Flatfish and sharks of the Polish Baltic Sea

Whale Shark Day, which falls on August 30, is an excellent opportunity to remember the sharks and rays of the Polish Baltic Sea. The festival of the rest of the chimeras, sharks and rays falls on July 14, and is therefore overshadowed by the celebration of the demolition of the Bastille. The subject of the presence of these fish known to us mainly from movies has been regularly recurring in the Polish media for several years, where one can find “reports” of sharks threatening swimmers or eating fish out of fishing nets for our fishermen [e.g.: 20, 21,22, 23, 24].

A second, independent reason for the importance of this topic is the plans of the European Commission and the United Nations to more effectively protect all cartilaginous fish of the All-ocean. All of them, that is, even those hated as cannibals and/or fishing pests. Also those caught en masse as a delicacy or miracle drug for potency. And then there are the well-liked ones, suffering precisely from an excess of affection, such as manta rays and mobula, which everyone wants to take photos with underwater or show them to toddlers in the oceanarium [4, 5, 6].

It is therefore worth taking a closer look at the representatives of elasmobranchs swimming in our sea.

In the Baltic Sea it swims and a shark is named

Flatfish, sharks and sawfish are cartilaginous fish that belong to the subclass of elasmobranchs. They get their name from the location of the mouth and nostrils on the underside of the head. The group includes about 950 species of fish, usually predatory. So, when enjoying a vacation in the Baltic, should we be afraid of sharks? Experts from Polish oceanariums reassure that our sea (especially the “Pacific”) is too desaturated to be home to species familiar to Poles on vacation in Egypt or the Maldives.

The SharkSider website [19] lists more than a dozen species of sharks found in the Baltic Sea, but they primarily live near the Danish Straits. Farther south and east they venture only after saltwater inflows from the North Sea. These, in turn, are becoming rarer as a result of climate change, as our former cod fishermen know all too well.

On our side of the Straits it is relatively common to see herring lamna Lamna nasus – a fast and skilful species, according to some, dangerous to sailors or swimmers (like any large, wild and predatory animal – especially when it feels attacked).

Only four species of cartilaginous fish are reported as certain to occur in Polish territorial waters. They are:

• Two species of not-so-large sharks: the common th ornback Squalus acanthias and the black thornback Etmopterus spinax;
• One species of typical stingray: the ray radiata, or star ra y Amblyraja radiata (listed as “ray” in Polish translations of the EC and EP);
• one species of typical sawfish, specifically the fine-toothed sawfish Pristis pectinata [7, 8, 9, 12, 13, 14, 15, 17, 18].

I am writing here about “typical” species, as many “atypical” ones are known, representing intermediate links, combining features of stingrays and sharks. This includes, for example, the entire family of rockfish, now known as guitarfish. We also know of a few exceptions among elasmobranchs, such as parasitic species, carrion-eaters and plankton-eaters. We only became aware of some of them in the 20th century. and rather haphazardly, such as the deep-sea big-tooth shark, one of the three (along with the basking shark and the whale shark) gentle giants that filter plankton [9, 16].

How endangered are native elasmobranch species? Are you afraid of the shark or about the shark?

The presence of spiny dogfish in our waters is not surprising. It is the most common of the world’s cartilaginous fish and one of the most resistant to human pressure and natural environmental stressors representative of this cluster. It belongs to the small to medium-sized sharks, as females usually reach 1.2m in length, males usually up to 1.6m, rarely 2m. Globally, it has been assigned “only” the VU – vulnerable category [8, 11]. Thus, it is as threatened with disappearance as the bison, porpoise or mountain toad in Poland [10]. It can live as long as 75 years, but reproduces at a truly tortoise-like pace, as the standard gestation period for it is about 2 years [8, 11].

The black th orn (known in English as “silk belly,” velvet belly)is second only to the thorn in number, as well as size. It can glow in the dark, as can many of its relatives, and it can do so already in embryonic life. At the same time, it is one of the few fish for which no use has been found for millennia, although much searching has been done. For centuries, dead spiny dogfish were caught accidentally, during crawfish and shrimp hunts, and simply thrown overboard.

Only recently have the seas become so overfished that it has become profitable to process these babies into bone meal or animal feed. Some hope lies in their resistance to heavy metals (Cd, Cu, Hg, Zn), which accumulate in fats. Bionicists hope to work out the mechanism of their immunity at the cellular and tissue levels.

