The dangers of introducing farmed trout into wild waters
There
appears to be widespread acceptance, among fishery managers and angling
clubs throughout the U.K., that stocking wild rivers and lochs with
farmed trout will improve the quality of the fishing on those waters,
despite warnings from biologists that stocking with non indigenous
farmed trout may often be detrimental to native stocks, migratory fish
and the river and loch habitat in general.
I believe that there are very few circumstances where the
introduction of farmed trout into a river or loch can be justified. Such
an introduction may be necessary, for example, where a river is
recovering from an incidence of severe pollution that may have wiped out
the natural stock. In general, though, in a healthy river with a good
stock of wild fish, artificial stocking is likely to be
counter-productive and might, in the long term, have a serious, and
perhaps irreversible, adverse effect on the river and its truly wild,
and very valuable, fish stocks. There is likely to be pressure from a
number of anglers who wish to catch bigger fish than their river or loch
might produce naturally (and who are perhaps unaware of the damage that
might be done to wild salmon and trout stocks by the introduction of
farmed trout). There are, on the other hand, many anglers who would much
rather catch wild trout on a wild fishery, even if the average size is a
bit smaller. That is not to say that a river or loch should be neglected
and left entirely to its own devices. The fishery and its wild fish
stocks should be preserved and nurtured wherever possible. Habitat can
be improved, spawning areas opened up, predators controlled, pollution
prevented, professional advice sought - all paid for by the not
inconsiderable sum which might otherwise be spent on artificial
stocking. By encouraging voluntary catch and release, allowing for a
reasonable number of trout for the pot, it should be possible, in many
rivers and lochs, to maintain a healthy, self sustaining stock of wild
trout. I think anglers are becoming increasingly receptive to the idea
of catch and release. We realise how valuable, and fragile, our wild
trout and salmon stocks are and I think most of us would be happy to
limit the number of fish we kill for the sake of their survival. I must
stress, though, that I am not in favour of total compulsory catch and
release. We should all be able to take the odd fish for the pot. That,
after all, is what the whole business of fishing is about.
As I understand it, there are some very good reasons to discontinue the
stocking of wild waters with non-indigenous farmed trout:
COST
The money spent on artificial stocking can be put to better use.
A relatively small proportion of stocked trout might actually be caught
by anglers, especially on rivers. Some might fail to adapt to the
natural environment and die, some will fall prey to disease or
predators, while others will swim downriver and out to sea, unlikely to
return. I have read of one study, done on the River Dove by an
Environment Agency scientist, which estimated that only 3% of stocked
trout survived the winter. The money currently spent on the artificial
stocking of our rivers might be better spent on habitat improvement
etc., which would help maintain a self-sustaining stock of wild fish.
ENVIRONMENTAL COST OF FISH FARMING
The environmental cost of fish farming, whether it be salmon
farming on the west coast or inland trout farming, for both fishmonger
and fishery, must be weighed very carefully. The fish farms pollute the
environment. More importantly, though, it takes approximately 4 tonnes
of fish protein to produce one tonne of farmed trout or salmon. A high
percentage of the pellets used in the salmon farming industry, in
particular, is derived from essential marine prey species like sandeels,
hoovered from the sea by factory ships. While much of the fish protein
and oil in trout pellet feed manufactured in the UK is, more sensibly,
now derived from waste products of the fish processing industry, much of
the content of imported pellet feed can still come from prey species.
This is a criminally inefficient use of our fragile marine resources
which, through the unnecessary depletion of an essential part of the
marine food chain (the small prey fish like the sandeel), threatens
essential stocks of sea fish like cod and haddock and game fish like
salmon and sea trout, on which we depend for our sport, not to mention
the many species of sea birds at risk of malnutrition through lack of
sandeels.
DAMAGE TO WILD FISH STOCKS
Perhaps the most important worry about artificial stocking is the
potential damage done to the wild stocks in the river - stocks of
salmon, trout and sea trout. Stocked fish, particularly if stocked in
numbers and sizes incompatible with the river or loch habitat, can represent one of the biggest
threats to wild fish. The stocking of fish derived from a non indigenous
source might, over a period of time, dilute the wild gene pool, which
has adapted over millennia to the local conditions. Larger stocked fish tend to displace
smaller wild fish. The
stocked fish, however, are less likely to spawn successfully so that,
when the wild fish have been forced out, there are fewer trout left to
spawn successfully. More farmed trout are then required to supplement
the ever decreasing stock of wild fish and the problem is compounded.
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