I'm just back from filming on Dorset's River Frome, that glorious little river that I visited just a couple of weeks back.

On one level, my trip was a phenomenal success. I've always wanted a UK three pound grayling and, like buses, they came along in profusion. My very first cast of the shoot produced one of 3.12. This was followed up by a second monster at 3.11.

The second day I managed a scraper three and was nearly disappointed with one of 2.8. It was magical stuff and I count myself hugely privileged to be able to fish such a river. However, look a bit more deeply under the surface of this triumph and there are dark clouds to be witnessed.

We had been filming on a bend and moved upriver. We came back an hour later and found a half-consumed grayling of around a couple of pounds.

There were otter tracks all around and the culprit could not be mistaken. In all probability, that animal had watched us come and go before making its move. I was personally horrified. I've always felt, and many times written, that big, wild fish develop defences against otter attacks. How wrong can I be?

A second incident shook me. A river-keeper told me that he had recently witnessed a cormorant in the submerged branches of an overhanging tree. Outside the branches four of its colleagues were waiting for frightened fish to be flushed out.

Not only are cormorants resourceful and cunning but this shows, too, that the idea that sanctuary can save our fish is a complete illusion. There is virtually no problem that cormorants cannot overcome.

I drove home for a chub day on the river. It panned out to be almost an exact parallel of my time on the Frome.

I was guiding and we caught chub. That's great but virtually all of the fish, all mature, bore scars of previous attacks by either cormorants or otters.

One of the chub had most of his tail eaten, though well healed. Most of the chub had signs of cormorant attacks down the flank either raw or, once again, largely healed. Of course, these fish are the survivors and the vast majority of their year class are now history.

On both the Frome and the Wensum, what was very noticeable was the complete lack of small fish.

On the Frome, the only grayling were massive ones. On the Wensum, it's ages now since I've caught any chub less than three or four pounds.

We have to break through the modern mantra of habitat, habitat and more habitat. This is what environmentalists learn at university and bring back into the natural world.

I'm not a dinosaur. I know that habitat is essential but it's not everything. You also have to have fish to make use of that habitat and, on many, if not most of our upper rivers, there are simply not enough stocks to thrive and replenish. When small fish do manage to come through, their chances of being picked off by cormorants are depressingly high.

We've got the habitat, so we need the fish. Many anglers will remember when there was a thriving fish farm run by the authorities at Hellesdon.

That was a massive asset. Fish were transferred backwards and forwards across the region and waters in need of stocking got the fish required.

Now, there is absolutely nothing like this. The EA have stocked barbel, of course, in the past but I can't remember the last time I heard them talk about stockings of anything in the future.

And, if we do find fish to restock our upper rivers we've then got to protect them. We're not in the business of just feeding more and more cormorants.

That's foolhardy. We have to stir ourselves and apply for cormorant licences on a catchment by catchment basis.

Believe me, unless we act now, in 10 years we will all be fishing behind fences, the fish newly arrived on the back of a lorry. I can't imagine a worse fishing scenario.