Mystery in Alaska

Teeter 14

MYSTERY IN ALASKA

MYSTERY IN ALASKA

SHANE TEETER

BIOLOGY 1308

DR. ROSE

02 JULY 2012

INTRODUCTION

There is a great mystery that has yet to be solved lurking in the snow covered wilds of Alaska. No; it isn’t the Northern lights and I have yet to see a Yeti that matches those enormous footprints. These are not it. The great mystery is the decline in the numbers of Steller sea lion off the Alaskan coast. There was a time when the Steller sea lion was considered a nuisance to fisherman and had become the competition for local commercial fisherman.

“In 1934 Secretary of Interior J.A. King declared “It has been determined that sea lions occur in excessive numbers in the waters of Alaska and are inflicting serious economic loss on the fisheries.” [16 USC 659]. By the 1950’s localized depletion of salmon by Steller sea lions was perceived as a threat to commercial fishermen, so the state sanctioned efforts to reduce sea lion numbers. After the mid-1970s, Steller sea lion numbers declined drastically. In the 1990’s, competition with commercial fishermen was perceived as a threat to sea lions; therefore fisheries have been managed to reduce the potential localized depletion of pollock, cod, and atka mackerel. Since the 1990’s, stellar sea lions have been the subject of intensive conservation efforts, political and biological debate, and an unprecedented research initiative.” (Wynne, 2005)

This case study is going to take a scientific approach to try and answer the burning question. Why is the sea lion population still dwindling? We have uncovered some experimental data that we will share with you and use in developing our theories about why this population continues to dwindle in the east. We have also included research from other well-known scientists who have been studying and recording information on the decline in Steller sea lions since the 1980’s.

HYPTOHESES

“The North Pacific Universities Marine Mammal Research Consortium has found that since 1980, more than 75 percent of the steller sea lion (Eumetopias jubatus) population has disappeared. This major disappearance has happened in the west and has pushed the Steller sea lion to be listed as a threatened endangered species while the eastern population has remained stable. There could be many causes ranging from pollutions, storms, predation, diseases, or a change in geographical behaviors…

To try and solve the Steller sea lion mystery, we formulated a couple hypotheses as to why the Steller sea lion population has declined. Our first hypothesis is that the predators of the Steller sea lion were the main cause of the decline in Steller sea lion population.

The question that has been asked by many scientists, however, is why the population of the western Steller sea lion is declining while the eastern population is increasing? Our group has a hypothesis that answers this question and it is that the western Steller sea lion are undergoing and are more affected by nutritional stress than the eastern Steller sea lion.

METHODS

We are not experts and we do not have any prior experience scientifically studying Steller sea lions. We have to use current scientific data from scientists in the field and our own understanding of that data to develop our results. Our method for our first hypothesis was using the data from Lance Barrett-Lennard’s study The impact of killer whale predation on Steller sea lion populations in British Columbia and Alaska and the study Killer appetites: assessing the role of predators in ecological communities by USC students Terrie M. Williams, James A. Estes, Daniel F. Doak, and Alan M. Springer.

The second hypothesis uses data from D.A.S. Rosen and A.W. Trites in their published journal titled Digestive efficiency and dry-matter digestibility of Steller sea lions fed herring, pollock, squid, and salmon. Through these experiments and case studies, we will attempt an experiment that will try to prove that the western Alaskan sea lions are nutritionally stressed due to the lack of herring and over population of pollock. This experiment will take place in a laboratory setting and contain five 300 feet deep tanks. Each tank will contain different combinations of herring, pollock, or sea lions, depending on what results need to be found. The one and most important rule in this experiment is to limit the amount of times the sea lions are disturbed. The reason being is to try to simulate the sea lion’s natural habitat as close as possible.

The following resources for this experiment are as follows:

·  7 Western Sea Lions (3 Females about to have pups, 3 pups from birth, 1 Male)

·  7 Eastern Sea Lions (3 Females about to have pups, 3 pups from birth, 1 Male)

·  Pollock population

·  Herring population

·  Herring/Pollock food (phytoplankton)

·  5 tanks

·  Scientific staff (scientists, marine biologist, sea lion keeper, technologist, geneticist, transportation)

·  Depth Readers/ Transmitters

The 1st and 2nd tank will contain herring and pollock. The observation of both tanks will allow us to see the pollock and herring without any other variables to corrupt the data gathered about the species. Both of these tank observations are very important because the information can tell us what the sea lions are getting nutritionally when eating these fish and see directly how the pollock and herring react in a setting under study.

1.  The first variable is the nutritional value. The study of what nutritional factors come from the consumption of herring or pollock that will be analyzed to see what an individual Steller sea lion receives in nutrition when digesting either.

2.  The second variable is the depth at which individual herring and pollock dwell in during certain stages of living. This study can give us insight to what depths these fish usually live, hunt and are hunted for their food.

3.  The third variable is the reproduction rate. This will allow us to see how fast the population of the herring or pollock will replenish itself to feed the hungry sea lions.

4.  The fourth variable will be the recorded age of the specimens. Age is important to know when looking at the herring and pollock because this will give us an idea of the relationship between juvenile and adult survival. Obtaining this data should be done in the beginning and at the end of the experiment for variation and comparison.

The 3rd tank will contain pollock and herring combined. This tank and the data it represents is equally important as it can give us an idea of the predator vs. prey relationship between these two fish.

1.  The first variable is the amount of herring and pollock eaten by pollock. Pollock tend to prey upon themselves, as well as herring.

