Sustainability
Sustainability of freshwater fisheries and ecosystems
Throughout their lives fish are exposed
to a wide range of pressures from natural environmental factors and
human activities. Understanding how these activities affect
fish populations is fundamental to controlling their impacts and
maintaining sustainable fisheries which, where appropriate, can
support commercial and recreational exploitation. Salmonid
species, in particular, require near-pristine freshwater conditions
and are therefore important indicators of environmental
quality. However, different species can be affected in a
variety of ways by activities which directly or indirectly change
the physical or chemical environment; thus, while salmonids require
clean gravel in which to bury their eggs, other species may depend
on good marginal weed growth for this life stage.
The nature of impacts can also vary
significantly. Clearly we have greatest concern for factors
which cause major losses or prevent the access of fish to important
parts of their habitat, however there is growing evidence that fish
are affected in a range of more subtle ways. For example some
chemical contaminants have sub-lethal effects which impair
communications between individuals by means of pheromones and thus
affecting their ability to breed. Furthermore, there are
growing concerns about the wide range of factors which
independently may have no significant effects on fish but when
operating in concert may have serious consequences.