Fish migrations in the context of Poland

Wędrówki ryb

We associate spring and autumn with bird migrations. Nevertheless, other organisms, including so-called bi-environmental fish, also move long distances during these seasons. Therefore, World Fish Migration Day is celebrated either on May 16 or October 24. In mid-May, migration ends and egg-laying begins in many sturgeon, including the western Acipenser sturio and the Baltic Acipenser oxyrinchus oxyrinchus.

May marks the end of the spawning of the stingray Osmerus eperlanus, and the beginning of the spawning of the sea lamprey Petromyzon marinus, the alloz Alosa al osa or the cert Vimba vimba. Spring is also the egg-laying season for our and American eels in the Sargasso Sea. In turn, autumn marks the end of migration and the beginning of spawning in many salmonids, including our Salmo salar. Late autumn also marks the end of the runoff of adult European eels Anguilla anguilla from freshwater into the sea. Also in October, the first young eels in the montee stage begin to reach European shores. Fish migration is an important component of many ecosystems.

Fish migration – who should be interested in it

The biology of migratory fish has made them a very valuable component of the ichthyofauna, of insane interest not only to anglers and cooks, but also to conservationists and hydrologists planning the construction of new and retrofitting of existing cross-basins. Ignorance of basic facts and terminology on fish migration is sometimes particularly undesirable in contractors of Project Information Sheets (PIEs) for projects on watercourses. It is therefore worth recalling the most important definitions and pointing out the simplifications that are common today.

Relic species, relic names

In the last century, bi-environmental fish were a much better indicator of the good health of aquatic environments than sedentary species and ecotypes. Today, this is changing, as most of these gill wanderers are either extinct or have become completely dependent on stocking. Many examples can be provided by the recent history of domestic fauna and fisheries management. Certa and sea trout played a key role in the lives of fishermen of the lower and middle Vistula until the Wloclawek barrage was erected. The last native fine salmon from the Drava River became extinct in the 1980s. In the 1970s. Today there is a wild herd there again, but from specimens from the Latvian Daugava.

There is a lot of talk about the migration of salmon and eels, but knowledge about the migration of fish from other families is falling into oblivion. The creators of the fish descriptions in the Polish Red Book of Vertebrates already lamented a few decades ago that even the most experienced, educated fishermen have no idea that species such as the parrotfish Alosa fallax and allozoans used to exist in our waters. They also found it difficult to distinguish between native sturgeons restituted by scientists and activists and exotics escaped or intentionally released from breeding [5].

Early naturalists coined two terms still used today in science and didactics – anadromous and catadromous migration. In Greek, ana means upward, and dromos means run, draft or current of water. So anadromous fish travel upstream, from the depths of the sea they flow through rivers towards streams and even the streams of the Alps and Carpathians. The root and meaning of the term catadromous is equally clear, since katadromous translates as downward, toward the bottom, in the depths, under something.

The famous American ichthyologist and aquarium guru George S. Myers (1905-1985) proposed in 1949. four more adjectives, also based on classical Greek:

  • Diadromous (from gr dia – by) refers to all fish that migrate for reproduction between fresh and salt waters, and ana-, and catadromous;
  • Amphidromous (from Gr amfo – both, all), in turn, refers to species that migrate between seas and rivers or lakes for purposes other than reproduction, e.g.: food or to wintering grounds;
  • Potamodromous(potamos – river) describes species that undertake fairly long migrations within a single river. A river, on the other hand, can be viewed either as a single, large ecosystem, or as a continuum of a multitude of separate ecosystems, albeit different fish lands or contrasting microhabitats, such as rapids and deeps;
  • oceanodromous(okeanos – ocean) refers to species that migrate thousands of kilometers across the ocean, albeit without entering freshwater. The oceanodromic stocks are mostly, but this does not apply to our Polish cod and herring from the southern part of the Baltic.

Only the first of the above terms has spread more widely, although all four appear in some Polish biological dictionaries [2]. However, it doesn’t permeate from there to the KIPs, maybe sometimes only to the environmental assessment reports. Fish from previous geological eras, such as lampreys and sturgeon, are therefore characterized using the vocabulary of previous cultural eras.

