Russia increases Sevastopol defenses
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They are part of a multi-layered defense which counters air, surface and underwater threats.
It looks like the dolphins, at least some of them, differ with the orcas in choosing sides.
Russia appears to have doubled the trained dolphins defending Sevastopol naval base in Crimea. This is part of a gradual tightening of defenses in response to Ukraine’s growing ability to reach the strategic city. Despite the wider focus on missiles and maritime drones, Russia evidently takes the threat of Ukrainian special forces seriously.
The number of trained dolphins has increased from 3-4 to 6-7. They are trained to intercept divers who might sabotage the port.
More at the Naval News article.