2. The Case of the Missing Sea Otter

(Modified from “The Missing Sea Otter” Alaska Seas and Rivers Curriculum)

Lesson at a glance: Students will be introduced to the kelp ecosystem.

Goal: Students will know the sea otter food chain and biologic community in a kelp forest.

Oregon Content Standards:

Science

5.2 Interaction and Change: Force, energy, matter, and organisms interact within living and non-living systems.

5.2L.1 Explain the interdependence of plants, animals, and environment, and how adaptation influence survival.

Ocean Literacy: Essential Principles and Fundamental Concepts

5. The ocean supports a great diversity of life and ecosystems.

5.d. Ocean biology provides many unique examples of life cycles, adaptations and important relationships among organisms (symbiosis, predator-prey dynamics and energy transfer) that do not occur on land.

Materials:

Sea Otter Story Part 1
Diagram of cross- section of a beach (see file at bottom of page)

Estimated Time:

Activity:

Engage:

Locate the Aleutian Islands on a map and explain that this place has a similar kelp ecosystem of its’ coasts as Oregon.

With the whole class, read the “Sea Otter Story Part 1” about sea otters in the Aleutian Islands while displaying sea otter data tables. Insure that the students know what the data tables and graphics represent.

Discuss with the students:

What do the graphs tell you?
As a scientist, what questions do the data prompt?
What do you think happened to the otters?

Explore:

Post a large diagram showing a cross-section of a beach with intertidal and subtidal zones depicted. Explain what those terms mean. You can draw or write in the plants and animals in the appropriate zones as they are mentioned and discussed during this investigation. Ask students to write a definition of “ecosystem” in their science notebooks. Since they may not have an understanding of the term, the definitions may be brief of incomplete. They will continue to develop their understanding throughout the unit.

With the whole class together, share and discuss the definition of “ecosystem.”

Show the video clip of Jean-Michel Cousteau: Ocean Adventures Kelp Forest Video (youtube). While watching the clip, have students take notes of species in their science notebook.

Do a KWL activity with the students following the video. Ask the students what they know about sea otters and their ecosystem. Students can follow along recording the KWL in their science notebooks.

As a whole group, brainstorm what would have to be understood in an otter’s ecosystem in order to understand the otter population decline in the Aleutian Islands: (food needs, need for shelter, adaptations to their environment, what dangers are in the environment- predators, pollution, how they are used by people). This information will be added to the “W” section of the chart- What they want to learn, or what do they think they will need to learn to understand the otter’s ecosystem.

Assign readings to small groups as research to discover the ecological relationships that will help solve the eco-mystery. Ask students to take notes and make illustrations in their science notebooks as they read.

Reading 1: Sea Otter Biology and History in the Aleutian Islands

Reading 2: The Producers in the Ecosystem

Reading 3: Consumer: Marine Invertebrates and Fish in the Kelp Forest

Reading 4: Consumers: Marine Mammals

Explain:

Student groups report their research to the class as pieces of the mystery to be solved.

Students summarize their research on clue cards with illustrations on one side and facts on the other side.

Ellaborate:

Have students create a food chain diagram. This can be done as a class mural of the sea otter/kelp/urchin ecosystem, showing the relationship between organisms.

Evaluation:

Will be done later in the unit.

Sea Otter Story Part 1

On a summer day during the early 1990s, Jim Estes was in his skiff off the island of Shemya, searching for sea otters as he had done many times in the last 20 years. Despite the sometimes terrible weather, the Aleutian Islands were his favorite place in Alaska. He had first come here in the 1970s to study the otters and their ecosystem. He had suspected then that they played a very important role in that ecosystem. Although he now lived in California and taught at the University of California in Santa Cruz, he returned to the Aleutians again and again to continue his study.

When he first came to Alaska, there had been no otters anywhere near this island. They had disappeared from the Aleutian Islands by 1900, except for a few small groups far from Shemya. Sometime in the late 1980s or early 1990s, they had returned.

He stayed close to shore because he knew that otters could only dive and find their food on the bottom in shallow water. He began spotting otters. At the end of the day, when he tallied up all the groups of sea otters that he counted near Shemya, the numbers were relatively low. This is what he expected to find, however, for an area that had only recently been recolonized by the otters.

A few days later, he surveyed the waters around Amchitka, 250 miles to the east in the Rat Islands. Here, he expected to see large numbers of otters as he had in the past, even during the 1970s when he first began to study them. But today he was surprised. Where were all the otters? He made sure he was doing the same type of boat survey he had in the past. Something had changed.