Thus, among the native species of Poland, we have:

  • more than a dozen anadromous, from the families of lamprey, sturgeon, salmonid, herring, smelt and even carp (certa and blowfish Pelecus cultratus);
  • only one typically catadromous species: the European eel and an optional catadromous or amphidromous species: the flounder (flounder Platichthys flesus);
  • several potamodromous (notably the mumps Chondrostoma nasus and the European dace Leuciscus leuciscus, to which the previously unsuspected long-distance migrants bream, roach or zander are increasingly being added [2]);
  • a few oceanodromous, which appear quite rarely in our country (such as the horse mackerel Trachurus trachurus, many cod, such as the saithe Pollachius virens, the poutfish Trisopterus esmarkii or the haddock Melanogrammus aeglefinus, known more from fish and chips than from Baltic fryeries).

Sturgeon, salmon, lamprey – charismatic species of our waters

Among the country’s anadromous fish we find a few celebrities, called charismatic, umbrella species or flagship species in the case of protected species. These are, first and foremost, the shortfin mako sturgeon and the noble salmon mentioned at the outset. Both species have been introduced back into Polish waters for years and have received time and attention in the media and at scientific picnics. If the Oder and Vistula rivers are again unobstructed for them, and the spawning grounds in the tributaries become seedbeds for local populations, this will mean that the remaining species of long-distance migrants will also return of their own accord. Or with a little human help. At least that’s how we imagine the revitalization of our rivers.

The sea lamprey has become equally rare in Europe. It is noteworthy that in the United States and Canada, where it ended up by accident, the situation of this species is the opposite. It is practically absent in our country, so any investment that could potentially hinder its reintroduction raises public resistance. In its new homeland, on the other hand, it is being eradicated (not very successfully) as an invasive alien species, devastating native fish, crucial for wildlife and fisheries.

Eel migrations have fired the human imagination for thousands of years. The prevailing view is that only females of this serpentine fish travel inland via rivers and lakes Males stay within brackish waters. For several years, there have been increasing reports that not only males, but also some females of European and Japanese eels are not making their way up rivers and streams. These matters remain as dark as the interiors of eel mink, for data from chemical analysis of otoliths and fatty acids have been found to be in open contradiction to parasitological data. We will discuss them in more detail in another article, as well as the issue: eel in the context of the Polish case [1, 3, 4].

Also worth mentioning here is flounder as a migratory species, discussed less frequently than eel. Flounder quite often ascends rivers, breeding in waters with significant salinity and a temperature of 3-7°C at a depth of 30-300 m. Specimens from the Polish part of the southern Baltic trundle from March to May in the Gdansk, Arkona and Bornholm Depths, possibly in the Slupsk Trough.

Protection of migratory fish in Polish law

Currently, 2 anadromous species – sea lamprey and shortnose sturgeon – are strictly protected in our country, as well as one potamodromous species – Hucho hucho hucho (since 2017). Partial protection was given to the river lamprey, alloza and parpocha, as well as the blowfish – individuals from outside the Vistula Lagoon. A separate Ministry of Agriculture regulation protects bi-environmental fish crucial to the economy: eel and sea trout. The rest of the migratory species are protected through conservation periods and sizes, catch limits, the establishment of closed spawning circuits, and possibly reserves and parks. I described these matters more extensively in a previous text on the Red list of fish – fish and lampreys in the new list .


Photo. masthead: Brandon/Unsplash

In the article, I used, among other things. From the works:

  1. Arai T. (2020). Ecology and evolution of migration in the freshwater eels of the genus Anguilla Schrank, 1798. Heliyon, 6(10).
  2. Brönmark C., Hulthén K., Nilsson P.A., Skov C., Hansson L.A., Brodersen J. & Chapman B.B. (2014). There and back again: migration in freshwater fishes. Canadian Journal of Zoology, 92(6), 467-479.
  3. Dębowski P., Bernaś R., Skóra M. & Morzuch J. (2016). Mortality of silver eel (Anguilla anguilla) migrating downstream through a small hydroelectric plant on the Drawa River in northern Poland. Fisheries & Aquatic Life, 24(2), 69-75.
  4. Durif C.M.F., Arts M., Bertolini F., Cresci A., Daverat F., Karlsbakk E., …. & Browman H.I. (2023). The evolving story of catadromy in the European eel (Anguilla anguilla). ICES Journal of Marine Science, fsad149.
  5. Glowacinski Z. (ed.) (2001) Polish red book of animals. Vertebrates. PWRiL, Warsaw.
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