Echolocation is the ability to orient by transmitting sound and receiving echoes from objects in the environment. As a result of a Marco-Polo type activity and subsequent lesson, students learn basic concepts of echolocation. They use these concepts to understand how dolphins use echolocation to locate prey, escape predators, navigate their environment, such as avoiding gillnets set by commercial fishing vessels. Students will also learn that dolphin sounds are vibrations created by vocal organs, and that sound is a type of wave or signal that carries energy and information especially in the dolphin's case. Students will learn that a dolphin's sense of hearing is highly enhanced and better than that of human hearing. Students will also be introduced to the concept of bycatch. Students will learn what happens to animals caught through bycatch and why.

After learning how echolocation works, students discuss how net designs can be made easier for dolphins to "see" using echolocation and therefore less likely for dolphins to entangle themselves in. Engineers also borrow concepts such as echolocation from nature. For instance, sonar on submarines is simply a type of echolocation Dolphin Echolocation Bycatch Sound Marine Mammals Food Chain Ecosystem Knowledge from participating in the activity Basic knowledge of a food chain and energy pyramid (for 7th and 8th graders) Very basic knowledge about the human sense of hearing and the nervous system Student should be able to define "echolocation" and list three benefits for the dolphin species. Students should be able to state that dolphins have a better sense of hearing than humans Students should be able to define all lesson key words and be able to make statements in a discussion that relate the keywords to dolphins and their behaviors in the ecosystem. Students should be able to explain why dolphins need their echolocation abilities especially when hunting deep below the ocean's surface. Students should be able to reply that dolphins are mammals and not fish, and give at least one reason why. Students should be able to define by-catch and explain what happens to the animals affected. Students should be able to explain how dolphins can use echolocation to avoid nets. Students will be able to discuss how nets can be better engineered to protect dolphins from bycatch by taking advantage of echolocation. If there is access to the video, "In the Wild--Dolphins with Robin Williams", produced by PBS, this is a great way to start off the lesson on dolphins. This is an entertaining and informative video where Robin Williams attempts to communicate with dolphins in captivity in the Bahamas and Hawaii. Also, you can motivate the students by asking the question, "How do you think dolphins perceive nets?" and then follow up with a discussion of echolocation and how dolphins can track objects and their surfaces by using clicking sounds and hearing how they bounce off of another object. After the activity, perhaps some time later, have the students discuss the activity. Use the discussion questions provided in the attachment section to help spur the curiosity of the students and their involvement in the discussion. Since the students most likely enjoyed the activity they will be excited and likely have a lot they want to share with the rest of the class. Use the discussion questions provided as a guide to keep the discussion educational and related to the subject at hand. During the discussion, allow the students to discuss their answers and theories without giving out the correct answers just yet. Instead respond to the students by asking related questions that get the students thinking even more! After the discussion (allow 15-20 min), clear up any misconceptions students made in their responses to discussion questions. Be sure to point out that the activity or game played was only a simulation of how echolocation works and doesn't directly show what actually happens in real life. For instance, in the game the dolphin sends a signal and the objects, be it fish or rock, respond by sending a signal back to the dolphin. Students may get confused and think that the fish actually generated the signal that the dolphin receives and interprets, when in reality the sound wave simply bounces off the fish and the fish has no clue that it is on the dolphins "radar screen" at all. Be sure to clear up these misconceptions. Next, create and show a transparency of the dolphin's anatomy labeling the features in the head that are key to its echolocation ability. Using the echolocation diagram and dolphin anatomy attachments can work well. If possible (esp. for a 7th grade class), compare this diagram with a diagram showing the anatomy of the human ear and