|This paper was written as part of the 1999 Alaska Ocean Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.|
in part by each of the following:
East Anchorage High School
AbstractWithin recent decades, there have been signs of significant declines in the Steller sea lion (Eumetopias jubatus) populations in the Bering Sea and the Gulf of Alaska. So far, scientists have not been able to identify a primary cause of this rapid decline, although many theories have been introduced. Scientists at the North Pacific Fishery Management Council discussed the possible effects of a regime shift and overall changes in the ecosystem. A change in fish populations may be influencing the diet of the Steller sea lions. A decrease in fatty nutritious fish and an increase in less nutritious fish may be causing a delay in pup development or result in less healthy adults (Trites, 1998 and Sottile, 1995). Large scale changes in oceanic currents and upwelling occurrences may also influence availability of prey items (Blackburn, 1998). We have also explored the effects of pollution, which may have caused changes in reproductive rate and the age at sexual maturity (Alaska Department of Fish and Game, 1998). Breast milk can transfer disease and oil contamination to pups which have not yet formed sufficient antibodies. Genetic fragmentation and inbreeding may be augmenting already existing weaknesses (Fahrig, 1997). The increase of sea lion primary predators, killer whales, have also been noted by fishermen (Drage, 1998). Subsistence hunting and incidental killings of Steller sea lions by fishermen are estimated to have remained constant since the initial population decline began. Impact by man through environmental degradation has increased. In looking at the effect of disease and parasitism on sea lions, we found that the number of deaths has remained relatively constant.
Population DeclineAs of April 1997, the Steller sea lion, a marine mammal inhabiting the waters of Alaska, was reclassified on the Endangered Species List. Originally placed on the Threatened Species List in 1990 after scientists noted their declining numbers, the action triggered the beginning of an international concern for the future of the Steller sea lion. Scientists are in agreement on the magnitude of the decline, but not on the reasons causing the decline. It is estimated that populations have been decreasing for more than 35 years.
In a conversation with Sarah James, a native of the Gwitchin Tribe, we learned that hundreds of Steller sea lions were observed in the 1960s, and now they are rarely seen. Irena Alexakos, an Alaskan conservationist, stated that fishermen failed to report numerous Steller sea lions tangled in fishing trawls in the 1970s. Population declines have also been noted in other areas of the state. A census count in the Kenai to Kiska area in 1975 counted 150,000 sea lions. In 1989 only 25,000 were found in the same area.
Best estimates find that populations have declined from 192,000 adults and juveniles in 1965 to 52,200 animals in 1994. Populations in Alaska, from Prince William Sound east and south, show that numbers of sea lions are remaining constant or slightly increasing, while populations west and north of Prince William Sound are dramatically declining. No data on population numbers exist prior to 1964 (Boyd, 1995). According to Boyd (1995), the western population has declined 81 percent. This is consistent with a 75 percent estimate decline in the past ten years as reported by William Fox, NOAA assistant administrator (Gordon, 1990). Population declines from 1977 to 1996, as recorded by the National Marine Fisheries Service, are depicted in Figure 1. There is nearly a 100 percent chance the western Steller sea lion population will be extinct in the next 65 to 100 years, biologists with the National Marine Fisheries Service predict. (Whitney, 1997).
Suggested reasons for population declineReasons for the decline may be different in the present than they were originally. Compared to the past when overfishing and pollution were found to cause declines in the Steller sea lion population, time has magnified some alternate sources. Recent studies highlight oil pollution as part of changes in abortion and reproduction rates, and age to sexual maturity. Many other issues, which may have been previously overlooked, are taking on more importance. Now factors such as global warming and a regime shift in Alaskan coastal waters have been shown to augment the decline, most likely by creating nutritional deficiencies. The deterioration of health may create an increased susceptibility to both disease and the invasion of parasites. With an increase in human population comes additional competition for prey items and a decrease in essential Steller sea lion habitat. Numbers have dropped to such a point, that even with restoration plans, such as those recently release regarding the impact of commercial pollock fishing on Steller sea lions, the population decline may be beyond human control. Commercial fishing can have unexpected and undesirable effects, and is therefore risky and requires impartial management (Trites, 1998). Although many researchers are working hard to curb the decline and promote population growth, the delay in action and obtaining information on the source of the decline may result in Steller sea lion extinction.
