Unlike Other Marine Mammals, the Sea Otter Does Not Have a Layer of Blubber (Fat) to Help

NAME ______PER ______DATE ______

THE KELP FOREST COMMUNITY

MATERIALS: Colored pencils

BACKGROUND:

Unlike other marine mammals, the sea otter (Enhydra lutris) does not have a layer of blubber (fat) to help keep it warm. If an otter's fur gets coated with oil or any other substance, the otter can easily die from cold and exposure.

The sea otter is the largest member of the weasel family. Southern sea otters typically reach about four feet in length. Females average 45 pounds, while males average 65 pounds. Alaskan or northern sea otters can reach up to 100 pounds.

Sea otters are found in the shallow coastal waters of the northern Pacific. Their historic range stretched from the Kurile Islands of Japan, along the coast of Siberia and the Aleutian Chain and down the Alaska and British Columbia coast to Baja California.

Sea otters are one of the only mammals other than primates known to use tools. Otters use small rocks or other shellfish to pry prey from rocks and to hammer or pry open their food. They can dive up to 180 feet when foraging for food. These intelligent animals live in shallow water and prefer kelp forests, sometimes anchoring themselves in one place by wrapping strands of kelp around their bodies while they rest.

Sea otters are a keystone species in the kelp forest ecosystem, eating sea urchins, clams, snails, sea stars, squid, octopuses and abalone. When present in healthy numbers, they keep sea urchin populations in check. When sea otters decline, however, urchin numbers explode—as does their grazing pressure on bull kelp. The urchins chew off the attachments keeping bull kelp in place, causing them to die and float away. This decimates kelp beds and sets off a chain reaction that depletes the food supply for other marine animals and in turn causes their decline. Urchin Bed - Sea otters prey on sea urchins, keeping their populations in Recent data collected by both the Fish & Wildlife Service balance. and the U.S. Geological Survey show that the sea otter population is declining.

The decline may be due to increased predation by killer whales. Killer whales normally don't eat sea otters because they are too small. The whale's usual food source, Steller sea lions and harbor seals, have declined drastically in recent years, however, causing the whales to shift to sea otters. PROCEDURE: a. Highlight in each population the largest value. This is the peak population size. b. Calculate the percent by dividing the value given by the peak population size. c. Graph each population as a percent. The graph is already set up for you. Use a different color pencil for each population and make a legend.

POPULATION SIZE YEAR SEA URCHINS SEA OTTERS Pounds (millions) Percent Number (x 1000) Percent 1972 1 75 1976 0.5 - - 1977 1.5 - - 1979 1 - - 1980 0.5 - - 1981 0.5 - - 1982 0.5 - - 1985 2.5 - - 1986 10 - - 1987 24 - - 1988 31 - - 1989 27 - - 1990 18 - - 1991 16 - - 1992 12 30 1994 8 28 1995 6 26 1996 6 - - 1997 5 24.5 1998 3 - - 1999 3 24 2000 5 22.5 2001 4 - - 2002 6 - - 2003 2 - - 2004 1 6 Change in Population of Sea Otters and Sea Urchins in California

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Kelp Bed Canopy Loss in Ventura and Los Angeles Counties )

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o 0 P 1905 1925 1945 1965 1985 2005 Time (years) QUESTIONS :

1. What is a keystone species?

2. In the kelp forest, what is the keystone species? What does it eat?

3. What organism feeds primarily on kelp?

4. What is affecting the kelp population rate of growth?

5. What controls the size of the sea otter population?

6. Marine biologists are trying to farm (grow) kelp to increase the amount of kelp. a. What would you expect to see happen to the sea urchin population? Why?

b. The sea otter population? Why?

7. Is the sea otter population increasing today? What’s affecting the sea otter population? Explain.

8. Why do you think there was a spike in the sea urchin population in the late 80s and early 90s?

9. Why do you suppose the population of sea urchins is declining even though their predators (sea otters) are declining?

10. What recommendations would you make to help save the kelp forests in California?

11. Create a food chain for the kelp forest community. Be sure to use the following organisms: fish, kelp, sea urchin, killer whale, and sea otter.