discuss differences in functions. Be sure to explain the functions of features like the Nasal sacs, Melon, Panbone (or lower jaw), etc. Also discuss how the swim bladder of fish and other aquatic creatures is a hollow organ that produces the main echo during echolocation. Following this explanation, ask the students why they think it might be harder to receive an echo from a fishing net. Close this brief discussion by defining by-catch and talking about its negative implications for the dolphin species (possible endangerment/extinction). A misconception the students may make during this discussion is that the nets do not actually catch fish but only dolphins (which is what happened in the game) which may confuse the true concept of by-catch. Let them know that in reality the nets are meant to catch fish but also can catch dolphins in the process. Before giving out the worksheet, if time permits attempt to lecture or discuss the following topics. Students should already have some preliminary knowledge on topics like food chains and the human senses: Predator-prey relationships. What eats what? Classification of the dolphin (Mammal vs. Fish). Other detection techniques of organisms (i.e. sight, smell, sound, taste, feel) Frequency (faster vibrations = higher frequency, vice versa); sounds with different frequencies will come from different objects during echolocation. Density (dolphins can roughly determine the density of objects during echolocation; density=mass/volume). Echolocation: the ability to orient by transmitting sound and receiving echoes from objects in the environment. Frequency (vibrations per second or Hz) Wavelength (lambda, meters) Sound pressure level (dB or decibels) Wavelength = speed of sound(meters/second) / frequency Humans can hear from 20 to 20,000 Hz Ultrasonic > 20 kHz Infrasonic < 20 Hz Attenuation is the dissipation of signal strength with distance (less sound intensity the further away) Effects of wavelength - high frequencies/short wavelengths attenuate rapidly in water. Low frequency/long wavelength sound waves travel farther in water with less attenuation. Echolocation is comprised of three distinct processes: 1) Sound production, 2) Sound reception 3) Signal processing The Dolphin auditory nerve has twice the amount of nerve fibers as the human auditory nerve. Source of Echolocation Signals (controversial-need more experiments to confirm): A. Larynx (Purves & colleagues) B. Nasal Sacs (Norris & colleagues). "The dolphin is able to generate sound in the form of clicks, within its nasal sacs, situated behind the melon. The frequency of this click is higher than that of the sounds used for communication and differs between species. The melon acts as a lens that focuses the sound into a narrow beam that is projected in front of the animal. When the sound strikes an object, some of the energy of the sound wave is reflected back towards the dolphin. It would appear that the panbone in the dolphin's lower jaw receives the echo, and the fatty tissue behind it transmits the sound to the middle ear and hence to the brain. It has recently been suggested that the teeth of the dolphin, and the mandibular nerve that runs through the jawbone may transmit additional information to the dolphin's brain. As soon as an echo is received, the dolphin generates another click. The time lapse between click and echo enables the dolphin to evaluate the distance between it and the object; the varying strength of the signal as it is received on the two sides of the dolphin's head enable it to evaluate direction. By continuously emitting clicks and receiving echoes in this way, the dolphin can track objects and hone in on them. The echolocation system of the dolphin is extremely sensitive and complex. Using only its acoustic senses, a bottlenose dolphin can discriminate between practically identical objects that differ by ten percent or less in volume or surface area. It can do this in a noisy environment, can whistle and echolocate at the same time, and echolocate on near and distant targets simultaneously, feats that leave human sonar experts gasping." http://www.inkokomo.com/dolphin/echolocation.html The sonar of dolphins may be the most sophisticated of all sonar systems, biological or man-made, in shallow waters and for short ranges. The Atlantic bottlenose dolphin emit short-duration (50--70 (microseconds), high-frequency (120--140 kHz), broadband (40--50 kHz) echolocation signals with peak-to-peak amplitudes up to 228 dB. The type of signals used by dolphins play a significant role in their sonar discrimination capabilities. They have been observed detecting, classifying, and retrieving prey that is buried in sandy bottom up to a depth of about 0.3 m. In