Herring Clupea harengus

Distribution

Herring (Figure 9.21) are widely distributed across the north-eastern Atlantic shelf between Newfoundland and the British Isles, and also in the Arctic. They extend south to the area of Gibraltar on European coasts, and south to Cape Hatteras on the North American coast. However, it is only in northern areas that they are sufficiently abundant to be commercially valuable. They have now become scarce in some areas, such as the North Sea where they were once immensely abundant and they now no longer support the great fisheries they once did. This is discussed further below. With such a wide distribution, it is not surprising that the herring exhibits a number of local races, distinguished by features such as the number of vertebrae and by differences in spawning times and growth rates. A very similar form, Clupea pallasii, extends in the North Pacific from Japan to the coast of British Columbia, and also occurs in the North Atlantic. Herring-like fish are found in many other areas, including fresh water.

Herring are pelagic fish of mainly offshore areas, making inshore migrations in great shoals for spawning in certain coastal localities, after which the shoals disperse and the spent fish move out to deeper water, reassembling offshore as feeding shoals. They are therefore caught mainly using ring nets and purse seines.

Life history

When herring are preparing to spawn, they congregate in huge shoals as they approach their spawning grounds. They are the only commercially important marine teleosts in British waters to lay demersal eggs. A spawning female deposits

Figure 9.21 The herring, Clupea harengus. Identification features: 1 = Single dorsal fin

in middle of back; 2 = Rounded belly (no keel); 3 = Smooth gill covers (not ridged). (Modified from British Sea Fishes, F. Dipper (1987), by kind permission of Robert Irving and Underwater World Publications Ltd.)

10 000-60 000 eggs on inshore banks of small stones and gravel. The eggs are 0.9-1.5 mm in diameter, heavier than water, and form sticky masses which readily adhere to the stones, seaweeds, maerl and to each other. They are often densely packed in layers several eggs deep. Most races spawn in depths from 15 to 40 m but some oceanic races spawn on offshore banks as deep as 200 m (Hodgson, 1967; Parrish and Saville, 1965, 1967).

The precise location and limits of herring spawning grounds have been difficult to determine because herring eggs are not easily found by dredging. It seems that the selected sites are quite patchily spread with eggs. Apart from dredging, the situation of spawning grounds is approximately known from observing the position of ripe and newly spent herring, the occurrence of herring larvae in tow net hauls, and by noting the places from which trawlers bring up 'spawny' haddock, i.e. haddock engorged with herring eggs, on which they prey. The distribution of spawning grounds in the North Sea can also be very roughly equated with the distribution of predominantly gravelly areas.

Around the British Isles, different races of herring can be found spawning at almost any time of year, though there is a peak in the warmer months. The major spawning shoals are of two principal races, oceanic (Atlanto-Scandian) and shelf herring. Oceanic herring have an extensive range in deep water in the North Atlantic, Arctic and Norwegian seas. There is a major movement by spring-spawning shoals of oceanic herring towards the Norwegian coast. Those which approach the British coasts form winter-spring spawning shoals between February and April around the Hebrides, Orkney and Shetland Isles and along the Irish and Scottish coasts. These shoals occur mainly in water of oceanic-neritic type (see Section 4.7.1) where the temperature lies between 5 and 8°C.

The shelf herring of the North Sea, English Channel, Minch and Irish Sea form mainly summer-autumn spawning shoals. The North Sea shoals spawn from the Shetlands to the east coast of Scotland from July to September; off Northumberland, Yorkshire and Lincolnshire between August and October; off the East Anglian coast between October and December; and in the eastern English Channel

Figure 9.22 Main areas of herring spawning around the British Isles as determined by egg surveys. All the spawning areas shown belong to autumn or winter spawning herring. Spring spawner numbers are relatively very small. The previously very important Dogger Bank spawning grounds are now of little significance due to the collapse of the stocks. Dark areas are spawning grounds; paler areas are nursery grounds;--------indicates feeding area.

Numbers in sea areas refer to the average international catch in tonnes during the period 1973-77.

(From Lee, A.J. and Ramster, J.W. (eds) (1981). Atlas of the Seas around the British Isles. MAFF, London. © Crown Copyright, 1981.)

Figure 9.22 Main areas of herring spawning around the British Isles as determined by egg surveys. All the spawning areas shown belong to autumn or winter spawning herring. Spring spawner numbers are relatively very small. The previously very important Dogger Bank spawning grounds are now of little significance due to the collapse of the stocks. Dark areas are spawning grounds; paler areas are nursery grounds;--------indicates feeding area.

Numbers in sea areas refer to the average international catch in tonnes during the period 1973-77.

(From Lee, A.J. and Ramster, J.W. (eds) (1981). Atlas of the Seas around the British Isles. MAFF, London. © Crown Copyright, 1981.)

near the north French coast from December to January. These shoals are found in neritic water at 8-12°C.

Slight morphological differences have been noted between the two groups. Both show variation in the number of vertebrae between 54 and 59, with a mean vertebral count slightly above 57 for the oceanic herring and below 57 for the shelf herring. There are also slight differences in the number of gill-rakers, number of keeled scales on the ventral surface and in the structure of the otolith. The oceanic herring are slower growing, later maturing, longer lived and reach a larger size than the shelf herring. It is now generally considered that the two groups, both of which can be further subdivided into several more or less distinct stocks, are biologically separate units with no appreciable interbreeding.

In water of 5-6°C, herring hatch in about 22 days, at 11-12°C in 8-10 days. The newly hatched larva is about 6-8 mm long and at first depends on the food reserves of the yolk-sac. After hatching, the larva swims to the surface. During the period of resorption of the yolk-sac the larva develops a mouth and begins to feed at first mainly on diatoms, copepod eggs and early copepod larvae. As the herring larva becomes larger, it takes the later larval stages of copepods and the adults of small copepods such as Paracalanus and Pseudocalanus. Until it reaches a length of about 45 mm, when about three months old, the larva has a thin, eel-like appearance.

