska.

But could an apparent absence of young be related to a critical time of year, such as winter, when young animals might have difficulty finding food? Are longer foraging trips an indicator of nutritional stress? To answer these and other questions, a team of Consortium researchers conducted a series of observations over four years (1995–1998) at four haulout sites across Alaska, surveying both stable and declining Steller sea lion populations.

Meaning in Weaning

Huddled for countless hours behind camouflaged blinds at each haulout site, the researchers surveyed the seasonal patterns of attendance (i.e., time on shore nursing vs. time at sea foraging) of mature females with pups (0–12 months) and yearlings (13–24 months). Yearlings appeared to nurse less as winter turned to spring and summer, which suggest a possible gradual weaning process in which the yearlings began to forage more and more frequently.

Most Steller sea lions weaned shortly before their first or second birthdays, and weaning almost always appeared to begin in spring (April to May), before the start of the following breeding season.

This result is none too surprising: each pup represents a major investment of time and energy to the mother, and it does not make evolutionary sense for a mother to wean her pup at a time of year that is not optimal for its survival. Weaning a pup in summer just before the next breeding season would also allow the mother to return to the rookery in time to give birth and mate.

Males tended to wean later than females, and some pups were observed to nurse for as long as three years. This apparent plasticity in the timing of weaning suggests that females in nutritionally stressed populations, such as those in western Alaska, may nurse their pups for an additional one or two years to enhance the pups’ chances of survival. But in so doing, these females also lose the opportunity to breed that year.

Shifts in the timing of weaning may be a natural mechanism for population control with high proportions of pups suckling well beyond the first

year indicating a population that is approaching carrying capacity. In contrast, pups in a healthy and growing population might wean at just one year, enabling their mothers to breed again that same year. In the Gulf of Alaska and Bering Sea, young sea lions require a lot of energy to grow and may require their mothers to convert energy-poor pollock into energy-rich milk.

Seasonal Patterns

Of particular interest was the way in which foraging times changed over the course of a year. Would sea lions have a harder time finding prey during winter than during summer? Could such a pattern lead to nutritional stress in areas of decline? Counter to expectations, no significant differences were seen between haulout populations in the time that lactating Steller sea lions spent at sea or on shore. This suggests that lactating sea lions did not have more difficulty capturing prey from winter through summer in the area of decline, compared to where sea lion numbers increased.

It seems that the incidence of longer foraging trips in winter does not appear to foreshadow nutritional stress: this trend was observed in both stable and declining populations. Rather, it confirms the view that lactating sea lions make a greater investment in their young during winter than during spring or summer.

Trites, A.W., B.P. Porter, V.B. Deecke, A.P. Coombs, M.L. Marcotte and D.A.S. Rosen. 2006. Insights into the timing of weaning and the attendance patterns of lactating Steller sea lions (Eumetopias jubatus) in Alaska during winter, spring and summer. Aquatic Mammals 32:85-97.

from milk To fish The WeAning of sTeller seA lions in AlAskA

fi e l d s t U d i e s – a N N U a l r e P o r t 2006–2007 • page 1�

along the rugged Alaskan coast, nestled between the Gulf of Alaska and the eastern Aleutian Islands, Kodiak Island is a natural waypoint for marine life. The breakwater at Kodiak Harbor provides a convenient haul-out for dozens of local Steller sea lions, attracting a small but highly specialized group of killer whales dubbed the “Kodiak Killers”.

A group of six whales that spend part of each winter around the city of Kodiak, the Kodiak Killers are unusual because they seem to specialize in hunting Steller sea lions. In addition to a 25-foot long male, who is a particularly efficient predator of both juvenile and adult sea lions, the group includes two adult females, two juveniles born in 2002 and a calf born in 2005.

For the past four years, veteran killer whale expert Craig Matkin has worked with the Consortium to

study the role of killer whales in the decline of Steller sea lions and fur seals in the western Aleutians.

While many generalizations have been made about Alaska’s transient killer whales across their range, their diet and behavior appear to vary from area to area. In the summer and fall in the eastern Aleutians, for example, fur seals are emerging as the most important prey for killer whales, while Steller sea lions are infrequently hunted.

This picture is quite different a short distance away, near False Pass at the end of the Alaska Peninsula, where other transients specialize in hunting migrating gray whales in spring. In Prince William Sound and Kenai Fjords the threatened population of transients known as the AT1’s displays rather different predatory habits, preying mainly on harbor seals and Dall’s porpoises.

Many of these killer whale populations are small and may need to develop very different habits in order to survive. A number of researchers believe the transient killer whales pass on these different hunting traditions through matrilineal groups.

The fact that the Kodiak Killers are successfully building their numbers is testament to their success at hunting Steller sea lions, which appear to be a considerably more challenging prey than harbor seals and fur seals. Despite the Kodiak Killers’ unpredictable appearances – a few dozen days between February and April each year – they are estimated to collectively take an average of two juvenile sea lions (weighing about 150kg each) for every 36 hours they are present. Based on data from feeding studies of captive whales, this rate of consumption is probably about average for a group of wild killer whales.

Does such consistent predation present a threat to Kodiak’s Steller sea lions? There is not enough information to be certain. When a declining population is trying to recover, any animal removed is one less animal that could potentially produce offspring and help the population recover. The important question is whether or not this predation is preventing recovery: if the reproductive potential of the animals is high enough, it could offset losses by predation.

Data on killer whale predation in Alaska is spotty at best; Matkin is combining his own first-hand behavioral observations with population data derived from photo identification work. These data will help him to estimate how much prey a population of killer whales needs to eat, based on its size and predatory preferences.

on The TrAil of The kodiAk killersdo seA lion speCiAlisTs pose A popUlATion ThreAT?

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cAptive studies

Studies on captive Steller sea lions are a key part of the Consortium’s scientific program. By working with sea lions housed at the Vancouver Aquarium and the Open Water Research Station, Consortium researchers can investigate a number of hypotheses explaining the decline of their wild counterparts. This research forms a scientific bridge between observations made in the wild and inferences generated by computer models of animal physiology and behavior.

There are currently 12 animals in the captive research program, ranging in age from 3–13 years old; the focus continues to be on younger animals as this is the portion of the wild population deemed to be most at risk.

