|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:
AbstractFor the past 30 years, we have seen a decline in the Steller sea lion (Eumetopias jubatus) population. It is our belief that the majority of the decline is due to the altering of the fish populations.
As humans fish the seas, they are removing competitors to the walleye pollock. Although this fish is very important to the Steller sea lion (Fig. 1), they are pushing out other species that are also important to the sea lions. The pollock is a low quality food and when sea lions are forced to rely heavily on them, they do not provide as much energy. This slows down their metabolism and development. The older the sea lion the less energy he/she needs, it is harder for younger males to replace the older ones. Due to the fact that males control harems, if they are not replaced, they keep breeding and reduce the amount of genetic variability. This may cause flaws in the genotype.
Another cause for the decline of fish may be due to the warming of the earth's oceans. As the waters warm, the plankton (the basis for the fish diet) move north to cooler water. The fish end up following their food and since the sea lions breed in the same place as they were born, they do not go after the fish.
In the winter, the pollock stay deeper in the water and the Pacific herring move out to sea, past the range of the sea lions. All of this weakens the sea lions and makes them more vulnerable.
We also believe that the hunting of the sea lion, done up until 30 years ago, has been an under-recognized cause. When pups were killed, they decimated the entire generation. This will forever scar the sea lion population, since those pups and their offspring will never breed. This also limits the genetic pool.
Finally, we believe, a small part of the decline is due to a natural population cycle. One such example is that between the Lynx and Hare.
Introduction StatementAlaskan waters, though cold and remote, are bountiful with sea life, including sea mammals and sea birds. Humans have viewed these waters as a limitless supply of natural resources for thousands of years; but we were wrong. For the last 30 years, fishermen, scientists, and researchers, have noticed a sharp decline in the Steller sea lion population.
In the 1960's, there were reports of over 227,000 sea lions in the entire state of Alaska and in 1994 that number has declined to 43,200 animals (R.J. Small and D.P. DeMaster, 1995). Several reasons have been proposed over the years that explain the decline of the sea lion population. They range from over fishing to the natural population cycle, even though there has been no clear and convincing evidence given for any of these proposed ideas.
In this examination we will try to determine from our collected materials, reasons and solutions for the decline of the Steller sea lion population. We will look at several factors, including the above mentioned, over fishing and the natural population trend.
Species DescriptionThe Steller sea lion belongs to the genus and species Eumetopias jubatus. The sea lion population in Alaska is divided into two different species, the eastern and western groups (Fig. 2). In this essay, we will mainly be looking at the western population. The two species are defined as any animal west of Cape Suckling (144 degrees W) and the eastern population is any animal east of Cape Suckling. While the western population is considered endangered, the eastern population is considered threatened. Some populations near and around British Colombia are remaining relatively stable. There is also a difference between the western and eastern groups, in the mitocondrial DNA (Steller Sea Lion Recovery Group, 1998).
Sea lions are the largest otariid, with marked sexual dimorphism. Males weigh in at an average of 566 kg and a length of 282 cm. Females weigh in at 263 kg and a length of 228 cm. At birth, pups weigh 23 kg and are 112 cm long.
It is believed that sea lions evolved in the temperate waters of the North Pacific Ocean (Repenning and Tedford, 1977). The first fossils of sea lions were found in California and were dated between three and four million years old.
At birth, pup's coats are a chocolate brown, but the tips of the hairs are colorless, producing a frosty effect. As the animal ages, their coat lightens to a yellowish cream color as the color pattern differs in various parts of the body.
For pupping and breeding, the sea lions will gather on well-defined rookeries. The largest males will select a territory, which they will defend from mid-May through mid-July; which is the same time in which females will give birth. After giving birth, females go into estrus, and breed again, however, the egg doesn't implant until October. Some females begin breeding by age three, giving birth the following year. By their sixth year, almost all females are breeding. Although physically able to breed by age three to six, the males must wait until they are able to hold a territory, between ages eight to ten.
FISHIt is believed by many that one of the main causes of the Stellar sea lion decline is due to the over-fishing of their primary food source. Some believe the main food source for the Stellers is the walleye pollock. Determining the main food source is very difficult. The diet of the Stellar sea lions varies greatly depending on whom you ask, location, and time of year (Fig. 1). We believe that pollock is the main food source and the Pacific herring is second choice of the Steller sea lions. These are the two species we will be dealing with in this report. Other foods of the Stellers include capelin, salmon, squid, Pacific cod, and octopus.
