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Ecologically important fish habitats

Recently hatched thornback ray Raja clavataMany factors influence the distribution of fish, including water depth, temperature and salinity, sediment type and seabed topography, location of potential predators and availability of prey.

Some species of fish can have very specific habitat requirements, for example Fries's goby typically associates with the burrows of Nephrops. Other species of fish are more generalist and species like lesser-spotted dogfish can be found on mud, sand, gravel and rock, and in waters from close to shore to the edge of the continental shelf. 

However, some certain geographical areas or types of habitat can be of particular importance to fish at various stages of their life cycle. Such habitats can include spawning grounds, mating grounds, egg-laying grounds, nursery grounds, feeding grounds and migration routes.

  • Spawning grounds are those sites where fish aggregate to spawn. Many teleosts are broadcast spawners, in which the eggs and sperm are shed into the water and, after fertilization, the developing eggs and larvae remain in the plankton for a period of days to weeks.  
  • Sharks, skates and rays have internal fertilization, and the adults of some species may aggregate on specific mating grounds during the breeding season.
  • Some species of fish lay eggs on the sea floor, including skates, herring and black sea bream. Skates deposit their eggs (mermaid's purses) on suitable substrates, although it is unclear as to whether they have discrete egg-laying beds. Herring lay their eggs on coarse sand and gravel, often in well-defined areas. Black sea bream will make nests, and the adult will guard the developing eggs.
  • Nursery grounds are those areas where juveniles may concentrate. Preferably, nursery grounds should be areas where there are few predators (or access to refuges from predators), an abundance of suitable prey and environmental conditions that maximise their growth.
  • Many species of fish feed on a variety of prey species, however, in some areas and/or at certain times of the year, a particular prey species can be very abundant, and fish may congregate on such feeding grounds. These feeding grounds may be related to features on the sea floor, such as sand banks, or oceanographic features, such as fronts and other areas of high productivity.
  • Many species of fish make migrations, and in some instances the migration route is well defined and in a restricted area, for example in the case of fish moving through estuaries.

It is also important to note that such ecologically important habitats can be site-specific and used every year for some species, whereas important habitats for other species can be more variable and change over time.

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Last Modified: 27 April 2014