2.  The second variable is the rate and amount of fish eaten at each stage of life as they are in it. This can help us understand if a certain stage of life of one of the fish is being over hunted and perhaps affecting the diet of the sea lions. The most affective method to accomplish this is to take data on all stages of life in the beginning and end of the experiment.

The 4th and 5th tank will contain herring, pollock, and sea lions of the west and east, separated west and east in the two tanks. This observation will prove to be the most affective because it will support the ideas behind the argument of western vs. eastern sea lions possessing genetic differences, eating differently, and being different in any other way.

1.  The first variable to record is how much each type of sea lion eats. Juveniles and adult sea lions will be recorded and compared using the data collected showing how much they eat and the percentage of what type of fish they eat. This can be done through collecting scat (remainders of food left, mostly bones) of the animals throughout the month. This data will be recorded and compared against each individual animal separately and by group (western and eastern).

2.  The second variable will be the measuring of the individual sea lions (weight and size). This can show us if the growth rate in western and eastern sea lions differ from one another as this could be a secondary result of the lack of nutrients or proof of changing genetics.

3.  The third variable will be the recorded values of the observations and the overall health of each individual sea lion. The physical appearance (teeth, coat, etc) should be recorded. The mental health exhibited by each subject, such as the social network between the sea lions, should be studied for anything out of the ordinary (especially in pups). The appetite of each individual sea lion should be recorded. If any sea lion is not eating normally, this particular individual should be studied further to identify the possible cause of this nutritional imbalance. If a correlation between a western or eastern sea lion not having an appetite is found, this would definitely need more study.

4.  The fourth variable used will be genetic testing results. A genetic variation between sea lions of different origin may be a contributing factor in the problematic nutritional stress of sea lions in recent years. This test should be done at the appropriate age and done only once. Blood tests to find any genetic discrepancies or diseases should be noted and presented in this study.

Once all of the information is compiled and recorded from the tank experiments, the remainder of fish and sea lions will be released back into the sea. Before finally releasing the sea lions back into the sea, they will be fitted with depth readers and location transmitters. Data from these readers will enable scientists to see how far juvenile and adult sea lions dive to reach their food. A correlation could be found with the depth of how far a sea lion dives to find food and the age of that sea lion. These transmitters will allow the scientists to see where the sea lions go to hunt for food. Collecting scat samples throughout their year and in different seasons to see any variable changes in type of fish digested and the estimated amount of each type is a good way to continue the experiment and validate your research.

This case study also highlighted the importance of energy considerations within food chains by examining the population decline of Steller sea lions along the western Alaskan coast.

RESULTS

In regards to our first hypothesis, we discovered that there are various reasons that help explain why the Stellar Sea Lion population is on the decline. In Lance Barrett-Lennard’s study, he found “The stomach of a dead killer whale that washed ashore in Prince William Sound in the summer of 1992 contained flipper tags from 14 Steller sea lions. Using a number of techniques, they developed a mathematical computation and computer simulation that concluded that predation by 'transient' killer whales may account for a significant portion of the total annual mortality of sea lions in Alaska and British Columbia. The effects of predation on a robust sea lion population (consisting of over 100,000 animals) are minimal, but with smaller populations (<50,000) the effects are more significant, and may even be sufficient to drive a population decline. The authors conclude that killer whales did not cause the sea lion decline, but may now be a significant contributing factor. The model suggests that as many as 18% of the sea lions that die each year in Alaska are taken by killer whales.” (Barett-Lennard et al. 1995)

Given that information, one has to wonder, why it was only recently that there has been a major population decline. In researching this we also found “…changes in prey resources for killer whales occurring in the Aleutian Islands during this time period could initiate such a dietary shift. One recent hypothesis concerning a change in the prey base of killer whales begins with the demise of the great whales through intensive post-World War II commercial whaling… In the absence of this once abundant prey resource, killer whales that fed on the great whales would have been forced to find other means of satisfying their high energy demands. We hypothesize that pennipeds, including harbor seals, Steller sea lions, and possibly northern fur seals, and sea otters were taken sequentially as the killer whales progressively fed on less profitable prey” (Williams et al. 2004)

The results for our second hypothesis were: “The four prey items differed in both their size and their composition. Pollock and salmon were the largest prey items in both length and mass. Herring had the greatest energy density, while squid had the lowest energy density (and the highest water content)… The results of our study indicate that the Steller sea lions were deriving 7.09 kJ/g (0.954 × 7.43 kJ/g) of apparent digestible energy from herring, 4.35 kJ/g (0.939 × 4.63 kJ/g) from pollock, and 3.34 kJ/g (0.904 × 3.70 kJ/g) from squid. Since our sea lions were unable to maintain body mass while eating squid and Pollock. Pollock have much larger, bony structures that pass undigested through the gut, compared with the smaller, delicate bones of herring and the almost completely digestible squid (except for the beak).” (Rosen, D.A.S., and A.W. Trites, 2000)

Another key factor in steller sea lion intake is the fact that herring usually swim in schools (big groups) and are easily seen while the pollock blends in with the seafloor to avoid predators. The Pollock also dwell in deeper waters during the winter and cause a severe drop in the availability as a source of food and energy.

DISCUSSION AND CONCLUSION

Humans were allowed to hunt sea lions because they were thought to be an abundant, competitive, nuisance animal decimating the commercial fishing industry. It is highly likely that humans bear some responsibility for the decline in the Steller sea lion population, but there are several other factors potentially influencing the western population, for example there are bio-toxins, killing and harassment, commercial harvest, subsistence harvest, incidental take by fisheries, illegal shooting, and entanglement in marine debris, disease and parasites, disturbance, nutritional stress and global climate. As of 2001, the population was about 175,000.