Weddell Seal Population Count Activity
By Jean Pennycook
Knowing 'how many' of any animal is one of the first questions researchers seek to answer when they study a population. Getting that answer is not always easy. If you wanted to know how many robins were in your county how would you do that? If you wanted to know how many deer were in the forest, what would be your procedure? How about whales in the ocean? Unlike plants that don't move, each specie of animal provides its own challenges when it comes to population counts.
Scientists have been monitoring the Weddell seal population in the McMurdo Sound area near Ross Island, Antarctica for several decades. Here are some of the questions they have asked over the years:
How many seals are there?
Are their number increasing or decreasing?
How many had pups this year?
What would cause one group of seals to increase in numbers, while another one declines?
Do the seals move around or stay in the same area?
How many are in the water compared to on the ice?
How do we know we counted them all?
If you would like to read about research on seals here are some websites to go to.
There are many factors to consider both biotic (living factors like amount of food, predators, diseases), and abiotic (non living factors, weather, ice conditions) when formulating answers. It takes creativity, long term commitment to the project and many long hours working around and near the seals to make a statement with supporting evidence about how many seals there are, or if the population is changing over time.
Many people think seals are easy to count. There is no place for them to hide when they are out of the water. They are not afraid of people so don't run away, and if they are with a pup, the adult stays in the same location for several days. However it is not that easy. There are seals all over the place as new cracks in the ice create new suitable locations for feeding and many seals move to these new areas. Counting individuals is difficult unless they are tagged because it's hard to know if we counted this one yesterday or not. To solve these problem scientists are using satellite images that can take a picture of a large area at one moment in time. They then can count them using a computer.
In this activity, we ask for your help in counting the seals using satellite images. Scientists need all the help they can in creating an accurate count. We hope you will take the time to join our team and help do the counting. However, even that is not always easy. Satellite images are from a long way up, many seals look like rocks, how do we know our count is accurate? To help with accuracy researchers add a process called ground-truthing, which means they also do a ground count and compare it with the satellite photo. They do it on the same day and time as the photo which doubles the count and helps us with the confidence level of the real number. But we can't be everywhere all the time.
Part 1 Getting started.
Go to the full activity (http://z.umn.edu/seals) to see pictures of groups of seals which are easy to count. To make a complete count of the population we need to find all the groups in the McMurdo Sound region. This would mean traveling by snow machine all over the sea ice to look for groups. It is fun, but takes a long time and many days are very cold, windy and hard to see. In addition, researchers would like to minimize the use of motorized vehicles in Antarctica to help preserve the pristine environment these animals enjoy.
Go to the full activity (http://z.umn.edu/seals) to see a map of the study area. It is part of McMurdo Sound called Erebus Bay. You can see it is a large place and impossible to be everywhere at once.
Taking a picture with a satellite is helpful but there are still some problems.
We can match what is in the satellite photo with what we saw on the ground which is called ground truthing but we cannot do this every time.
What can scientists do to make sure they have the most accurate counts? Discuss with your groups and come up with some ideas.
Part 2 Seal Counting Tutorial. full tutorial with images can be found here. http://z.umn.edu/seals (You can also download the Powerpoint Tutorial)
After you complete the tutorial you are now ready to do the real counts. Remember, we do not know how many seals are here, your numbers are as good as ours. The range of counts for Picture #2 when 5 people counted was 61-66. What did you get? We need help with this count as the more confirming counts we receive, the greater our confidence is that the number we provide in our report is accurate.
Part 3. Seal Counts for Erebus Bay Download the images here: http://z.umn.edu/seals. Every season new images will be uploaded for a long term study by your classroom.
Divide the photos in file 'A' between members of your group.
Use the computer or any system you would like to count the seals. Create a table for your data recording the photo number and the counts. If more than one person counts the same photo make sure you list all the numbers for comparison and decide on one number to assign for that photo.
Add up the numbers from all the photos to make a claim about the number of seals in the McMurdo Sound region a specific date. This number represents all the seals we can see.
What percent of the seals in the total population are the seals in the pictures? In other words of all the seals in the sound, what % are on the ice so we can count them at any given time. What procedure would you do to find out where the others are and how many there are?
These are questions researchers ask themselves. There is no right or wrong answer, only educated guesses. What do you think? Record your thoughts in your science notebook and discuss them with your group or class.
Part 4 Annual changes in populations.
In photo file 'B' and 'C' are images of the same locations as file 'A' only one month later and two months later. Make your counts using the same system you used in Part 2.
How has the population changed?
Why do you think there are more/less seals now than before?
Which set of photos gives us a more accurate count of the total population.
What does this tell you about taking accurate population counts of animals.
Part 5. Changes over time.
The photos in 'D' and 'E' are photos of the same locations and time as file 'B' only one year ago and four years ago.
Make your counts using the same system you used in Part 2.
How has the population changed over this time frame?
Why do you think there are more/less seals now than before?
Describe some factors, biotic or abiotic, that would cause the population to change.
If you wanted to find out what was causing the population to change over time, what information would you collect? Make a list in your notebook. How would the information help you make a claim about the change in the seal population of Erebus Bay. For instance you may want to know how many pups were born in each year, that way you could estimate an increase in the population.
Part 6. Conclusion.
Thank you for helping us count the seals in these pictures. Send your data to the email below in the form of a table or chart. Come back next year when there will be a new set of pictures to count.
We would also like to know your answers to these questions.
Was counting the seals easy or hard?
What system did you use to count the seals in the photos?
Do you think being a seal researcher would be a fun career?
Thank you for taking part in our research. Send your numbers to this email: firstname.lastname@example.org