Sampling Little Fish in Big Rivers: Larval Fish Detection Probabilities in Two Lake Erie Tributaries and Implications for Sampling Effort and Abundance Indices

Abstract

Larval fish are frequently sampled in coastal tributaries to determine factors affecting recruitment, evaluate spawning success, and estimate production from spawning habitats. Imperfect detection of larvae is common, because larval fish are small and unevenly distributed in space and time, and coastal tributaries are often large and heterogeneous. We estimated detection probabilities of larval fish from several taxa in the Maumee and Detroit rivers, the two largest tributaries of Lake Erie. We then demonstrated how accounting for imperfect detection influenced (1) the probability of observing taxa as present relative to sampling effort and (2) abundance indices for larval fish of two Detroit River species. We found that detection probabilities ranged from 0.09 to 0.91 but were always less than 1.0, indicating that imperfect detection is common among taxa and between systems. In general, taxa with high fecundities, small larval length at hatching, and no nesting behaviors had the highest detection probabilities. Also, detection probabilities were higher in the Maumee River than in the Detroit River. Accounting for imperfect detection produced up to fourfold increases in abundance indices for Lake Whitefish Coregonus clupeaformis and Gizzard Shad Dorosoma cepedianum. The effect of accounting for imperfect detection in abundance indices was greatest during periods of low abundance for both species. Detection information can be used to determine the appropriate level of sampling effort for larval fishes and may improve management and conservation decisions based on larval fish data.

Received August 12, 2013; accepted March 7, 2014

ACKNOWLEDGMENTS

We thank N. Arend, C. Becher, D. Bennion, P. Bichier, E. Bouckaert, J. Craig, E. George, S. Ireland, C. Jovanovic, G. Kennedy, K. Lincoln, M. Kuebbeler, B. Manny, E. MacDonald, M. McLean, S. Panek, R. Mapes, A. Maran, J. Ross, B. Sander, J. Sutherland, and P. Thompson for their help with field work and laboratory work. Thanks are also extended to W. Ingram for his help implementing abundance indices and to S. Bolmquist and B. Peoples for their comments, which greatly improved this manuscript. This work was funded by the Great Lakes Restoration Initiative Template 70: Fish Habitat Enhancement Strategies for the Huron–Erie Corridor, and NOAA award number NA09OAR41718. This is contribution 2014-07 of the University of Toledo Lake Erie Center and 1846 of the U.S. Geological Survey Great Lakes Science Center. Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.