Wildlife campaigners have given a cautious welcome to trials of new net designed to reduce the number of dolphin deaths.
Dolphin deaths have been blamed on bass trawlers
Scientists are testing a net off the south west coast with a trap door-style separator grid for dolphins.
The move follows concern over an increasing number of the mammals being caught in nets used by fishermen catching sea bass in British and French waters.
More than 270 dead dolphins have been found in Devon and Cornwall so far this year, compared with 216 for the whole of last year.
Laila Sadler, RSPCA marine wildlife officer, said: "There is no cause for rejoicing yet.
"No evidence has been provided to show dolphins swimming through the escape hatch. "
It is imperative that investigations continue into evaluating the long-term effectiveness of this device
The scientists from St Andrews University in Scotland said that in 82 hauls over a seven-week period, only two dolphins were caught in the nets.
Ms Sadler said: "That's good news, but it may be that fewer dolphins than usual entered the trial net because they were put off by the strange appearance of the separator grid, in the same way that birds are deterred by scarecrows.
"Or the appearance of the apparently solid "wall" of the grid discouraged them.
"If the "wall" was the reason, then this is particularly good news since it should continue to have the same effect.
"However, if the grid acts like a scarecrow, dolphins could become accustomed to it and resume feeding in the nets.
"It is imperative that investigations continue into evaluating the long-term effectiveness of this device."
Fisheries minister Elliott Morley said the results were very encouraging, and he would be pressing the industry to adopt the new nets.
But he warned that if dolphin deaths in the South West were not reduced in the short term, he could not rule out closing the bass fishery.