Efficiency of Two-Way Weirs and Prepositioned Electrofishing for Sampling Potamodromous Fish Migrations

Abstract

Potamodromy (i.e., migration entirely in freshwater) is a common life history strategy of North American lotic fishes, and efficient sampling methods for potamodromous fishes are needed to formulate conservation and management decisions. Many potamodromous fishes inhabit medium-sized rivers and are mobile during spawning migrations, which complicates sampling with conventional gears (e.g., nets and electrofishing). We compared the efficiency of a passive migration technique (resistance board weirs) and an active technique (prepositioned areal electrofishers; [PAEs]) for sampling migrating potamodromous fishes in Valley River, a southern Appalachian Mountain river, from March through July 2006 and 2007. A total of 35 fish species from 10 families were collected, 32 species by PAE and 19 species by weir. Species richness and diversity were higher for PAE catch, and species dominance (i.e., proportion of assemblage composed of the three most abundant species) was higher for weir catch. Prepositioned areal electrofisher catch by number was considerably higher than weir catch, but biomass was lower for PAE catch. Weir catch decreased following the spawning migration, while PAEs continued to collect fish. Sampling bias associated with water velocity was detected for PAEs, but not weirs, and neither gear demonstrated depth bias in wadeable reaches. Mean fish mortality from PAEs was five times greater than that from weirs. Catch efficiency and composition comparisons indicated that weirs were effective at documenting migration chronology, sampling nocturnal migration, and yielding samples unbiased by water velocity or habitat, with low mortality. Prepositioned areal electrofishers are an appropriate sampling technique for seasonal fish occupancy objectives, while weirs are more suitable for quantitatively describing spawning migrations. Our comparative results may guide fisheries scientists in selecting an appropriate sampling gear and regime for research, monitoring, conservation, and management of potamodromous fishes.

ACKNOWLEDGMENTS

This research was funded by grants from the North Carolina Wildlife Resources Commission, U.S. Geological Survey, U.S. Fish and Wildlife Service, Duke Energy, and World Wildlife Fund. Assistance with funding administration was provided by Scott Van Horn, Hugh Barwick, Mark Cantrell, Judy Takats, Helen Crockett, and Wendy Moore. Joe Hightower, Ken Pollock, Wayne Starnes, and Tim Grabowski offered constructive suggestions on equipment construction, sampling design, and data analysis. Robert Jenkins, Mark Cantrell, and Steve Fraley were valuable sources of knowledge on the fishes and environment studied. We appreciate the field assistance from many friends and colleagues, including Hannah Shively, James Cornelison, Melissa Johnson, Calvin Yonce, Brad Garner, Michael Fisk, Patrick Cooney, Ryan Spidel, and Tyler Averett. We also thank Brian Jonasson, Kevin Whalen, and anonymous reviewers for their thoughtful input on previous manuscript drafts. The North Carolina Cooperative Fish and Wildlife Research Unit is jointly supported by North Carolina State University, North Carolina Wildlife Resources Commission, U.S. Geological Survey, U.S. Fish and Wildlife Service, and Wildlife Management Institute. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.