Whales were once hunted for oil, meat, and many other things that people used in everyday life. Whalers killed many whales, decreasing whale populations until many large whale species almost became extinct. Despite the end of hunting over−30 years ago, some of these species still only survive in small numbers. Some species are so rare that scientists do not know how many whales there are in the population, where they live, how they move through the oceans, or if they have special areas to feed, breed, and raise their calves. Some whales, like gray and humpback whales, live closer to the land in shallower waters where the sea floor is a gentle, sandy slope away from the coast. This area is called the continental shelf. Whales living on the continental shelf have recovered from whaling and are fairly easy to study. But whales, such as blue whales and fin whales are large and live in deeper waters far from the coast, called oshore areas. At the end of the continental shelf is a steep drop that creates a cli face under water, where the water becomes very deep very quickly. This is called the continental shelf break. It is here that the larger whales like to live, which makes it very hard for scientists to study them.

Using recordings from hydrophones is a very good way to get information about whales. Using these instruments, we can survey in bad weather and in the dark, which would be very hard or impossible if we were in a boat or plane. But there are a few things we cannot tell just from listening to hydrophone recordings. When we hear a call, we know there is a whale in that location, but unless we hear lots of calls together, we do not know whether there is more than one whale. Also, hearing lots of calls does not mean there are lots of whales, we could just be listening to one very chatty whale! Whales might not call as much when they are eating and they may call more when they are trying to find other whale friends or a mate. We heard thousands of whale calls in our experiments, and this told us when and where whales were and, in some cases, what they were doing, but there may be many more whales that we did not hear. The more surveys done, and the more listen to the oceans, the more we will know about whales and how they use these areas. Protection of these areas of the oceans might help whale numbers grow and species to survive. For example, areas that are important to the whales could be conserved as sanctuaries or marine protected areas or, for species closer to shore, rules about boating near whales may reduce the disturbance caused by humans. In general, our work and the work of other scientists can help conservationists and decision makers establish ways to protect whales, so that they will be around and healthy for many years to come.

Regards,

Jessica

Managing editor

International journal of pure and applied zoology