The Giant Gerrard Rainbow Trout of Kootenay Lake: Are Anglers Driving the Boom-Bust Cycles in the Trophy Fishery?

The Gerrard rainbow trout (Oncorhynchus mykiss) of Kootenay Lake are exceptionally large wild rainbow trout with trophy (>9 kg) individuals a relatively frequent occurrence during boom periods.  However, to the consternation of anglers and guides, booms are punctuated by busts with a periodicity of approximately seven years.  The current fishery regulations permit each angler who purchases a conservation tag to harvest five large (> 50 cm) rainbow trout annually.  Although the regulations limit the number of fish that each angler can harvest they do not place any restrictions on the total number of anglers.  It is therefore possible that the bust phases are caused by several years of over-exploitation when anglers flock to Kootenay Lake during the boom to harvest trophy rainbow trout.  Other possible explanations include inter-annual variation in incubation success at the primary spawning gravels, juvenile survival during the tributary rearing period and inlake kokanee (Oncorhynchus nerka) abundance.

In order to test whether variable exploitation is driving the boom and bust cycles an acoustic and high-reward tagging program was initiated to estimate the levels of natural and fishing mortality in large Gerrard rainbow trout and bull trout (Salvelinus confluentus) through time.  The study, which is in the third of seven years, is providing valuable insights into mortality rates, movement patterns and life-history timing.  The mortality data collected to date is consistent with angler-driven cycles.