Lesson E10: Changing Populations in Water

Key Ideas     Unit Checklist

  Video Lesson

How do aquatic populations indicate ecosystem health? Watch this video to learn more about how aquatic populations change over time.

 
 

  Lesson E10: Changing Populations in Water


Figure E.3.10.1 – Whales are large aquatic mammals.

Figure E.3.10.2 – Whale hunting was widespread in the 1800’s.


Figure E.3.10.3 – People hunted whales for oil and baleen.
Reading and Materials for This Lesson

Science in Action 8
Reading: Pages 381–385

Materials:
No additional materials needed for this lesson.

Hunting Whales

People have hunted whales for thousands of years. For example, the Inuit in northern Canada survived by whale hunting. They ate whale meat, carved whalebones into spear tips, and wove whale baleen into baskets and fishing line.

Commercial whaling by Europeans started in the 1600s. Europeans originally hunted whales for meat. However, by the 1800s, whales were increasingly hunted for their oil instead. Whale blubber fat can be boiled to obtain a clean-burning oil. Before the invention of electricity, wealthy people burned whale oil in lamps to produce light.

Whale hunting by Indigenous people maintained sustainable whale populations. After commercial whale hunting started, whale populations in the Atlantic Ocean started to drop. With the invention of fast-travelling steamships and guns, whaling expanded to the Pacific and Arctic Oceans, further decreasing whale populations. When fossil fuels and electricity were adopted in the 1900s, whaling nearly stopped, but whales had already become an endangered species.

Today there is an international ban on whaling. Despite international objections, the countries of Iceland, Norway, and Japan still commercially hunt whales for meat. It is also acceptable and permitted for Aboriginal people to carry out traditional, sustainable whale hunts.

 Watch More

Whaling

Watch this video to learn more about the controversial practice of whaling that still happens today.

 
 
Figure E.3.10.4 – People fished cod for 500 years off the coast of Newfoundland.
Figure E.3.10.5 – Codfish has a mild flavour which people enjoy eating.

Catching Too Many Fish

Figure E.3.10.6 – Overfishing led to a collapse of the North Atlantic cod population.
Overfishing happens when people catch more fish than a fish population can replace through reproduction. Overfishing decreases fish populations.

Modern fishing methods contribute to overfishing. Trawler boats drag large nets along the seafloor, which scoop up everything in their path. Any undesired fish and organisms caught by the net are thrown back into the ocean, and might be killed in the process. Sonar, an underwater mapping technology based on sound waves, allows boats to quickly find large schools of fish.

These advances in fishing technology allow fishers to catch more fish. However, overfishing has several negative consequences. Overfishing disrupts ecosystem food chains. If fish populations disappear, fishers lose their jobs. Overfishing threatens a main food source of many people around the world.

Overfishing had dramatic consequences in the Atlantic Canada cod fishery. People fished cod off the coast of Newfoundland for 500 years, but better fishing technologies led to a dramatic increase in the number of fish caught after 1950. By 1992, the cod population decreased so much that the Canadian government banned cod fishing. This put many people in the Maritime provinces out of work.

 Watch More

Overfishing

Watch this video to learn more about the current state of fish populations around the world.

 
 
 
 
Overfishing is a threat to populations of all fish species. This video explains more.

 
 
Figure E.3.10.7 – Fish stocks are born and raised in hatcheries.
Figure E.3.10.8 – Fish stocks are released into some lakes and rivers.

Fish Stocking

Figure E.3.10.9 – The Cold Lake fish hatchery is helping to restock walleye in Alberta lakes.

Many people like to fish for catch-and-release sport, or for food. Fish stocking is a practice that supplies rivers, lakes, and ponds with adult fish for sport fishing. Fish stocking increases the population of certain fish species in waterways.

Fish stocks in rivers or lakes are often non-native species. Scientists do careful studies to make sure that an introduced fish species won’t disrupt an ecosystem. Stock fish are raised in hatcheries, and released into waterways as adults. Alberta has many lakes and ponds stocked primarily with rainbow trout fish. Rainbow trout are native to the Athabasca river system in northern Alberta, but have been introduced to other aquatic areas in Alberta.

Fish stocking can also be used to increase native fish populations. Walleye is a species of fish native to Alberta that people enjoy catching and eating. The Cold Lake Hatchery hatches and rears walleye, which are stocked into some Alberta lakes to supplement fish populations.

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Alberta Fish Stocks

Watch this video to learn more about how Alberta lakes and ponds are stocked with fish.

 
 
 
 
Watch this video to learn more about the Cold Lake fish hatchery.

 
 

  Connections 

Figure E.3.10.10 – Zebra mussels are native to the Black Sea in Eurasia.
Figure E.3.10.11 – Asian carp threaten the Great Lakes.

Connections – Environment
>> Invasive Aquatic Species
Invasive species are non-native organisms that are introduced to an ecosystem. With no natural predators, invasive species populations can grow rapidly and take over an ecosystem.