Consortium studies on captive sea lions are roughly divided into three categories: basic physiology, bioenergetics and nutrition. Additionally, the animals are used to develop and test various techniques and technologies that can be applied to studying animals in the wild. These opportunities enable scientists to evaluate the usefulness of proposed field studies before they are undertaken, and to help interpret their data.

Aquarium-based studies on Steller sea lions in 2006–07 included studies of seasonal variability in nutritional stress, and the diving physiology and foraging decisions of sea lions in an open water environment.

Just as many people prefer to eat heavier foods in winter and lighter meals in summer, the Steller sea lion diet also varies with the seasons. Sea lion appetites peak during winter and again during the spring, while they resiliently adapt to smaller meals and periods of fasting in the summer.

Changing ocean conditions can limit the availability of key energy-rich prey species such as sandlance and herring, causing prolonged food shortages and nutritional stress—a factor that may be contributing to the dramatic decline in Western Alaska’s Steller sea lion population.

If sea lion diets vary with season, are the effects of nutritional stress also seasonally dependent? If so,

what is the most reliable indicator of nutritional stress? To answer these and other questions, researchers conducted controlled feeding trials on captive Steller sea lions at the Vancouver Aquarium, assessing their physiological response to brief shortages of different prey over four seasons.

Winter Woes

Under brief periods of nutritional stress, the sea lions lost body mass faster during colder seasons than during warmer seasons. These changes coincided with predicted food/energy requirements for wild Steller sea lions, suggesting that they may be more susceptible to intense nutritional stress during winter (see Figure �).

This finding is particularly important for young sea lions, who allocate most of the energy they consume to growth and development. An unusually severe winter might be lethal to an animal that is already nutritionally stressed due to a shortage of key prey.

These findings have important implications for sea lion conservation. Scientists frequently gauge an animal’s health based on its body condition, or relative lipid reserves. However, lipid stores undergo natural seasonal changes that do not necessarily reflect changes in overall health; and because the sea lions use both lipids and protein during periods of nutritional stress, the relative amount of lipid does not change significantly even when the sea lions lose substantial weight. Assessments of body condition on a seasonal basis could produce a more accurate picture of overall health.

Kumagai, S., D.A.S Rosen and A.W. Trites. 2006. Body mass and composition responses to short-term low energy intake are seasonally dependent in Steller sea lions (Eumetopias jubatus). Comparative Biochemistry and Physiology 179:589-598.

seAson of The seA lionis nUTriTionAl sTress seAsonAlly dependenT?

Figure �: Total body mass loss (black bars) of sea lions while eating herring or pollock was significantly higher in winter. The contribution of lipid loss to total mass loss is shown for herring (medium bars) and pollock (light bars) diets. The sea lions lost more mass from lipid stores while consuming pollock than when consuming herring, except in the summer when the pattern was reversed (they appeared to gain lean body mass while losing overall body mass).

c a P t i v e s t U d i e s – a N N U a l r e P o r t 2006–2007 • page 1�

sea lions must periodiCally haul out on shore to rest, reproduce, and raise their young – giving scientists a prime opportunity to learn more about them. But studying a sea lion on land is like studying a nesting bird: it only reveals one part of the picture.

Once a sea lion disappears beneath the surface in search of food, its body becomes a finely tuned diving machine. The longer the dive, the more likely the sea lion will find food. But diving uses energy, and a foraging dive is a careful balance between spending energy – the energetic cost of foraging – and taking it in.

Studies suggest that a sea lion can extend the duration of a dive by automatically decreasing its metabolism and by modifying its behavior – taking fewer flipper strokes, for example – to consume less energy at depth. To determine the metabolic costs of diving to various depths and durations, a team of scientists recently studied a trio of trained female Steller sea lions diving in open water.

What’s in a Breath?

The study made use of a floating respiratory dome designed to measure the amount of oxygen consumed before and after a dive. In each open-water trial, a trained sea lion dove repeatedly from under the floating dome to a submerged target light, which was suspended at various depths. When the underwater light was turned off, the sea lion resurfaced under the respiratory dome. Oxygen consumption was then calculated from the pre- and post-dive measurements.

The sea lions used more energy (i.e., consumed oxygen at a higher rate) as swimming distance increased, but used less oxygen on deeper dives. This may be because sea lions become less buoyant as they dive deeper (and as water pressure increases), requiring fewer flipper strokes to stay submerged

and thereby conserving oxygen. Dive depth and swimming distance also had a much greater effect on their metabolism than environmental factors such as water temperature, which fluctuated widely over the study but did not appear to affect results.

Predicting Food Requirements

After gathering the data, the researchers constructed a model to predict the oxygen consumption of sea lions diving in the wild. This model estimated that an adult female Steller sea lion requires 18kg of food per day when diving to 10m but only 8kg of food if diving to 300m! The model also provides a useful tool to determine how fluctuations in prey availability — such as a shift from capelin to cod — might affect the foraging strategy of wild sea lions and the overall health of their populations.

Although wild sea lions can dive to depths of 100m, the trained sea lions in the study have so far only been studied up to 30m (100 feet), leaving unanswered questions about the effects of extreme depth on diving metabolism. However, the study provides valuable first insights into how Steller sea lions balance their energetic costs and benefits when diving to depth.

Hastie, G.D, D.A.S. Rosen, A.W. Trites. 2006. The influence of depth on a breath-hold diver: predicting the diving metabolism of Steller sea lions (Eumetopias jubatus). Journal of Experimental Marine Biology and Ecology 336:163-170.

proBing The depThs on A single BreAThhoW mUCh energy does A diving seA lion Use?

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Figure �: The relationship between dive depth and rate of oxygen consumption (relative to average energy expenditure f[x]=0). Sea lions used less energy when diving to deeper depths.

understanding the Causes of change in the North Pacific requires a commitment to long-term research: solutions need a concerted effort and are unlikely to come quickly. With this understanding, the Consortium was formed to address issues concerning interactions between marine mammals and fisheries in the North Pacific.

In 2006–2007, Consortium-funded research resulted in 39 peer-reviewed publications, book chapters, and dissertations. In addition, Consortium researchers were engaged in 26 studies, many of which are ongoing.