Regime shift and change in Steller sea lion dietWhile attending the North Pacific Fisheries Management council meeting this past November, we heard scientists and fishermen referring to a regime shift in Alaskan waters. The regime shift is thought to have begun in the mid 1970s, and brought on a change in species composition. Some fish populations increased, while others decreased. This may be attributed to an increase in water temperature. Fish with high fat content and greater nutritional value for the Steller sea lions decreased, while pollock and other less nutritional fish increased in numbers. In our conversation with Chris Blackburn, from the Alaska Groundfish Data Bank, she noted that pollock were not located on the continental shelf until the mid 1970's when waters warmed. This change in pollock distribution substantiates the occurrence of the regime shift.
At the same conference, fishermen, such as Stinson, said that fishermen were not in competition with the sea lions over pollock. Stinson and Trites (1998) both state that pollock preyed upon by Steller sea lions are found higher in the water column, and are generally juveniles; while fishermen trawl at deeper depths and primarily for adult fish. Adult pollock have been shown to be cannibalistic and will feed on juveniles of the same species. Therefore, the capture of adults may help increase juvenile fish populations targeted by sea lions. The relationship between commercial fisheries and Steller sea lions is not always apparent. Alverson (1998) notes that sea lion populations in Southeast Alaska are more abundant while living in an area of high fishing vessel activity.
Alverson (1998) used data from earlier studies to show the invalidity of prior notions regarding the interaction of fisheries and Steller sea lions. He disproved the idea that pollock were a major prey item before their decline in the 1970's. That prior to the significant growth of the pollock populations in the Bering Sea and Gulf of Alaska (during the 1970's) small fatty fish species such as capelin, sand lances and herring, probably formed the major elements of the diet of the Steller sea lion throughout most of the Gulf of Alaska... (pg. 3)
The regime shift has caused a change in the Steller sea lions' diet. It is believed this change is detrimental to the sea lions. Trites (1998) stated that a change in diet from a variety of fish, consisting of herring, capelin, eulachon, and sand lances, to a diet consisting primarily of pollock has three main drawbacks. Pollock contain less energy than the herring. Second, the sea lions burn more energy digesting pollock than herring. Third, it costs a sea lion more energy to digest the larger quantity of fish needed to compensate for the lower energy content. (Pg. 7)
A change in their diet may have caused a change in deaths and birth rates of Steller sea lions. It also causes stunted growth, iron deficiencies, and increased susceptibility to predation and diseases. They are also more likely to have reproductive failures (Alverson, 1998). Recent studies have shown, as reported by federal fisheries managers, that pollock fishing in the Bering Sea is harmful to Steller sea lions. In the December 5, 1998 edition of the Anchorage Daily News, Andy Rosenberg, deputy director of the National Marine Fisheries Service, is quoted as saying, "We've got heavy fishing in areas where Stellers are disappearing. It's clear there is a problem." (Pg. A-1).
Nutritional DeficienciesScat and stomach contents are used by a variety of researchers exploring the roles of heat increments of feeding, digestive efficiency, stomach telemetry, stable isotopes, energetic, exercise, thermoregulation, blood chemistry, morphology, and hormones as related to the reduction of sea lions in declining areas, and the stability of sea lion populations in others. Modeling is being used to predict and analyze their hypotheses. Therefore, in the near future, it may be possible to narrow the scope of conservation and repletion efforts constructively. Energy is expended in capturing prey items. Steller sea lions in Western Alaskan waters are feeding primarily on less fatty fishes, such as walleye pollock, as compared with previous prey items, such as fattier fishes like herring (Trites, 1998). The less nutritional food sources must be consumed in greater quantity for energy levels to be maintained, as well as for successful reproduction and nursing. In a study conducted by Trites, captive Steller sea lions were exclusively fed pollock, and were offered as many as they desired. They did not increase their intake to make up for the nutritional lack. Furthermore, more energy is burned in the breakdown of larger meals, so either way the food is not meeting Steller sea lion needs.
