Study Reveals Patterns in the Survival and Movement
of Lake Trout Stocked in Lake Michigan
BY MATTHEW KORNIS, GREEN BAY FWCO-GREAT LAKES FISH TAGGING AND RECOVERY LAB
of lake trout stocked in the four major stocking areas. CPUE accounts for sampling
effort and number of fish stocked in each stocking area. Credit: Matt Kornis, USFWS
Lake trout were the top predator in the Great Lakes until overfishing and invasive sea lamprey caused their populations to crash by the 1960s. Since that time, rehabilitating this native species has been a major priority of federal, tribal, and state agencies. Up to 3 million lake trout have been stocked annually into Lake Michigan, where the species was completely eliminated, to restore populations of this native species and provide fishing opportunities for anglers.
Although lake trout are stocked throughout the lake, efforts have focused on four historically important spawning grounds in Lake Michigan to encourage wild reproduction. Coded-wire tags (small pieces of wire inserted into the snout ) have been used since the mid-1980s to identify genetic strain, length at stocking, and hatchery of origin of lake trout stocked in each of these four areas. Recovery of coded-wire tagged lake trout in annual spring gillnet assessment surveys coordinated among state, tribal and federal agencies since 1998 has allowed us to assess patterns in lake trout survival and movement after stocking.
this study. Lake trout stocked in these areas
received coded-wire tags from 1985 – 2004.
Credit: Matt Kornis, USFWS
each Lake Michigan management unit (e.g.,
MM-2, WM-6) that were wild fish. Data are
from 5,794 lake trout captured by anglers
and sampled by the Great Lakes Mass
Marking Program in 2015. Credit: Matt
Our results indicated that lake trout stocked in the Northern Refuge had substantially lower survival compared to other sites, likely due to sea lamprey predation and commercial fishing in that area of the lake. Higher survival of fish stocked at other sites, especially Julian’s Reef in Illinois, corresponded with areas where wild (non-stocked) juvenile and adult lake trout have been observed with increased frequency in recent years. Stocked lake trout from genetic strains that originated from wild Lake Michigan fish prior to their demise also had greater survival in central and southern Lake Michigan, where sea lamprey predation and fishing on lake trout is relatively low. A lake trout genetic strain from Seneca Lake, New York, has also been stocked in Lake Michigan due to their resistance to sea lamprey, but has somewhat lower survival in central and southern Lake Michigan compared to the remnant Lake Michigan strains. Finally, more than half of the lake trout stocked offshore in southern Lake Michigan (i.e., Southern Refuge and Julian’s Reef sites) were recovered in nearshore waters where they would be accessible to recreational anglers.