We have undertaken a solid field program, a strong captive research program and major analytical research initiatives. Specifically, a multi-disciplinary research program has been mounted to elucidate the factors responsible for the decline of Steller sea lions in Alaska. Our studies also account for issues related to harbor seals, northern fur seals and whales, which we believe will attract greater attention in the years to come.

Research in 2007–2008 will continue with a balance of short-term and long-term projects. These are designed to address and draw conclusions about changes occurring in the North Pacific and the role that commercial fisheries and other factors may have played.

sUmmAry

s U M M a r y – a N N U a l r e P o r t 2006–2007 • page 1�

Ban, S. and A.W. Trites. in press. Quantification of terrestrial haulout and rookery characteristics of Steller sea lions. Marine Mammal Science.

Gregr, E. and K. Bodtker. in press. Adaptive classification of marine ecosystems: identifying biologically meaningful regions in the marine environment. Deep-Sea Research Part 1.

Hastie, G.D., D.A.S. Rosen, and A.W. Trites. in press. Reductions in oxygen consumption during dives and estimated submergence limitations of Steller sea lions (Eumetopias jubatus). Marine Mammal Science.

Heymans, S.J.J., S. Guénette and V. Christensen. in press. Evaluating network analysis indicators of ecosystem status in the Gulf of Alaska. Ecosystems.

Huynh, M.D., D.D. Kitts, C. Hu, and A.W. Trites. in press. Spawning affects the nutritional value of Pacific herring, Clupea harangus pallasii. Journal of Comparative Biochemistry and Physiology.

Rosen, D.A.S, A.J. Winship, and L. Hoopes. in press. Thermal and digestive constraints to foraging in marine mammals. Philosophical Transactions, Royal Society of London B.

Trites, A.W., D.G. Calkins and A.J. Winship. in press. Diets of Steller sea lions (Eumetopias jubatus) in southeastern Alaska from 1993 to 1999. Fishery Bulletin.

Trites, A. W., V. B. Deecke, E. J. Gregr, J. K. B. Ford, and P. F. Olesiuk. in press. Killer whales, whaling and sequential megafaunal collapse in the North Pacific: a comparative analysis of the dynamics of marine mammals in Alaska and British Columbia following commercial whaling. Marine Mammal Science.

Carter, S.K., G.R. VanBlaricom, and B.L. Allen. 2007. Testing the generality of the trophic cascade paradigm for sea otters: a case study with kelp forests in northern Washington, USA. Hydrobiologia. 579:233-249.

Cheneval, O., R.W. Blake, A.W. Trites, and K.H.S. Chan. 2007. Turning maneuvers in Steller sea lions (Eumetopias jubatus). Marine Mammal Science 23:94-109.

Deagle, B.E., and D.J. Tollit. 2007. Quantitative analysis of prey DNA in pinniped faeces: potential to estimate diet composition? Molecular Ecology 8:743-747.

Gelatt, T., A.W. Trites, K. Hastings, L. Jemison, K. Pitcher, and G. O’Corry-Crowe. 2007. Population trends, diet, genetics, and observations of Steller sea lions in Glacier Bay National Park. Pp. 145-149. in J. F. Piatt and S. M. Gende (eds.). Proceedings of the Fourth Glacier Bay Science S ymposium, U.S. Geological Survey Scientific Investigations Report 2007-5047.

Guénette, S., S.J.J. Heymans, V. Christensen, and A.W. Trites. 2007. Ecosystem models of the Aleutian Islands and Southeast Alaska show that Steller sea lions are impacted by killer whale predation when sea lion numbers are low. Pp. 150-154. in J. F. Piatt and S. M. Gende (eds.). Proceedings of the Fourth Glacier Bay Science Symposium, U.S. Geological Survey Scientific Investigations Report 2007-5047, Juneau , Alaska.

Hoopes, L.A. 2007. Metabolic and thermoregulatory capabilities of juvenile Steller sea lions (Eumetopias jubatus). PhD thesis, Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX.

Matkin, C.O., L.G. Barrett-Lennard, H. Yurk, D. Ellifrit, and A.W. Trites. 2007. Ecotypic variation and predatory behavior among killer whales (Orcinus orca) off the eastern Aleutian Islands, Alaska. Fishery Bulletin 105:74-87.

Matkin, D.R., J.M. Straley, and C.M. Gabriele. 2007. Killer whale feeding ecology and non-predatory interactions with other marine mammals in the Glacier Bay a region of Alaska. Pp. 155-158. in J. F. Piatt and S. M. Gende (eds.). Proceedings of the Fourth Glacier Bay Science Symposium, U.S. Geological Survey Scientific Investigations Report 2007-5047.

Rea, L.D., D.A.S. Rosen, and A.W. Trites. 2007. Utilization of stored energy reserves during fasting varies by age and season in Steller sea lions. Canadian Journal of Zoology 85: 461-482.

Rosen, D., A. Fahlman, G. Hastie, and A. Trites. 2007. Laboratory studies in wildlife conservation: the case of the Steller sea lion. Comparative Biochemistry and Physiology Part A 146:S84.

Springer, A.M., G.B. Van Vliet, J.F. Piatt, and E.M. Danner. 2007. Whales and whaling in the North Pacific: oceanographic insights and ecosystem impacts. pp. 245-261. in J.A. Estes, R.L. Brownell, D.P. DeMaster, D.P. Doak, and T.M. Williams (eds.), Whales, whaling, and ocean ecosystems, University of California Press, Berkeley, CA.

Tollit, D.J., S.J. Heaslip, R.I. Barrick and A.W. Trites. 2007. Impact of diet index selection and the digestion of prey hard remains on determining the diet of the Steller sea lion (Eumetopias jubatus). Canadian Journal of Zoology 85:1-15.

Trites, A.W., A.J. Miller, H.D.G. Maschner, M.A. Alexander, S.J. Bograd, J.A. Calder, A. Capotondi, K.O. Coyle, E.D. Lorenzo, B.P. Finney, E.J. Gregr, C.E. Grosch, S.R. Hare, G.L. Hunt, J. Jahncke, N.B. Kachel, H.-J. Kim, C. Ladd, N.J. Mantua, C. Marzban, W. Maslowski, R. Mendelssohn, D.J. Neilson, S.R. Okkonen, J.E. Overland, K.L. Reedy-Maschner, T.C. Royer, F.B. Schwing, J.X.L. Wang, and A.J. Winship. 2007. Bottom-up forcing and the decline of Steller sea lions (Eumetopias jubatus) in Alaska: assessing the ocean climate hypothesis. Fisheries Oceanography 16: 46-67.

