The Low Abundance and High Catchability of Large Piscivorous Ferox Trout (Salmo trutta) in Loch Rannoch, Scotland

Ferox Trout are large, long-lived piscivorous Brown Trout (Salmo trutta). Due to their exceptionally large size, Ferox Trout are highly sought after by anglers while their life-history strategy, which includes delayed maturation, multiphasic growth and extended longevity, is of interest to ecological and evolutionary modelers. However, despite their recreational and theoretical importance, little is known about the typical abundance of Ferox Trout or their vulnerability to angling. To rectify this situation a 16 year mark-recapture study was conducted on Loch Rannoch, which at 19 km is one of the largest lakes in the United Kingdom. A hierarchical Bayesian Jolly-Seber analysis of the data indicates that in 2009 the population of Ferox Trout in Loch Rannoch was approximately 69 individuals. The results also indicate that a single, often unaccompanied, highly-experienced angler was able to catch roughly 8% of the available fish on an annual basis. It is recommended that anglers adopt a precautionary approach and release all trout with a fork length ≥ 400 mm caught by trolling in Loch Rannoch. There is an urgent need to assess the status of Ferox Trout in other lakes.