Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
Green Bay Fisheries Office Produces Sea Lamprey Induced Mortality Rates for Lake Trout in the Great Lakes
Midwest Region, February 28, 2007
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The Green Bay Fisheries Resource Office collaborated with state and tribal biologists to facilitate the assessment modeling process in Lakes Superior, Huron and Michigan. 


Recently, John Netto, generated estimates of sea lamprey induced mortality for the treaty management units in Lakes Superior, Michigan, and Huron.  A logistic regression was fit to state, tribal and federal agency observations of sea lamprey wounds on lake trout to generate a model of wounding rate as a function of fish length. 


The wounding rates are then combined with growth models for each unit and assumptions regarding the probability of surviving a lamprey attack to generate estimates of sea lamprey induced mortality rates for all years and ages of lake trout included in the assessment models. 


This year’s estimate of 2005 mortality based on 2006 data indicates that trends in sea lamprey mortality differ among the lakes. 


In Lake Huron, lake trout mortality from sea lamprey were similar to last year’s estimate and remain low relative to the rest of the time series. 


In Eastern Lake Superior, estimates of sea lamprey mortality  decreased by nearly 50% from last year after increasing the previous two years. 


In northern Lake Michigan, estimates of mortality increased this year suggesting that the declining trend in sea lamprey mortality seen last year is not continuing.    


Sea lamprey induced mortality estimates for Northern Lake Michigan were the highest of the areas included in the analysis.  


Since the harvest limits for 1836 Treaty waters are based on total mortality limits, the level of sea lamprey induced mortality directly influences the level of lake trout harvest available for recreational and tribal commercial fisheries.

Contact Info: Larry Dean, 612-713-5312, Larry_Dean@fws.gov
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