Bredesen, E.L., A.P. Coombs, and A.W. Trites. 2006. Relationship between Steller sea lion diets and fish distributions in the eastern North Pacific. pp. 131-139. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Deecke, V. B. 2006. Studying marine mammal cognition in the wild: a review of four decades of playback experiments. Aquatic Mammals 32: 461-482.

DeMaster, D.P., A.W. Trites, P. Clapham, S. Mizroch, P. Wade, and R.J. Small. 2006. The sequential megafaunal collapse hypothesis: testing with existing data. Progress in Oceanography 68: 329-342.

Fay, G. and A.E. Punt. 2006. Modeling spatial dynamics of Steller sea lions (Eumetopias jubatus) using maximum likelihood and Bayesian methods: evaluating causes for population decline. pp. 405-433. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Gallucci, V.F., I.G. Taylor, K. Erzini. 2006. Conservation and management of exploited shark populations based on reproductive value. Canadian Journal of Fisheries and Aquatic Sciences 63: 931-942

Guénette, S., S.J.J. Heymans, V. Christensen, and A.W. Trites. 2006. Ecosystem models show combined effects of fishing, predation, competition, and ocean productivity on Steller sea lions (Eumetopias jubatus) in Alaska. Canadian Journal of Fisheries and Aquatic Sciences 63: 2495-2517.

ConsorTiUm pUBliCATionspUBliCATions AvAilABle for doWnloAd AT www.marinemammal.org

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Hastie, G.D., D.A.S. Rosen, and A.W. Trites. 2006. The influence of depth on a breath-hold diver: predicting the diving metabolism of Steller sea lions (Eumetopias jubatus). Journal of Experimental Marine Biology and Ecology 336: 163-170.

Hastie, G, D.A.S. Rosen, and A.W. Trites. 2006. Studying trained Steller sea lions in the open ocean. pp. 193-204. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Hori, B. 2006. Long term soft tissue fixation and mechanical reliability of a ceramic housing for a new radio frequency transmitter. MASc thesis. University of British Columbia, Vancouver, BC. 188 pages.

Joy, R., D.J. Tollit, J.L. Laake, and A.W. Trites. 2006. Using simulations to evaluate reconstructions of sea lion diet from scat. pp. 205-222. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Kucey, L., and A.W. Trites. 2006. A review of the potential effects of disturbance on sea lions: assessing response and recovery. pp. 581-589. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Kumagai, S., D.A.S. Rosen and A.W. Trites. 2006. Body mass and composition responses to short-term low energy intake are seasonally dependent in Steller sea lions (Eumetopias jubatus). Journal of Comparative Physiology B 176: 589-598.

Lea, M.A., and B. Wilson. 2006. Techniques for real-time, active tracking of sea lions. pp. 235-253. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

London, J.M. 2006. Harbor seals in Hood Canal: predators and prey. PhD thesis. University of Washington, Seattle WA. 100 pp.

Marcotte, M.L. 2006. Steller Watch: timing of weaning and seasonal patterns in numbers and activities of Steller sea lions at a year-round haulout site in Southeast Alaska. MSc thesis, University of British Columbia, Vancouver, BC. 74 pp.

Punt, A.E. and G. Fay. 2006. Can experimental manipulation be used to determine the cause of the decline of western stock of Steller sea lions (Eumetopias jubatus)? pp. 435-454. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Richmond J.P, T. Jeanniard du Dot, D.A.S. Rosen, S.A. Zinn. 2006. Effects of prey composition on the endocrine response to nutrient restriction and re-alimentation in Steller sea lions (Eumetopias jubatus). Symposia of the Comparative Nutrition Society, Vol. 6, Keystone, Colorado, pp 136-141.

Rosen, D.A., D.J. Tollit, A.J. Winship, and A.W. Trites. 2006. Potential effects of short-term prey changes on sea lion physiology. pp. 103-116. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Rosen D.A.S, A.J. Winship, L.A. Hoopes. 2006. Interacting physiological constraints to foraging behavior in marine mammals. Symposia of the Comparative Nutrition Society, Vol 6, Keystone, Colorado, pp 151-156.

Scordino, J. 2006. Steller sea lions (Eumetopias jubatus) of Oregon and northern California: seasonal haulout abundance patterns, movements of marked juveniles, and effects of hot-Iron branding on apparent survival of pups at Rogue Reef. M.Sc. thesis, Oregon State University, Corvalis. 112 pp.

Soto, K., A.W. Trites, and M. Arias-Schreiber. 2006. Changes in diet and maternal attendance of South American sea lions indicate changes in the marine environment and the abundance of prey. Marine Ecology Progress Series 312: 277-290.

Tollit, D.J., S.G. Heaslip, B.E. Deagle, S.J. Iverson, R. Joy, D.A.S. Rosen, and A.W. Trites. 2006. Estimating diet composition in sea lions: which technique to choose? pp. 293-307. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Trites, A.W., S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.). 2006. Sea lions of the world. Alaska Sea Grant College Program, University of Alaska Fairbanks. 664 pp.

Trites, A. W., V. Christensen, and D. Pauly. 2006. Effects of fisheries on ecosystems: just another top predator? pp. 11-27. in I.L. Boyd, K. Camphuysen and S. Wanless (eds.), Top predators in marine ecosystems: their role in monitoring and management, Cambridge University Press, Cambridge.

Trites, A.W., B.P. Porter, V.B. Deecke, A.P. Coombs, M.L. Marcotte and D.A.S. Rosen. 2006. Insights into the timing of weaning and the attendance patterns of lactating Steller sea lions (Eumetopias jubatus) in Alaska during winter, spring and summer. Aquatic Mammals 323: 85-97.

Winship, A.J., A.M.J. Hunter, D.A.S. Rosen, and A.W. Trites. 2006. Food consumption by sea lions: existing data and techniques. pp. 171-191. in A.W. Trites, S.K. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K.M. Wynne (eds.), Sea lions of the world, Alaska Sea Grant College Program, University of Alaska Fairbanks.