The larval fish are pelagic and drift with the currents. There is some mixing of broods from different areas and a high proportion of larvae from the North Sea and west coast spawning grounds drift considerable distances into nursery grounds situated in the shallow central and southern North Sea (Heath and Richardson, 1989). Extensive nursery areas exist along the shallow coastline of the Netherlands, Germany and Denmark, and in large estuaries such as the Thames Estuary, the Wash, the Moray Firth and the Firth of Forth (Figure 9.22).

When the young fish reach about 5 cm long, they become able to swim more strongly and start to form shoals actively moving into the shallow inshore nursery and feeding areas. Here they form large shoals known as 'whitebait' which often contain a mixture of young herring and young sprats. At this stage, the food consists largely of small crustacea; for example, the larvae of shrimps and prawns, and estuarine copepods such as Eurytemora hirundoides. The young herring remain inshore until near the end of their first year of life, and then start to move offshore. Areas such as the Dogger Bank support large numbers of young fish. By now the fish are mostly some 4-8 cm in length and during their second year these fish grow to some 13-18 cm in length but are still extremely thin.

In their third year these herring fatten, and feeding shoals of the immature fish often approach the English coast during the mid-summer. Throughout life the food is predominantly planktonic, mainly copepods, but also includes chaeto-gnaths, pteropods, hyperiid amphipods, appendicularians, decapod larvae and fish eggs. They sometimes feed on other fish, for example Ammodytes. The type of food varies seasonally to some extent and also varies from place to place according to the nature of the plankton.

By the end of their third year they have reached the 'fat herring' stage, and the flesh has become rich in oil for which they are particularly prized by man. During their fourth year, i.e. as Group III fish, the majority of southern North Sea herring become sexually mature. The oceanic fish of the northern part of the North Sea and the Norwegian coast mainly reach maturity later, between their fifth and eighth years. The maturing virgin fish leave the young fish shoals and join the adult spawning shoals.

Certain patterns of movement can be discerned in herring. For example, there are diurnal changes of vertical distribution associated with changes of illumination, the fish usually forming compact shoals on or near the sea-bed during daylight, and approaching the surface during darkness to feed on the plankton. There is also the annual cycle of migration of the adult fish, when they congregate in huge shoals and move into shallow water to spawn, followed by a dispersal to deeper water and the formation of feeding shoals (Nichols and Brander, 1989; Rankine, 1986).

Several factors influence the movement of the feeding shoals; in particular, the condition of the plankton. Where there is an abundance of suitable zooplankton food, the feeding shoals tend to amass, and the numbers of herring can sometimes be correlated with the numbers of Calanus. On the other hand, herring are seldom found in water heavily loaded with phytoplankton. It has been suggested that this is due to an 'exclusion' effect (see Section 5.3.4) but because such water usually contains very little zooplankton, the absence of herring shoals may simply be due to the scarcity of herring food.

The quality of the fish depends upon the abundance and nature of their food. The valuable oiliness of the herring reflects the fat content of the plankton, which in turn depends to some extent upon climatic conditions. Generally, a warm, sunny summer produces a rich plankton and provides fish in excellent condition for the autumn fishery. A copious diet of copepods produces a specially oily flesh. If the food consists mainly of pteropods, the fat content of the flesh is poorer.

Fishery and over-exploitation

For many years it was thought that the stocks of North Atlantic herring were so large as to be virtually inexhaustible no matter how intensively fished. As long as fisheries were conducted mainly by drift nets exploiting only the shoals approaching the spawning grounds, this may well have been true. Although the size and movement of herring shoals were subject to many fluctuations, appearing and disappearing in unpredictable ways with the consequent rise and decline of particular local fisheries, there was seldom any overall shortage of herring. However, during the years following 1948 an intensive trawl fishery for immature herring developed on the North Sea nursery grounds, capturing huge numbers of herring in age groups I, II and III for conversion to fishmeal for cattle and poultry food. Far more fish were destroyed in this way prior to spawning than had ever previously been taken from the adult shoals by drift nets.

The capturing power of pelagic fishing techniques has also been greatly increased in recent years. Drift nets have been largely replaced by ring nets, purse seines and pelagic trawls which enclose shoals that have been accurately located by sonic fishfinders. In the 1930s, although herring were heavily fished according to the methods of those times, the total annual catch of herring from the north-east Atlantic then averaged under 1.5 million tonnes. By 1965 and 1966 the landings obtained by newer methods were over 3.5 million tonnes per year. These huge catches were followed by a dramatic decline of landings. In 1969 the catch had fallen to 1.4 million tonnes and by 1976 to less than 800 000 tonnes.

The devastating effects of a combination of the industrial fishery for immature herring and the more intensive fishing of adult shoals caused the North Atlantic herring stocks to collapse and in 1977 a total ban was imposed on the fishing of herring over virtually the whole area in the hope of some recovery of stocks. By 1983 the population had partially recovered and fishing began again with limits on size and numbers taken. However, these measures have not been entirely successful and stocks appear once more to have stopped increasing. The recent history of north-east Atlantic herring fishing is a sorry example of failure to utilize rationally a major natural resource which, if properly managed, could provide large quantities of highly nutritious food for direct human consumption. A major part of the excessive landings of the mid-1960s was processed as fishmeal for animal rearing.

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Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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Responses

  • efrem
    How deep is north sea near the coast of east anglia?
    9 years ago
  • gormadoc
    Are herring eggs caught in drift nets with adult herring?
    9 years ago
  • Bacco
    Can you fish for herring in the firth of forth?
    8 years ago

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