Winter spawning of glacial relics of the Baltic Sea

Among the fishes of the All-Ocean, we will meet many more species spawning in winter than in freshwater. In rivers and lakes, December marks the end of the spawning of many salmonids and the beginning of burbot. In the Atlantic, on the other hand, this is the spawning time of the halibut we know so well from our plates, as well as many peculiar species. Some of them are living monuments to the cooler phases of the climate in the gray waters of the Baltic: the long-billed striped bass Lumpenus lampretaeformis, the four-horned hen (hornbill) Myoxocephalus quadricornis , and the bottomfish Liparis liparis. Due to the rarity of their occurrence and their importance to science, all three have lived to see species protection in our country (partial from 2014 to the present). The fourth kingfisher among our fish is the unprotected oystercatcher Pholis gunnelus [1, 2, 5, 7, 9, 12, 14].

Winter spawning of the ribbonfish

The banded eel belongs to the family of stychiidae of the order Perchidae. As its name suggests, it is characterized by its ribbon-shaped, highly elongated body, making it somewhat similar to an eel. With its naked, pointed head with relatively large eyes, thread-like ventral fins and a long dorsal fin extending from head to tail, it looks quite amazing. Its sides and back are colored light brown with a blue or green tint, decorated with a marbled pattern, while its belly is green-yellow. It lays eggs on the bottom in December and January. These eggs are few in number, about 1,000 grains per female.

Freshly hatched larvae float in the depths of water (pelagial) for about 3 months. They then feed on plankton. When they grow up, they descend to the bottom and begin, like their parents, to feed on small benthic fauna. They become sexually mature after 3 years, and live to a maximum of 9. Lumpenus lampretaeformis is most commonly found in the North Atlantic: from the White Sea through Greenland, Szpicbergen, the Faroe Islands and the coast of Scotland to Labrador; further south – in the Danish Straits, the Baltic Sea, off the coast of Massachusetts – in a scattering, as a remnant of colder climatic eras. The striped bass prefers greater depths, 30-200 meters, usually over sandy or muddy bottoms. The gray waters of the Polish Baltic are too sweet and too warm for it. It seeks places that are exceptionally cool and most heavily saline [2, 5, 11, 15].

About the chicken that was not a rooster

Hornbill and demersal, on the other hand, are representatives of the order Scorpenocephalans, belonging to the cephalopod and demersal families, respectively. The four-horned hen is a typical inhabitant of cold Arctic and Atlantic waters. It needs cold and well-oxygenated places. It is less concerned about salinity, which is why in North America, Scandinavia and Russia it is found in estuarine sections of rivers or in lakes, for example: Onedze [1, 2, 5, 9, 10, 12, 14]. Polish Wikipedia still classifies it as a member of the family of headwaters, but some ichthyologists have recently moved it to the related family Psychrolutidae, which lacks a Polish name. A typical member of that family – the blobfish Psychrolutes marcidus – has remained the hero of many memes for more than 10 years as the world’s ugliest fish.

The hornbill owes its name to the presence of four seemingly insignificant, but easily discernible, papillate outgrowths on its flat, sort of frog-like, head with a broad snout. It has a characteristically tapering, somewhat laterally flattened tail. Its spotted gray-brown pattern camouflages it perfectly on a rocky bottom. Unlike the ribbonfish, it prefers the shallows. Here it hunts mollusks, crustaceans and small fish. It moults like the ribbonfish – from December to January. It lays more eggs, from 2 to 9 thousand grains per female.

As in the case of many other fish that produce few eggs (from sticklebacks to pikeminnows to prairie fish), the male guards the deposit. M. quadricornis is the largest mature among small fish, as it lives up to 14 years. The IUCN has assigned the quadricornis hen the lowest category of threat “least concern (LC)”. This is an overly optimistic estimate, especially for relict populations from the Baltic Sea, Karelia lakes, Finland and Sweden. They, after all, can’t retreat northward, fleeing climate warming and pollution. In summer they save themselves from the heat by descending to depths of 100 meters, but there they are increasingly dying in anaerobic zones [4, 5, 6, 8, 12, 14].

Small is precious

Most sources cite the example of the common denfish Liparis liparis (not to be confused with the small, green man-eating Liparis loeselii Liparis loeselii – because the latter is a plant!), typical of the colder shelf waters of the northeastern Atlantic, from New Earth and the Barents Sea through the Norwegian and Celtic Seas to the English Channel. As early as almost a century ago, there were claims that the Baltic population had evolved into a separate species of the bearded dunlin L. barbatus. This taxonomic approach fundamentally changes our view of this evolutionary lineage (population group). It should be reflected in a more serious approach to the conservation of this inconspicuous fish. The dennik, due to its hollow, slippery skin, laterally flattened tail, perpetually bloated belly and seemingly oversized head, looks like a huge tadpole.

