Alaska Sea Grant

Supporting Materials

Where Have All the Salmon Gone? Teacher Notes

Formative Assessment Probes

The brief, formative assessment resources included with these units are called "assessment probes." They are called "probes" sockeyebecause they are designed to probe and uncover student thinking. Teacher and researcher Page Keeley has written extensively about the probes as part of the Curriculum Topic Study approach to analyzing science and mathematics topics. See the Curriculum Topic Study website for more information. 

These probes are designed to be used diagnostically and formatively. They are intended to help you to tap into students' thinking about particular science topics -- topics that are identified by the National Science Education Standards as significant and developmentally appropriate for the target age level of the unit. While they are intended to sample students' thinking (and to probe for common misconceptions), they are NOT intended to measure what students have learned as a result of the unit content. We encourage you to use these tools--and to develop your own--to better understand each student's development as a learner, and to modify your teaching accordingly.

Ongoing assessment throughout the investigations is important for several reasons. It can reveal when students are confused or have misunderstandings, need more time to investigate, or need more explanation. You can tailor the investigations to meet the needs of your students, and change direction whenever necessary. Frequent assessment does not have to be time consuming or tedious. A quick assessment can give you a lot of information about student comprehension and understanding.

The purpose of this probe is to elicit students’ ideas about the ways organisms interact with and depend on one another in various ways.


The best answer is B: Bears, eagles and sea lions all depend on the salmon for food. If the salmon were not there, some of the animals may not be able to live there anymore. All the animals listed depend on salmon for food, and although salmon isn't the only thing they eat, salmon is an important part of their diet. If there were no salmon, some of the animals would more than likely leave the area.

Choice A is not the best choice because even though all the animals listed depend on salmon for food, that is not the only thing they eat and they will not all die.

Choice C is not the best choice because even though all the animals listed depend on salmon for food, and although salmon isn't the only thing they eat, salmon is an important part of their diet. If there were no salmon, some of the animals would leave the area.

"Every species is linked, directly or indirectly, with a multitude of others in an ecosystem. Ecosystems are shaped by both the nonliving environment and by its inhabitants, including humans." "Students may not regard food as a scarce resource for animals and, hence, may not consider competition among species for food resources." (Atlas of Science Literacy, Vol. 2, p. 32)

Lower elementary-school students can understand simple food links involving two organisms. Yet they often think of organisms as independent of each other but dependent on people to supply them with food and shelter. Upper elementary-school students may not believe food is a scarce resource in ecosystems, thinking that organisms can change their food at will according to the availability of particular sources (Leach et al., 1992)

Administering the Probe
Allow students to read the scenario individually. Students should choose the idea that they think best describes what might happen if there were no more salmon in the area. Make sure that students understand they need to explain their reasoning.

Grade Level Curricular and Instructional Considerations

Children build understanding of biological concepts through direct experiences with living things and their habitats, including observation and interactions with the natural world. The idea that organisms depend on their environment and on other organisms is not well developed in young children. In grades K-4, the focus should be on making sense of the way organisms live in their environments and on establishing the primary association of organisms with their environments. This should be followed in upper elementary by the secondary ideas of dependence on various aspects of the environment and of behaviors that help various animals survive. (National Science Education Standards, p. 128).

Children often understand a link between two organisms, but more often think in terms of the organisms acting independent of each other and as often dependent upon people. Students also tend to use common language rather than scientific terminology to explain their understanding and terms like “community” or “interdependence” can be confusing. For example, students can select pictures to produce a balanced community of consumers and producers, but few use the idea of interdependence to explain their selection. (Making Sense of Secondary Science, p. 60-61).

Introduction to simple food chains as a prelude to food webs may contribute to children failing to use ideas about interdependency to explain relationships in complex ecosystems. Many students think that a population high on a food chain is a predator of all the organisms below it. In addition, some students believed the change in prey population would have no effect on its predator population, while others believe an organism can change its food source if it needs to. Some students saw energy adding up through an ecosystem, such that a top predator would have all the energy from the producers and other consumers in the chain. (Making Sense of Secondary Science, p. 60-61).

Related National Science Education Standards

K-4 The Characteristics of Organisms

  • Organisms have basic needs. For example, animals need air, water, and food; plants require air, water, nutrients and light. Organisms can survive only in environments in which their needs can be met.

K-4 Organisms and Their Environments

  • All animals depend upon plants. Some animals eat plants for food. Other animals eat animals that eat plants.
  • An organism's patterns of behavior are related to the nature of that organism's environment, including the kinds and numbers of other organisms present, the availability of food and resources, and the physical characteristics of the environment. When the environment changes, some plants and animals survive and reproduce, and others die or move to new locations.

5-8 Populations and Ecosystems

  • A population consists of all individuals of a species that occur together at a given place and time. All populations living together and the physical factors with which they interact compose an ecosystem.
  • Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and some microbes are producers – they make their own food. All animals, including humans, are consumers, which obtain food by eating other organisms. Decomposers, primarily bacteria and fungi, are consumers that use waste materials and dead organisms for food. Food webs identify the relationships among producers, consumers and decomposers in an ecosystem.

Related Benchmarks for Science Literacy

3-5 Interdependence of Life

  • For any particular environment, some kinds of plants and animals survive well, some survive less well, and some cannot survive at all.


Related Probes in Uncovering Student Ideas in Science by Page Keeley.

