Lake trout reproduction in Lake Champlain

Native lake trout Salvelinus namaycush were driven to extirpation in Lake Champlain in the early 1900s. Possible causes include overharvest, predation on adults by sea lamprey Petromyzon marinus, and predation on fry by rainbow smelt Osmerus mordax. Efforts to restore a lake trout fishery began in 1972 when a coordinated stocking program was initiated. Attempts to control sea lamprey populations began in 1990. Despite these management actions, reproduction by stocked fish has not resulted in large, naturally produced year-classes. This is the first formal study to quantitatively assess the level of natural reproduction by lake trout in Lake Champlain. In 2000-2002, we located 14 potential lake trout spawning sites and evaluated the habitat characteristics and level of spawning activity at each site. Passive egg collectors revealed that eggs were deposited at 8 of 14 sites, egg abundance ranging from 1.9 to 9,623 eggs/m(2). In 2001 and 2002, lake trout fry were collected in emergent fry traps at three of five sites; catch per unit effort ranged from 0.08 to 2.38 fry(.)trap(-1.)d(-1). We were unable to collect naturally produced juvenile lake trout through bottom trawling. We also examined adult lake trout size structure and abundance data collected annually by state agencies to determine whether there was a trend in the percentage of unmarked lake trout in the population. The percentage of unclipped lake trout in Lake Champlain decreased steadily from 1982 (2.6%) to a maximum in 2000 (10.4%), and then decreased to 5.7% in 2001. The high levels of egg and fry abundance, the failure to collect lake-produced juveniles, and the low percentage of unclipped adult fish all suggest that a recruitment bottleneck is present during the postemergent fry life stage.