Fishing Lines: Giant skate as big as a snooker table but we can't pot one

We never managed to see the pink seagull. Oban has many attractions: delightful harbour, wealth of history, gateway to Mull, Barra, South Uist and Islay. But we just wanted to see the Oban flamingo. This famed bird, which had ornithologists steaming up their binoculars with excitement when it first appeared, is actually an ordinary herring gull. However, it was also an environmental protest.

Oban has more than its share of fish farms, and they're not doing the seabed any favours. Their waste output is equivalent to the sewage discharge of a small town. Salmon fed in cages develop an unattractive grey-coloured flesh. True pink flesh comes from wild fish eating prawns, shrimps and other crustaceans. But people won't buy grey salmon, so farmed fish are duly dyed.

There's even a colour chart that "farmers" can use to achieve designer salmon of just the hue they want (another very good reason to avoid farmed fish). So one day an Oban fisherman got hold of some of this dye and turned a passing seagull into Scotland's most famous bird by feeding it with a dye-laden fish.

A true story, because I met a man who knew the man...

We didn't catch any giant skate either. That was the real purpose of the trip. It wasn't much of a consolation to find out that ours was the first expedition all year in which our skipper, Adrian Lauder, has failed to catch even one. All we landed were two dogfish.

Things are looking gloomy for these great, prehistoric flatfish that can grow as big as a snooker table. Adrian said 70 per cent of the skate he now catches have been tagged. A couple of years ago, it was 40 per cent. When I first fished for them, recaught fish were a rarity. Sounds like stocks are slumping.

Locals reckon these huge skate could grow as large as 500lb, though the British record is 227lb. "They are just so big, and live in such deep water, that you can't get the really big ones up," says Adrian. "We've had fish on for two hours or more, and never got them offthe bottom."

Every one caught is tagged as part of a programme run by the science department of Glasgow Museums, for very little is known about giant skate. They live in fast currents, at depths of 500ft or more, which makes them pretty hard to study. You can't research them in an aquarium, either. Even a "baby" of 100lb is nearly 6ft long and about the same across.

But here's the really bad news. We struggled to find a spot to fish because in every likely area there were longlines. "Do you know what they get for one of these big skate at the market?" asked Adrian. "Just £5. Not much for a fish that is probably decades old, is it? It's the wild west up here. Look at those buoys. No markings. That's because if a ferry gets its propellers caught in those lines, who can they blame?"

He despairs of the future. "These days the scallop dredgers use spikes that are 18 inches or more. We're catching skate with huge gouges across their backs. These great skate are now extinct in the North Sea and Irish Sea. It's time we started looking after what we've got here. But at this rate, it is going to be too late for the skate here too."