Ecologically important fish habitats
Many factors influence the distribution of fish,
including water depth, temperature and salinity, sediment type and
seabed topography, location of potential predators and availability
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
- 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
- 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
- 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.