Case Study: Sea Otters
Oiled sea otters were the icons of the spill and its effects, and remain one of the area’s most compelling animals. While overall population numbers in western Prince William Sound have recovered, local populations in heavily-oiled areas have not recovered as quickly.
Sea otters excavate pits while foraging for food, including their preferred food item, clams. Sometimes these pits are excavated in the intertidal zone. Using depth recording instruments, researchers have looked at the data from more than 10 million dives. These data have shown that sea otter diving activities within the intertidal zone are centered around the zero tide elevation, and up to +1-2 feet above that. Although they have a fur coat, sea otters lack the thick, insulating layer of blubber found in other marine mammals. Thus, they rely on a high caloric intake to maintain their body temperature. To do this, otters must consume about 25% of their body weight each day. This requires each otter dig thousands of pits each year.
Sea otters usually have very small home ranges of a few square kilometers. In these small ranges, it is unlikely that the otters are avoiding areas of lingering oil when foraging. Unfortunately, when clam beds and lingering oil patches overlap, it is likely that digging pits continues to expose sea otters to oil. The otters digging activities do reduce the amount of subsurface oil in the long term: in the process of digging a pit, sediments and the subsurface oil are released and re-suspended in the water and exposed to weathering.
Current Trustee Council-funded studies monitor environmental damage from the remaining oil. Additional studies have been funded to determine where else in the spill-affected area subsurface oil may persist, and what, if anything, to do about it.
Following the oil and its impacts over the past 20 years has changed our understanding of the long-term damage from an oil spill. Because of the scope and duration of the restoration program, lingering oil and its effects were discovered and tracked. As a result, we know that risk assessment for future spills must consider what the total damages will be over a longer period of time, rather than only the acute damages in the days and weeks following a spill. Beaches in the Gulf of Alaska are unique because of their composition and structure, and the lack of waves and winter storm action. This, along with the colder temperatures, is partly why oil has persisted and remained toxic here. The potential for long-term damage remains wherever oil persists after an oil spill, whether it is buried in the ocean bottom, marshes, mangroves, or other habitats that are not dynamic.
Photo: At high tide, sea otters digging pits for clams create sediment plumes carried by the ocean current.
Photo: At low tide, hundreds of sea otter pits are revealed on a single beach in Prince William Sound.
Photo: sea otter with pup. Photo credit: Randy Davis, Texas A&M
Long Term Effects of Initial Exposure to Oil
In addition to the continued impacts of lingering oil discussed above, several species have not demonstrated full recovery from the initial damage caused by the spill. The status of killer whales is a clear example of these long-term effects.
Case Study: Killer Whales
Killer whales are individually identifiable and fortunately in Prince William Sound they were photographed starting in 1984, five years prior to the spill. Thus, researchers knew the numbers and associations of the whales at the time of the spill. Two groups of killer whales were photographed in slicks of oil in the weeks following the spill. These two groups lost approximately 40% of their numbers by 1990, and an additional five whales after 1990. One of these, the AB pod, is a “resident” fish-eating group of killer whales, and does show some signs of recovery. The second group is a small, unique population known as “AT1.” They are “transient” killer whales that feed on marine mammals. They show no signs of recovery and continue to decline.
The losses to killer whale populations resulted primarily from the initial, acute exposures to the spill. Most carcasses were not found following the spill—which was not surprising since killer whale carcasses are known to sink—but the missing individuals have never been seen or photographed again. It is thought that the damage to killer whales from the spill, like many of the mortalities of other marine mammals, was caused by the inhalation of the oil’s toxic fumes, as all of these species had to breath air from a few inches above the slick.
Whale pods are integral, matrilineal families. So a spill that kills any of the key members of the pod, especially reproductive-age or older females, can have far reaching consequences. The reproductive capacity of the pod was reduced by the loss of females which even under ideal conditions have a low reproductive rate, with only about half of newborn calves surviving. Since pods are matrilineal, the loss of these females means that the leaders of the pod are also lost. Some of the females that disappeared following the spill also had young offspring that died in the first few years after the spill, likely due to the loss of their mothers. In addition, the AB pod has shown signs of an unusual social breakdown within the group, with one matrilineal group leaving to join a different pod. This is a phenomenon not seen in any other resident pod in the North Pacific.
Resident killer whales in Alaska have generally been increasing since the 1980s. However, the recovery of the AB pod is slower than the growth of other fish-eating pods in Prince William Sound or in Southeast Alaska. Their full recovery to pre-spill levels will likely take an additional decade or more, if their recovery is not further compromised. For the transient AT1 population, there appears to be no hope for recovery. There has not been a successful recruitment to the pod since prior to the spill. This unique population will likely become extinct as the remaining members continue to age and die.