On the other hand, the high accumulation of heavy metals discourages their use as food. Perhaps it is because of this that the colchicine herd has grown since the 1970s. In the 1970s. fell by only _1/5, allowing the International Union for Conservation of Nature (IUCN) to conclude that the “silk bellies” are not threatened by anything . Pregnancy of thorns lasts about a year, the number of young ranges from 6 to 20 per litter, with females living up to 22 years and males up to 18. Unfortunately, many specimens are infected with Anelasma squalicola barnacles, causing infertility in their hosts [7, 17].

Starry stingrays special guests in Baltic waters

The only representative of stingrays proper, occasionally venturing into Polish territorial waters, remains the radiant ray (star ray).It can be found in the oceans of the entire Blue Planet, but it definitely prefers colder waters. Indeed, most specimens reside in the cold waters of the far North. If it gets closer to the equator, it swims in deeper layers with lower temperatures. In the course of evolution, it has lost the venom spines typical of stingrays. It can, however, change color. It is a bottom predator, hunting crustaceans and fish. As a “lover” of cod, capelin and shrimp Pandalus borealis has been competing with humans for food for several centuries.

Despite this, you don’t hear about its deliberate extermination, and bycatch (the part of the catch that includes non-target species caught accidentally) and ghost nets are cited as the most common reasons for the decline in numbers. It is also caught on purpose – after all, humans are omnivorous. The U.S. administration has been considering reducing fishing quotas for the species for years, or even placing the stingray under protection. Still, not enough data has been collected to justify such measures [3].

The dramatic paradox of the lack of protection of the fine-tooth saw

Another species found in the Baltic is the smalltooth sawfish. I associate this species with our eel. Not only because it is third in the high seas and only occasionally flows up rivers, but mainly because it is among the Critically Endangered Species (CR) listed in the Washington Convention, yet still not under species protection. Paradoxically, therefore, it is allowed to catch sawfish or exterminate them as fishing pests, it is allowed to ravage their habitat, but it is not allowed to transport them across national borders (including in the form of fillets, tooth necklaces or whole stuffed specimens). The meat of young sawfish is still considered a delicacy, but many more of them are killed by bycatch and pest control [1, 2, 4].

Why are the European Commission and environmental organizations paying so much attention to spodousti?

The cluster of elasmobranchs is proving to be one of the most threatened groups of aquatic organisms with extinction. Many factors contributed to this. In addition to habitat degradation, bycatch, the presence of ghost nets and poaching, their biology is contributing to their disappearance. Flatfish and sharks are almost always K-striders with long reproductive cycles and low or very low numbers of offspring. So what if they are sometimes oviparous (like the aforementioned star rays), when they lay no more than 300 eggs a year? What is this compared to the millions of egg grains of bonefish? There is no shortage of oviparous and even fully viviparous forms among them, developing placentas analogous to those of mammals. Giving birth to one and only young every couple of years (like in elephants) has contributed to the disappearance of mobulas and mantas, so eagerly watched by divers [9].

The second reason for their extinction is the political affiliation of their habitats, including spawning, wintering and most important feeding grounds, to international waters, in simple terms, therefore, “nobody’s waters.” Also, analogous to the case of benthic bivalve fish, ONLY international cooperation can save these marine migrants [4 ,5, 6].

Is the Baltic too sweet for the shark? Not to get too cute!

The practical absence of sharks and their low activity in the waters of the southern Baltic, including around our beaches and cliffs, is explained by their typically marine nature. Journalists first frighten the public with the presence of chondrichthyans, and then reassure them that these fish would not live long in our country. Or at least they would remain inactive. That’s because they need a lot of energy for osmoregulation, especially in waters as desaturated as the Baltic. In the articles, no one explains how the physiology of a shark or ray actually differs from that of bony fish. Superficial explanations, however, do not convince everyone. Why?

If only because not all sharks have the same environmental requirements. Such a black thorn, for example, which enters Polish waters, often feeds in the estuaries of rivers. And the fine-toothed sawfish is even a typical species of lower sections of rivers and sweetened lagoons [1, 2].

So, with the Baltic Sea getting warmer and warmer, and stripped of most of its potential prey (small and medium-sized fish, porpoises, seals), are we sure we are not threatened by shark raids on Polish bathing beaches?

