Tagging has been especially important in studies of animal migration. Much of what we know about animal behavior in the wild including migration patterns is due to the fact that scientists have developed methods for tracking animals from one remote location to another. Tagging is one of the most useful of these methods. It helps scientists to study animals over time and to create hypotheses based on their behavior. Where do animals go at different times of the year? How far and how fast do they travel? Are they "residents" living in one particular area, or "nomads," wandering great distances in search of food? These are some of the mysteries tagging helps to solve. Animals are first captured, then scientists or well-trained volunteers record the exact date, location, and basic biological information. The biological information includes species, sex, size, age, reproductive status, method of capture, stomach contents, etc. The animal is then tagged and released until it is re-captured in another location at a later date. Information is collected and sent back to the original institution responsible for the tagging. From studying this data scientists can create and test hypotheses about an animals' rate of growth, travel patterns, age, food sources, and more. They are also able to describe the behavior of whole groups of animals, such as identifying pupping grounds or shark nurseries where large numbers of sharks migrate to give birth. Sharks are some of the most mysterious of all animals and tagging is the primary method by which we understand their migration. Because sharks travel such enormous distances beneath the surface of the ocean, there is still a great deal to be learned about their migratory patterns. Scientists are studying where, when, how and why sharks migrate, as well as what factors help or hinder their migration. Like most animals, sharks seem to migrate in search of plentiful food or to special locations to breed. Some, such as the blue shark, have been tracked for thousands of miles, yet very little is known about them. Others, like the nurse shark, travel relatively short distances and seem not to migrate at all. In unique cases, like the bull shark, sharks even migrate from salt to fresh water in search of food.