THE CORMORANT
From the
Red List to the Pest
List
The (Great) Cormorant Phalocrocorax carbo has been persecuted for centuries because of its fish eating habit. From being almost extinct
in Germany in 1950, it was declared
a protected species from the beginning of the 1970s. Populations have increased and are today larger and more stable
as in preceding centuries.
The welcome increase in the species
generates a potential source of conflict between conservationists on the one hand and anglers and fishermen on the other.
In many EU states there is either a regular hunting season for the bird, or breeding colonies have been systematically destroyed.
In Germany alone permits are granted annually
to shoot some 6000 cormorants.
The reasons
for the positive population trend
The placing of the cormorant under
protection in the 1970s is the main reason for its spread during the past decades. In addition food availability has improved.
The drainage of agricultural nutrients into lakes and rivers promotes the development of many fish species providing the birds
with rich pickings.
The increase of the species on
inland waters in winter is also connected with the improved climatic conditions in Central Europe.
Other than in the past, the cormorant in Central Europe is presented today with straightened
river courses without oxbow lakes and overgrown banks, and a large number of open flooded gravel pits and fish ponds. The
waters over-stocked by the anglers are an open invitation to the birds to spend the winter in these areas plentiful in fish.
The former winter quarters in the Mediterranean area are deserted.
Food
Cormorants are fish eaters preferring
prey between 10 and 20 cm in length. Before such fish reach a size suitable for human requirements they are naturally subject
to a high mortality rate. As a result the damage to stocks by the cormorant is relatively small.
The daily nourishment requirement
of wintering birds lies between 400 - 500 g fish, increasing to 700 g in the breeding season. Cormorants which hunt in salt
water need only 200 - 300 g fish in winter and 500 g during the breeding period, due to the high fat content of salt water
fish.
In waters with natural surroundings
species of little interest to anglers such as Roach Rutilus rutilus, Rudd scardinius erythrophthalmus and Chub leuciscus cephalus are caught. In Switzerland
it has been established that 60% of fish taken of wintering Cormorants are Roach.
Angling club fish ponds, straightened
river courses, flooded gravel pits and reservoirs are usually characterised by an artificially high fish stock. As the cormorant
mostly hunts fish swarms, it is natural that the larger part of the cormorants prey is taken from the fish ponds.
Cormorants take primarily young
and sick fish. Of Roach caught by cormorants in a Swiss lake, 30% of the fish were infected with the tapeworm Ligula intestinalis, whereby only 3% of the total of the fish in the lake were infected. Hunting cormorants
concentrate on these sick, slower and weaker fish and thereby contribute to a healthy fish stock.
Influence
on fish stocks
It is impossible to estimate fish
stocks in river systems and lake districts. As many fish species regularly migrate, from the ocean into the tiniest stream,
the influence of predators at particular points cannot be determined. The cormorants fish uptake can only be established therefore
in small, closed waters such as fish ponds. With this background, the numbers and percentages often introduced into the discussion
on the alleged damage to fish stocks by cormorants is more than questionable.
The hunting success of the cormorant
in waters with natural surroundings is very low. Trees and water plants at and overhanging the banks, together with structurally
rich oxbows, offer the fish a large number of hiding places. The birds hunt only in the open areas of wide open waters.
Angling club fish ponds, straightened
river courses and flooded gravel pits are usually characterised by a lack of varied structure. This leads to a loss of 20
60% of stocks to hunting cormorants in Carp cyprinus carpio breeding ponds. The fish population in such pond systems is unnaturally
high, the fish have no protection and the small fish normally preferred by the Cormorants are usually completely removed by
the pond managers.
In rivers, lakes and natural ponds
looked after by angling clubs the losses to cormorants are considerably less, amounting to less than 10% of the total stock.
The proportion of fish species of little interest to anglers caught by cormorants is usually over 50 % of all fish taken.
Fish protection
without the shotgun
On waters threatened by cormorants,
such as fish breeding ponds, fishermen, local authorities and conservationists should work hand in hand in improving the natural
structure of the areas. This includes in particular the planting of exposed bank areas with groups of trees and the creation
of shallow water areas and reed beds.
Structural improvement of waters
leads not only to rest and protection zones for the fish; they also lead to the creation of new spawning grounds. Through
this a more vigorous fish population is promoted which can better cope with losses to cormorants.
A steel wire construction over
the ponds can also provide effective protection.
It has been established that single
warning shots in winter quarters do not frighten off the birds. They simply move to other ponds which results in a greater
energy requirement which has to be met by increased food intake.
If all possible measures implemented
to protect fish stocks fail, and the birds cause provable damage, the fishermen affected should receive financial compensation
from the state.
Humans and cormorants can co-exist
without any problems. Where the birds can actually cause damage, in the rule at fish ponds, there are enough protection measures
available. Hobby anglers, who at present complain the most about cormorants, should concentrate instead on improving the living
conditions of their fish and reduce the unnaturally high and damaging size of the fish stocks in the waters they manage. They
should also be advised that cormorants have hunted in European waters for a long time and that, in the 21st Century,
competition jealousy and unfounded quasi-scientific theories will have no influence on the implementation of urgently required
nature and species protection measures throughout Europe.
Source: Komitee gegen den Vogelmord
website
http://www.komitee.de/projekte/brd/kormoran.html
Translation © David J A Conlin
2004