By nature it is short lived, usually 3 years. It moults slightly longer than the others, from November up to and including March. Its translucent, dirty yellow, sticky, demersal (bottom) eggs are laid in walnut-sized clumps. It sticks to colonies of bryozoans, caviomorph polyps, algal molds or the crevices of stones. The denworm larvae hatch after 6-8 weeks. They are characterized by a bulbous shape and are 5.5 mm long. They lead, like the tapefish, a pelagic lifestyle, drifting with the currents often over great distances. When they grow to 16 mm in length and grow a ventral sucker, they descend toward the bottom and begin an adult lifestyle, catching crustaceans, less frequently fish and polychaetes [3, 4, 5, 7, 9, 12, 14].

Oystercatcher shares features with predecessors

The oystercatcher Pholis gunellus is a member of the oystercatcher family of the order perch. In appearance, it resembles the ribbonfish due to its ribbon-like body, covered with a thick layer of mucus. Like the denfish and henfish, it inhabits coastal shallows, descending to 100 meters in summer. Baltic forms, compared to typical Arctic and Atlantic forms, are dwarfed (20 instead of 30 cm long), found from the White and Norwegian Seas to the Delaware Bay.

It moults from November to January, in waters of 0-2°C. It is ostracophilic, like tropical cichlids, when it lays its eggs into empty shells, rather than in psotic mounds between rocks. It produces remarkably few eggs, raptly 80-200 grains of 1.7-2.2 mm in diameter per egg. Interestingly, the fry are cared for by both parents (mainly the mother?), not just the father. P. gunellus larvae lead a pelagic, planktonic lifestyle. After reaching 3 cm in length, they switch to an adult, demersal lifestyle. Oystercatchers live up to 5 years [2, 5, 7, 9, 12, 14].

How (not) glacial relics?

Experienced fishermen and scientists warn that mere listing of protected species will do little to change the situation of Baltic glacial relics. It is much more effective to protect entire ecosystems. First of all, it is necessary to prevent further overfertilization (eutrophication) of the waters of our sea. It leads to the formation of anaerobic zones near the bottom and blooms of poisonous cyanobacteria. That’s why it’s so important to use less fertilizer inland, and then protect the Baltic’s catchment area through buffer zones of rivers and ditches.

Let’s leave the remnants of reed beds and riparian areas! Let’s create new buffer zones! And the Baltic kingfishers and the rest of the fishery will thank us! In the sea itself, too, there is much to be done. It is very important to have the right timing and technologies for carrying out hydrotechnical works, related to leisure, harbor and energy infrastructure, especially when erecting new wind farms and digging aggregates. The latter are not lacking on the shoals of our economic zone. After all, in addition to the well-known amber, we have quite a lot of iron-manganese concretions, construction aggregates or heavy minerals. It is worth giving up fishing gear that destroys the structure of the bottom, especially vegetation and shoals of mollusks. Fuel spills and sunken munitions also do not serve ichthyofauna [1, 2, 5, 7, 9, 10, 12, 13, 14, 16].

In the article, I used, among other things. z:

1. Amirowicz A. (2023). Our protected fish: gobies, staghorn and other small fish. Chrońmy Przyr. Ojcz. 79(4): 68-79.
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7. Mankowski, W. (1951). Ichthyology for marine fishermen. Marine Publishers, Gdańsk.
8. McAllister, D. E., & Aniskowicz, J. (1976). Vertebral number in North American sculpins of the Myoxocephalus quadricornis-complex. Journal of the Fisheries Board of Canada, 33(12), 2792-2799.
9. Nikolski, G. (1970). Detailed Ichthyology. PWRiL Warsaw.
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11. Pieckiel, P., & Wawrzyniak, W. (2016). First record of rare fish snake blenny Lumpenus lampretaeformis (Walbaum 1792) in the Puck Bay. Bulletin of the Maritime Institute in Gdańsk, 31(1), 7-10.
12. Rutkowicz, S. (1982). Encyclopedia of marine fish. Maritime Publishing House, Gdansk.
13. Spikkeland, I., Kinsten, B., Kjellberg, G., Nilssen, J. P., & Väinölä, R. (2016). The aquatic glacial relict fauna of Norway-an update of distribution and conservation status. Fauna Norvegica, 36, 51-65.
14. Terofal, F., Militz C, (1996). Marine fish. Świat Książki, Warsaw.
15. Więcaszek, B., Sobecka, E., Szulc, M., & Górecka, K. (2018). Case study of the diet and parasite fauna of and extremely rare fish species Lumpenus lampraeteformis (Perciformes, Stichaeidae) from the Gulf of Gdańsk (south Baltic Proper). Fisheries & Aquatic Life, 26(1), 73-77.
16. https://naszbaltyk.pl/zasoby-naturalne/ [dostęp 30.11.2024]