Searching for Sounds in the Sea

Engagement

20-30 Minutes

Ask students to listen carefully to several different underwater sounds and try to determine if they are animal or non-animal sounds. Choose a variety so students hear some natural event sounds, marine mammal sounds, and some non-natural, such as a boat or ship. If possible, do not show the web page to the students. They should just listen. Keep a list of which sounds you played for the students. You will visit these same sounds later in the investigation.

Discuss experiences they might have had with sound underwater. Do they think things sound differently underwater than they do on land? If so, why?
Ask students to brainstorm reasons why scientists might want to listen to underwater sounds? What kinds of information can they obtain? How are the sounds they listen to recorded under water?

Show students theSounds in the Sea PowerPoint, part 1 . Discuss the various methods of studying whales on slides 4-6. To view the notes for the slides, choose View…Notes Page. Notes are also provided for the slides as a separate note file . Spend time with slides 7-16, providing explanation about sound and how it travels.
You might review with students what they learned about sound when they learned about sonar in Investigation 3.
For more information, visit the Science of Sound in the Sea

Tell students that researchers are listening for one particular whale in the Bering Sea: the North Pacific right whale, and share the following information:

The right whale is one of the most endangered whales in the world. Few of these whales remain in the Atlantic or the southern hemisphere and the North Pacific right whale (Eubalaena japonica) is extremely rare. There may be fewer than a hundred of these animals in the waters offshore of western Alaska and a few hundred closer to Siberia and Japan. Scientists are working hard to locate these whales and to get an accurate estimate of their population. They are developing studies to collect data on this mysterious and critically endangered whale. The data will help them to decide how they can assist in the whales’ survival.

LisaShow Sounds in the Sea PowerPoint, part 2 and Sounds in the Sea PowerPoint, part 3 . These slides provide information about the right whale, and explain how Lisa Munger is studying the right whale using acoustics.

Exploration​

50-55 Minutes

Play a variety of whale sounds. Ask students to listen carefully to how they might be similar and how they might be different.

Activity: On the Trail of a Whale. This activity was adapted from On the Trail of a Whale
Introduce the activity by discussing the following with students:

We can often tell who is talking without even seeing them. Each individual person sounds a little different. They may talk a little higher or a little lower (different frequency), or they may talk faster or slower, or they may have an accent. So without even looking, we can figure out who is talking. The same thing is true about most whales and dolphins. Many species have vocalizations that only they make, and some populations even have “accents” that distinguish them from other populations of the same species (e.g., killer whales, humpback whales).

We can tell where someone who is talking is located without looking. This is because we have two ears – two separate sound receivers. When someone is talking, each ear hears or receives the sound at a different time because our ears are a different distance away from the person talking (the difference being the size of your head). Scientists call this time difference the time-of-arrival difference. Our brain turns that time difference into a distance and direction. This gets complicated when a sound comes from directly above your head because then the sound reaches your ears at the same time. To prevent that problem, you’d need at least three sound receivers. Does anyone have three ears? I hope not! However, scientists are using underwater listening stations that the U.S. Navy placed over much of the North Pacific and North Atlantic. If the scientists are lucky, they may be able to hear whales vocalizing on three or more sound receivers. They would then use the same process to locate the vocalizing whale as we do to find the talking person. Since the vocalization arrives at each receiver at a different time, the time-of-arrival difference between each pair of sound receivers can be calculated. Scientists can then draw lines (hyperboles) that represent equal time differences between each pair of hydrophones.
Where the lines cross is their best guess at where the whale was when it vocalized. “X”
does mark the spot!

For this activity, you will need a large area such as a playground, field, or large gymnasium. If possible, create an outline of the Bering Sea using tape, rope, cone markers, etc. Then use tape, string or rope to designate latitude and longitude lines. See the Bering Sea Map for shapes and latitude and longitude. The minimum space should be 5 feet for each 10 degrees of latitude or longitude. The actual Bering Sea is very large, so be sure you tell students that the “Bering Sea” represented on the floor or playground is not true to size, and is just a representation to use for this activity.

1. Ask students the following questions: If you were a marine biologist researching whales, how could you distinguish individual whales from each other? How could you follow an individual whale to observe its behaviors? And don’t forget that whales dive and are only at the sea surface about 20% of the time!

Students may have some quick answers, but make sure they break down the problem – first they must find the animal they are looking for, then they must follow that individual animal throughout its habitats, day and night.

