|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:
Linda Clayton, Team Coach
Historically, the Steller sea lions, Eumetopias jubatus, ranged from California north and northeast along Alaska, to the coasts of Russia and Japan. From 1956-1960 there were approximately 140,000 Steller sea lions. In the 1970's the Steller sea lion population started a steady decline. From 1981 to 1996 their population declined by 70% in just 15 years. It's estimated at the current rate of decline the western population, which includes all the Steller sea lions living west of the 144 degree West meridian, will be extinct in the next 100 years. Therefore, the next 20 years are crucial to the Steller Sea Lion survival. There have been numerous possible reasons discussed for the Steller sea lion decline. Some of the reasons are entanglement, incidental takes, pollution, harassment, disease, changes in prey availability due to overfishing, oceanographic changes, predation, shooting, commercial pup harvests and subsistence harvests. But not all of these possible causes are thought to be major reasons for decline.
Steller sea lions are born on rookeries, (see figure 1) which are usually large rock outcroppings facing the open sea. The mothers usually come to the rookeries a couple of days before their pups are born. After the pups are born, they are weaned in a year and roam around for a couple of years. At age three, both male and female Steller sea lions return to the rookeries on which they were born. Females mate but males wait until they are older to mate when they can challenge the more dominant males. When they are not at the rookeries, they are out on the open ocean, hunting for food. Steller sea lions usually eat herring, pollock, octopus, squid and rockfish.
It is widely considered that there are several reasons for the population decline, not just one. A big factor is the quality of the sea lion's food. Normally, Steller sea lions eat a variety of food including herring, capelin, pollock, squid, octopus, and flatfish. A recent shift in the ocean environment has caused a decline in the population of herring and capelin and a big increase in the population of the pollock. So, now the main food source for the Steller sea lion is pollock. Compared to herring with a relatively high fat content, ollock has a low fat content. In addition, pollock also requires more energy to digest. This diet may adversely affect Steller sea lions' health.
Besides the change in the type of food available to the Steller sea lions, there has also been a temperature change in the ocean. This causes the metabolic rate of the Steller sea lions to go up. Because of this the Steller sea lion needs to obtain more energy from their food, which they can't get from the pollock they are eating now. Not having enough energy causes the Steller sea lion to become unhealthy which increases their susceptibility to diseases like heartworm, and the Calici virus. The Calici virus is being studied in a wide range of animals, including pigs, rabbits and a variety of marine animals. So far it is known to affect animals in the Pacific Rim countries and can be transmitted from land to sea and vice versa. The symptoms include blistering of the skin, pneumonia, abortion of the fetus, encephalitis and diarrhea. This virus has been in existence for more than 65 years, but most studies were conducted on pigs with research on marine animals done only in the last 20 years. The sea lions are also more prone to predator attacks when they are unhealthy. During research done by the ADF&G, it was found that a lot of Steller sea lion females were giving birth prematurely from a month to a couple days before they were due.
Another possible cause of declining numbers in the Steller sea lion stock we researched was that, in the past, a lot of sea lions were killed due to entanglement and incidental takes. Since the early days of keeping statistics these causes have been greatly reduced. During the 1990-1991 fishing seasons NMFS (National Marine Fisheries Service) observers recorded incidental take of Steller sea lions for six different fisheries within the western stock of the Steller sea lion population. The observers watched the groundfish trawl, long line, and pot fisheries for the Bering Sea fisheries. The same three types of fisheries were observed for the Gulf of Alaska and in Prince William Sound. The total mortality rate of the Bering Sea and Gulf of Alaska fisheries was 19 annually. There were 14 deaths in Prince William Sound annually. This adds up to about 33 Steller sea lion deaths per year. This data was found using logbook reports and observer's notes. Although there could have been more killed, any number less than 77 is considered to be insignificant.
A major reason some people think the Steller sea lions are declining is the fact that the fisheries, especially pollock trawlers, are competing for the Steller sea lion's main food source, pollock. From looking at charts (see figure 2) which show the Steller sea lion decline, it can be seen that the Steller sea lion population started declining at about the same time that the pollock fisheries started to expand. But, studies have shown that even though the pollock fisheries take approximately 2/3 of the total population of pollock, leaving 1/3 of the fisheries for the Steller sea lions, Steller sea lions don't appear to be suffering because of overfishing. It appears that the low energy content of the pollock, is causing a major problem.