Habitat Change V2, p. 143

Killer Whale Math

Terrie Williams and her colleagues wanted to calculate whether it was possible that killer whales had eaten the missing sea otters.

They started with this information:

  1. 40,000 otters were missing.
  2. They had disappeared over a period of six years.
  3. Sea otters provide the following food values:
    Female sea otter 23 kg x 1.81 kcal/g = 41,630 kcal per female otter
    Male sea otter 34 kg x 1.81 kcal/g = 61,540 kcal per male otter
    On the average, a sea otter provides 51,505 kcal
  4. Killer whales need the following amounts of food:
    Female killer whale needs 51 kcal x 3784 kg = 193,000 kcal per day
    Male killer whale needs 59 kcal x 4870 kg = 287,331 kcal per day
    On average, a killer whale needs 240,165 kcal per day
  5. There were an estimated 4000 killer whales in the area, but 90% of them had a diet of fish only.

If killer whales fed only on sea otters, how many sea otters would one killer whale need to eat every day?

240,165 kcal needed by killer whale/51,505 kcal provided by sea otters = 4.6 sea otters needed per day

How many sea otters could one killer whale eat in six years?

365 days x 6 years x 4.6 sea otters per day = 10,074 sea otters

How many killer whales would be needed to eat 40,000 sea otters, if they ate nothing but sea ottters?

40,000 otters/10,074 otters per killer whale = about 4 killer whales

What is the estimated number of killer whales in the area that eat marine mammals?

90% eat only fish, so 10% of the 4000 killer whales, or 400 killer whales might eat sea otters

If there were 400 killer whales eating otters as part of their diet, what is the average number of otters that each would have to eat, in order for 40,000 sea otters to disappear?

40,000 sea otters/400 killer whales = 100 otters per whale in six years

or 100/6 = 16.6 otters per year per killer whale

That would be about one otter every (365/16.6) 22 days.

How many male or female sea otters could a pod of one male and four female killer whales eat in one year?

A male killer whale would need to eat 5 (4.66) male sea otters or 7 (6.9) females per day.

A female killer whale would need to eat 3 (3.1) male sea otters or 5 (4.6) females per day

1 male killer whale could eat 1825 males per year or 2555 females per year

+ 4 females could eat 4380 males per year or 7300 females per year = 6205-9855 otters per year

How long would it take them to eat 40,000 sea otters?

One pod could eat 40,000 sea otters in 4 to 6.5 years

Six Hypotheses

Hypothesis #1: The sea otters died of starvation.

What the Scientists Did:

They captured some sea otters and weighed and measured them.

They measured the time it took for otters to dive and return to the surface with an urchin or another type of food item. Then they compared their data with data that had been collected in 1970s and 1980s.

What They Found:

The otters were larger and heavier in the 1990s.

The otters took shorter dives in the 1990s.

#2: The sea otters died of a disease.

What the Scientists Did:

They looked for dead otters that had washed up on beaches so they could examine them.

What They Found:

They found very few dead bodies. If a disease had swept through the otter population, they would have expected more.

They found no evidence of disease in the dead otters that were examined.

#3: The sea otters died from toxic pollution.

What the Scientists Did:

They looked for sources of toxic pollution, including evidence of oil spills.

They looked for dead sea otters that had washed up on beaches so they could examine them.

They collected other animals from the sea otter food chain and tested them for pollutants such as heavy metals that would become concentrated at higher levels in the food chain.

What They Found:

They found very few, and small, sources of pollution in the Aleutian Islands and no evidence that an oil spill had occurred that had not been reported.

They found very few dead bodies. If pollution had killed a lot of otters, they would have expected more.

The bodies they did examine did not have high loads of pollution.

The animals lower in the food chain did not have high loads of heavy metals or other pollutants.

Hypothesis #4: The sea otters died as a result of human harvests of the otters themselves or from becoming entangled in fishing gear.

What the Scientists Did:

They looked at the records of subsistence harvests of sea otters by people who lived in Aleutian Island communities.

They looked at the records from people who fished around the Aleutian Islands to see how many sea otters had became entangled in their nets and died.

What They Found:

The harvest of sea otters by people in the communities was small, about 100 otters per year.

There were few reports of otters getting entangled in fishing nets or other gear.

Hypothesis #5: The sea otters did not die; they moved somewhere else.

What the Scientists Did:

After surveying all of the Aleutian Islands in 2000, they surveyed the Alaska Peninsula coast and all of the shoreline of Kodiak for sea otters.

What They Found:

Sea otter numbers had declined everywhere in this area.

#6: The sea otters were eaten by killer whales.

What the Scientists Did:

They asked the scientists who had been studying killer whales if they had observed killer whales attacking and eating sea otters.

They looked for other observations, by fisherman or people in local communities, of killer whales attacking and eating otters.

They looked for dead killer whales washed up on beaches so they could look at the contents of their stomach.

What They Found:

Killer whale scientists had observed only a few attacks over the many years that they had studied killer whales.

One attack was observed in the Aleutian Islands in 1992.

Nine more attacks were observed over the next several years.

One killer whale was found dead with the remains of five sea otters in its stomach along with nine harbor seals.

Map of Aleutian Islands and Bering Sea

Map of Bering Sea and Aleutian Islands

Click image for PDF version.

Alaska Sea Grant University of Alaska Fairbanks Alaska Department of Education and Early Development NOAA