Herring are schooling fish found in temperate waters across the North Pacific and North Atlantic Oceans, including the Baltic Sea. Their schools can number in the millions, making them a significant presence in marine environments. The diet of herring plays a substantial role in marine ecosystems.
What Herring Eat
Herring primarily function as filter feeders, consuming microscopic organisms collectively known as plankton. Their diet largely consists of zooplankton, which are tiny animals drifting in the water column. Common zooplankton prey include copepods, such as Calanus finmarchicus and Calanus hyperboreus, and euphausiids, also known as krill, like Thysanoessa inermis and Meganyctiphanes norvegica. They also consume amphipods and the larval stages of various marine organisms.
While zooplankton form the bulk of their adult diet, young herring, particularly larvae, may also feed on phytoplankton, which are microscopic plant-like organisms. The specific composition of a herring’s diet is often opportunistic, meaning they consume what is most abundant and available in their immediate environment.
How Herring Feed
Herring employ a filter-feeding mechanism to consume their planktonic diet. They swim with their mouths open, allowing water to flow through their oral cavity and over their gills. Located on their gill arches are specialized structures called gill rakers. These gill rakers act like a sieve, straining microscopic organisms from the water as it passes through, while allowing the water to exit through the gill slits.
The structure and spacing of these gill rakers are adapted to efficiently capture tiny prey. Schooling behavior also enhances their feeding efficiency by concentrating prey, making it easier for individual fish to capture food.
Dietary Variations and Ecological Impact
A herring’s diet can vary depending on its life stage and the seasonal availability of prey. Larval herring may initially feed on smaller plankton, transitioning to larger zooplankton as they grow. Environmental factors like water temperature, wind speed, and water transparency also influence their feeding activity and prey selection.
Herring occupy an important position in the marine food web as a link, transferring energy from lower trophic levels to higher ones. By consuming large quantities of plankton, they convert this energy into a form accessible to larger predators, including fish like Atlantic cod, bluefish, and tuna, as well as marine mammals such as whales and seals, and various seabirds. This energy transfer also influences nutrient cycling within their ecosystems. Their abundance and role as forage fish make them sensitive indicators of marine ecosystem health, and their populations are closely monitored.