The Herring: A Successful Species?

The herring has an elaborate racial system closely linked to its spawning habits. Its demersal eggs are laid in a wide range of environments from the deeper parts of the continental shelf to the intertidal zone and in a wide range of salinities and temperatures between latitudes 35 and 70°N. Depending on the race, spawning occurs in all months of the year and the relationship between fecundity and egg size is correlated with the season, with high fecundity and small eggs in the summer and fall and low fecundity and large eggs in the winter and spring. The herring is specially adapted in other respects. There is a complex camouflage system based on silvery layers of guanine crystals in the skin, a specialised retina, and a very complex acoustico-lateralis system linked to the swimbladder. It is physostomous, allowing rapid vertical movements of wide amplitude, and strongly schooling in habit with the facility to switch from particulate to filter-feeding. Filter-feeding can continue in darkness. Although many herring stocks have been overfished, there is no reason to suppose that they cannot recover, to the historical high levels, if properly managed. The stock size varies from millions to hundreds of tonnes, depending on the race, and this has interesting implications for the stock-recruitment relationship