Comparison of Two Sampling Designs for Fish Assemblage Assessment in a Large River

Abstract

We compared the efficiency of stratified random and fixed-station sampling designs to characterize fish assemblages in anticipation of dam removal on the Penobscot River, the largest river in Maine. We used boat electrofishing methods in both sampling designs. Multiple 500-m transects were selected randomly and electrofished in each of nine strata within the stratified random sampling design. Within the fixed-station design, up to 11 transects (1,000 m) were electrofished, all of which had been sampled previously. In total, 88 km of shoreline were electrofished during summer and fall in 2010 and 2011, and 45,874 individuals of 34 fish species were captured. Species-accumulation and dissimilarity curve analyses indicated that all sampling effort, other than fall 2011 under the fixed-station design, provided repeatable estimates of total species richness and proportional abundances. Overall, our sampling designs were similar in precision and efficiency for sampling fish assemblages. The fixed-station design was negatively biased for estimating the abundance of species such as Common Shiner Luxilus cornutus and Fallfish Semotilus corporalis and was positively biased for estimating biomass for species such as White Sucker Catostomus commersonii and Atlantic Salmon Salmo salar. However, we found no significant differences between the designs for proportional catch and biomass per unit effort, except in fall 2011. The difference observed in fall 2011 was due to limitations on the number and location of fixed sites that could be sampled, rather than an inherent bias within the design. Given the results from sampling in the Penobscot River, application of the stratified random design is preferable to the fixed-station design due to less potential for bias caused by varying sampling effort, such as what occurred in the fall 2011 fixed-station sample or due to purposeful site selection.

Received July 21, 2013; accepted November 6, 2013

ACKNOWLEDGMENTS

We thank the collaborators and those who assisted with this project: field technicians from the University of Maine, including Silas Ratten, Ryan Haley, Morgan Burke, Ethan Lamb, Rich May, and Greg Labonte; volunteers and alternate field help, including Phill Dionne, Ann Grote, Rob Hogg, Meghan Nelson, Megan Patridge, Phill Adams, Jake Poirier, Imre Kormendy, Margo Relford, and Marius Mutel; the Penobscot River Restoration Trust, including Charlie Baeder, Blaine Kopp, Cheryl Daigle, and George Aponte-Clark; the Maine Department of Inland Fisheries and Wildlife, including Jason Seiders, Scott Davis, Joe Dembeck, Merry Gallagher, and Peter Bourque, the Maine Department of Marine Resources, including Joan Trial and Oliver Cox; Rory Saunders of the National Oceanic and Atmospheric Administration; Joshua Royte of the Nature Conservancy; and Brandon Kulik of the Kleinschmidt Associates. We also thank John Achramowicz for fabricating the metalwork on our electrofishing boats, the Penobscot Indian Nation for providing us with permitting and access to tribal waters, and private landowners who allowed us to launch boats from their property. We also thank Walter Keller, two anonymous reviewers, and the associate editor for critiques that improved the quality of this manuscript. This work was supported in part by an award from the National Oceanic and Atmospheric Administration Restoration Center through the American Recovery and Reinvestment Act. The views expressed herein are those of the author(s) and do not necessarily reflect the views of the Penobscot River Restoration Trust, the National Oceanic and Atmospheric Administration or any of their Members or subagencies. This work was also supported in part by the University of Maine, the U.S. Geological Survey Maine Cooperative Fish and Wildlife Research Unit, and the Maine Outdoor Heritage Fund. Sampling was conducted under IACUC protocol numbers A2005-08-01 and A2011-06-04. This work is Maine Agricultural and Forest Experiment Station Publication Number 3359 and is based on research supported in part by Hatch Grant Number ME08367-08H from the USDA National Institute of Food and Agriculture. Mention of trade names does not imply endorsement by the U.S. Government.