Cormorant – a bird that dares to eat fish


“As a result of the perpetrators’ deliberate, criminal actions, 250 to 300 chicks were killed, and dozens of cormorant eggs were destroyed. More than 100 nests were also destroyed, “reported a spokeswoman for the Żnin District Police Station in early May. “Police officers have charged the 53- and 54-year-olds with violating the provisions of the Animal Protection Act regarding the killing of animals. (…) They face up to three years in prison.” The crime occurred at a cormorant colony on an island on Lake Tonovo, in the southwestern part of the Kuyavian-Pomeranian province. Boot marks were still visible on some of the slaughtered chicks.

Similar events occur every year, but rarely on this scale. The last hecatomb of cormorants took place in June 2005, when someone got into the colony at the Jeziorsko reserve and killed about 600 chicks. He ripped off their wings and paws, broke their spines, and tore off or decapitated their heads. They lay on the ground, floated on the water, hung from trees and bushes. Among them, the ones that threw themselves from their nests in terror were dying. Feathers, blood and trepidation everywhere. It looked like the work of a madman. But a madman doesn’t walk around with a ladder, doesn’t act as a team or for show. He is also rarely protected by a conspiracy of silence. The perpetrators of that massacre have not been identified.

The Vikings believed that the souls of people who died at sea and whose bodies were never found eventually made their way to the lucky island of Utrøst, from where they sometimes came in the form of cormorants to see their loved ones. The early Scandinavians saw cormorants as semi-sacred beings, and in their seiches a good sign. The more birds gathered in one place, the more luck they augured. In esoteric books, the cormorant symbolized responsibility, courage and a willingness to take matters into one’s own hands. He said: do not be afraid, go down even to the very bottom, if it helps you find your way to happiness.

But it was not this vision that ultimately dominated the imagination of later European converts to Christianity. They believed that Satan, who lurked in paradise to tempt Eve, first perched on the Tree of Life in the form of a cormorant. And all because he was black (which since the early Middle Ages has been inextricably associated with Evil and death), and on top of that, he was still big. It was not helped either by the name cormorant, derived from the Brythonic language, with which the mythical sea giant was called in those parts, or by the fact that in many regions of Europe until the 17th century. Cormorants were commonly used to catch fish. Tamed and trained birds were fitted with rings around their necks to prevent them from swallowing larger pieces, a practice still followed in traditional corners of China or Japan.

The cormorant – the myth of the insatiable pest

When their connivance with the devil was finally forgotten, the problem turned out to be… a wolfish appetite for fish. Ironically, it is not us who symbolize greed, avarice and intemperance, but the cormorants. Back in the early 19th century. European cormorants lived in colonies, the largest of which could number tens of thousands of nests. Both birds and people had plenty of room, and neither one nor the other lacked fish. Despite this, there has been increasing talk of cormorant invasions and the fact that they are eating fish, after all, not for them, but created for us.

So war was declared on them. For the next hundred years with a cover, they were exterminated at all costs. In Germany and Denmark, the military was regularly employed to combat the birds, among others. Using… cannons. There, as in many other countries, they were exterminated completely. Within our borders at that time, around 1925, there were still 150 pairs, nesting in several small colonies. Systematically culling cormorants caught their breath only when people got busy with organized killing of each other. After World War II, things began to move in a better direction, but the myth of the insatiable pest persisted, and in various countries, regardless of legal status, cormorants were persistently persecuted. And then something happened that to this day no one can explain.

Cormorant baby boom

In the late 1950 s. and 60. across the continent, sea ravens (as they used to be called) began to arrive, and the increase in their numbers continued uninterrupted until the early 2000s. Cormorant baby boom. This is well illustrated by events in our own backyard, where the then very rare cormorant was given the status of a protected species (in 1952). Another important date was September 28, 1957, when the Minister of Forestry and Timber Industry established an almost eleven-hectare reserve in Kąty Rybackie “to preserve and protect the natural breeding site of the black cormorant Phalacrocorax carbo and the gray heron Ardea cirenea.” When documentation work began for the reserve, which turned out to be a turning point in the history of cormorant conservation in Poland, their nests had not been seen there for decades.