Metabolic rates change with seasons, due to different energy needs for breeding and molting, and decrease with age. Pollock populations moved onto the continental shelf. Whenever prey populations move or fluctuate, or are in patchy groups, this changes the energy burnt by the sea lions. Energy is also expended in keeping body temperature constant. At the University of British Columbia, Dr. Rosen is currently measuring effects of water temperatures found in the ocean on sea lions. Russ Andrews uses small metal pills which track temperature changes in the stomach of sea lions. In this manner, times of feeding can be noted, because of the decrease in stomach temperature, due to the consumption of fish at ocean temperature. He hopes to eventually be able to determine which species of fish is being consumed.
Skinfold thickness was tested for reliability in determining the condition of Steller sea lion pups in their natural habitats. Studies suggest that this is not an accurate possibility since skinfold thickness seems to be a result of bodymass, not a determination of nutritional condition of the sea lion. Knowledge of this relationship may prove to be helpful in other research projects. Rosen is also conducting experiments to assess blood composition change in relation to nutrition and food intake. So far his experiments suggest that seasons and age play a role in the sea lion's biochemical response. The research describes three hormones which are found in increased levels in humans with eating disorders, such as anorexia or bulimia. Tania Zenteno-Savin, at the University of Alaska Fairbanks, conducted experiments on Steller sea lions deprived of food that checked for the same hormonal changes. Results support that hormones may be an indicator of nutrition, but more research needs to be conducted before scientists can accurately interpret hormone levels and their significance.
Higher pup mortality, thinner blubber, and decrease in size of sea lions in the 1980s as compared to the 1950s through the 1970s are a few facts that tend to support the theory of malnutrition.
Local Climatic ChangesModerate climate changes have occurred where Steller sea lions dwell. It is a common belief that these changes are due to global warming and El Nino; however, there is no evidence that links either as a reason for Steller sea lion decline. Mounting concern is being directed toward the Aleutian low pressure system. It is expected to cool the Northeast Pacific climate over the next ten years, becoming even colder by 2005. These conditions are similar to those that existed between 1950 and 1970. The regime shift is partly due to atmospheric changes.
We had wondered if the fur might be weaker in Steller sea lions where declines are occurring, possibly allowing increased exposure to harmful ultra violet rays. The fur is of poorer quality in the Gulf of Alaska and Bering Sea, but this is thought to be an effect of fungal patches, which may be linked to nutritional deficiencies (Trites, correspondence, 1998).
We know that ozone depletion has caused an increase in ultraviolet rays. This in turn kills phytoplankton. Could this have an effect throughout all trophic levels? In fact, primary and secondary producers, as well as nutritional fish, some seabirds,and of course marine mammals, including Steller sea lions, are decreasing. Dr. Springer (UA) found that the reduction of whale populations compounds these declines. The change in community composition which began in the 1970s were concentrated in the area of Steller sea lion declines (Eastern Bering Sea and Gulf of Alaska). This created a decline of biomass, which changed energy flows through the trophic levels, reducing the numbers of sea lions, harbor seals, fur seals and certain seabirds.
Direct Human ImpactWhen Steller sea lions were listed on the threatened species list, the number that were allowed to be killed incidental to commercial fishing was reduced to 675 from 1,350 animals. The mortality of the western stock of Steller sea lions due to commercial fishing averaged 35 animals per year, 14 animals are taken by Alaska Groundfish fisheries annually.
