Intro To Herring

Atlantic herring (Clupea harengus) are teleost fish, a member of the Actinopterygii (ray-finned fish) class. Teleost are the most numerous type of fish currently extant, with around 96% of living fish species being teleosts. (As an aside, both humans and rats are descended from the Sarcopterygii, the ‘lobe-finned fishes’ class). As per their name, Atlantic herring can be found on both sides of the northern Atlantic ocean, preferring colder and coastal waters. They can grow up to 45cm in size and live in large schools, some of which can contain billions of fish and stretch over a cubic mile. Needless to say, they are the most abundant extant fish species in the world. Herring are highly important to the fishing industry, both as a food and as a bait fish.

Physical Capabilities

Like many free-swimming fish, herring bodies are fusiform in shape, making them streamlined and efficient swimmers. They generally swim around 3mph, although their speed can vary depending on the surrounding water temperature.

Herring have an excellent sense of hearing, and unusually have ducts connecting the inner ear to their gas bladders. Although the exact function of these ducts is unknown (in other vertebrates the organ is used for balance by sensing gravity), it likely performs an auditory mechanism.

The scales of herring are (generally speaking) soft and prone to damage. They are also sensitive to water pollution, requiring free-flowing water to hatch their eggs. Unlike a lot of fish herring do not possess a lateral line (a line of sensory organs along the flanks).

Feeding And Nutrition

Herring feed on zooplankton, such as copepods, krill, and larvae. Their large schools make them very effective feeders- when hunting each fish swims a set amount of distance from each other, so that if a copepod darts out the way of one it will end up in the mouth of another. Water entering the mouth is filtered through gill rakers (bony/cartilaginous projections attached to the gill arches), which trap their small prey yet allow the water to flow freely out.

Like all teleost fish herring can extend their jaws outside the mouth, protruding them forward. In larger fish this allows them to seize prey and drag it back inside the mouth; as a herring’s prey is generally microscopic this ability is rarely used for feeding.

Lifestyle

Atlantic herring prefer to live in cold coastal waters and estuaries, rarely venturing into deep or warm waters. These restrictions are mainly due to the location of their zooplankton prey and the temperature requirements for breeding.

Herrings reach sexual maturity at around 3 years of age. Different geographical populations will spawn at different times. Females do not brood their eggs, instead releasing them into the water (up to 40,000 at a time) to be externally fertilised by males. The fertilised eggs will then sink and adhere to a solid surface, such as plant material or hard substrate. A fertile school can produce so many eggs they can cover the seafloor in a ‘carpet’ of eggs. Provided the water temperature is suitable (eggs will only mature in cooler temperatures) the eggs will hatch within 1-3 weeks, the tiny young being fully independent from birth.

Herring are well known for living in large shoals and schools (note: a shoal is a group of fish congregating together, a school is a group of fish travelling together). As mentioned above, schools can reach immense sizes of several billion fish; migrating schools may sometimes link together to form long ‘chains’ stretching miles in length. Although frequently targeted by predators, shoals provide excellent protection for individual fish and also increase opportunities to both feed and breed.