Fish in the Black Sea also suffer from the extreme heat

published on 7/22/24 11:55 AM

Photo: Pixabay

The unbearable heat wave that has hit the Balkans in recent weeks, causing scorching fires in Bulgaria as well, is threatening living organisms in the Black Sea. Ecologists are warning that the record high temperatures are not only disastrous for humans and plants, but also for some marine life.

Over the last 8-9 years, there has been a trend in Bulgaria of shifting seasons and longer summers. The heatwaves start as early as the end of May and reach their peak in early July, both in the ambient air and in the sea water.

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These factors have serious and sometimes disastrous consequences for the fish in the Black Sea, says Assoc. Prof. Dr. Violin Raykov from the Institute of Oceanology in an interview with BNR-Varna. In his words, organisms in the coastal zone are particularly threatened, especially in shallower areas.

"The most favoured are organisms that move quickly. If somewhere the temperature is very high, fish, mammals, those that in the Black Sea are larger and faster-moving, manage to save themselves from this effect by migrating further inside the sea where the temperature is lower and favourable for their existence," says Dr. Violin Raykov.

Fishermen complain that every morning they enter the sea but come out of the water "empty-handed". This has been the case since the end of June. Mostly jack mackerel and gobius are missing. When asked by a reporter of BNR-Burgas how fishing is going at the moment, Kiril Zheglev from the fishermen's association "Mena" in Nessebar answered like this:

"At the moment it is almost zero due to the fact that the water is too warm. The gobius is a bottom fish, it likes the rocky sea bottom and when there is warm water, there is no oxygen, the fish becomes lazy, hides under the rocks and waits for better conditions to survive. Those fish that are warmer survive. Minimal numbers of barbel are currently being observed. The jack mackerel are generally withdrawing at this time, we expect it back in the fall."

The marine inhabitants are bailing out of the heat in every way possible. But they don't migrate north, they just head down to the cooler depths of the Black Sea, which don't get as hot from the sun, in anticipation of better times.

"In organisms of less mobility, the stress is greater, because as the temperature rises, the oxygen in the water decreases and leads to an overdevelopment of phytoplankton," says Dr. Violin Raikov. "When "blooming" during the day, microalgae produce oxygen, but in the evening they consume it. This produces the effect of hypoxia - a sharp reduction in oxygen. As a consequence, the attached and less mobile organisms die."

During the months of July and August, fish in the coastal areas and in Varna lake have their bellies turned, and in most cases they are either drained of energy or dead. Alongside the unusually high sea water temperatures, fisherman Kiril Zheglev also reported another worrying trend:

"In recent years we have seen invasive species for our region - blue crabs are getting caught. Fish not native to our region are appearing in the Black Sea. There are all sorts, there are an awful lot of white crabs, there are black crabs.... When I was a kid there were hardly any crabs and it was an event to catch one. Now it's not like that anymore. In Italy they make soups out of them, broths. In Bulgaria nobody considers them as a raw material, but maybe one day we will use them here too," says the fisherman.

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Compiled by Veneta Nikolova based on interviews by Petya Mihova from BNR-Burgas

Photos: BGNES, BNR, Radio Varna

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