The Effects of Large-Scale Lake Trout Suppression Efforts in Lake Pend Oreille, Idaho

The nonnative lake trout Salvelinus namaycush population in Lake Pend Oreille, Idaho increased exponentially from 1999-2006.  This led to an unsustainable level of predation on kokanee Oncorhynchus nerka and threatened the persistence of a trophy rainbow trout Oncorhynchus mykiss fishery and native bull trout Salvelinus confluentus population.  In response, an aggressive lake trout suppression program was implemented in 2006 using both incentivized angling and contract netting (gill nets and deepwater trap nets).  Since 2006, anglers have harvested 65,156 lake trout, while netting has removed 68,956 lake trout.  Based on mark-recapture estimates, the population declined 65% from 2006-2008; another estimate will be completed in 2012.  In addition, standardized trap net catch rates, which provide an index to adult abundance, declined 82% from 2006-2011.  Juvenile lake trout were first targeted in 2009 and catch rates declined by 61% from 2009-2011.  Kokanee biomass reached a record low in 2007, but has steadily increased and is now approaching levels from the late 1990s.  To date, suppression efforts have led to a major reduction in lake trout abundance and allowed a nearly collapsed kokanee population to rebound.  Further, results support the hypothesis that suppression of lake trout in a large, deep lake is achievable.