Status of Injured Species and Services
In November 1994, the Trustee Council adopted an official list of resources and services injured by the spill as part of its Restoration Plan. When the Restoration Plan was first drafted, the distinction between the effects of the spill and the effects of other natural or human-caused stressors on injured natural resources or services was not clearly delineated. The spill was recent, the impact to the spill-area ecosystem was profound, and adverse effects of the oil on biological resources were readily apparent. As time passes, however, the ability to distinguish the effects of the oil from other factors affecting fish and wildlife populations becomes more difficult.
Through hundreds of studies conducted over the past twenty years, we have come to understand that the Prince William Sound ecosystem is incredibly complex and the interactions between a changing environment and the injured resources and services are only beginning to be understood. For example, seabirds will have difficulty recovering without the recovery of herring which is a vital food source; species in the intertidal zone will continue to be compromised until we can determine the amount and distribution of lingering oil; and human services cannot be recovered until rockfish, herring, and cutthroat trout are recovered. These complexities and the difficulties in measuring continuing impacts from the spill mean that determinations about the status of a resource or service contain some inherent uncertainty.
Now, twenty years after the spill, there are two species that continue to be listed as “not recovered,” ten species and four services listed as “recovering” (including Barrow’s goldeneyes, added to the list in 2008 based on their continuing exposure to oil), five listed as “unknown,” and ten listed as “recovered.”
Pacific Herring Population in Prince William Sound Remains Depressed
Herring were affected in 1989 by the spill, and the herring numbers in Prince William Sound are still too low to sustain a commercial fishery. The 1989 year class had the lowest recruitment ever measured. However, that alone does not explain the present low populations of Prince William Sound herring. Their population crash was detected in 1993, some three years after the spill. In addition, herring populations historically fluctuate and can be affected by a myriad of factors. Due to these factors, there continues to be debate as to when the decline started and whether it was directly linked to the spill.
While the cause of the continued decline in Prince William Sound herring populations remains uncertain, it is certain that the sound cannot be considered recovered until healthy herring populations have returned. Herring harvests had always been a vital resource for human communities in the sound prior to the spill. Herring also provide crucial biological links between species within the ecosystem. Forage fish, such as herring, connect the production of algae and zooplankton to large predators such as other fish, birds, and marine mammals. The recovery of some seabird populations is likely affected by the depressed herring population. Herring, rich in natural oils, contain significant amounts of energy. The oceanic ecosystem and its inhabitants rely on such energy transfers, and herring, even with the depressed numbers of today, are likely to play a critical role in energy transfer to other species.
Herring recovery is a current focus of Trustee Council studies. The vital role herring play for both human and marine animal communities is clear, but the path to restoring this important species is uncertain. Herring populations are driven by complicated forces, including disease, predation, and oceanographic dynamics. Any proposed restoration for this species will require a careful understanding of these complex dynamics.
Photo: Killer whales surfacing in Prince William Sound. The AB resident and AT1 transient killer whale groups have suffered long-term damage from the initial exposure to Exxon Valdez oil.
Photo: small net of herring pulled on board boat. The population of herring in Prince William Sound is still too low to sustain a commercial fishery.
Photo: Schools of herring which appear as dark spots in this aerial view of a cover, ball together in response to predators.
Table: Status of Injured Species and Services
Not Recovering: Resources are showing little or no clear improvement since spill injuries occurred.
Recovering: Substantive progress is being made toward recovery objectives. The amount of progress and time needed to achieve recovery vary depending on the resource.
Recovered: Recovery objectives have been met
Recovery Unknown: Limited data on life history or extent of injury; current research inconclusive or not complete.
Human Services: which depend on natural resources were also injured by the oil spill. The services below are categorized as “recovering” until the resources upon which they depend are recovered.
Recreation and tourism
Photo: Thick-billed murres rest on a rocky cliff in the Gulf of Alaska. Murres were considered recovered by 1997.
Research, Monitoring, and Restoration
The Leap in Knowledge and Why It Matters
In 1991, the Trustee Council was formed to restore Prince William Sound and the Gulf of Alaska to the "healthy, productive, world-renowned ecosystem" that existed before the spill. The Trustee Council recognized that there was little direct intervention that could be done, such as rearing and releasing seabirds. In an effort to protect habitat important to injured species, they developed a habitat protection program that purchased lands or established conservation easements. Recognizing that the sea cannot be protected through acquisitions, another strategy for long-term protection was adopted, using research and monitoring to increase knowledge of the injured species. The resulting knowledge was used to develop tools to support sound management decisions for the health of those populations and the people who depend on them.