Winship, A.J., and A.W. Trites. 2006. Risk of extirpation of Steller sea lions in the Gulf of Alaska and Aleutian Islands: a population viability analysis based on alternative hypotheses for why sea lions declined in western Alaska. Marine Mammal Science 22: 124-155.

Burek, K.A., F.M.D. Gulland, G. Sheffield, K.B. Beckman, E. Keyes, T.R. Spraker, A.W. Smith, D.E. Skilling, J.E. Evermann, J.L. Stott, J.T. Saliki and A.W. Trites. 2005. Infectious disease and the decline of Steller sea lions (Eumetopias jubatus) in Alaska: insights from serology data. Journal of Wildlife Diseases 41:512-524.

Ban, S.S. 2005. Modelling and characterization of Steller sea lion haulouts and rookeries using oceanographic and shoreline type data. Masters thesis. University of British Columbia, Vancouver BC. 103 pp.

Cheneval, O. 2005. Biomechanics of turning manoeuvres in Steller sea lions (Eumetopias jubatus). Masters thesis. University of British Columbia, Vancouver BC. 64 pp.

Deagle, B.E., D.J. Tollit, S.N. Jarman, M.A. Hindell, A.W. Trites and N.J. Gales. 2005. Molecular scatology as a tool to study diet: analysis of prey DNA in scats from captive Steller sea lions. Molecular Ecology 14: 1831-1842.

Deecke, V. B., J.K.B. Ford and P.J.B Slater. 2005. The vocal behavior of mammal-eating killer whales (Orcinus orca): communicating with costly calls. Animal Behavior 69:395-405.

Guénette, S. and V. Christensen. 2005. Food web models and data for studying fisheries and environmental impacts on Eastern Pacific ecosystems. Fisheries Centre Research Reports 13(1), 237 pp.

Kucey, L. 2005. Human disturbance and the haulout out behavior of Steller sea lions (Eumetopias jubatus). Masters thesis. University of British Columbia, Vancouver BC. 75 pp.

Miller, E.H., A.W. Trites, and Ø. Wiig. 2005. International survey of scientific collections of Steller sea lions. Fisheries Centre Research Reports 13(6), 69 pp.

Olawale, K.O., R.J. Petrell, D.G. Michelson and A.W. Trites. 2005. The dielectric properties of the cranial skin of five young captive Steller sea lions (Eumetopias jubatus) and a similar number of young domestic pigs (Sus scrofa) and sheep (Ovis aries) between 0.1 and 10 GHz. Physiological Measurement 26:626-637.

Rosen, D. A. S. and A.W. Trites. 2005. Examining the potential for nutritional stress in young Steller sea lions: physiological effects of prey composition. Journal of Comparative Physiology B 175: 265-273.

Trites, A.W. and R. Joy. 2005. Dietary analysis from fecal samples: how many scats are enough? Journal of Mammalogy 86:704-712.

Willis, K. and M. Horning. 2005. A novel approach to measuring heat flux in swimming animals. Journal of Experimental Marine Biology and Ecology 315:147-162.

Willis, K., M. Horning, D.A.S. Rosen and A.W. Trites. 2005. Spatial variation of heat flux in Steller sea lions: evidence for consistent avenues of heat exchange along the body trunk. Journal of Experimental Marine Biology and Ecology 315:163-175.

Gauthier, S. and J.K. Horne. 2004a. Acoustic characteristics of forage fish species in the Gulf of Alaska and Bering Sea based on Kirchhoff-approximation models. Canadian Journal of Fisheries and Aquatic Sciences 61: 1839-1850.

Gauthier, S. and J.K. Horne. 2004b. Potential acoustic discrimination within a boreal fish assemblage. ICES Journal of Marine Science 61: 836-845.

Hoopes, L.A., L.D Rea, D.A.S Rosen, and G.A.J Worthy. 2004. Effects of body condition on resting metabolism in captive and free-ranging Steller sea lions (Eumetopias jubatus). Symposia of the Comparative Nutrition Society 2004. No. 5, pp 79-82.

Hunt, K.E., A.W. Trites and S.K. Wasser. 2004. Validation of a fecal glucocorticoid assay for Steller sea lions (Eumetopias jubatus). Physiology and Behavior 80: 595-601.

Kitts, D.D., M.D. Huynh, C. Hu, and A.W. Trites. 2004. Seasonal variation in nutrient composition of Alaskan pollock (Theragra chalcogramma). Canadian Journal of Zoology 82:1408-1415.

Kumagai, S. 2004. Seasonal differences in physiology of captive Steller sea lions (Eumetopias jubatus) in response to short-term low energy intake. Masters thesis. University of British Columbia, Vancouver BC. 95 pp.

Porter, B.T. and A.W. Trites. 2004. Suckling attempts during winter by two non-filial Steller sea lion pups. Mammalia 68:23-26.

Rosen, D.A.S., G.D. Hastie, and A.W. Trites. 2004. Searching for stress: Hematological indicators of nutritional inadequacies in Steller sea lions. Symposia of the Comparative Nutrition Society 2004. No. 5, pp 145-149.

Rosen, D.A.S. and A.W. Trites. 2004. Satiation and compensation for short-term changes in food quality and availability in young Steller sea lions (Eumetopias jubatus). Canadian Journal of Zoology 82:1061-1069.

Soto, K.H. 2004. The effects of prey abundance on the diet, maternal attendance and pup mortality of the South American sea lion (Otaria flavescens) in Peru. MSc thesis. University of British Columbia, Vancouver BC. 73 pp.

Soto, K., A.W. Trites and M. Arias-Schreiber. 2004. The effects of prey availability on pup mortality and the timing of birth of South American sea lions (Otaria flavescens) in Peru. Journal of Zoology London 264: 419-428.

Tollit, D.J., S.G. Heaslip and A.W. Trites. 2004. Sizes of walleye pollock consumed by the Eastern stock of Steller sea lions (Eumetopias jubatus) in Southeast Alaska from 1994-1999. Fishery Bulletin 102: 522-532.

