Wildlife photographers have recorded two separate attacks by bottlenose dolphins on harbour porpoises in the Moray Firth.
The incidents from earlier this month happened close to shore at Chanonry Point on the Black Isle.
Researchers at Sea Watch Foundation said such attacks are rare, and the cause of the aggressive behaviour had still to be fully understood.
The images were taken by Alister Kemp and Jamie Muny.
Mr Kemp said: "In the hundreds if not thousands of hours I've spent photographing the dolphins, I have never witnessed such an attack."
Mr Muny said: "I was saddened and shocked by the whole event and at the same time there is a feeling in my heart that tells me that I am lucky to have witnessed this very rare event, but have no doubt it is something that I will not want see again, it was brutal."
Chiara Giulia Bertulli, sightings officer for Sea Watch Foundation, said: "The cause of these incidents is not clear, but aggressive interactions could be due to the high co-occurrence of the two species which can result in competition over a shared food resource, occasionally leading to the death of the smaller species, although other theories have included misdirected infanticide.
"The changing testosterone levels in male dolphins could also influence the extent and seasonality of these attacks."
Last week, scientists at the Scottish Marine Animal Stranding Scheme said injuries found on a dead porpoise that had washed up at Rosemarkie on the Black Isle indicated that it had been attacked by dolphins.
The injuries included damage to its skull and many broken ribs.