Campaigners called for fast-track measures to protect marine wildlife as the number of sea birds killed by a mystery pollutant was estimated to have risen to almost 300.
Fishing minister Richard Benyon faced a barrage of demands from Westcountry conservationists to speed up the process of designating marine conservation zones.
The RSPB accused the Conservative minister of "faffing about" as the latest figures from the RSPCA centre at West Hatch in Somerset showed that 294 birds, mostly guillemots, had been affected by the spillage.
The RSPB South West regional spokesman Tony Richardson pressed the minister at a public meeting in Devon to explain the "puzzling" decision to remove sea birds from a list of creatures protected under the proposed 31 aquatic zones, including 15 off the South West coast.
New zones could give the creatures the chance to "bounce back", he added, as his organisation claimed up to 600 could have been coated in the damaging mineral oil and washed up on beaches from Dorset to Cornwall.
Mr Benyon vehemently denied an accusation that the Government used economics as a "sole driver" of its conservation agenda and said too many environmental groups adopted a pessimistic "glass half-empty" attitude.
But he said every effort was being made to identify the culprits, adding: "There is a very clear international protocol which governs how we allow the shipping industry to behave and we are looking very closely at which vessel has dumped whatever it has in terms of washing out its ballast. We must resolve this issue because we don't want this in the future."
Wildlife campaigners, environmentalists and fishermen gathered at South Devon College, near Paignton, yesterday to quiz the minister at an event hosted by fellow Conservative and Totnes MP Dr Sarah Woolaston.
There is anger that the 31 new zones to be given increased protection is such a small proportion of the 127 "underwater national parks" recommended by independent advisors to create a network of wildlife-protected sites in the UK's seas.
The 15 earmarked off the South West coast were signed off from 58 previously earmarked by the Finding Sanctuary independent body after two years' work.
Mr Benyon was told time was running out for spiny sea horses at the Studland Bay marine reserve in Dorset, where numbers have plummeted from 58 to just seven in the space of a year.
The Newbury MP claimed efforts to make sure the zones were "evidence-based" was slowing up the costly process.
He said he was not prepared to draw a "meaningless" line on the map if it was not "credible", closing areas to UK boats only to see foreign trawlers "plunder" stocks.
The Government consultation period ends in March.