Since the Exxon Valdez settlement in 1991, hundreds of peer-reviewed research, monitoring, and general restoration projects have been completed. The magnitude of the restoration program has resulted in a leap in knowledge about the marine environment. It has established baseline information for many species that was not available before the spill as well as significant improvements in the tools that fish and wildlife managers use to evaluate the populations of injured species.
This gain in scientific knowledge and practical management tools is of increasing value in light of the accelerated effects of climate change in Alaska. Specifically, the additional knowledge gained through these projects assists in detecting and tracking vital oceanographic and atmospheric changes, and has greatly contributed to the development of adaptive management strategies and tools to deal with this rapidly changing marine ecosystem.
Sidebar: Scientific Collaboration, Integration, and Peer Review In order to ensure the highest quality research and monitoring, the Trustee Council requires that all research be independently peer-reviewed. The Trustee Council also encourages researchers to collaborate and where possible, integrate studies. This has promoted a new level of cooperation across agencies, non-governmental organizations, and academic institutions. EVOSTC-funded researchers share data sets and results in a collaborative climate.
Photo: Trustee Council funded studies of the effects of the Exxon Valdez oil spill on salmon, especially at critical life stages has fundamentally changed our understanding of oil toxicity.
Understanding the Marine Ecosystem
In the 1994 Restoration Plan, the Trustee Council outlined an ecosystem approach to restoration. Even before the Plan was final, however, they began investing funds in an organized effort to better understand the marine ecosystem. This approach has provided and continues to provide more information on fish, marine birds, and mammals than ever anticipated. These projects benefit commercial and sport fisheries, aquaculture, subsistence, recreation, and tourism. Most prominent among them are three ecosystem-scale projects known primarily by their acronyms, SEA, APEX, NVP, and the current suite of projects focusing on herring and their role in the ecosystem.
The Sound Ecosystem Assessment (SEA) project was the largest project undertaken by the Trustee Council, funded at $22.4 million over a six-year period (from 1994-2000). SEA had dozens of integrated components designed to obtain a clear understanding of the factors that influence productivity of pink salmon and Pacific herring in Prince William Sound. It was conceived in 1993 in Cordova, Alaska by scientists working with the fishing community after the Sound suffered a collapse of the herring fishery and erratic returns of wild and hatchery pink salmon. This project produced vital information about the survival of juvenile salmon and herring and demonstrated the variable effects of wind and ocean currents on plankton, the tiny plants and animals at the very base of the food chain. SEA provided new insights into ocean currents, winds, nutrients, salinity, temperatures, and mixing, and how these physical factors influence plant and animal plankton, prey, and predators in the food web.
The Alaska Predator Ecosystem Experiment (APEX) investigated the lack of recovery in seabirds injured by the spill. When this study began in 1994, none of the seven seabird species on the injured resources list was considered recovered. This eight-year, $9.7 million project looked at the availability of forage fish and a wide-range of ecological processes to understand the lack of recovery. The data gathered was critical in advancing our knowledge of how seabirds select their food and in determining the effect of lower-quality food sources on reproduction. This experiment also helped to define the importance of herring, a high quality food source for seabirds, in the restoration of the Prince William Sound ecosystem.
Photo: Seabird populations were dramatically reduced by the oil spill. Subsequent studies have increased our understanding of the ecosystem dynamics between seabirds and their food sources, as well as providing 20-year data sets from which to track future population shifts.
The Nearshore Vertebrate Predator (NVP) project was a six-year study (1995-2001) of factors limiting recovery of four indicator species that use the nearshore environment. The possible factors included: food availability, continued damage from oil, and population demographics. The $6.4 million project focused on two fish-eaters,river otters and pigeon guillemots, and two species that feed on shellfish and other invertebrates, harlequin ducks and sea otters. Nearshore areas were the hardest hit by the Exxon Valdez oil, which clung to beaches and polluted waters on each succeeding tide. When this project was designed, all four predators exhibited signs of stress in oiled areas. For sea otters and harlequin ducks, long-term effects continued in the oiled areas, as shown by the lack of population recovery in these areas, and symptoms of oil exposure in harlequin ducks. At the time, researchers predicted that food was the most likely factor limiting recovery, but their studies proved that it was not. When large quantities of lingering oil were discovered in 2001, it became clear that there was linkage between known effects and the remaining oil.
Photo: Depressed populations of harlequin ducks and other species in northern Knight Island led to the discovery of the continued effects of lingering oil.
Integrated Herring Restoration
The lack of recovery of Prince William Sound herring continues to be of major concern to the people who live in the region, scientists, and the Trustee Council. Herring are an injured species and are essential to other species injured by the spill. Therefore, the Trustee Council has initiated a herring restoration effort that utilizes an ecosystem approach.
Recovery of herring is a complex task, as the causes for the lack of recovery are poorly understood and herring play a critical role in the ecosystem. Thus, the precautionary principle to “first do no harm” is of primary importance.
