Under the relevant international agreements, Turkey may close the Turkish Straits during wartime, and chose to exercise that option. After Turkey closed the Turkish Straits, ships not based in the Black Sea were not allowed to traverse the Turkish Straits and enter the Black Sea.

So basically, the fighting has mostly been between the vessels of the Black Sea Fleet and Ukraine; the others cannot approach Ukraine and have been mostly uninvolved in the war.

The Black Sea Fleet has seen major losses.

The ongoing Russo-Ukrainian War led to major operations and losses due to Ukrainian missiles and umanned surface vehicles including the flagship Moskva and several landing vessels. Additionally, there was a 2023 Ukrainian missile strike against the Black Sea Fleet HQ in Sevastopol itself.[8][9] After another attack on 24 March 2024, a Ukraine spokesperson said that they had disabled or damaged one third of the fleet during the war.[10] In June 2024, Ukraine claimed it was now highly likely that they had destroyed all of the Black Sea Fleet's missile carrier capability based in Crimea.[11] By early 2026, it was reported that, despite no longer having a navy, Ukraine's surface, sub-surface and aerial drone capabilities had effectively driven the Russian fleet from open waters, forcing it to seek shelter in ports on the eastern Black Sea that themselves were no longer fully secure.[12]

The Baltic Fleet has seen limited involvement.

Deployed in Ukraine since the start of the invasion in 2022, the Baltic Fleet's 11th Army Corps reportedly suffered heavy losses in the initial stages of the war.[67] In 2024, amid increasing tensions with NATO and as part of a comprehensive re-organization of Russian Ground Forces, it was reported that the 11th Army Corps had been transferred from the control of the Baltic Fleet to the command of the Leningrad Military District.[68]

In 2024, the Russian Buyan M-class corvette Serpukhov was reportedly sabotaged in Kaliningrad by Ukrainian special forces, putting the vessel temporarily out of service.[69] In 2025, the Baltic was emerging as a flashpoint region in tensions between Russia and NATO, in particular around the activities of Russia's shadow tanker fleet. The Baltic Fleet was assuming an increasingly prominent role in protecting vessels of this tanker fleet from potential disruption or seizure by NATO countries. The fleet has also played a more prominent role in trying to sustain the Russian navy's Mediterranean Sea Task Force in the face of limitations imposed by Turkey related to the use of the Turkish Straits, and in the context of the Russo-Ukraine War, which have combined to restrict the ability of the Black Sea Fleet to fulfill that role.[70][71]

That being said, I would assume that to the extent that the Kremlin can, it has redirected resources away from the other fleets and to the conflict. I doubt that they have been well-resourced recently (even by Russian Navy standards, which has seen serious under-resourcing over time).