Tollit, D.J., S.G. Heaslip, T.K. Zeppelin, R. Joy, K.A. Call and A.W. Trites. 2004. A method to improve size estimates of walleye pollock and Atka mackerel consumed by pinnipeds using digestion correction factors applied to bones and otoliths recovered in scats. Fishery Bulletin 102: 498-508.

Zeppelin, T.K., D.J. Tollit, K.A. Call, T.J. Orchard and C.J. Gudmundson. 2004. Sizes of walleye pollock and Atka mackerel consumed by the Western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1998-2000. Fishery Bulletin 102: 509-521.

Burek, K.A., F.M.D. Gulland, G. Sheffield, D. Calkins, E. Keyes, T.R. Spraker, A.W. Smith, D.E. Skilling, J. Evermann, J.L. Stott and A.W. Trites. 2003. Disease agents in Steller sea lions in Alaska: a review and analysis of serology data from 1975-2000. Fisheries Centre Reports 11(4) 26 pp.

Daniel, R.G. 2003. The timing of moulting in wild and captive Steller sea lions (Eumetopias jubatus). MSc thesis. University of British Columbia, Vancouver, B.C. 64 pp.

Donnelly, C.P., A.W. Trites and D.D. Kitts. 2003. Possible effects of pollock and herring on the growth and reproductive success of Steller sea lions: insights from feeding experiments using an alternative animal model, Rattus novegicus. British Journal of Nutrition 89: 71-82.

Heise, K., L.G. Barrett-Lennard, E. Saulitis, C.O. Matkin and D. Bain. 2003. Examining the evidence for killer whale predation on Steller sea lions in British Columbia and Alaska. Aquatic Mammals 29: 325-334.

McPhee, J.M., D.A.S. Rosen, R.D. Andrews and A.W. Trites. 2003. Predicting metabolic rate from heart rate for juvenile Steller sea lions Eumetopias jubatus. Journal of Experimental Biology 206: 1941-1951.

Milette, L.L. and A.W. Trites. 2003. Maternal attendance patterns of lactating Steller sea lions (Eumetopias jubatus) from a stable and a declining population in Alaska. Canadian Journal of Zoology 81: 340-348.

Rosen, D.A.S. and A.W. Trites. 2003. No evidence for bioenergetic interaction between digestion and thermoregulation in Steller sea lions, Eumetopias jubatus. Physiological and Biochemical Zoology 76: 899-906.

Springer, A.M., J.A. Estes, G.B. van Vliet, T.M. Williams, D.F. Doak, E.M. Danner, K.A. Forney and B. Pfister. 2003. Sequential megafaunal collapse in the North Pacific Ocean: An ongoing legacy of industrial whaling? Proceedings of the National Academy of Sciences of the United States of America 100: 12223-12228.

Tollit, D.J., M. Wong, A.J. Winship, D.A.S. Rosen and A.W. Trites. 2003. Quantifying errors associated with using prey skeletal structures from fecal samples to determine the diet of the Steller sea lion (Eumetopias jubatus). Marine Mammal Science 19: 724-744.

Trites, A.W. 2003. Food webs in the ocean: who eats whom, and how much? pp. 125-143. in M. Sinclair and G. Valdimarsson (Eds), Responsible Fisheries in the Marine Ecosystem. FAO, Rome and CABI Publishing, Wallingford.

Trites, A.W. and C.P. Donnelly. 2003. The decline of Steller sea lions in Alaska: A review of the nutritional stress hypothesis. Mammal Review 33: 3-28.

Winship, A.J. and A.W. Trites. 2003. Prey consumption of Steller sea lions (Eumetopias jubatus) off Alaska: how much prey do they require? Fishery Bulletin 101: 147-167.

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Andrews, R.D., D.G. Calkins, R.W. Davis, B.L. Norcross, K. Peijnenberg and A.W. Trites. 2002. Foraging behavior and energetics of adult female Steller sea lions. pp. 19-22. in D. DeMaster and S. Atkinson (eds). Steller sea lion decline: is it food II? University of Alaska Sea Grant, AK-SG-02-02, Fairbanks.

Benson, A.J. and A.W. Trites. 2002. Ecological effects of regime shifts in the Bering Sea and eastern North Pacific Ocean. Fish and Fisheries 3: 95-113.

Carter, S.K. and G.R. VanBlaricom. 2002. Direct effects of experimental harvest on red sea urchin populations in San Juan Channel, Washington. Fishery Bulletin 100:662-673.

Cottrell, P.E. and A.W. Trites. 2002. Classifying prey hard part structures recovered from fecal remains of captive Steller sea lions (Eumetopias jubatus). Marine Mammal Science 18: 525-539.

Matkin, C.G., L. Barrett-Lennard and G. Ellis. 2002. Killer whales and predation on Steller sea lions. pp. 61-66 in D. DeMaster and S. Atkinson (eds). Steller sea lion decline: is it food II? University of Alaska Sea Grant, AK-SG-02-02, Fairbanks.

Rosen, D.A.S. and A.W. Trites. 2002. Changes in metabolism in response to fasting and food restriction in the Steller sea lion (Eumetopias jubatus). Comparative Biochemistry and Physiology 132: 389-399.

Rosen, D.A.S. and A.W. Trites. 2002. Cost of transport in Steller sea lions, Eumetopias jubatus. Marine Mammal Science 18: 513-524.

Rosen, D.A.S. and A.W. Trites. 2002. What is it about food? Examining possible mechanisms with captive Steller sea lions. pp. 45-48. in D. DeMaster and S. Atkinson (eds). Steller sea lion decline: is it food II? University of Alaska Sea Grant, AK-SG-02-02, Fairbanks.

Trites, A.W. 2002. Predator-prey relationships. pp. 994-997. in W.F. Perrin, B. Wursig, and H.G.M. Thewissen (eds.). Encyclopedia of Marine Mammals, Academic Press, San Diego.

Trites, A.W. and B.T. Porter. 2002. Attendance patterns of Steller sea lions (Eumetopias jubatus) and their young during winter. Journal of Zoology, London 256: 547-556.

Winship, A.J, A.W. Trites and D.A.S. Rosen. 2002. A bioenergetic model for estimating the food requirements of Steller sea lions (Eumetopias jubatus) in Alaska, USA. Marine Ecology Progress Series 229:291-312.

