Evidence of Continued Progress toward the Rehabilitation
of Lake Trout in Northern Lake Huron
BY STEPHEN LENART ALPENA FWCO
Credit: Joseph Gerbyshak
During May and June, staff from the Alpena Fish and Wildlife Conservation Office (Alpena FWCO) conducted a juvenile lake trout survey in 1836 treaty waters of northern Lake Huron (Alpena north to Hammond Bay). This study was designed to index juvenile lake trout abundance and collect biological data on juvenile lake trout for population models developed for lake trout stocks in northern Lake Huron.
During the survey, Alpena FWCO staff conducted 20 graded-mesh (2.0-3.5”) gill net lifts at randomly selected locations (Figure 1) in two Lake Huron lake trout management units: MH-1 (Rogers City north) and MH-2 (Rogers City south to Black River). Biological data were collected from all lake trout encountered, including length, weight, sex and maturity, diet, visceral fat index, and lamprey wounding. Similar biological data were collected from non-target species. Tissue samples were taken from unclipped (presumably wild) lake trout for future DNA analysis.
2011-2013. Diamond markers denote 2013 proportion wild for each 50 mm length bin.
Credit: Stephen Lenart
Fifty-four lake trout less than 500 mm (a commonly accepted size cutoff for juveniles) were captured during 2013. Thirty-six of the 54 juveniles were of wild origin, based on the absence of fin clips. Lake trout between 350 and 450 mm in length dominated the catch in 2013, providing continued evidence for the strong year classes that dominated the 2012 survey (Figure 2).
All lake trout less than 350 mm in length were of wild origin. Juveniles were evenly dispersed among the depth strata sampled (100-150’ and >150’) and were captured at all of the ports surveyed, though catch rates for wild juveniles were highest near Rogers City, where 58% of the wild juveniles were captured. Total catch-per-unit-effort (CPUE) of juvenile lake trout (wild plus hatchery) was 1.7 fish per 1000 feet of net in 2013. CPUE of wild juveniles increased two-fold from 2012 to 2013 (0.56 to 1.13). Hatchery juvenile CPUE increased from 0.12 in 2012 to 0.56 in 2013.
Multiple cohorts of wild juvenile lake trout continue to be observed in the population, suggesting that mechanisms that favor natural reproduction remain in place. These results demonstrate continued progress toward the rehabilitation of lake trout in northern Lake Huron.