Research into herring issues has been initiated, while a recovery plan with a myriad of alternatives, is being developed. The alternatives range from increased research to better understand and manage herring to direct intervention activities such as supplementation and increased harvest of competitors and predators. None of these potential actions are trivial, some are controversial, and all will require time and effort to evaluate cost and effectiveness.
Understanding the Parts of the Ecosystem: Fish, Wildlife, and Other Projects
Along with ecosystem-wide projects, numerous targeted studies have also yielded significant new information about species impacted by the spill and management tools. For example, before the spill, long-term killer whale datasets were from studies of whales in British Columbia, Canada. As a result of Trustee Council funding, we now know more about Prince William Sound and Gulf of Alaska killer whales than other populations, including how they bioaccumulate toxins. Targeted studies have also resulted in a dramatic increase in knowledge about sea otters, sea ducks, and other species. The following is a list of some of the more recent efforts and other noteworthy projects.
Photo: Three researchers in a zodiac boat in Prince William Sound with tidewater glacier in the background. One researcher is holding an “H” shaped radio tracking device. Researchers continue to monitor recovery of marine birds injured by the spill, including black oystercatchers being tracked with radio telemetry in 2007.
Sea Bird Surveys Provide Long-term Data and Effects
The area affected by the Exxon Valdez oil spill supports a high abundance and diversity of marine birds throughout the year. Approximately one million marine birds inhabited the area prior to the spill, of which an estimated 100,000 to 300,000 initially died. The Trustee Council has funded marine bird research and monitoring projects since 1990, which have provided important insights into the ecology of seabirds, as well as the process of recovery from the oil spill. In turn, these data provide a window into the health and recovery status of the ecosystem as a whole. For example, research and monitoring of the harlequin duck, indicated the unanticipated duration of exposure to lingering oil in the nearshore zone, as well as the subsequent effects on individuals and populations. This work has been important for understanding the consequences of chronic exposure to residual oil still available to birds and mammals in the spill area, long after the immediate, acute effects are over. In addition to documenting the processes and constraints to recovery from the spill, the research and monitoring funded by the Trustee Council, have provided datasets that serve as benchmarks to detect future changes in the ecosystem.
High-Pressure Beach Washing Damages Clams and the Beach
Hardshell clams were devastated during the spill and the following cleanup. At the time of the spill, the push was to remove as much oil as quickly as possible, a difficult task in the remote Alaskan environment. High-pressure washing was often conducted to remove oil from beaches. Although it was unknown at the time, this approach removed the fine sediments from the beach and altered the physical structure or “armoring” of the beach. The initial injury to hardshell clams came with waves of toxic oil mixed in the water, but was then exacerbated by the subsequent pressure washing. The pressurized washing also broke apart the interlocking cobble layers near the surface which protect the fine sediments from storm action. Studies in 2002 found that these early injuries continue as many of these habitats have not recovered. This affects not only clams, but also the sea otters, other animals, and people that rely on clams for food. It now appears that nature will require several more years, possibly decades in some areas, to restore the clam habitat, and thus the clams.
“Bar Codes” Protect Wild Salmon Stocks
In the early 1970s, pink salmon runs in Prince William Sound had crashed. An aggressive enhancement program was developed that included the construction of hatcheries. By 1986, there were five hatcheries operating in Prince William Sound, releasing hundreds of millions of salmon annually. These hatcheries needed to be able to distinguish hatchery-raised fish from wild fish, to be sure that not too many wild fish were being caught. Fisheries managers began marking the hatchery fish with coded wire tags, but inserting and reading coded wire tags is time consuming, expensive and requires a large sample size.
The Trustee Council provided funding to provide Prince William Sound hatcheries with heaters to create thermal marks on pink salmon otoliths. Otoliths are hard, bone-like structures located directly behind the brain of bony fishes. Visible rings on thin cross-sections can be used to age fish. Thermal marks are created by heating the water temperatures when the fish are embryos to produce distinct bar code-like patterns on the otolith. The marks are preserved in the otoliths of adult fish. They are relatively inexpensive to apply and all fish in a hatchery can be marked without harm. The use of thermal marking (instead of wire tags) provides fisheries managers more accurate information at a reduced cost, allows fisherman to target hatchery fish, and ensures that wild stocks are not overfished. Thermal marking has been used by researchers to identify Prince William Sound salmon in the high seas and to investigate factors that influence marine survival. Because so many Alaskan hatcheries are located in Prince William Sound, this investment had significant results.
Photo: A salmon swims below the surface of the Kenai River, bank and forest visible above the waterline. Research has led to the development and adoption of new tools to improve management of salmon and other species.