Walleye PollockThe walleye pollock (we will refer to it as simply pollock for the rest of the report) is the most abundant species in the eastern Bering Sea, and second most abundant in the Gulf of Alaska (Fig. 3). For fisheries management, they are divided up into three groups: eastern Bering Sea, Aleutian Islands, and Aleutian Basin.
It is commonly believed that the fishing of the pollock in sea lion areas is the main cause for the decline. We do not believe that this is so.
It has been documented that while the population of pollock is at a record high, the sea lion population is still declining. The National Research Council said in 1996, that the probable cause of marine mammal decline was due to physical changes and human exploitation of predators. This has caused a shift, so that the pollock are no longer being hunted naturally. As the pollock numbers increase, they are competing for space and food with more nutritious foods.
We do believe that the pollock fishery is having a direct impact on the sea lion population. It is, however, not as serious as some believe. As you can see, the sea lions have adjusted their diet, as not to compete with the fisheries (Fig. 4). While the fisheries are taking the mid- size fish, the sea lions are taking the smaller and larger sized fish. There has also been a change in the age distribution of pollock (Figs. 5 and 6). The average life span of the fish has gone up. However, between 1992 and 1995, there was a sharp drop in the numbers of smaller, or juvenile pollock. These smaller fish are what the young pups rely on as a basis for their nutrition after they stop nursing.
We do believe that there is a relationship between the pollock and the herring population (Fig. 7). As the pollock population rises, the herring population falls and visa versa. Our data shows the herring is at its low point thus compounding the lack of herring for the Steller sea lions. This trend is most likely natural, but the overall decline could be related to over fishing.
One of the main reasons we believe the fishing of pollock has not had a drastic effect on the sea lion population is because pollock are a relatively low quality food. Research done by the North Pacific Universities Marine Mammal Research Consortium showed that when the sea lions were put on a high quality food such as Pacific herring, then switched to a low quality food such as pollock, the sea lions were not able to maintain body mass. In 1993 a scatological survey of sea lion feces showed a large percent of its content was Pollock (North Pacific Universities Marine Mammal Research Consortium).
Pacific HerringThe Pacific herring (henceforth we will refer to it just as herring) is what we believe to be the second most important food for the sea lions (Fig. 1). In 1981 a study showed the herring made up 20.6% of the sea lions stomach content, preceded by pollock at 58.3%. We believe that the herring is the most important food for the sea lions because it is a high quality food source, more so than the pollock. The herring catch record shows that the population varies wildly and since herring is not suspected to be a major contributor to the sea lion decline, there has been limited studies on the species and its niche.
Our Conclusions (Fish)Since the pollock population is forcing other species out of their normal territory, the sea lions are being forced to exist on a low quality food. So what does this mean? When the sea lion leaves its mother, it must depend on smaller fish than an adult would. The decline of the mid-size or juvenile pollock is something that will last for more than a year. The lack of fish for that particular generation of sea lions will be around for the life span of those fish. Also, the fisheries are taking the medium size fish, which the young pups rely on. So, this results in the younger sea lions not being able to get enough food. The size decrease is visible in females, too (Figs. 8 and 9). This lack of food may also be slowing down the males' ability to reproduce. Since it takes several years after sexual maturity for males to maintain a harem, a slowed maturation would limit the number of breeding males (Figs. 10 and 11). The older males do not need as much food, so this adds to the inability of younger males to replace older ones. When there is a smaller breeding group, imperfections in the genotype begin to appear and weaken the population.
Another blow to the population occurs during winter. If the sea lions are not able to gain enough blubber to keep them warm, they will have to struggle harder and spend more energy to gain food in the winter. This proposes yet another problem. The pollock dive deeper in the winter and the herring leave shore altogether. This means the sea lions are spending more energy, in a cold climate, for a low quality food. There is documented proof that sea lions do not dive as long, or as deep in the winter.
El Nino can also play a role in the decline of the Steller sea lions. As the water warms, it cause the plankton to move north to cooler water. This forces the fish to move north with the plankton. Since female Steller sea lions often breed in the same locations as they were born, they force the males to stay, also, losing out on the fish that have moved north.
