Fisheries management.
Ecology & Bio manipulation
What is Ecology?
The study of living creatures and their interactions within the environment.
Fisheries management should be based on sound ecological principles. For
example, improving wild fish stocks should involve looking at each stage of
the life-cycle needs and working to provide for those needs.
In contrast, some heavily stocked Stillwater course fisheries pay little or no
attention to the ecology of their waters- the fish are at such high stock
densities that most aquatic plants and possibly all large invertebrates are
wiped out. This has many nock on and severe adverse affects.
Habitat availability and habitat destructionAquatic plants, invertebrates and fish species have particular requirements
for their preferred habitat. Each species has preferences for water quality,
flow, depth nature of lake/riverbed, weed cover, etc. Some species have
fairly specific habitat requirements; others can live in a wide range of
environments. For example, trout need cool, well-oxygenated water ideally
flowing over rocky or gravel riverbed; carp will live in such an environment
but excel in warm, static ponds where oxygen levels vary greatly.
Habitat destruction can be caused by (for example) pollution, engineering
operations (e.g. land drainage), climate change, seasonal factors, siltation,
plant encroachment, and fishery management practices. Certain plant and
fish species can destroy habitat for other species. For example, the fringed
lily or Parrots feather weed can totally choke a pond, excluding light and
killing off many other pond inhabitants.
Heavy stocks of carp can be extremely destructive of Stillwater
environments. Shoals of Carp/bream feeding on soft-bottomed lakes stir up
sediment, heavily colouring the water, stopping light penetrating the water
and stunting or inhibiting aquatic vegetation. The only plants to survive will
be microscopic algae floating close to the surface. In the absence of weed,
cover is lost for Zooplankton such as Daphnia and these unprotected
creatures preyed upon by the fishes. The loss of Zooplankton means the
algae grow unhindered by grazing from the zooplankton. Large colonies (or
blooms) of algae can create enormous variations in oxygen levels, high by
day, and potentially fatally low for the fish by night. Additionally, the loss of
rooted plants means that any weed spawning species have nowhere to
incubate their eggs and no protection for the young. In this complex way,
carp/bream have altered the habitat for plants, invertebrates and other
fish; these affects have been observed at 200lbs/acre of Carp and perhaps
a great deal less!
By managing waters in an ecological way we will prevent these problems
from getting out of hand, and with at least one water beginning to show
signs of imbalances it is time to take action.
Removing some of the tree cover to allow bankside and aquatic vegetation
to recover is just the beginning. We need to look at our stock levels and
reintroduce marginal weed beds to provide sanctuaries for Zooplankton
and invertebrates, essential in a well-balanced eco system. There is a fine
balance to be achieved, as it would be impossible to attain high levels of
bio diversity within our waters whilst maintaining good fishing for the
average club angler. The two simply do not mix as with a low stock of carp
comes a type of angling that suits only the strong willed! Personally I
prefer to fish the low stocked lakes rich in aquatic life, and hope that
Tolpits is managed this way as it has and hopefully always will be the jewel
in our crown. The other waters on our complex should provide more
prolific fishing for those that simply want to catch a carp/ or other species
and don’t have the time to hunt like we have to on Tolpits.
This requires a great deal of thought and effort to get the balance right,
too few fish and the fishing is too hard for most, too many and the ecology
of the lake suffers. This causes all kinds of issues as already mentioned but
most importantly the fish are stressed, not the kind of angling any of us
want.
Bio manipulation
Deliberate alteration of the biological community to achieve a desirable and
planned change in environment
Bio manipulation is the first line of approach in restoration of fisheries. It is
essentially the removal of stockfish to a level that reduces the “forward
switches” (cause of problems associated with intensive recreational use in
fisheries)
Some major problems associated with over stocking of none piscivorous
fish are1) Phytoplankton dominance (Algae) over macrophytes (leafy stemmed
plants).
2) Clouding of water.
3) Depletion of zooplankton communities
4) Erosion of banks
5) Eutrophication
Nutrient enrichment.
Eutrophication or excessive nutrient input has been recognised as one of
the most destructive impacts on water quality. Excessive nutrients
encourage the growth of algae’s, which block light from the leafed plants,
which form the basis of lake ecology. Preventing or removing excessive
nutrients and encouraging a diverse range of leafed plants has now been
recognised as one of the key methods in water enhancement. Improper
stock management has also been a factor associated with the decline in
many fisheries.
The occurrence of nuisance species such as blue green algae (a
Cyanobacteria, (not a true algae) or filamentous algae, true and green
species of algae like (Spirogyra, Mougeotia and Zygnema) has became an
increasingly important element of water management. Algae species may
bloom to nuisance levels in the presence of excessive nutrient levels and
low water mixing conditions (wind, flow etc) Nutrient removal or
prevention form the most effective methods for algae control. The addition
of floating islands and wind blown water mixers has also grown in recent
years to alleviate these issues. Barley straw and ultra Sonics have also
been investigated as a means of preventing nuisance growth of algae. Bio
manipulation of fish stocks together with re establishment of weed growth
are recognised as being the most successful methods for fishery
restoration.
To give you some insight into what constitutes a healthy balanced food
chain I will explain the theory in what is known as the pyramid of numbers.
This is a way of calculating the waters ability to sustain a particular stock
level of fish, without bait.
