Tag: Black Sea

New Way of Conservation: An Acoustic Device Helps Reduce Bycatch of Endangered Black Sea Porpoises

A new study published in Nature Conservation shows that not all acoustic deterrent devices may be effective in protecting the Black Sea porpoise, Europe’s smallest marine mammal.

Guest blog post by Dr. Dimitar Popov

The endangered Black Sea harbour porpoise (Phocoena phocoena relicta) is facing a critical fight for survival. As Europe’s smallest marine mammal, this isolated population is being pushed toward extinction by bycatch – the unintentional entanglement in fishing gear. The crisis is most acute in the Black Sea turbot fishery, where recent estimates reveal that more than 10,000 porpoises die annually.

Led by a strong motivation to address threats to this iconic species, a team of Bulgarian researchers has carried out a four-year trial study of 57 hauls seeking effective solutions to reduce porpoise mortality. The study, now published in Nature Conservation, found bycatch in 61% of all hauls, accounting for 189 cetaceans: 182 harbour porpoises, five bottlenose dolphins, and two common dolphins.

Bycaught Black Sea harbour porpoises. Photo credit to Dimitar Popov.

The trials did not begin promisingly, as the first two models of acoustic deterrent devices (pingers) tested, proved ineffective at reducing bycatch.
the researchers noted

This initial setback prompted the team to search for an alternative solution, eventually leading to a breakthrough with the PAL Wideband pinger, an acoustic deterrent device developed in Germany.

PAL Wideband pinger attached to a fishing net. Photo credit to Dimitar Popov.

Field trials demonstrated that this device can reduce harbour porpoise bycatch in the Black Sea by approximately 74%. Researchers believe the specific acoustic signals, namely the wider frequency band (between 10 and 150 kHz) emitted by the PAL Wideband model, contributed to its effectiveness, as it was the only one of the three pingers tested, that successfully deterred porpoises from approaching fishing nets.

Map of the conducted trials involving PAL Wideband pingers in 2020 and 2021. Credit to Popov et al., 2026

“Other recent studies have highlighted significant shortcomings in the conservation of harbour porpoise populations in European waters,” the researchers stated. This underscores the urgent need for effective strategies to reduce bycatch, the leading human-induced cause of mortality for the species.

Mitigation measures could include spatio-temporal closures of high-risk fisheries in areas where harbour porpoises are most abundant, as well as the adoption of alternative or modified fishing gear, including the use of acoustic deterrent devices.
the experts noted

black sea harbour porpoise in a net — Bycaught Black Sea harbour porpoise. Photo credit to Dimitar Popov.

Among the available options, the use of effective pingers, supported by appropriate financing mechanisms, is increasingly seen as one of the most practical and widely accepted approaches to reducing bycatch while maintaining profitable fishing operations.

Not all acoustic deterrent devices are equally effective in reducing the bycatch of the harbour porpoise in the Black Sea.
the researchers concluded

Their findings demonstrate that certain pinger models fail to mitigate porpoise bycatch in the bottom-set gillnets specifically used to target turbot.

The study underscores the importance of careful selection and testing of deterrent devices and emphasizes that this distinction must be explicitly taken into account in the development of targeted and effective strategies to reduce bycatch in Black Sea fisheries.

If you are interested in other marine research from Bulgaria, take a look at the topical collection “Black Sea ecosystem in the spotlight” which includes this study.

Original source:

Popov D, Meshkova G, Dimitrov H, Panayotova M (2026) Can pingers mitigate the bycatch of the endangered Black Sea Harbour Porpoise? Nature Conservation 63: 1-15. https://doi.org/10.3897/natureconservation.63.183768

Microplastic contamination of Black Sea fish threatens marine ecosystems

Five commercially important fish species from the Bulgarian Black Sea coast were found to be contaminated with microplastics.

Guest blog post by Stephany Toschkova, Sevginar Ibryamova, Darina Ch. Bachvarova, Teodora Koynova, Elitca Stanachkova, Radoslav Ivanov, Nikolay Natchev, Tsveteslava Ignatova-Ivanova

One of the main problems of the world’s oceans, reported by many scientific studies, is microplastic pollution. It is also one of the main sources of pollution in the Black Sea. Our new study in BioRisk details microplastic contamination in five fish species important for commercial fishing (Garfish, Мullet, Knout goby, Pontic shad, and Mediterranean horse mackerel). The fish were collected from the Sozopol area of the Bulgarian Black Sea coast.