Gerber, L.R. and G.R. VanBlaricom. 2001. Implications of three viability models for the conservation status of the western population of Steller sea lions (Eumetopias jubatus). Biological Conservation 102: 261-269.

Hirons, A.C., D.M. Schell and D.J. St. Aubin. 2001. Growth rates of vibrissae of harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus). Canadian Journal of Zoology 79: 1053-1061.

Hirons A.C., D.M. Schell and B.P. Finney. 2001. Temporal records of d13C and d15N in North Pacific pinnipeds: inferences regarding environmental change and diet. Oecologia 129: 591-601.

Hunter, A.M.J. and A.W. Trites. 2001. An annotated bibliography of scientific literature (1751-2000) pertaining to Steller sea lions (Eumetopias jubatus) in Alaska. Fisheries Centre Research Reports, Vol 9 (1). 45 pp.

Trites, A.W. 2001. Marine mammal trophic levels and interactions. pp. 1628-1633. in J. Steele, S. Thorpe and K. Turekian (eds.). Encyclopedia of Ocean Sciences, Academic Press, London.

Winship, A.J., A.W. Trites and D.G. Calkins. 2001. Growth in body size of Steller sea lions (Eumetopias jubatus). Journal of Mammalogy 82: 500-519.

Berman, M., and L. Rea. 2000. The effects of food deprivation on serum lipid concentration and content in Steller sea lions (Eumetopias jubatus). pp. 13-16. in C.L.K. Baer (ed.). Proceedings of the Third Comparative Nutrition Society Symposium, No. �. Pacific Grove, California, August 4-9, 2000.

Donnelly, C., A.W. Trites and D.D. Kitts. 2000. Alternative models for assessing the role of nutrition in the population dynamics of marine mammals. pp. 41-45. in C.L.K. Baer (ed.). Proceedings of the Third Comparative Nutrition Society Symposium, No. �. Pacific Grove, California, August 4-9, 2000.

Hunter, A.M.J., A.W. Trites and D. Pauly. 2000. Estimates of basal metabolic and feeding rates for marine mammals from measurements of maximum body length. pp. 103-106. in C.L.K. Baer (ed.). Proceedings of the Third Comparative Nutrition Society Symposium, No. �. Pacific Grove, California, August 4-9, 2000.

Jonker, R.A.H. and A.W. Trites. 2000. The reliability of skinfold-calipers for measuring blubber thickness of Steller sea lion pups (Eumetopias jubatus). Marine Mammal Science 16: 757-766.

Rea, L.D. and T.R. Nagy. 2000. Changes in serum leptin levels during fasting and food limitation in Steller sea lions (Eumetopias jubatus). pp. 171-175. in C.L.K. Baer (ed.). Proceedings of the Third Comparative Nutrition Society Symposium, No. �. Pacific Grove, California, August 4-9, 2000.

Rea, L.D., D.A.S. Rosen and A.W. Trites. 2000. Metabolic response to fasting in 6-week-old Steller sea lion pups (Eumetopias jubatus). Canadian Journal of Zoology 78: 890-894.

Rosen, D.A.S. and A.W. Trites. 2000. Pollock and the decline of Steller sea lions: testing the junk-food hypothesis. Canadian Journal of Zoology 78: 1243-1258.

Rosen, D.A.S. and A.W. Trites. 2000. Assessing the role of nutritional stress in the decline of wild populations: a Steller case of scientific sleuthing. pp. 182-186. in C.L.K. Baer (ed.). Proceedings of the Third Comparative Nutrition Society Symposium, No. �. Pacific Grove, California, August 4-9, 2000.

Rosen, D.A.S. and A.W. Trites. 2000. Digestive efficiency and dry-matter digestibility of Steller sea lions fed herring, pollock, salmon and squid. Canadian Journal of Zoology 78: 234-239

Rosen, D.A.S., L. Williams and A.W. Trites. 2000. Effect of ration size and meal frequency on digestive and assimilation efficiency in yearling Steller sea lions, Eumetopias jubatus. Aquatic Mammals 26: 76-82.

Stelle, L.L., R.W. Blake and A.W. Trites. 2000. Hydrodynamic drag in Steller sea lions (Eumetopias jubatus). Journal of Experimental Biology 203: 1915-1923.

Trites, A.W. and R.A.H. Jonker. 2000. Morphometric measurements and body conditions of healthy and starveling Steller sea lion pups (Eumetopias jubatus). Aquatic Mammals 26: 151-157.

Yurk, H. and A.W. Trites. 2000. Experimental attempts to reduce predation by harbor seals (Phoca vitulina) on outmigrating juvenile salmonids. Transactions of the American Fisheries Society 129:1360-1366.

Burg, T., A.W. Trites and M.J. Smith. 1999. Mitochondrial and microsatellite analyses of harbor seal population structure in the Northeast Pacific Ocean. Canadian Journal of Zoology 77: 930-943.

Rea, L.D., D.A.S. Rosen and A.W. Trites. 1999. Seasonal differences in adaptation to prolonged fasting in juvenile Steller sea lions (Eumetopias jubatus). The FASEB Journal 13(5): A740.

Rosen, D.A.S. and A.W. Trites. 1999. Metabolic effects of low-energy diet on Steller sea lions, Eumetopias jubatus. Physiological Zoology 72: 723-731.

Springer, A.M. 1999. Summary, conclusions, and recommendations. pp. 777-799. in T. Loughlin and T. Ohtani (eds.). The Bering Sea: physical, chemical, and biological dynamics. Sea Grant, University of Alaska Fairbanks.

Trites, A.W., P. Livingston, S. Mackinson, M.C. Vasconcellos, A.M. Springer and D. Pauly. 1999. Ecosystem change and the decline of marine mammals in the Eastern Bering Sea: testing the ecosystem shift and commercial whaling hypotheses. Fisheries Centre Research Reports 7 (1), 106 pp.

Trites, A.W., P. Livingston, M.C. Vasconcellos, S. Mackinson, A.M. Springer and D. Pauly. 1999. Ecosystem considerations and the limitations of ecosystem models in fisheries management: insights from the Bering Sea. pp. 609-619. in Proceedings of Ecosystem Considerations in Fisheries Management. 16th Lowell Wakefield Fisheries Symposium and American Fisheries Society joint meeting. Anchorage, Alaska, USA. September 30 – October 3, 1998. Alaska College Sea Grant Program AK-SG-99-01.

