WebQuest: Sensory Biology & Right Whales - Introduction
WebQuest written by Jill C. Fegley & Sara M. Lindsay (2006, updated 2015)
Overview: Help Save the Right Whales
The North Atlantic right whale is one of the most endangered species in the world. Two major causes of death for endangered North Atlantic right whales are ship collisions and entanglements in fishing gear. To reduce the number of human-induced injuries to right whales, the Endangered Species Act requires that an Early Warning System be developed which would alert mariners to the presence of right whales to diminish the number of collisions with ships. This act also requires Maine fishermen to modify their fishing gear in areas where whales are common to help reduce right whale entanglements.
In this WebQuest, students are part of a team of specialists trying to devise a method to reduce whale mortality caused by either entanglement or ship collisions. The team studies the feeding behavior, migration patterns and geographical distribution of Northern right whales. One member of the team will research the sensory biology of whales to determine how they “see” and “hear” in their environment. Another specialist will examine current research and technology involving sonar and echolocation. Specific issues associated with whale entanglements and collisions will also be explored.
The Gulf of Maine is one of the world’s most diverse and biologically productive marine habitats. The landward edge of the Gulf of Maine runs from Nova Scotia, Canada, to Cape Cod, Massachusetts. Over 2,000 species of plants and animals can be found within this marine environment. Every spring, rivers carry melting snow to the Gulf of Maine. This makes the water colder, less salty, and more productive than other parts of the Atlantic Ocean. The strong ocean currents also bring nutrients and food to the plants and animals that live here.
The Gulf of Maine is home to a variety of large whale species including humpback whales (Megaptera novaeangliae),finback whales (Balaenoptera physalus), minke whales (Balaenoptera acutorostrata), sei whales (Balaenoptera borealis) and right whales (Eubalaena glacialis). All of these are baleen whales, which feed on the abundant supply of plankton found in the Gulf of Maine. Approximately 3,500 of these individuals migrate into the Gulf of Maine each summer. During the winter months these baleen whales return to warmer waters where they breed and calve.
Right whales have a worldwide distribution but contain three distinct small populations in the North Atlantic, North Pacific and southern oceans. Although there are three distinct populations, there are only two species of right whales: northern right whales, which have populations in the North Atlantic and North Pacific, and the southern right whale, which is only found in the southern hemisphere. Both northern right whale populations are in danger of becoming extinct. The North Atlantic right whale population, numbering only 300 individuals, is one of the most endangered species in the world. The southern population of right whales is approximately ten times larger (3,000 – 4,000) than the population of the northern species and has only increased in size in the last 15 years.
The North Atlantic right whale, Eubalaena glacialis, is a slow moving, surface-feeding animal that was hunted in the early 20th century to near extinction. This species was targeted by whalers because they were easy to capture and floated to the surface when killed, thus they were the “right” whale to be hunted. In addition, right whales yielded a tremendous amount of oil, meat, and whalebone. Despite a total ban on hunting right whales since the 1930’s, populations of this species have not shown signs of increasing.
Current threats to right whales include collisions with ships, entanglement with fishing gear, habitat destruction, and changes in food availability due to climate fluctuations (Fujiwara & Caswell, 2001). Ship collisions kill more right whales than any other documented cause of mortality. The right whale is particularly susceptible to ship strikes because of its habit of resting near the surface, its slow-moving pace as well as its surface courtship and skim-feeding behavior. Often, the whales are not killed outright but are fatally injured by propeller blades, and eventually die because of injury or loss of function. After ship-strikes, entanglement in fishing gear is the leading cause of known mortality in the endangered North Atlantic right whale population. More than 60% of North Atlantic right whales have scars from entanglement in fishing gear such as lobster pots and sink gillnets (Waring et al., 1999). Obviously both causes of mortality need to be reduced in order for the population to recover. If we could prevent only two deaths of female right whales per year, the population level would increase (Fujiwara & Caswell, 2001).
Strong currents combined with large tidal fluxes in the Gulf of Maine cause significant challenges to offshore lobstermen. To avoid large gear losses, lobstermen not only weigh down their traps with cinder blocks, steel bars and bricks but they also link several lobster traps together with rope. This allows them to find their gear more easily, because if they find one buoy it will lead them to several more. The ropes, called ground lines or tailer ropes, are often made of polypropylene, which floats. These ropes tend to arc or loop upwards towards the surface. When large, baleen whales feed they swim with their mouths open and often accidentally catch the fishing line in their mouths. As the whales twist and turn, trying to disentangle themselves they often make matters worse and cause the rope to cut into their skin; sometimes it goes clear down to the bone.
In a world where sight is limited, many marine animals rely on sound to accomplish many tasks. For cetaceans, such as whales, hearing is arguably their most important sensory system. Whales and dolphins have three times more neurons devoted to hearing than any other animal. For these organisms, sound is a key element for survival and hearing is a key component of communication, mate selection, and predator avoidance. Sounds are also produced during feeding and to help navigate underwater.
There are two ways that sound is used: passively and actively. In passive acoustics, the animal makes no sound of its own but instead listens and interprets the sounds made in the environment. In active acoustics when sound is used actively it is first created by a source and then received by a “listener” which could be another whale or technology. Some active acoustic systems have separate sources and receivers (e.g., underwater telephones). Other active acoustic systems (sonar/echolocation) emit a sound which bounces off an object and returns to the receiver. By analyzing the return signal, information about the object such as its size, shape, orientation, direction, speed and composition can be obtained. The distance that whales can “hear” in the environment is much greater than the distance that they can “see”.