Mediterranean horse mackerel. Photo by Donald Davesne
Knout Goby. Photo by Aleksandr_Levon
Мullet. Photo by Roberto Pillon

Our results show a wide variety of micropollutants originating from commonly used items such as plastic cups, stirrers, bags, soft drink bottles, fishing nets, packaging, аnd personal hygiene products. These objects systematically enter the Black Sea and degrade into microplastic particles. Microplastics (MPs) were found in all studied tissues of the fish in the form of pellets, fibers and fragments. Pellets were found most frequently, followed by irregularly shaped fragments, while fibers were the least numerous.

Stereomicroscope picture of morphological types of microplastics (arrowheads) recognized in the studied specied from: A) Garfish; B) Mullet C) Pontic shad and D) Mediterranean horse mackerel.

The bulk of the isolated plastics are made of polyethylene (PE) and polyethylene terephthalate (PET). PE is found in plastic bottles, cups, stirrers, and plastic bags. This polymer is very light and floats on the surface of the sea because its density is lower than that of water. PET, on the other hand, is denser than water and more likely to sink and accumulate in it and in organisms living on the seafloor. These polymers are widely used in fabrics, nets, ropes, and strings used for fishing, one of the main economic activities in the Black Sea. The predominant polymer type, PE, corresponds to the content of manufactured plastics all around Europe, as almost half of the plastics produced in Europe are reported as PE.

The sinking and sedimentation of plastics relate to the fact that the upper layer of the Black Sea is less dense than that of other seas. Furthermore, the weight of these particles increases due to the accumulation of marine plants and nutrients on them, and this can affect the distribution of plastics and their sedimentation on the seabed.

A satellite image of the Black Sea. Photo by NASA/GSFC/MODIS

Judging by the obtained results and the amount and type of polymers found in the study and the literature, the source of contamination, in our opinion, can be mainly attributed to domestic wastewater discharges coming from the washing of synthetic fabrics. In Bulgaria, wastewater is discharged – directly or after purification – into marine and freshwater ecosystems, as is the case in other neighbouring countries along the Black Sea coast. However, detailed studies are needed to prove this hypothesis.

Considering the wide variety of MP types detected in the digestive tracts of the fish, we assume that they regularly ingested MPs during feeding. Many nutrients are also held on the plastic particles, which deceives the fish into perceiving them as food.

microplastics under a microscope — Microplastics under a microscope. Photos by GTM NERR

Microplastics under a microscope. Photos by GTM NERR

It has been reported that plastics smaller than 1000 μm can reach the digestive tract or the gills of fish, and in turn can cause adverse effects such as a weak immune response or reduced fertility.

MPs can also accumulate in predatory fish species. Unfortunately, very limited research was performed on bioaccumulation and biomagnification in food webs, therefore more studies are needed to reach this conclusion.

MPs enter seawater food chains in different pathways and threaten entire ecosystems through their ability to transport pollutants, pathogenic microorganisms, and alien species. Bearing in mind the intensifying economic activity on the Black Sea coast and the consequent influence on the riverine water quality, river mouths can be considered potential sources of MPs. Particularly concerning is the area near the Kamchia River mouth, which is the biggest intra-territorial river in Bulgaria, entering directly into the Black Sea, with a catchment area of more than 5 300 km². This catchment and the entire Black Sea coast, where agriculture is well developed is a potential source of MPs, which have the ability to absorb and release toxic chemicals of organic and inorganic origin such as bisphenol A, PCBs and DDT, creating an additional potential risk to human health.

A satellite image showing the Kamchia River mouth.

Humans are exposed to BPA in the environment they live in, from the air we breathe to the food and drinks we consume. So, even if BPA intake is below accepted limits, this does not guarantee that the additive will not accumulate and cause more pronounced effects and chronic toxicity in the food chain, given its tendency to accumulate.

It is important that future research determines the toxicological side effects of plastic ingestion for fish communities in both benthic and pelagic habitats. However, even if we stop introducing plastics into the water system, both groups of fish will continue to be impacted, since the number of microplastics can increase due to the breakdown of larger plastics in the environment.

Invasive species as biomonitors of microplastics in freshwater ecosystems?