Basically each part of the food chain decrease in volume by a factor of 10,
basically this means that in order for us to stock 1 acre of water with
100kilos of carp or other fish species we must have 1’000kilos of
invertebrates such as shrimp snails etc and 10’000kilos of vegetation!
Bait enables us to stock at considerably higher than “natural” levels but it is
a fine line between overstocking/imbalances or a sustainable fishery.
When you consider that 100kilos of carp is only 220lbs it means that in
order to have a healthy stock we must have no more than 5x20lb carp
10x10lb carp and 20lbs of mixed species like roach Rudd bream etc per
acre. This level of stocking would allow for a predation factor equivalent to
1x 20lb pike or 10x2lb perch. All this in 1 acre of water, which means that
over all we must reduce the stock to a sustainable level, usually this is
between 500-600lbs per acre, depending on the overall richness of the
water. Stock figures over 800lbs per acre are considered intensive.
There is a strong relationship between common carp (Cyprinus carpio)
stocking and switches to algal dominance. Common carp grow to large size
and in areas where they are not native, including the UK and Australia,
have, as adults, no predators. They forage in sediment, greatly disturbing
the habitat by stirring up the mud, and feed directly on plants, often
uprooting those they do not eat. Large bream (Abramis brama) have
similar effects. In a survey of lakes in Sites of Special Scientific Interest in
England, some 25% were found likely to have been damaged by carp
introduction. On a wider basis the proportion is likely to be higher.
Many modern fisheries experience all of the above symptoms, Tolpits is
starting to show signs of algae dominance, and though at present the
exact cause is unknown to me it could be several factors. The problem on
Tolpits is due to a brown algae form, and severe algae blooms are
associated with wide fluctuations in D.O counts (dissolved oxygen) Algae
will periodically “bloom” though the word bloom is a scientific term used
strictly for explosions in blue green algae. These algae problems can only
occur when excessive eutrophication and depletion of algal grazers has
occurred and that basically means that the plant growth could not utilise
the nutrient loading of the water fast enough to remove its supply to the
algae.
The algae can multiply faster than the macrophytes and hence a bloom
occurs. This bloom utilises oxygen during the night to respire rather than
Carbon dioxide, as does all the vegetation within the system. The worst
D.O fluctuations occur as the algae bloom peaks then dies, the decaying
bloom depleting vast amounts of oxygen as bacteria utilise oxygen to break
down the dead organic materials.
Under such extreme stresses the older and weaker or stressed fish will
struggle and sometimes die as has happened recently on Tolpits. However
it is only those old and weak that will die and unfortunately it is nature’s
way. However we must acknowledge the need to take measures to ensure
our waters are managed in a sound and ecological manner, harnessing
nature rather than trying to remedy by artificial means as and when they
occur, as it is often too late.
Nature’s wayNature has a way of resolving in -balances and it does this with sublime
perfection, but our intervention and uneducated manipulation and use of
habitats affects nature’s ability to cope with the extreme fluctuations in
environmental and biological factors.
If we was to take a look at a natural lake that is unmolested by fisheries
practice we would find a perfect balance of organisms within the system.
The water would almost always be clear, weed would be present in large
volumes and the invertebrate life forms would be visible everywhere.
In a well-balanced environment nature controls problems such as algae
blooms by the principles laid down in the pyramid of numbers. If algae
were to suddenly find a surplus of nutrient and multiply the populations of
micro inverts would balloon to graze on this sudden excess supply of food.
Wild organisms are built to take advantage of this type of situation,
utilising it to boost their populations and breed. Once the grazers dominate
the algae less food is available and the grazers die off or are preyed upon
to the point where they are once again sustained by a natural production
of algae. This is nature’s way and it works with consummate ease when
allowed to.
If we look after the nature within our fisheries the nature will look after our
fish. If the balance is right no intervention of stocks would need to be
undertaken and the risks associated with new introductions eradicated.
The need and purpose of ecological management in fisheries should be
obvious and modern principles and researches all indicate a trend towards
a more sustainable and natural approach to fisheries management.
Carp and other fishes thrive & grow big living in bio-diverse healthy
environments “The Black Mirror” being the ultimate example. The lake she
lives in, a site of scientific interest that literally crawls with life due to the
lakes diverse flora and fauna. Time after time these biologically diverse
lakes throw up truly special fish, and if your still convinced that carp grow
big because of boilies I’m afraid you’ve been had by the hype! Boilies do
add to the food availability, but there is no substitute as far as healthy
growth is concerned for good old-fashioned bugs and other water born
goodies. No matter how much effort we put into baits we can never
reproduce the nutritional profiles of natural tucka. A lot of successful
anglers on the big carp scene stalk with naturals, why? Carp know
instinctively what’s good for them and a natural diet provides vital trace
elements that can’t be duplicated adequately in pellets or boilies. Carp just
don’t fair well on boilies and pellets alone, in fact if it’s all they get it will kill
them in the end. If that’s not enough reason to secure bio-diversity within
our waters what is?
So now we know plenty of good reasons to start looking after the ecology
of our lakes and rivers, not just for the benefit of our fish and the growth
rates or even just for the return of the Emperor. By managing the ecology
of our waters we take responsibility for the environment and strengthen
our position in an increasingly anti sport world.
Next time we will look at the organisms that make up the food chain in a
balanced lake and their roles in the aquatic environment.