The herring is such an everyday fish -every high street fishmonger has trays of these shiny, silvery fish with reddish gills – that few of us give it a second glance. This familiarity can sometimes cause problems when an angler catches a herring – the gleaming blue-backed fish with golden tints does not look like the dead fish on the fishmonger’s slab.
More errors are made distinguishing young herring from sprats and shads than almost any other fish. All members of the herring family have slender bodies, a short dorsal fin, distinctly forked tail and no lateral line. Their oily flesh makes them an ideal bait food for many bigger species. The edge of the herring’s upper jaw is rounded and unlike the shad there is no notch in the midline. The dorsal fin starts in front of, or above, the base of the pelvic fins – in the sprat it is behind the pelvics. The sprat and shad both have a row of sharp scales on the belly, but the herring does not.
Herring live in the open sea down to depths of 250m (820ft). They swim in shoals which sometimes contain thousands of tons of fish. In European waters several different races of herring exist – each with separate spawning grounds, feeding habits and migration patterns. At one time herring were abundant, but overfishing on the part of various countries has reduced numbers greatly. This in turn led to the disappearance of blue fin tuna in the North Sea – a species which relied heavily on herring shoals for food.
There are still plenty around, but nothing like the millions of fish that once seasonally passed along British coasts, and certainly not enough to be of much commercial value.
One of the best known migrations was in the North Sea – after spawning, the herring travelled southwards in an anti-clockwise direction to end up off the Kentish coast.
Follow the plankton
The shoal follows food to the surface at night, moving to deeper water at dawn. Unlike many plankton-feeding fish, the herring does not simply swim around with its mouth open, but selects food items by sight. It occasionally eats small crustaceans, shrimps and large numbers of young fish.
Most of the herring groups around the British Isles spawn in autumn – spring spawners are found too but their numbers are relatively small. Each shoal returns to the same spawning ground year after year. Most fish that feed at the surface also lay their eggs there, but the herring differs by spawning close to the sea bed. The female lays up to 50,000 eggs which sink to the bottom, forming a carpet up to 20 eggs deep over the sea bed.
The eggs hatch a fortnight later as scale-less, transparent larvae, and swim towards the surface to float among the plankton. Within a few weeks they reach a length of 5cm (2in) and drift with the current into estuaries and coastal waters. They form huge shoals along with young shad – known collectively as whitebait.
The young fish remain inshore for up to a year before moving into deeper water. It is not until they are sexually mature at two to three years old that they join the adult shoals and begin the annual migration to their birthplace.