Commercial fishing nets often trap "unprofitable" animals in the process of catching target species. In this activity, students experience the difficulty that fishermen experience while trying to isolate a target species when a variety of sea animals are found in the area of interest. Then the class discusses the large magnitude of this problem. Students practice data acquisition and analysis skills by collecting data and processing it to deduce trends on target species distribution. They conclude by discussing how bycatch impacts their lives and whether or not it is an important environmental issue that needs attention. As an extension, students use their creativity and innovative skills to design nets or other methods, theoretically and/or through hands-on prototyping, that fisherman could use to help avoid bycatch.

Bycatch, the unintended capture of animals in commercial fishing gear, is a hot topic in marine conservation today. The surprisingly high level of bycatch about 25% of the entire global catch is responsible for the decline of hundreds of thousands of dolphins, whales, porpoises, seabirds and sea turtles each year. Through this curricular unit, students analyze the significance of bycatch in the global ecosystem and propose solutions to help reduce bycatch. They become familiar with current attempts to reduce the fishing mortality of these animals. Through the associated activities, the challenges faced today are reinforced and students are stimulated to brainstorm about possible engineering designs or policy changes that could reduce the magnitude of bycatch.

Students drop marbles into holes cut into shoebox lids and listen carefully to try to determine the materials inside the box that the marbles fall onto, illustrating the importance of surface composition on dolphins' abilities to sense materials, depth and texture using echolocation. This activity builds on what students learned in the associated lesson about bycatching by fisheries and how it affects marine habitats and species, especially dolphins. Students learn how echolocation works, why certain animals use it to determine the size, shape and distance of objects, and how people can take advantage of dolphins' echolocation ability when developing bycatch avoidance methods.

Bycatch can be defined as the act of unintentionally catching certain living creatures using fishing gear. A bycatched species is distinguished from a target species (the animal the gear is intended to catch) because it is not sold or used. Marine mammals (whales, dolphins, porpoises), seabirds, sea turtles and unwanted or undersized fish are some examples of animals caught as by-catch The incidental capture of these animals can significantly reduce their populations. The most well known example of by-catch may be the unintentional mortality of spotted and spinner dolphins in the tuna fishing industry. "Dolphin-Safe" tuna was a result of this interaction (Be prepared to discuss how this came about with students, as it is something close to their daily lives). One important aspect to consider when discussing this issue is that laws protect some of the animals caught as by-catch (Marine Mammal Protection Act and Endangered Species Act). In this lesson, students will first be shown pictures of entangled marine animals and will discuss the definition of by-catch This will lead to discussions on why by-catching exists, how it impacts specific animals as well as humans, whether the students believe it is an important issue, and how by-catch can be reduced.

Students experience a simulation of echolation, using the sensory method to walk along a path while blindfolded. This relates to the issue of bycatching by fisheries, which they learned about in the associated lesson. Bycatching affects marine animals, especially dolphins, which use echolocation to identify the location of objects in the water, but have difficulty identifying nets, and thus are often caught accidentally. Students learn how echolocation works, why certain animals use it to determine the size, shape and distance of objects, and how humans can potentially take advantage of dolphins' echolocation ability when developing bycatch avoidance methods.

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 by-catch Students will learn what happens to animals caught through by-catch and why.