Several invasive species threaten aquatic ecosystems in Canada. Zebra and quagga mussels were introduced into North America in the late 1980s by ocean ships. These mussels have spread all over freshwater lakes in Ontario, Quebec, and Manitoba. Their large populations consume lots of plankton, reducing the amount available for native species. Zebra and quagga mussels attach to surfaces like rocks, where they can cut swimmers’ feet. They also clog water pipes.

As of 2016, zebra and quagga mussels have not spread into Saskatchewan, Alberta, and British Columbia. These provinces are taking measures to prevent the spread of zebra and quagga mussels. Cleaning, draining, and drying boats is the best way to prevent spreading mussels. Mandatory boat inspections on highways are helping make sure that boats are free of mussels before they enter lakes.

Another invasive species that threatens Canadian waterways is the Asian carp. In the 1970s, this fish was introduced from China into the United States by farmers. During floods, some Asian carp escaped into the Mississippi River and started reproducing. Asian carp are huge freshwater fish – they can grow to be 40 kg! These large fish eat lots of plankton, which creates a food shortage for native fish. A few Asian carp have recently been found in the Great Lakes, but there is not yet any evidence that they are reproducing in great numbers.

Figure E.3.10.12 – Zebra mussels have invaded eastern Canadian rivers and lakes.
Figure E.3.10.13 – Quagga mussels cover a shipwreck in Lake Huron.

 Watch More

Invasive Aquatic Species

Watch this video to learn how boat owners can help stop the spread of freshwater invasive species.

 
 
 
 
Watch this video to learn about the Asian carp threat in the Great Lakes.

 
 
 
 
Watch this video to learn about boat inspections and the Alberta Aquatic Invasive Species Program (AESRD).

 
 

 Think β€’ Interpret β€’ Decide 

Figure E.3.10.14 – A typical food chain in Lake Winnipeg: Plankton - Cisco - Walleye.
Figure E.3.10.15 – Zebra mussels feed on plankton. They are transported between lakes on boats.

Lake Winnipeg Zebra Mussels

Lake Winnipeg is a large lake located in Manitoba. This ecosystem contains many food chains. Figure E.3.10.14 is an example of one: Plankton β†’ Cisco β†’ Walleye

In 2013, zebra mussels were discovered in Lake Winnipeg. Zebra mussels feed on plankton. Scientists monitor the populations of different species in Lake Winnipeg. An experiment counting populations of different species in Lake Winnipeg is summarized on the following graph.


 
Questions
After you have finished examining the food chain and graph, carefully consider the following questions. Then, type or write your answers. When you have your answers, click the questions for feedback.

The scientists observed that after 2013, the zebra mussel population in Lake Winnipeg increased. The zebra mussel population increase coincided with a decrease in cisco and walleye populations in Lake Winnipeg.
Walleye feed on cisco, and cisco feed on plankton. A healthy population of plankton is required for cisco to survive. In turn, a healthy population of cisco provides a food source for walleye. When zebra mussels entered Lake Winnipeg, they started feeding on plankton, which reduced the available food source for the cisco population.
Once they were introduced to Lake Winnipeg, the population of zebra mussels rapidly increased. Zebra mussels fed on plankton, which meant that less cisco survived, because their food source was reduced. The cisco population decreased, and because walleye eat cisco, this caused the walleye population to decrease as well.


Coral Reefs

Corals are small aquatic animals. Corals grow hard exoskeletons that provide a habitat for many other aquatic species. 25 percent of all ocean species live in coral reefs.

Due to climate change and other human activities, coral populations are decreasing. As the size of coral reefs decreases, so do the populations of other species.

Click here to Explore with Elsie about changing coral reef populations.



  Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.

Unit E Lesson 10 Self-Check

Instructions


Complete the following 6 steps. Don't skip steps – if you do them in order, you will confirm your understanding of this lesson and create a study bank for the future.

  1. DOWNLOAD the self-check quiz by clicking here.

  2. ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.

  3. COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.

  4. REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.

  5. SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.

  6. CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!

Be a Self-Check

Superhero!



Self-Check Quiz Answers

Click each of the suggested answers below, and carefully compare your answers to the suggested answers.

If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.

Several seasons with low precipitation does not allow puddles of standing water to form. This creates less places for mosquitoes to lay eggs and hatch. Frogs eat mosquitoes, and less hatching mosquitoes reduces a main frog food source. As a result, less frogs can survive and the frog population decreases.
Organisms such as fish require oxygen for cellular respiration. Less dissolved oxygen in the ocean would reduce the number of organisms that could survive in the ocean. Less dissolved oxygen would reduce populations of aquatic organisms.
Zebra mussels are an invasive species to North America. The Rideau River habitat provided plankton food for the mussels, causing their population to explode. A lack of natural predators did not help reduce the zebra mussel population.
The population of underwater plants in the lake would decrease because surface algae blocks sunlight that the plants need to make their food by photosynthesis.
The cod fishery collapse is a long term population change. The population did not return to its original levels over a few months or a year. Nearly 25 years later, the cod populations have only recovered a small amount compared to their original levels.