SOCIAL ECONOMICSTraditionally, Steller sea lions were hunted and used by native Alaskans. The hides were made into clothing, boots, and boot coverings. The Chinese used the whiskers for cleaning opium pipes.
Most of the Steller sea lions taken via subsistence, 99% were taken from the western population and the majority, 79%, were taken by Aleut in the Aleutian and Pribilof Islands. For 1992 and 1993, the mean annual take for the stock was 514 animals. Of the animals taken, 29% were adults, 61% were juveniles, 7% pups, and 3% were of an unknown age. Sex-specific kills were 62% males, 16% females, and 22% were of unknown sex (R.J Small, and D.P. DeMaster, 1995).
Steller sea lions were used by fur farmers for fox meat, as well as dog food for mushers. Between 1964 and 1972, sea lions pups were taken commercially. The skins were used for making coats, boots, gloves, and other such garments. However, in 1972, the Marine Mammal Protection Act was passed to protect marine mammals (Alaska Department of Fish and Game, 1997).
In the waters around rookeries and hallouts, sea lions keep within a close distance of their habitat. These waters supply an abundant food source for an important age bracket of the sea lions, juveniles. Over the years, commercial fisheries have taken a great deal of the remaining fish in the sea lions diet, pollock. Even though studies show that pollock are not a great source of nutrients for the sea lions, they are some of the only fish that these mammals have left to prey upon.
Fisheries have absconded with the essential sized pollock for juveniles, 25-35 cm long. This has been devastating since the sized fish are found in an area that is accessible by the juvenile sea lions due to their inability to dive past 50 feet.
The government has taken steps to protect the Steller sea lion population with no-entry buffer zones were established around rookeries and hallouts (Fig. 12). Ground fish trawling has been prohibited within 10-20 miles of certain rookeries (Fig. 13). Also, spatial and temporal allocations of pollock, in the Gulf of Alaska, were set up for the Steller sea lions and other pollock dependent species.
Our Conclusions (Social Economics)Due to the taking of the young pups' twenty years ago, an entire generation of Steller sea lions has been damaged. This will haunt the Steller sea lions for longer than that generation was alive. The population had to deal with not having the same amount of offspring as there would have if those juveniles were never taken. Every breeding season this problem is compounded because those juveniles never had offspring, and those offspring never had offspring, and so on. Throughout the years the population hasn't been at its maximum because of that missing generation.
POPULATION CYCLESWe believe that one of the factors contributing to the decline of the Steller sea lion is not completely unnatural. Throughout nature, predators and prey have a fairly predictable cycle of interactions. As the prey population goes up, then so does the predator population. When the prey cycle begins to fall, the predator population follows. The famous example is the lynx and hare relationship.
It is one of our beliefs that this interaction could be going on now. The Steller sea lions are playing the role of the prey, and we the humans, and several other species, i.e. killer whales, are the predators.
Although the number of the Steller sea lions is falling, some reports show a slight increase in population. A study done by R.J. Small and D.P. DeMaster showed between 1989 and 1994 that the Bering Sea population increased by 1,000 animals. However, in the other two study areas, the Gulf of Alaska and the Aleutians, showed a decrease. Likewise, state wide over the same time period, the overall population dropped 23,000 animals.
Our Conclusions (Population Cycle)It is possible that if we leave the Steller sea lions alone their population would return to the maximum carrying capacity. However, there is always an air of uncertainty in any science. It may be years before we understand how much of the decline we, as a species, are responsible for and how much was mother natures doings.
Overall Views & Suggestions
Coming to the end of the report the Dimond NOSB team would like again to state a few reasons why we believe the Steller sea lions are declining, and a few suggestions to slow the decrease.
Global warming is a natural process, it is unstoppable, and nothing can be done about the change in climate and the warming of the earth's oceans. When the temperature rises organisms, such as plankton, move towards cooler water. On the subject of the Steller sea lions, their plankton is traveling north causing the fish they depend on to follow the plankton, and since the sea lions breed and remain where they were born, they do not. We believe that if the ocean temperature stopped increasing, and dropped, fish the sea lions depend on as a high-energy source will return south.