addition, controlled echolocation experiments have shown that dolphins can discriminate wall thickness, material composition, shape, and size of targets. Gillnets are fishing nets made of monofilament line, a translucent plastic material. Dolphins have trouble seeing these nets in the water and have to use echolocation to detect them. Larger mesh nets (nets with bigger squares of monofilament) are more difficult to detect because there is less monofilament in the nets (i.e. larger holes). We don't know why dolphins become entangled. One hypothesis is that dolphins mistakenly blunder into these nets because they aren't paying attention to where they are going; another hypothesis is that the dolphins get fish out of the nets and become entangled in the process. In order to reduce bycatch (catching dolphins and other non-target species) in nets, fishery managers are suggesting the use of smaller mesh gillnets, gillnets with metal in the monofilament (reflective nets) or pingers (instruments that make noise attached to nets) to scare dolphins away from the fishing gear. The study of echolocation has enabled scientists to better understand and engineers to better protect dolphins and other marine mammals. Number of repetitions per unit of time (cycles per sec) The distance between the point on one wave and an identical point on the next wave. Time between each repetition (seconds per cycle) or wavelength. A message containing information that is transmitted and received. The ability to orient by transmitting sound and receiving echoes from objects in the environment. Vibrations; A form of energy that travels in waves through a medium. The dissipation of signal strength with distance through a medium. A simple way of showing how energy in the form of food passes from one organism to another. A system involving the interactions between living organisms and the physical environment. Living or once-living organisms in the environment The non-living physical features of the environment (e.g. water, nets, boats) Single sheet of webbing that hangs between a floating line and a weighted lead line; an example of a stationary net (one that is not pulled through the water) The catching and killing of marine life, including sea turtles, birds, and fish of the species not targeted by the fishery, or that are either of the wrong size or sex to be of optimal value. Your Ears do the Walking Can You Hear It? What is echolocation? (definition above) Why is echolocation important to dolphins? (locate and capture prey, escape predators, and navigate in a dark ocean environment) How does attenuation, frequency, size of object, distance of object effect the effectiveness of echolocation? In looking at the various predator-prey relationships in the dolphin ecosystem, how is energy transferred through that ecosystem? Give an example of a food chain in the dolphin ecosystem. What is by-catch and what happens to the animals affected? Ask questions like: "Why is echolocation important?" and "Why should we care whether or not dolphins can detect nets?" The students should be challenged to think of new methods of technology to change the effects of by-catch Give students a worksheet with exercises (see the attachment section) to quiz what they learned. Students can be challenged to write about how by-catch affects dolphins and how we may prevent it using what they learned. Conduct research and discuss their findings on human ear and hearing. Contrast with Dolphin hearing. Au, W.W.L. The Sonar of Dolphins. Springer-Verlag, New York. Barrett-Leonard, L.G. et al. 1996. The mixed blessing of echolocation: differences in sonar use by fish-eating and mammal-eating killer whales. Animal Behavior 51: 553-565. Cranford, T.W. et al. 1996. Functional morphology and homology in the odontocete nasal complex: implications for sound generation. Journal of Morphology 228: 223-285. Deecke, V.B. et al. 2002. Selective habituation shapes acoustic predator recognition in harbour seals. Nature 420: 171-173. Harrison, Sir Richard, et. al. Whales, Dolphins and Porpoises. New York: Facts on File, Inc., 1994. Mark Carwardine, The Book of Dolphins. Dragon's World Ltd, 1996. http://www.inkokomo.com/dolphin/echolocation.html http://library.thinkquest.org/17963/head.html "In the Wild with Robin Williams" video 1997. Available at amazon.com Marine Mammal Biology, An Evolutionary Approach. 2002. Edited by: R. Hoelzel. Blackwell Science, Ltd., Oxford, U.K. Biology of Marine Mammals. 1999. Edited by: J. Reynolds III and S. Rommel. Smithsonian Institution, WDC, USA Sample Echolocation Discussion Questions Echolocation Diagram Dolphin Anatomy Transparency Assessment 6th grade Echolocation Worksheet Assessment 7th grade Echolocation Worksheet