Porpoise were reported near the Kessock Bridge this year.
The UK Government has agreed to investigate concerns that proposed oil and gas exploration in the Moray Firth threatens bottlenose dolphins.
The Whale and Dolphin Conservation Society (WDCS) said it had received an assurance that potential risks to marine life would be looked into.
In March, the society collected 18,000 signatures and statements from 25 experts opposing development.
The industry has said any work would be sensitive to the environment.
In December 2007, the UK Government announced that it was likely to allow oil and gas development in blocks within the Moray Firth Special Area of Conservation as part of a new licensing round.
Sarah Dolman, WDCS head of policy for Scotland, welcomed the government's assurances on investigating the threat to dolphins.
She said: "This is a step in the right direction.
"However, we remain concerned that the government has so far failed to take into account all the possible threats to the dolphins and their collective impact."
The Moray Firth provides habitat for several species of marine mammals
Porpoise, an animal not seen regularly in the sea around the Kessock Bridge at Inverness for a number of years, was thought to be making a comeback.
Earlier this year, Charlie Phillips, of the WDCS, said porpoise sightings had been reported.
They were most likely preying on sand eels.