Estimated annual subsistence harvest of Steller sea lions is around 500 animals. According to Wolfe and Mishler (1994) most are taken by Aleut hunters in the Aleutian and Pribilof Islands. This estimate was not based on direct observations and independent observers, it was based on a survey of hunters and in households. The survey required hunters to remember how many animals had been shot, killed, and recovered for up to one year. This was a fundamental weakness of the report, making the estimates questionable.
In Boyd's paper on Steller sea lion research (1995), he suggested that the level of subsistence harvest has declined in the past few years. The level of subsistence hunting through the early 1990s was likely to have been 2 percent of the western population. There has also been arguments that the harvest is directed at killing males and is concentrated around the Pribilof Island area.
There is hardly any direct evidence that illegal killing of Steller sea lions is contributing to current population decline. Boyd stated anecdotal evidence from interviews with fishermen who stated that illegal killing and indiscriminate shooting have been widespread and could be continuing to the present day. Further research has also shown that pinnipeds are not greatly affected by subsistence hunting, but direct human exploitation, such as incidental killings and harm to the environment, can affect their populations.
Increase in predator populationThere are two known primary predators of the Steller sea lion; killer whales and humans. It has been estimated that killer whales consume 18 percent of Steller sea lion populations annually (Boyd, 1995). As the sea lion populations decline, the more susceptible they become to any and every kind of danger including predation (Ferraro, 1998 interview).
Many fishermen have noticed more activity between killer whales and sea lions close to fishing docks. Jay Stinson, in giving public testimony at a North Pacific Fishery Management Council hearing, suggested that killer whales are becoming more aggressive closer to shore (1998). Chris Blackburn, director of Alaska Groundfish Data Bank, disagrees with this observation. She believes that the killer whales have always been aggressive, but fishermen are just seeing more interactions now because the whales are less afraid of being near shore where there are more human interactions.
Killer whales are not held accountable for the initial decline of the Steller sea lion populations. John Roos, president of the Pacific Seafood Processors Association, also provided public testimony. He suggests that increases in predation may have significantly affected recent declines (1998).
Native Alaskans have been hunting Steller sea lions for many generations and are currently hunting marine mammals for their subsistence lifestyle. Subsistence harvest bring in about 3% of the Steller sea populations annually (Russe, public testimony). From the literature read, we conclude that subsistence hunting did not affect the initial population decline. However, since Steller sea lion numbers are now so low, the impact of hunting may harm present populations.
Contamination of EnvironmentLenore Fahrig (1997), in her paper on the relationship of habitat loss and fragmentation on population extinction states that the reduction of habitat is one of the destructive forces to a population, especially an endangered one. In addition to land habitat, which is essential to reproduction and birth, the open ocean, where Steller sea lions spend most of their time and where their prey dwell, are vital habitats for their success. Both of these habitats are polluted by humans.
Oil contamination is a concern, although the effects are not believed to be the greatest facing sea lions. They do, however, augment preexisting conditions and introduce new hazards. Neff (Geraci, et al, 1990) believes that consumption of oil is a result of preening and consuming contaminated food, rather than from the drinking of polluted water. The degree to which oil consumption will harm the sea lion varies with age and size of the animal, and current health condition. The more oil passed through the body, the weaker the membranes become, increasing the amount of toxins absorbed, and the subsequent harm done to the liver through buildup.
The most hazardous aspect of oil pollution to sea lions is inhalation of volatile, low molecular weight, hydrocarbons contained within the oil. This not only causes damage to the liver, but to the brain with neurological disorders, and to the lungs by causing congestion or pneumonia. Larger animals may be able to resist these effects, but may experience an increase in buoyancy due to a layer of oil. Animals in areas with colder waters also experience the effects of oil more than animals in warmers waters. This is due to the high fat content necessary for survival.
The toxins from oil are stored in lipids, but can be released over time in all marine mammals, more so in females through lactation. Pregnancy rates are dropping, and pup mortality is increasing, at least in part because of oil toxins found in Steller sea lion populations. Breast milk, having high lipid concentrations, passes these toxins directly to the pups, who have not yet formed protective and cleansing abilities to the extent of the adults. Increased pup mortality is commonly believed to be a major factor in the decline of Steller sea lions. Oil contamination decreases the number of sea lions in a population. As previously discussed, weaker and smaller adult populations are detrimental to the overall health of the population because of increased susceptibility to environmental stress.
