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IMPORTANT
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A Tale of Two
Fish
Our October 2001 contribution from Jon Beer
There were once two trout in a Scottish loch. They weighed 6 lb and 10
lb. Do I have your attention now? These are not mythical monsters mouldering
on some hotel wall. There is every chance that they are still alive and
well for they were both caught in June 1999 and returned, very carefully,
to the loch.
Before they were slipped back into the waters of Loch Garry they were
christened. I don’t know if there was any ceremony – if I had
caught trout of this size I would have gone for something fairly elaborate,
possible with printed hymn sheets. The larger fish was named Homer: which
made the smaller fish, of course, Bart. Homer and Bart are not father
and son: they were both twelve years old at the time they were caught.
Homer and Bart are those legendary creatures of the large lochs: they
are ferox trout.
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Loch Garry ferox trout |
Ferox simply describes a large trout that eats other fish. In Victorian times, a specimen with a persistent pimple on its bum was classified as a separate species, ferox trout were Salmo ferox - but then half the lakes in Wales were reckoned to have their own species of trout. A little later everything became Salmo trutta, variations on the theme of brown trout and a ferox was just a big one. Then, in the early 1980s, Ferguson and Mason reported that the ferox of Lough Melvin were genetically distinct from other trout in the lough and spawned in different places. Were ferox a different species or not? Fishermen are drawn to big fish like moths to a flame and yet virtually nothing is known about these biggest of all brown trout.
Ferox are difficult beasts to study. They haunt the depths of the larger lochs where they prey on char when char are available and small trout when they are not. The best chance of catching a ferox is to troll a dead one of these for many hours deep below the wild waters of a huge loch. That is not everyone’s idea of a good time. But there are strange, tortured souls who like that sort of thing. They are called Alistair.
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A 10lb 12oz ferox trout |
Alistair Thorne and Alisdair MacDonald are assistant scientific officers at the Freshwater Fisheries Laboratory in Pitlochry. Homer and Bart were their two subjects in a pilot study to assess the feasibility of tracking the movements of large ferox trout in the 800,000,000 cubic feet of Loch Garry. Homer and Bart were fitted with acoustic and radio tags behind the dorsal fin and slipped back into the water looking like a couple of miniature DC10s. That was the easy bit. Tracking the fish meant days and nights on the loch, in all weathers, waving radio antennae or listening devices. The results showed two things: first, and most important, it showed that it could be done. Second, it showed that ferox are surprisingly peripatetic. Brown trout, especially big brown trout, were thought to be extremely territorial. Homer and Bart were gypsies, cruising to all parts of the loch, moving a kilometre in a matter of hours. They were also shift-workers, moving into the margins to hunt in the hours of darkness – which is something worth knowing if you would like to meet one. As the season progressed the fish were tracked to the southern part of the loch and then up into the spawning burn at the head of the loch. It was here that they recovered Homer’s tags, loosened and lost as he rubbed against the banks and boulders of the stream. The recovery of this tag opened up some exciting possibilities.
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Radio tracking ferox trout |
The pilot study had been a resounding success. The Alistairs had shown that radio tagging ferox was possible. They knew that ferox roamed the loch: they did not know at what depth or why. But that recovered radio tag might be the key to unlocking these riddles. Data storage tags can take readings of depth and temperature every fifteen minutes for many weeks. By pairing a data-storage tag with a radio tag the position of a ferox trout could be found in three dimensions – provided you can get the tag back to retrieve this data. On a cod it would be tricky. But Homer and Bart - and most adult trout – find their way into the shallow waters of a spawning burn in the last week or so of October. An automatic listening station at the mouth of the burn would let the Alistairs know when the tagged fish had passed into the burn. They could locate the fish on the redds with the signals from the radio tag and catch it in flagrante, as it were, delicto - on the job: inconsiderate but necessary.
Just why the ferox roam about as they do is the subject of a further experiment. The ferox of Loch Garry dine on arctic char which live in shoals in the depths of the loch. Just where and how deep is not known. To find out, the Alistairs have tagged a couple of these small fish. As I write these words three tiny radio transmitters are bleeping their way through the chilly depths of Loch Garry. Two are on these 4-ounce char: the third is on the back of Bender, a 6_ lb ferox who just might be creeping up behind them. If things go badly for the char, the Alistairs just might get their hands on all three radio tags when Bender goes upstream to spawn a month from now.
I’ll let you know what happens.
Data-storage tags do not come cheap. Nor does the other stuff. The experiments that had started in the Alistairs’ spare time is now burgeoning into valuable research funded by The Wild Trout Trust and Scottish and Southern Energy plc.
The Wild Trout Trust supports work on conserving wild trout with advisory visits and grants. If you have a project which the Wild Trout Trust could support, please write to The Project Officer, Wild Trout Trust, 92-104 Carnwath Rd, London SW6 3HW. http://www.wildtrout.org
Jon Beer contributes regularly to publications including Trout & Salmon and The Telegraph. If you have any comments, do not hesitate to get in touch or use the message board.