Two years after it was founded, there were 117 of them (1,800 nationwide). In 2000, the area of the reserve was expanded to 102.54 hectares, and the colony from the Vistula Spit was considered the largest in Europe. It reached its record in the 2006 season – more than 11,500 pairs. Today there are about 4,500 active nests there, and 25,000-30,000 pairs nationwide. In contrast, the largest cormorant settlement on the continent is (or perhaps due to warfare was) probably the one in Crimea, with more than 14,000 nests.

Cormorant – eats only fish

In scientific terminology, the cormorant is referred to as a mono, specifically an ichthyophage. He eats only fish. The species does not matter. He flies to where the fish are plentiful and catches the ones that happen to be most plentiful. When the fishery empties, he flies elsewhere, because it doesn’t pay him to chase individual minnows. Especially since cormorants like to hunt in teams. Like the dolphins in David Attenborough’s films. As some of the birds swim in a tightening circle on the surface and just below it, the remaining birds bare and hold the shoal from below. After a while they will change.

Cormorants mostly catch fish that are 10 centimeters or more in length. How much more? It depends on their shape. Slender pike can be 30, even slimmer eels as large as 50, and crackly bream or perch as small as 20 centimeters. As with any angler, cormorants also have record-breaking performances. Mastering a large, strong and slippery fish is quite a challenge, and swallowing it can simply be dangerous. The amount of fish eaten per day depends on the season, condition and, above all, the family situation of the cormorant, and usually ranges from 146 to 700 grams. It happens that parents of several children bring more food to the nest, as well as that adult birds fast for several days.

Every fish caught by the birds becomes a thorn in the throat of the fishermen. In the 1990s, when the fast-growing cormorant population generated the most excitement, they calculated that they were catching 3,600 tons of fish a year. Maybe, but there were some serious methodological errors in this account. First and foremost, it was assumed that the so-called The biomass of fish in our waters is something constant, yet its value, even in farm ponds, is constantly changing.

The key to understanding what is happening in a lake or river is to trace the developmental path of the fish, or their age structure. One and the other is in the shape of a pyramid with a very wide base, which is formed by a fry. Every fish donkey dreams of one day becoming an alpha fish, but only a very few succeed. At subsequent levels, the vast majority of “competitors” drop out – due to disease, predators and, above all, competition and, of course, trapping. Take, for example, such an eel. One hectare of the reservoir is stocked with a hundred fry, of which 4-5 fish (2.5 kilograms) are eventually caught. What happened to the other 95 eels? They fell off in the race to the top of the pyramid, and since the calculations involve breeding conditions, the cormorants had nothing to do with their disappearance.

The second major error in the fishery’s balance sheet was the assumption that all fish eaten by cormorants would be caught by fishermen. National and external analyses show that cormorants at worst eat 5%, top 10% of what fishermen catch. We also know that ruffe, rudd, carp, undersized roach and perch and, in places, goby in our conditions account for 80% -100% of the prey of cormorants and about 30% of commercial catches, which would mean that the alleged “damage” caused by the birds melts to the level of statistical error. That’s not all.

Due to the intensive fertilization of fields, our waters are rapidly eutrophicizing (fertilizing and overgrowing), giving an advantage to carp fish such as carp, carp, bream and roach, and these are displacing species considered more noble, valued by fishermen and customers. And this is where the cormorants come to the rescue, focusing their attention primarily on the former. Is it possible that these birds could have a positive impact on economic fish and fisheries? Maybe they are not pests, but allies of fishermen? Today we know beyond a shadow of a doubt that natural predation has a positive effect on the condition and population of its prey and the ecosystem as a whole.

The exception in the business (and only business) equation with the cormorant may be the aforementioned eel, as there are many indications that this is the only fish the “black fisherman” will swim for, if he has a choice. Maybe it’s the extraordinary number of calories provided by the fatty eel, or perhaps its ideal swallowable shape? How about the taste or the fact that it burrows into the bottom during the day and is easy to pull out of there? Whatever the reason – cormorants like eels.

And one more thing: during the explosion of the cormorant population in Poland, catches increased several times, reaching the highest values in the 1990s. Someone will say that this is due to stocking. Sure, but at the same time we have proof that cormorants don’t eat all the fish. How is it that their numbers are increasing and the catches are not decreasing? Of course, a squadron of black birds visiting a small complex of breeding ponds is another story, but as far as we know, only those with strong suicidal tendencies land there, and besides, they are then allowed to scurry and chase them away.