For the 1992 and 1993 subsistence hunts it's estimated that there were 514 Steller sea lions killed. 99% of the sea lions killed were from the western stock of Alaska. About 62% were males, 16% females, and for 22% the sex was unknown.
During the years before 1970 there were annual Steller sea lion commercial pup harvests. These harvests ceased in 1972. Therefore, that isn't a factor recently but it could have hurt the Steller sea lion population in the past. When the ocean started changing there would have been fewer Steller sea lions and they could have declined more quickly.
There isn't much information about the effect pollution has on the Steller sea lions. But researchers like Maggie Castellini, of the ASLC (Alaska Sea Life Center) feel that there have not been enough studies done on this yet. Pollutants like metals and petrochemicals need to be studied in the ocean and along the shores by the rookeries to determine the effect on the Steller sea lion population.
Killer whales are the main predators of the Steller sea lions. Although these animals prey on the Steller sea lions, no statistics have been gathered to prove that they have a major impact on the population. According to Boyd Pottor a researcher with the ADF&G, some killer whales will only eat fish and others will only eat marine mammals.
What is being done to prevent the decline of the Steller sea lions?In 1990 all of the Steller sea lions in Alaska were put on the threatened list by the Endangered Species Act (ESA). Under the ESA, Steller sea lions are protected from federal actions that could endanger their existence. These actions could include fisheries and oil exploration. In 1997 Steller sea lions were divided into eastern and western population. The western population is the portion west of the 144 degrees West, with Cape Suckling as the dividing line. Also in 1997, the western stock was listed as endangered while the eastern stock remained threatened. In 1990 when all of the Steller sea lions were put on the threatened list, the NMFS formed the Steller sea lion Recovery Team. They set up several courses of action to try to help the Steller sea lions recover. A buffer zone of 3 nautical miles was created to keep fishermen and boaters away from the critical habitat areas around rookeries and hallouts in the United States. Another change made by the Steller sea lion Recovery Team (see figures 3 and 4) was to place three critical foraging areas in a no fishing zone. In late 1998 the Steller sea lion Recovery Team looked at how they could change the plan and what should stay the same. They are working on details to curtail the pollock fisheries in order to stop or lessen the decline of the Steller sea lions.
Figures 3 and 4
At the Alaska Sea Life Center several sea lion studies are taking place. One study is an on-site camera at a sea lion rookery in the Cheval Islands just outside and to the west of the entrance to Resurrection Bay. The monitor is located in the office of Dr. Donald Calkins at the Alaska Sea Life Center (ASLC). This is a new set up to monitor sea lion mating in the spring and study statistics have not been recorded as of yet.
Dr. Michael Castellini, a professor and the University and the Science Director at the ASLC, and staff are working on different related science studies which focus on testing blood chemistry samples. The samples are worked up for blood volume, oxygen stores, proteins, aerobic dive limit, oxygen transport, and whole blood metabolite distribution. They have found evidence that Steller sea lion pups are born with an elevated hematocrit value which dramatically increases the chance of possible disease states that can include the immune system. This can be compounded by physical or environmental stresses. Also in Dr. Castellini's laboratory, graduate students are studying the effects of different food sources on the captured sea lions, by doing caloric counts on the food as well as the sea lions. They test various foods for calorie content and observe their effects on the growth and health of sea lions.
Many communities are being affected by the declining populations of Steller sea lions. Pollock fishermen using factory trawlers, pots, or long lines fear that they would lose a lot of money as a result of the restrictions put of the pollock fishery. Communities with an on shore proccessor would not have as much fish to be processed and so could lose a lot of money and jobs. Therefore, the restrictions would affect a wide area even if a community's economy was not dependent upon fishing.
In conclusion our paper has offered a variety of possible clues as to why the Steller sea lions have declined. Many scientists feel that a lack of diet diversity along with disease, overfishing the food sources and other factors that have been mentioned are possible causes to this dilemma. We are still far from the answer but with each passing day we are getting a little bit closer.
No Trawl-Zones: Are they working? Maybe... Thesis by Wendy Dunlap. University of Alaska, Institute of Marine Studies. April 1998.
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Boyd Potor, ADF&G, Anchorage, Alaska. Researcher
Maggie Castellini, ASLC, Seward, Alaska. Research Assistant
Wendy Dunlap, Tammy Mau, and Heather Ellingboe, University of Alaska Fairbanks, Institute of Marine Science, Graduate Students doing interships at the Alaska SeaLife Center, Seward, Alaska