The idea of introducing a process of fish-hatching by artificial means was
first used at Loch Leven in 1867 by Sir Graham Montgomery. Taking Stormontfield
Ponds as a model, Sir Graham constructed a small number of hatching-boxes at
the mouth of the Black Burn, together with a small feeding pond in which the
hatched fry could grow before being released into the loch. The experiment
was a success, but it was not until 1909 when the lease to fish on Loch Leven
was taken on by the Tay Salmon Fisheries Company, were the present ponds at
Tarhill constructed and it became possible to hatch 300,000 fry each spring.
The purpose of artificially hatching the eggs was to supplement the stock
of brown trout in the loch. It proved so successful that the growth in catches
of Loch Leven trout rendered the operation unnecessary and it was shut down
in 1935. The clay-lined ponds remained unused and overgrown until 1983 when
the annual catches were trending sharply downwards. The ponds were repaired
and an egg-hatching facility, with rows of plastic trays and tanks, was established
again in the farm buildings at Tarhill and it remains in operation to the present
day.
Prior to fly-fishing from boats being introduced to Loch
Leven in 1850, the fishing had been done by net in large quantities. The
last year that nets were
used was 1873 and, since then, Loch Leven has gone on to become the world’s
most famous trout fishery.
After bumper years during the 1950s and 1960s, when average catches were in
the region of 40,000 per annum (peak was 85,883 in 1960), the annual catches
fell steadily during the 1970s to below 15,000. The hatchery and rearing ponds
were therefore reinstated in 1983 in an attempt to arrest the decline. Initially,
the operation was successful and catches improved steadily until 1989 when
37,432 brown trout were landed by anglers during the season.
However, changes in the ecology of Loch Leven then began
to result in the increased occurrence of algae. Dense algal blooms began
to appear, culminating
in “Scum Sunday” on 13th June 1992 when a toxic blue-green algae
washed up on the shores of the loch. Although these algal blooms may have had
little direct effect on the fish population per se (although they do affect
the level of oxygen in the water), the degradation of water quality and the
accompanying decline in macrophyte abundance served once more to threaten the
world-famous trout fishery.
The desperate situation led to the establishment of Loch Leven Area Management
Group, pulling together various interested parties and organisations. Their
subsequent report highlighted the high quantities of phosphates entering the
loch and they made a series of recommendations as to how to make the necessary
reductions.[[][[][[]]]The situation has subsequently improved significantly with the
annual input of phosphates currently running at about 50%% of previous levels.
Water quality has improved significantly and the occurrence of algal blooms
has become much less frequent and less severe[[]]].
However, back in 1993, in order to maintain the commercial viability of the
fishing operation, Loch Leven Fisheries were forced to take radical step of
seeking permission from Scottish Natural Heritage (SNH) to stock Loch Leven
with a limited number of rainbow trout. The limit was initially for 40,000
rainbows but this was later reduced and some 30,000, weighing up to 2lbs, are
now released into the loch each spring. Initially, this move created an uproar
within the trout angling community but opinions have since swung overwhelmingly
in favour.
Since 1983 when the hatchery and fishponds were resurrected,
around 2.5 million young (approx 6”) brown trout have been reared and released into the
loch. Approximately 1 – 1.5 million eggs are stripped from brown trout
that are trapped running the burns each autumn. The ova are then fertilised
and about 300,000 are hatched out in the rows of large tanks in the hatchery.
Surplus fertilised ova and first-fed fry are seeded in the loch’s feeder
streams. In addition to the 30,000 rainbows, on average about 150,000 six-inch
brown trout have been released into Loch Leven each year. However, enhancements
to the hatchery and rearing ponds will increase that figure for brownies to
around 350,000 – 400,000 per annum from 2003 in order to try to return
Loch Leven to its erstwhile position as one of the world’s most renowned
brown trout fisheries.
Rearing Cycle
October ~ December. Trout are trapped in cages as they attempt to
run up the burns to breed. The eggs are stripped from the females, using a
little careful manipulation, which does not injure the adult fish, and these
are immediately fertilised using milt from captured males.
The fertilised eggs are then laid out in trays and tanks. After roughly
55 days (depending on the water temperature), the new fry hatch from the eggs
and start to swim around with their yolk sacs still attached.
A crucial period for the young fry then occurs after a further 55
days or so when the yolk sac is exhausted and the fry have to make the transition
to eating fish meal.
In June, the fry are transferred to the larger rearing
ponds on the north shore of the loch where they remain until the following
April when, aged
16 – 18 months, they are released into the loch at an average length
of about 6”.