This study shows the need to carry out further studies of microplastics using different types of microscopic and spectral analysis. Even though microplastics may not pose a risk to humans who consume fish, these contaminants pose a potential risk to marine food webs and endangered species. We found particles of different sizes, types and colours in different fish species, and believe the variability of polymer types in fish can indicate the polymer types in water to some extent. Our results show that fish are important as ecological bioindicators and serve as a basis for future studies on microplastic pollution in tourist sandy beaches.

Research article:

Toschkova S, Ibryamova S, Bachvarova DCh, Koynova T, Stanachkova E, Ivanov R, Natchev N, Ignatova-Ivanova T (2024) The assessment of the bioaccumulation of microplastics in key fish species from the Bulgarian aquatory of the Black Sea. BioRisk 22: 17-31. https://doi.org/10.3897/biorisk.22.117668

Notice me! Neglected for over a century, Black sea spider crab re-described

After the revision of available type specimens from all available collections in the Russian museums and the Senckenberg Museum in Frankfurt-on-Main, as well as newly collected material in the Black Sea and the North-East Atlantic, a research team of scientists, led by Dr Vassily Spiridonov from Shirshov Institute of Oceanology of Russian Academy of Sciences, re-described Macropodia czernjawskii and provided the new data on its records and updated its ecological characteristics.

Even though recognised in the Mediterranean Sea, the Macropodia czernjawskii spider crab was ignored by scientists (even by its namesake Vladimir Czernyavsky) in the regional faunal accounts of the Black Sea for more than a century. At the same time, although other species of the genus have been listed as Black sea fauna, those listings are mostly wrong and occurred either due to historical circumstances or misidentifications.Now, scientists re-describe this, most likely, only species of the genus occurring in the Black Sea in the open-access journal Zoosystematics and Evolution.

The studied spirder crab species *Macropodia czernjawskii* in the wild, Tuaphat (near Gelendzhik), Caucasus, Black Sea.
Photo by Sergey Anosov

The spider crab genus Macropodia was discovered in 1814 and currently includes 18 species, mostly occurring in the Atlantic and the Mediterranean. The marine fauna of the Black Sea is predominantly of Mediterranean origin and Macropodia czernjawskii was firstly discovered in the Black Sea in 1880, but afterwards, its presence there was largely ignored by the scientists.

After the revision of available type specimens from all available collections in the Russian museums and the Senckenberg Museum in Frankfurt-on-Main, as well as newly collected material in the Black Sea and the North-East Atlantic, a research team of scientists, led by Dr Vassily Spiridonov from Shirshov Institute of Oceanology of Russian Academy of Sciences, re-described Macropodia czernjawskii and provided the new data on its records and updated its ecological characteristics.

“The analysis of the molecular genetic barcode (COI) of the available material of Macropodia species indicated that M. czernjawskii is a very distinct species while M. parva should be synonimised with M. rostrata, and M. longipes is a synonym of M. tenuirostris”,
states Dr Spiridonov sharing the details of the genus analysis.

All Macropodia species have epibiosis and M. czernjawskii is no exception: almost all examined crabs in 2008-2018 collections had significant epibiosis. It normally consists of algae and cyanobacteria and, particularly, a non-indigenous species of red alga Bonnemaisonia hamifera, officially reported in 2015 at the Caucasian coast of the Black Sea, was found in the epibiosis of M. czernjawskii four years earlier.

“It improves our understanding of its invasion history. Museum and monitoring collections of species with abundant epibiosis (in particular inachid crabs) can be used as an additional tool to record and monitor introduction and establishments of sessile non-indigenous species,”
suggests Dr Spiridonov.

The spider crab species *Macropodia czernjawskii* in the wild, Tuaphat (near Gelendzhik), Caucasus, Black Sea.
Photo by Sergey Anosov

***

Original source:

Spiridonov VA, Simakova UV, Anosov SE, Zalota AK, Timofeev VA (2020) Review of Macropodia in the Black Sea supported by molecular barcoding data; with the redescription of the type material, observations on ecology and epibiosis of Macropodia czernjawskii (Brandt, 1880) and notes on other Atlanto-Mediterranean species of Macropodia Leach, 1814 (Crustacea, Decapoda, Inachidae). Zoosystematics and Evolution 96(2): 609-635. https://doi.org/10.3897/zse.96.48342