surface to , but individuals can be found as deep as . Atlantic mackerel are migratory fish, spending the spring and summer closer to shore about out, with juveniles moving closer in to shore than adults. Occasionally, fish will even enter harbors, and those that do are usually juveniles. In the fall and winter they move farther out and farther south to the warmer waters on the edge of the continental shelf. They first come in to land in North America in April at the southern end of their range, but are found along the coast through their entire range by July. They start moving back out to sea again in September and are completely gone from the coast by December. Food availability increases greatly during the summer, and fish reach a peak for fat tissue in August, a mere four months after their lowest point in April. Biology and ecology The Atlantic mackerel is an active, fast-moving fish that must keep in constant motion to bring in enough oxygen to survive. It swims using short movements of the rear of its body and the caudal fin. Unlike other mackerel, Atlantic mackerel do not leap out of the water unless attempting to escape a predator. They form large schools, consisting of individuals of the same relative size, near the ocean surface during all seasons but winter. Because larger fish have a greater ratio of muscle mass to surface area, schools of larger fish are able to swim more quickly than schools made up of smaller individuals. Feeding When feeding on larger prey, schools tend to break down into shoals and individuals find food on their own. When consuming plankton, however, Atlantic mackerel form tight aggregations, open their mouths as wide as possible, and extend their operculums, swimming in a tightly packed school that acts like a series of miniature tow nets. Spaced only about the diameter of a single fish's mouth apart, this formation greatly reduces the ability of plankton to evade capture, as a plankton darting out of the way of one fish is likely to end up in the jaws of another. Copepods make up the majority of the Atlantic mackerel's diet, Calanus finmarchicus being the most abundant. Life history Like other mackerels, reproduction in the Atlantic mackerel is oviparous. Spawning occurs day or night in the spring and summer months, primarily within of shore, though it can