Possible answers:

Watch it as it comes to the surface for a breath. [Teacher: But then what do you do when it dives and you can’t see it anymore? And how do you know that the next whale you see is the same one you saw earlier?]
You could take pictures of the whale as it surfaces – some whales have distinct markings that allow scientists to differentiate individual animals. [But again, you need to guess where the animal will surface next, and then accurately identify the whale each time it surfaces. Plus, this requires lots of time on the ocean in a boat – very expensive. Any other ideas?]
If the students do not come up with sound/vocalizations on their own, lead them down that path with the following discussion:

Okay, let’s break down the problem. We’ve determined that we need to have some way of keeping track of individual animals while they dive and when they are at the surface. So if we can’t see them, what other senses do we have available to us? [Senses: taste, touch, sight, smell, sound]. That’s right: we could use sound. Use this question to prepare the students for the second part of the activity where they will be researchers trying to track 5 individual whales.

After discussing their answers and ideas, tell them that they are going to become researchers, looking for North Pacific right whales. You might want to let them listen to the sound of a right whale from the site you previously visited for whale sounds. They need to determine how many sound receivers to use and where to place them in the representative “Bering Sea” on the floor or playground, to track 5 individual whales. They can ask you questions to help them design this task.
Some questions the students may ask are:

• Where can the whales move? Answer: anywhere within the marked-out area
• How far do the receivers detect whales? Answer: 100 km away! 100 km = ~60 nautical miles = 1 degree of latitude. That is unique to the southern Bering Sea shelf because it is so flat and shallow for hundreds of kilometers– it traps sound and channels it for long distances.

Show the master map on an overhead and allow students to decide how many sound receivers they want to place in the water. Let them also decide where they should be located. On the map, mark the locations of the sound receivers by numbering them (e.g., SR1, SR2, etc.).

2. Designate five students to be the whales, and five students to be the whale trackers. Choose students who will act as Sound Receivers. Give them each a nametag and have them go to their designated spots. They can find their spots on the floor or ground, by finding the latitude and longitude on the map, then again on the floor area. Each Whale should be assigned a unique vocalization and a number. The Whale will move around the “Bering Sea” and quietly make their unique vocalization. The Sound Receivers should be blindfolded or keep their eyes closed. Their task is to track individual whales. When they hear a Whale, they should point in the direction of the Whale with one hand and note the Whale Number by raising their other arm and listing the Whale Number with their fingers.

3. If three or more Sound Receivers are pointing at the same Whale and identifying the correct Whale Number, that Whale’s Whale Tracker stops his/her Whale and records the Whale’s position and which Sound Receivers detected the Whale on the Right Whale Data Sheet. Once the data is recorded, the Whale continues moving around.

4. The Whales and Whale Trackers continue playing until each Whale has been detected at five differentright whale locations. After the activity is completed, the Whale Trackers should plot the detection locations of their Whale on the map.

Extensions:

1. Have extra students chatter in background (corresponds to an increase in ambient noise in the ocean).
2. Have an extra student be a tanker, an earthquake, etc. that travels/occurs throughout the North Pacific – how much harder is it for the receivers to hear the whales?
3. Have the whales vocalize less often.

Explanation

30-40 Minutes

Use the following questions to help students reflect on the “On the Trail of a Whale” activity:

1. How effective was this method in localizing Whales?
2. What difficulties would scientists encounter using this method?
3. What can scientists learn by tracking whales?

Remind students that in addition to listening to the sounds the whales make, scientists can also see the sounds. A spectrogram shows the energy and pitch of a sound and is something scientists can see. They can distinguish different species of whales by listening to the sounds and looking at the spectrograms. Introduce students to spectrograms of underwater sounds using the following resources:

How to read a spectrogram

Using the same sounds the students listened to in the first part of this investigation, ask students to try to match sounds and the corresponding spectrogram. Spectrograms for sounds listened to, and Spectrogram Key.

Ask students how they think looking at spectrograms in addition to just listening to the sounds might help scientists learn about the right whale?

Extension

You may want to discuss impacts of underwater sounds on both animals and scientists. Increased boat traffic, Navy SONAR, seismic exploration, etc. may impact the ability of scientists to hear natural sounds and impact the animals themselves. Students may research the seismic exploration in the Bering Sea and how it might relate to the right whale research and recovery.

Ocean Mammal Institute: Underwater Fact Sheets
See the Sea: Noise Pollution
National Geographic: U.S. Navy Sonar May Harm Killer Whales, Expert Says
National Geographic: Military Sonar May Give Whales the Bends, Study Says
Fisheries and Oceans Canada: Does Seismic Exploration Harm Whales and Fish?

Elaboration

30-40 Minutes

Have students create a 3-D map showing the topography of the ocean floor using Excel and the instructions provided. It might be helpful to demonstrate with the sample data provided excel chart.

Ask students if they can come up with other ideas of gathering the same data they did with the sampling tool.

Evaluation

15 Minutes

Ask students to respond to the following questions in their science notebooks.

Curricular Connections

Math: graphing and data analysis

Social Studies: Whaling History, Alaska geography, subsistence