Download CW26 - COMPETITION ON SABLE ISLAND Overview: Sable Island

CW26 - COMPETITION ON SABLE ISLAND
Overview:
Sable Island is a remote island about 180 miles (300 kilometers) east-southeast of Halifax, Nova Scotia.
Operated by a nonprofit group called the Sable Island Preservation Trust, the island has very few human
inhabitants but hosts scientists who come primarily to study wildlife. In part because of its inaccessibility
to humans, the island is an attractive breeding ground for gray and harbor seals, among other animal
species.
The gray seals of Sable Island have been thriving, but harbor seal populations have plummeted in recent
years. Scientists, including those working with National Geographic's Crittercam project, have studied the
seals' mating, lactating, and feeding behaviors in an attempt to find out why this is occurring. They've also
investigated the presence of sharks in the island's offshore waters to learn about patterns of shark
predation on the seals.
Crittercam has helped scientists discover that both gray and harbor seals feed on the same prey—tiny fish
called sand lances. Their feeding behaviors, however, are different. While harbor seals follow schools of
sand lances and eat fish that have strayed from the school, gray seals dig into the sandy ocean floor to find
fish hiding there.
In this lesson, you will discuss the concept of competition in nature and will learn about competition
between the gray seals and harbor seals of Sable Island. You will conclude by illustrating maps of the
island to show the seals' feeding behaviors and the shark's predatory activities, and you’ll write
paragraphs describing their maps.
Step 1
List three examples of competition in nature (between species for food, or to avoid predators)
1.
2.
3.
What characteristics have animals developed to maximize their potential to successfully compete in an
ecosystem? For example, animals with sharp teeth or claws are often at an advantage over animals
without such predatory or defensive assets.
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You will be focusing on Sable Island, a remote island off the eastern Canadian coast where two seal
species compete against each other in the same ecosystem.
Step 2:
Navigate to: National Geographic's Xpeditions Atlas. Ask them to select North America, Canada, and
Nova Scotia. On the Nova Scotia map, they can find Sable Island to the southeast of Halifax. How far is
Sable Island from Halifax?
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Look at these pictures of Sable Island and its seals. The island is an excellent seal habitat, particularly for
gray and harbor seals. Check out this site too: Sable Island: An Introduction
Step 3:
Read this Introduction to Sable Island.
Click on the left-hand link "Gray and Harbor Seals" and read this information. Answer the following
questions:

Which seals are thriving, and which are having trouble?

When do gray and harbor seals mate and give birth?
Now click the left-hand link "Research" and look at the 2nd picture. This gray seal has a Crittercam on its
back. While this page describes research on gray and harbor seal mating, scientists have also used
Crittercam to study the seals' eating habits and to learn about how these two seal species compete with
each other in their ecosystem.
Step 4:
Some IMPORTANT things scientists have found:


Sharks, including the great white shark, like to eat both species of seal. Harbor seal pups and
adults are smaller than gray seal pups and adults and are therefore easier for the sharks to
catch and eat.
Gray seals and harbor seals both eat sand lances, tiny fish that live just off the shores of Sable
Island. To catch these fish, gray seals swim close to the ocean floor and dig their snouts into
the sand to find hiding fish. Harbor seals, on the other hand, follow schools of sand lances
and catch fish that wander from the school.
Discuss with your partner and list below the ways that each of the above bullets relates to competition
between gray and harbor seals on Sable Island.
 Bullet 1 - Sharks eat both types of seal:

Bullet 2 – Gray seals and harbor seals both eat sand lances:
Now answer the following questions:

How does the presence of sharks affect competition between the seals?

How are the seals competing for food? Which food-seeking strategy seems to be the most
effective?