In 2003, Poland’s catch volume reached 203,300 tons, of which marine fish accounted for 160,300 and freshwater fish 43,000 tons. A decade earlier, in 1991, the total was 462 thousand tons. While the volume of marine catches is declining due to overfishing and the introduction of international limits, inland fisheries are either holding steady or growing year on year, with a total of about 80 thousand hectares of ponds, 140 thousand hectares of rivers and nearly 350 thousand hectares of lakes at their disposal. What would happen if a small percentage of the fish that swim in our waters were eaten by cormorants? And so it would be ridiculously little compared to what we throw away and waste.

Cormorants are most likely to establish their colonies near fishing grounds, usually no more than 30 kilometers away. They try to build their nests in hard-to-reach places – in our country these are mostly tall trees, most preferably on islands. It is true that the trees used by cormorants eventually die, but the nest-laden trees can then stand for up to several decades. Well, unless someone orders them to be cut down, thereby forcing the birds to occupy the next still green ones. (Against all appearances and logic, this is not an uncommon practice).

And so it must take another few years for new plants to start growing on the fecal-acidified soil. How many trees are withered annually in Poland due to cormorants? A dozen, a few dozen…? Seriously! Are we going to account for them, just like we account for fish? According to official figures, the State Forests will only be in business in 2020. cut down 38 million trees, and in another 40 each. How many millions have been cut or poisoned by highway workers, local governments, boards, yard and garden owners during this time? How much more will they cut…?

Finally, a handful of practical information from the media of the “Salamandra” association, whose representatives discovered the massacre of cormorants on Lake Tomsk, and then publicized the case and filed a criminal complaint:

  • “Yes, the cormorant can cause damage – especially in aquaculture (ponds) and during wintering.”
  • “In natural reservoirs, the cormorant generally contributes to maintaining an equilibrium that has been disturbed, for example, by predatory fishing, leading to an excessive reduction in the population of predatory fish. It mainly eats fish of little, zero or even negative economic importance, such as small carp: roach, bream, bleak, or perch: primarily the icrocerous ruffe and small perch (it also eats larger fish, but in the natural environment they make up a small percentage of its diet).”
  • “Due to the cormorant’s ability to cause damage and the lack of a threat to the species, it is under partial (rather than strict) protection, and on ponds that are breeding concessions, some of the prohibitions (such as scaring) do not apply at all.”
  • “There are legal and humane methods developed to protect, for example, ponds from cormorants, but, for example, oiling eggs, deterring ponds or even shooting are not effective measures in the long run, because they do not solve the cause of the increase in the number of cormorants – the disruption of the ecological balance in aquatic ecosystems.”
  • “Impacts with long-lasting effects are those that contribute to improving the balance of aquatic ecosystems, such as increasing the number of hiding places for small fish (including vegetation), increasing the proportion of predatory fish (including fall stocking and limiting their catch), postponing eutrophication, and limiting the formation of new cormorant colonies (permanent, “old” colonies tend to have low reproductive success (…)).”
  • “Among the counterproductive measures sometimes taken, that is, which usually contribute to an increase in the number of cormorants in the region, is the breaking up and dispersal of their breeding colonies – in new colonies, reproductive success is even several times higher than in old ones, and after a few years the total number of cormorants will increase (…).”
  • Therefore, an action similar to the one described at the beginning of the article (author’s note) “is not only illegal barbarism, but may also contribute to the growth of the cormorant population in the region and the scale of possible conflicts (…).”

Jacek Karczewski, naturalist, activist and tireless popularizer of nature. His third book, “See the Bird,” was recently published. Stories along the way.” Before her were “Her Majesty the Goose. Tales of Birds” and “Night of the Owls.” He is the author of numerous articles published in both traditional magazines and in the online space, as well as many publications of Jestem na pTAK! (until recently Birds of Poland), an association with which, as its co-founder and, until recently, long-time chairman of the board, he has been associated since its inception. Originator and copywriter of many projects implemented there, which are among the largest implemented in Poland to date, including appreciated and widely recognized social campaigns. Among the most notable implementations are Be on pTAK!, A bird too man!, There won’t be birds, there won’t be singing!, Night of the Owls, Garden on pTAK!, Bouquet from the fields, Swamps are good! or Orlik Ptak jakich Mało! He also cooperates with organizations outside of Poland.

Source: See the bird. Stories along the way, Poznan Publishing House, Poznan 2021

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