Fiction and truth

Verified, unembellished with fantasies facts about Polish nature, in this case about gophers observed sporadically in our territorial waters, turn out to be more interesting than “journalistic ducks” and unverified media reports. Knowledge of the country’s fauna is becoming more complete, including through citizen science. We have hard evidence of at least temporary, natural presence within our borders of many species previously considered exotics. The sightings/hearings in the Slowinski National Park alone include. The snowy owl, the turquoise (a large sea duck, not to be confused with the toucan!) or the pink flamingo.

Fish are much more difficult to observe than birds, if only because they usually “don’t have a voice” (although a screechfish taken out of the water “squeaks”). In the case of these aquatic vertebrates, we have data from bycatch fishermen, as well as observations by a small number of ichthyologists.

Thanks to them, we know that the fauna of Polish chondrichthyans, however poor in species and sparse in individuals, is as diverse as the entire nature of the Baltic Sea. This is because it features two very common, quite friendly (or at least harmless to humans) sharks, one stingray with its typical stingray problems, and finally one super rare in the world, but legally unprotected sawfish.

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

1. Carlson J., Wiley T., Smith K., Pristis pectinata, [w:] The IUCN Red List of Threatened Species 2020 [online], version 2020-2 [dostęp 17.08.2023]
2. Pristis pectinata. (English) in: Froese R. & Pauly D. FishBase. World Wide Web electronic publication. fishbase.org [accessed November 3, 2013, 17.08.2023].
3. Kulka D. 2020. Amblyraja radiata, [w:] The IUCN Red List of Threatened Species 2020 [online], version 2020-2 [dostęp 17.08.2023]
4. EC draft regulation https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A52022PC0304
5. Content of the Council of Europe position: https://www.consilium.europa.eu/media/65128/st10867-en23.pdf
6. Content of the position of the European Parliament https://www.europarl.europa.eu/doceo/document/TA-9-2023-0277_EN.html
7. Coelho R., Erzini K. 2008. Life history of a wide-ranging deepwater lantern shark in the north-east Atlantic, Etmopterus spinax (Chondrichthyes: Etmopteridae), with implications for conservation. Journal of Fish Biology. 73, 6: 1419-1443.
8. Ebert D. A., White W. T., Goldman K. J., Compagno L. J., Daly-Engel T. S., Ward R. D. 2010. Resurrection and redescription of Squalus suckleyi (Girard, 1854) from the North Pacific, with comments on the Squalus acanthias subgroup (Squaliformes: Squalidae). Zootaxa. 2612: 22-40.
9. Ebert D., Fowler S., Compagno L. 2013. Sharks of the world: a fully illustrated guide to the sharks of the world. Wild Nature Press, Plymouth.
10. Glowacinski Z. 2022. RED LIST OF VERTEBRATES OF POLAND – UPDATED VERSION (1ST AND 2ND DECADES OF THE XXI CENTURY). RED LIST OF POLISH VERTEBRATES – UPDATED VERSION (1ST AND 2ND DECADE OF THE 21ST CENTURY). Chrońmy Przyrodę Ojczysta 78, 2: 28-67.
11. Natanson L., McCandless C., James C., Kelsey H. J. 2017. Gestation period and pupping seasonality of female spiny dogfish (Squalus acanthias) off southern New England. NOAA Fisheries Scientific Publications. 4 (115): 473-483.
12. Nikolski G. 1970. Detailed Ichthyology. The crowd. Francis Staff. PWRiL, Warsaw.
13. Rembiszewski J., Rolik H. 1975. Cyclostomata et Pisces. Catalog of the Fauna of Poland. Vol. 24, pp. 251, 1975. Published. PWN and PAN – Institute of Zoology, Warsaw.
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15. Terofal F., Militz C. 1996. Marine fish. Translated and adapted by Henryk Garbarczyk and Eligiusz Nowakowski. Świat Książki, Warsaw.
16. Taylor L., Compagno L., Struhsaker P. 1983. Megamouth – a new species, genus, and family of lamnoid shark (Megachasma pelagios, family Megachasmidae) from the Hawaiian Islands. Proceedings of the California Academy of Sciences. 8 (43), s. 87-110.
17. Soaszek B. 2018. First record of the deep-water shark Etmopterus spinax (Chondrichthyes: Etmopteridae) from the southern Baltic Sea (Pomeranian Bay). Oceanology, 3, 60: 426-430.
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