His counts of otters near the islands seemed to confirm what the biologists who worked for the Aleutian Island National Wildlife Refuge had recently observed. In 1992, they had completed an extensive survey by airplane over the entire 500-mile stretch of the Aleutian Islands, and found much smaller numbers of otters compared to the last Aleutian Island-wide survey in 1965.

Here is what they found.The following chart shows information for all of the islands combined.

They also compared all of the otter counts and estimates for Amchitka (the Rat Islands) and Shemya (the Near Islands). This chart shows information for the island groups.

What had happened to all of the otters?

Sea Otter Biology and History in the Aleutian Islands

Although sea otters live in cold ocean waters, they don’t have a layer of fat or blubber like whales, seals, and sea lions. But they have one of the thickest fur coats of any animal, with 1,000,000 hairs to the square inch. By comparison, humans have only 100,000 hairs on their head. In fact, what keeps the otter warm is a double fur coat. The fine underfur next to the body traps heat, and very long guard hairs on top of that keep the underfur dry.

In rocky areas, sea otters prefer to spend most of their time in tall, thick beds of brown seaweed, or kelps. They wrap themselves up in the kelp to help them stay afloat when they rest and sleep. Inside the kelp stand, the waves are much gentler.

Sea otters have a favorite food in rocky areas—sea urchins. The otters dive down to the bottom of the kelp where the urchins are feeding, and they can stay under water for five minutes. They also eat snails and fish.

People harvest sea otters for their fur. The Unangans, some of the first Native people from Asia to reach Alaska, lived for thousands of years in the Aleutian Islands. They made warm, full-length coats, or cloaks, from the warm, luxurious fur of the otters. In 1741, Vitus Bering reached the Aleutian Islands and took sea otter pelts back to Russia. A large fur trade by Russians, Americans, and British killed nearly every sea otter in the Aleutian Islands by the late 1800s. In 1911, however, the sea otters were protected by an international treaty and they began to slowly recolonize the entire chain of islands. Visitors to the Aleutian Islands like to see and photograph the otters.

Sea otters spend a lot of time keeping their fur coat clean. If the fur becomes dirty, the sea otter is no longer waterproof and it will drown. Oil spills are especially dangerous to sea otters because the oil coats the guard hairs. When the otter cleans its fur, it swallows large amount of oil that can make it sick or kill it.

The Producers in the Ecosystem

Only two types of living things in the ocean make food using sunlight. These are called producers. One type is phytoplankton. Huge numbers of phytoplankton, most of them only visible under a microscope, drift with the currents and are food for the zooplankton such as copepods and young urchins.

The second type are the seaweeds, which are large algae. The largest seaweeds grow low in the intertidal zone and extend out into the subtidal zone. These are the kelps, large brown seaweeds that are glued to the rocks with their holdfast. Their long blades float at or near the surface of the water where they get sunlight to make food, which allows them to grow very fast. Their holdfast glue is very strong, and it can keep the huge kelp in one place even when strong currents and waves occur during storms.

Snails and sea urchins eat kelp, and fish, crabs, and many other animals find shelter within the dense kelp stands—called a kelp forest. Like a forest on land, the kelp forest provides food, places to hide, and a calm place away from the force of waves and winds. Many kelps die back in the winter and grow again the following spring. Large amounts of dead kelp are recycled by scavengers, including sea urchins, and decomposers.

Consumers: Marine Invertebrates and Fish in the Kelp Forest

Several types of animals depend on the kelp forest as their habitat. They find shelter there because the many tall blades of the kelp break the force of the waves. Inside the kelp forest, the water is calm and small animals can avoid being washed away by the waves. They also cling to the kelp and find hiding places from the other animals that want to eat them.

Sea urchins and snails eat the kelp, either when it is alive or after it has died back each year. Sea urchins feed at the base of the kelp, and large numbers of urchins can actually cut down a tall kelp. Crabs are the resident scavengers. Young salmon and other small fish that live in schools find shelter in kelp forests.

Consumers: Marine Mammals

Seals, sea lions, and killer whales live year-round in the waters near the Aleutian Islands. They eat fish, including salmon and small fish that live in schools. Gray whales and humpback whales migrate through the major passes in the Aleutian Islands to get to their summer feeding areas in the Bering Sea. These baleen whales eat small fish that live in schools and copepods, a type of zooplankton.

Two types of killer whales are found in these waters. Pods of resident killer whales stay together and stay around the same area and feed on fish, including a lot of salmon. Transient killer whales sometimes move through the area, roaming over long distances and preying on seals and sea lions. They may also prey on gray and humpback whales when they are migrating through the passes between the islands on their way to the Bering Sea.