Increased susceptibility to diseases and parasitesLike any other animal, the Steller sea lion is exposed to many parasites and diseases. Some of these include nasal mites, tapeworms, flukes, pneumonia, Leptospira pomona, and many others. Leptospira pomona is a bacteria that causes a large number of fatalities in sea lions. It is a suspected cause of abortions, and deaths in adult sea lions. Although this causes some deaths, it is not a large enough amount to be concerned about.
Disease and parasitism have not been studied as closely as they could. There is little known about how, and to what extent they are effecting Steller sea lions. Research is being done, but not a lot of information is available at this time. Diseases may cause some deaths; however, as far as we know, they are not a major cause for the decline.
Genetic changes and fragmentationLow genetic variability is believed to be potentially harmful because it increases the probability of extinction and reduces the ability of a population to cope with environmental variability. This is particularly true for endangered or threatened species and can result in the erosion of genetic variability and potentially increase the probability of extinction. (Dept. of Wildlife and Fisheries Sciences, pg. 96). Every living thing has unique genetic weaknesses. When populations become smaller, reproduction results in a concentration of these weaknesses. This may cause the population to become more susceptible to disease and stress.
Brickham's (1996) studies found that there are genetically different populations of Steller sea lions. The sea lions inhabiting the Aleutian Islands and Gulf of Alaska, which are experiencing population declines, genetically differ from Southeast Alaska populations. Chris Blackburn believes that genetic fragmentation is not a major factor of decline, due to males alternating among rookeries every few years, and therefore avoiding inbreeding. Brickham found that Steller sea lions have a high level of genetic diversity. Knowledge of Steller sea lion genetics can contribute to conservation efforts.
ConclusionIn our evaluation of research papers, conducting personal interviews, and contacts with a number of scientists, fishermen and conservationists, we have come up with a number of conclusions.
There is not one independent reason for the Steller sea lion population decline. The regime shift plays a significant role. Furthermore, attributes of the population decline in the past are not necessarily affecting the decline today. A regime shift has brought into abundance less nutritional fishes, such as pollock, and decreased the number of nutritional fatty fishes that were once a primary prey item for the sea lions. The regime shift may have been brought on in part by atmospheric changes as seen in the occurrence of El Nino and change in the Aleutian low pressure system. The Northeast Pacific is expected to cool through the next ten years, producing conditions similar to those in the 1950s and 1960s. Ozone depletion, another change in the atmosphere, has not been linked to sea lion decline.
Fungal patches have weakened fur in both the Bering Sea and Gulf of Alaska populations. This may be related to malnutrition. Thinner blubber and a smaller sized sea lion are also evidence of malnutrition. Blood composition studies are being conducted for the possibility of further supporting previous findings and providing new data on malnutrition in sea lions. The occurrences of other diseases have not been found to cause an increase in mortality.
There are distinct genetic differences in Steller sea lions located in various areas. Scientists are exploring genetic fragmentation as a possible reason for continued sea lion decline. Knowledge of genetic make-up may help formulate restoration plans.
We live in a time where technology is advancing at such as rapid rate, that scientific discoveries and computer applications of a year ago are outdated. In the past the cloning of a sheep was unbelievable. Now it is possible to clone many animals, with human cloning research undertaken. The day which optimal DNA composition can be chosen before birth, is approaching quickly. To many, these facts are scary, and consequences highly disputable.
Maybe someday we will produce test tube clones of endangered and ecologically important organisms, and we will obtain positive results. Health benefits may result for humans, as well as Steller sea lions, as a result of the combination of new cures found through the flora and fauna in both the rainforests and oceans. If we use technology wisely, maybe we can restore and maintain a balance for our wonderful earth and let nature fluctuate populations on her own.