The walleyed pollock, which is extremely abundant in the Bering Sea and the Gulf of Alaska, makes up 58.6% of the sea lions stomach content. As their numbers increase, they take up large amounts of space and food that more nutritious organisms could feed upon. Fisheries do not help this situation since they remove the young, juvenile pollock that the pups eat after they stop or cease to nurse. The absence of the young fish can lead to huge gaps in certain generations of sea lions. The Pacific herring, another source of food which gives the sea lions more energy than the pollock, are also being fished out of the sea and migrating to follow the moving plankton. We believe that if the fisheries take less juvenile fish the pollock population will shrink and not crowd out better quality fish.
The population cycle of predator and prey take part in the decline: The abundance of two animals, the predator eating more prey than he is used to decreasing the weaker number and creating a lower count of its kind. When this happens, the prey begins to increase and become abundant again while the declining predator begins to rise, as well. Man can be a part of this cycle also. Take into consideration the Alaskan Natives they killed sea lions for meat and useful body parts, using every part for a survival purpose. What is not an example of this cycle is the slaughter of sea lions for expensive commercialized products such as gloves, coats, and boots. The number of sea lions killed by diseases were few, stated the Steller Sea Lion Recovery Investigations during 1995 through 1996, but it is still another factor adding to the effects of their declining status.
All in all, we believe that the Steller sea lions should be left alone and be taken care of by the mother of all mothers, MOTHER NATURE. She is incredibly good at fixing our mistakes and over time we believe that the Steller sea lions will rebuild their population.
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Life History and Habitat Requirements of Fish and Wildlife. Alaska Habitat Management Guide. Juneau, Alaska. Alaska Department of Fish and Game, 1985.
Mercy, Deborah. The Steller Sea Lions In Jeopardy. Marine Advisory Program and the Alaska Department of Fish and Game (video), 1998.
National Marine Fisheries. Steller (Northern) Sea Lion. Washington, D.C. National Marine Fisheries. http://kingfish.ssp.nmfs.gov/tmcintyr/pinniped/steller.html.
National Oceanic and Atmospheric Administration. Draft Supplemental Environmental Impact Statement. Juneau, Alaska. National Oceanic and Atmospheric Administration, 1998.
National Research Council. The Bering Sea Ecosystem. National Research Council, 1996.
North Pacific Universities Marine Mammal Research Consortium. Marine Mammal Research/Newletter. Vancouver, British Columbia. North Pacific Universities Marine Mammal Research Consortium, 1997.
North Pacific Universities Marine Mammal Research Consortium. Marine Mammal Research/Newletter. Vancouver, British Columbia. North Pacific Universities Marine Mammal Research Consortium, 1998.
North Pacific Universities Marine Mammal Research Consortium. Steller Sea Lion-The Problem. Research and Conservation. Vancouver, British Columbia. Vancouver Aquarium. http://www.vancouveraquarium.org/conserv/stellers/steller/tests.html, 1998
North Pacific Universities Marine Mammal Research Consortium. Steller Sea Lion-Testing. Research and Conservation. Vancouver, British Columbia. Vancouver Aquarium. http://www.vancouveraquarium.org/conserv/stellers/steller/tests.html, 1998
Pitcher, Kenneth. Steller Sea Lion Recovery Investigations In Alaska, 1995-1996. Anchorage, Alaska. Alaska Department of Fish and Game, 1996.
Small, R.J. and DeMaster, D.P. Alaska Marine Mammal Stock Assessments. National Oceanic and Atmospheric Administration. http://kingfish.ssp.nmfs.gov/tmcintyr/mammals/sa_rep/alaska/stelwest.html, 1995.
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ACKNOWLEDGMENTSThe members of the Dimond High NOSB team have many people to thank for the production of this report. However, first and foremost, we must thank our sponsor, Mrs. E. Larman. Without her tireless effort in corralling us to do the work and collect the material, we would never have been able to motivate ourselves. Her overwhelming dedication to the National Ocean Sciences Bowl has been inspirational. She has sacrificed many hours of her personal time to assure that we complete this report.
We would also like to thank the National Oceanic and Atmospheric Administration, along with the Alaska Department of Fish and Game, whose published works provided the foundation of this report. Without their information, we would have been unable to assemble this assignment.
Finally, I would personally like to thank my teammates. Without their help, this report would never have been able to take off.
With much thanks to all,