Andrews, R.D. 1998. Remotely releasable instruments for monitoring the foraging behavior of pinnipeds. Marine Ecology Progress Series 175: 289-294.

Pauly, D., A.W. Trites, E. Capuli and V. Christensen. 1998. Diet composition and trophic levels of marine mammals. ICES Journal of Marine Science 55: 467-481

Rea, L.D., D.A.S. Rosen and A.W. Trites. 1998. Blood chemistry and body mass changes during fasting in juvenile Steller sea lions (Eumetopias jubatus). Proceedings of the Comparative Nutrition Society, Number 2, Banff, Alberta, Canada. August 14-19, 1998. pp. 174-178.

Rosen, D.A.S. and A.W. Trites. 1998. Changes in metabolism in response to varying energy intake in a marine mammal, the Steller sea lion. Proceedings of the Comparative Nutrition Society, Banff Alberta, August 1998, pp. 182-187.

Springer, A.M. 1998. Is it all climate change? Why marine bird and mammal populations fluctuate in the North Pacific. pp. 109-119. in G. Holloway, P. Muller, and D. Henderson (eds.). Biotic impacts of extratropical climate variability in the Pacific. ‘Aha Huliko’a Proceedings, University of Hawaii.

Trites, A.W. and D. Pauly. 1998. Estimating mean body masses of marine mammals from maximum body lengths. Canadian Journal of Zoology 76: 886-896.

Zenteno-Savin, T., and M.A. Castellini. 1998. Plasma angiotensin II, arginine vasopressin and atrial natriuretic peptide in free ranging and captive seals and sea lions. Comparative Biochemistry and Physiology 119C: 1-6.

Rosen, D.A.S. and A.W. Trites. 1997. Heat increment of feeding in Steller sea lions, Eumetopias jubatus. Comparative Biochemistry and Physiology 118A: 877-881.

Springer, A.M. and S.G. Speckman. 1997. A forage fish is what? Summary of the symposium. pp. 773-806. in Forage Fishes in Marine Ecosystems, University of Alaska Sea Grant Program Report 97-01.

Trites, A.W. 1997. The role of pinnipeds in the ecosystem. pp. 31-39. in G. Stone, J. Goebel, and S. Webster. (eds.). Pinniped populations, eastern north Pacific: Status, trends and issues. American Fisheries Society Symposium Report. New England Aquarium, Monterey Bay Aquarium, Monterey California, August 1997.

Trites, A.W., D. Pauly and V. Christensen. 1997. Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. Journal of Northwest Atlantic Fishery Science 22: 173-187.

Cottrell, P.W., A.W. Trites and E.H. Miller. 1996. Assessing the use of hard parts in faeces to identify harbor seal prey: results of captive feeding trials. Canadian Journal of Zoology 74: 875-880.

Hunt, G.L., Jr., A.S. Kitaysky, M.B. Decker, D.E. Dragoo and A.M. Springer. 1996. Changes in the distribution and size of juvenile walleye pollock as indicated by seabird diets at the Pribilof Islands and by bottom trawl surveys in the eastern Bering Sea. In R.D. Brodeur, P.A. Livingston, T.R. Loughlin, and A.B. Hollowed (eds.), Ecology of juvenile walleye pollock. US Department of Commerce, NOAA Technical Report NMFS 126: 125-139.

Springer, A.M. 1996. Prerecruit walleye pollock. Theragra chalcogramma, in seabird food webs of the Bering Sea. In R.D. Brodeur, P.A. Livingston, T.R. Loughlin, and A.B. Hollowed (eds.), Ecology of juvenile walleye pollock. US Department of Commerce, NOAA Technical Report NMFS 126: 198-201.

Trites, A.W. and P.A. Larkin. 1996. Changes in the abundance of Steller sea lions (Eumetopias jubatus) in Alaska from 1956 to 1992: how many were there? Aquatic Mammals 22: 153-166.

Larkin, P.A. 1996. Concepts and issues in marine ecosystem management. Reviews in Fish Biology and Fisheries 6: 139-164.

ConsorTiUm reporTsNorcross, B.L., B.A. Holladay and F. Mueter. 2000. Forage fish abundance and distribution at Forrester Island, Alaska. Institute of Marine Science, University of Alaska Fairbanks. Final contract report, NOAA Award No.

NA66FX0455.

Gerber, L.R. and G.R. VanBlaricom. 1997. Endangered Species Act (ESA) status of the western population of Steller sea lions based on the World Conservation Union (IUCN) classification scheme. Washington Cooperative Fish and Wildlife Research Unit, University of Washington, Seattle WA 98185.

Sampson, D. 1995. An analysis of groundfish fishing activities near Steller sea lion rookeries in Alaska. Oregon State University. Mark O. Hatfield Marine Science Centre, Oregon State University, 2030 S. Marine Science Drive, Newport Oregon 97365-5296.

Barrett-Lennard, L.G., K. Heise, E. Saulitis, G. Ellis and C. Matkin. 1995. The impact of killer whale predation on Steller sea lion populations in British Columbia and Alaska. University of British Columbia, Fisheries Centre, 2204 Main Mall, Vancouver, B.C. V6T 1Z4.

Cottrell, P., A.W. Trites and E.H. Miller. 1995. Assessing the use of hard parts in faeces to identify harbor seal prey: results of captive feeding trials. University of British Columbia, Fisheries Centre, 2204 Main Mall, Vancouver, B.C. V6T 1Z4.

Schaffner, A.A., S.B. Mathews and J.E. Zeh. 1994. Statistical considerations in assessing recent adult/juvenile census trends of Steller sea lions. University of Washington, Fisheries Research Institute, WH-10 Seattle WA 98195.

Gosine, R.G., and L. Gamage. 1994. Final report on an investigation of image processing techniques for the problem of automatic counting of sea lions from aerial video. University of British Columbia, Industrial Automation Laboratory, Department of Mechanical Engineering, 2324 Main Mall, Vancouver, B.C. V6T 1Z4.

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Marine Mammal Research UnitUniversity of British ColumbiaRoom 247, AERL, 2202 Main MallVancouver, B.C. Canada V6T 1Z4

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