Jonathan Pyatskowit takes stream discharge measurements on Isle Royale. - USFWS photo by Henry Quinlan

A brook trout captured during population assessments on Isle Royale. - USFWS photo by Jonathan Pyatskowit

Jonathan Pyatskowit and Henry Quinlan from the Ashland Fishery Resources Office sampled six streams on Isle Royale to describe fish community status and trends with specific interest in brook trout populations.  Washington Creek, Grace Creek, Big Siskiwit River, Little Siskiwit River, Siskiwit River, and Benson Creek were sampled Sept. 9-14, 2005.  Sampling is designed to detect changes in the fish population over several survey cycles. The sampling scheme uses a mark and recapture population estimate annually for three years followed by three years of no sampling and then three more years of sampling.  The stretch is electrofished one day and the brook trout marked with a caudal clip for identification during a subsequent recapturing event on day two.  A population estimate can then be calculated from this information.  In addition, brook trout were measured, weighed, scale sampled, and tissue (the caudal clip) collected for later genetic analysis.  All other fish caught were identified by species and counted. 

Habitat work is done during year 1 and again in year 7.  A total of 13 transects per stream are examined.  Habitat measurements consist of instream (discharge, width and depth, substrate, stream characteristic, and woody debris) and riparian (predominant vegetation, bank stability, and bank characteristic) measurements.  Habitat characteristics can be correlated with observed fish population estimates.