Name______________

Date________

Answer Key: Sea Otter Case Study

Instructions: This worksheet describes a case study of sea otters, which has been affected by some of the causes of environmental problems that we learned about earlier this week.  We will learn how such problems have an impact on animals and their food webs.  Read the sea otter case study and answer the questions at the end.

History:

On the coast of California during the 1700-1800s, the sea otter was hunted for its sleek and beautiful fur.  Fishermen also hunted these creatures because they believed that the otters were eating too many of the fish they wanted to catch.  This drove sea otters almost to extinction.  Without the sea otters, fishermen saw changes in the ecosystem.  Sea otters eat sea urchins and without the sea otters, the sea urchin population grew very quickly.  Sea urchins also eat kelp.  This mean that the sea urchins ate all the kelp beds which house fish.

What caused the rapid loss of sea otters in California?

Fisherman hunted sea otters for their fur and to “save” fish populations for economic benefits.

What was the effect of the loss of sea otters? Describe the chain reaction.

Sea otters are a keystone species. The loss of sea otters means loss of sea urchins, then kelp beds, then fish populations.

What do you think happened to the fish?

Should be able to predict that fish populations declined because kelp beds did.

History continued:

The fish began to disappear because they no longer could spawn in the kelp beds.  The fish were gone! The fishermen could no longer catch fish because there was no more fish.  In 1911, the International Fur Sea Treaty helped bring back the sea otters, which then help recovered the kelp beds, and the fish population as well.

Describe what happened to the other species when the sea otter was hunted to almost extinction. What is this an example of?

Without sea otters around, the sea urchin population boomed resulting in loss of kelp beds and loss of homes for fish.

This is an example of a trophic cascade.

Draw a picture of the food web that includes the fishermen, sea otters, sea urchins,  kelp bed and fish.

Should have sea otters sea urchins kelp beds fish. Fishermen can be drawn in to both fish and sea otters.