fishing lines: The mysteries of blennies from heaven

My friend Ian was determined that his university thesis would be an enduring testimonial to the proud name of Sturrock. He was at Bangor University studying marine biology and oceanography, and pondered for ages to devise a topic that was obscure but enduring, inconsequential yet inimitable. He chose the feeding habits of blennius pholis.

Not a lot was known about this tiny member of the blenny family, commonly called the shanny, and far less about its diet. Textbooks speculated that they had a liking for small crustaceans and particularly limpets, but nobody knew how they prised the little suckers off rocks.

Ian set up a large tank in his flat and set off to catch a shedful of shannies. That's when he ran into the first problem. Take a shrimping net to the seaside and you'll catch blennies in every rock pool. It is one of the most widespread of all British inshore fish. Except around Bangor, that is. After two increasingly desperate weeks, Ian caught one. He christened it Benny. Fortunately, finding limpet-encrusted rocks was easier.

Benny liked the rocks and made homes underneath them. But he made no effort to winkle off the limpets. Perhaps Benny fed in the dark, Ian reasoned. He sat up night after night under infra-red light, watching his two-inch fish take the occasional amble round the tank. But it didn't eat the limpets. It got thinner. In desperation, Ian crushed some limpets and threw them in the water. Benny churned up the tank in his feeding frenzy.

In fact, Benny never ate in public - at least, not what he was supposed to - unless he was hand-fed. It posed quite a problem when it came down to compiling his thesis. But Ian was a creative chap, and put together a dissertation that, for all I know, may still be the definitive work on blenny behaviour.

At the time, it struck me as a wonderfully impractical subject. But it's funny how such oddball topics have a habit of proving useful after all. Miran Aprahamian can scarcely have thought that doing his PhD on the life and times of British shad would prove to be the stuff of legend. But he is now acknowledged as the expert on this endangered species, whose salmon- like return to their birthplace is now confined to just four rivers in England and Wales.

Once they were so common that there were shad netting sites on the Thames opposite the Millbank prison and above Putney Bridge. Now both species are considered rare and the larger, the Allis, is so uncommon that it is protected under the Wildlife and Countryside Act - meaning you can't even fish for it.

That doesn't mean you can't catch one. I still treasure an infamous headline from Sea Angler: "I Suppose a Shad's Out of the Question", but on the Welsh Wye in particular, it's not. Allis and twaite shad travel upriver together, and the former is uncommon but not unheard of. I would like to boast that my shad expedition last week turned up one of these creatures, but it didn't. I caught a barrel ful of twaites, which competed to grab my spinner or fly. But I didn't see Allis, though locals said there were more around this year.

Miran was fascinated and pleased when I told him about this mini-resurgence, which says something about him and a great deal more about me for phoning with such news in the first place. I won't bore you with the conversation, which to anyone other than a shaddict was undeniably dull.

Still, it was revealing to discover that even the shad man didn't know much about their activities when at sea, or why they choose to swim 190km upriver to spawn, or why their populations have plummeted over the past century. There's clearly a further thesis to be written...