Ferox trout Salmo trutta; Linnaeus, 1758
Ferox trout is a widely used term for large predatory Brown trout. Although in the past, it was referred to as a separate species, Salmo ferox, this is no longer the case. The Ferox life history is one of a number of life strategies adopted by one species, the brown trout, Salmo trutta. Research into the genetics of Ferox trout, has shown them to be genetically distinct from other trout in some lochs (for example Lough Melvin, Ireland), but recent unpublished research from a variety of Scottish lochs has shown that this is not the case in all populations. Data from Loch Rannoch samples, for example, have shown that a wide genetic variability exists within its Ferox population.
Ferox trout display a wide variety of shape, colouration and spot patterns. The condition of individual fish is also very variable and depends on factors such as age, season, whether it had spawned during the previous winter and possible parasite infestation. The set of photographs to the right, of Loch Rannoch Ferox trout, shows this wide range clearly.
After subsisting on invertebrates, some brown trout switch to a diet based mainly on fish. Brown trout that switch to piscivory find that the switch not only boosts their growth, but also adds to their longevity. The current UK rod caught record stands at 31lb 12oz (14.4 kg). The oldest recorded ferox trout in the UK is a fish of 23 years of age.
Documented evidence of growth potential has been obtained from recent research carried out in Loch Rannoch where increases of over 300 per cent bodyweight have been recorded.
Diet and Behaviour
Ferox trout have an unjustified reputation as cannibals, in part due to the misuse of the word cannibal to describe any trout that eats fish. Ferox have a marked preference for Arctic charr. True cannibalism is probably less common than might be supposed - but in the absence of other prey fish, ferox will certainly prey on their own kind. Growth potential is influenced by the size spectrum of available prey.
Ferox trout are present in most if not all large Scottish lochs. They are highly prized by anglers and in recent years, angling pressure upon them has steadily increased. The number of ferox trout within the trout population of a loch has always been a matter of conjecture. A catch and release project carried out in Loch Rannoch since 1994, where 70 ferox have been tagged and released to date, has provided some unique data. Firstly, that if handled with great care, ferox trout can undoubtedly survive, and thrive, after catch and release. With nine recaptures to date, and several of these on more than one occasion, the indication is that there are not large numbers of ferox trout in the loch. The catch location data indicate that ferox trout are wide ranging, and do not hold specific territories.
Further research has been carried out in Loch Garry (Perthshire) to look in more depth, at the behaviour of Ferox trout. Using radio, acoustic and data storage tags, to look at spatial and diurnal movements.
The results so far, have verified observation made at Loch Rannoch with regards to territoriality. During a study undertaken in 1999, two large ferox trout were observed over a three week period and moved throughout the loch during the hours of daylight, moving distances of up to 1 km in a matter of hours. Observation on one of the fish during the hours of darkness on two separate occasions showed it to move into shallower water and become less active in darkness.
Research in 2010 used data storage tags (DST) (logging temperature and depth). Results are reinforcing nocturnal depth data observations made in the 1999 study. Three DSTs recovered to date show that the majority of deep dives are made during the hours of daylight. It is believed that these dives are foraging dives in search of prey.