A number of different species of forage fish are referred to as herring The most abundant is the Atlantic herring Herring are found worldwide in tropical and temperate ocean waters. Some species can even enter freshwater rivers. They travel together in large schools. Herring feed on plankton at night in upwelling zones, after spending the day in deeper waters They may hunt prey individually or swim with their mouths open and filter plankton out as water passes through their gills Herring have been an important part of the commercial fishing industry for over a century Overexploitation resulted in multiple crashes to the herring fishing market during the 1900s. Today, there are regulation in place that set catch limits for some species, but many population are now threatened by habitat loss and chemical pollution Much of the herring caught is utilized as bait for the lobster and tuna fishing industries Herring are also sold frozen, salted, and canned for human consumption Herring eggs are harvested and sold as a delicacy in some parts of the world Schools of herring will spawn as a group every year The time of year for spawning depends on the species and location The fish will release sperm and eggs into the water Eggs stick to the vegetation, rocks, or sand at the bottom of the seafloor Females can produce around 40,000 eggs per spawning season During this event, the ocean floor may become several centimeters thick with eggs Eggs hatch in around 2 weeks Only one in ten thousand eggs will survive until adulthood Juveniles form large schools and do not join the adults until they mature at about four years of age They grow about one foot (.3 m) long and may live over a decade Herring are an important part of the food web Animals such as seabirds, salmon, and marine mammals rely on them for consumption The dark coloration on their backs and light coloration on their undersides makes them hard to be seen by predators from above or below This is called countershading Some predators may attempt to herd herring into forming bait balls This is when the school packs tightly together in their last defense against predation For more marine facts, click the subscribe button!!!