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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Wildlife and Fisheries Science

First Advisor

Steven R. Chipps


fishes, strobe light, behavior changes, south dakota, lake oahe, environment


During the summers of 2004 and 2005 strobe lights were evaluated for their influence on (1) stress (plasma cortisol) and avoidance (distance moved away) responses across a broad range of fish taxa and (2) abundance (no./l) and distribution of zooplankton in Lake Oahe, South Dakota. To quantify stress and avoidance behaviors, representative fish taxa from five families were evaluated and included: Centrarchidae (largemouth bass Micropterus salmoides), Cyprinidae (fathead minnows Pimephales promelas), Ictaluridae (channel catfish Ictalurus punctatus), Percidae (yellow perch Perca flavescens), and Salmonidae (chinook salmon Onchorhynchus tshawytscha). Plasma cortisol concentrations (μg dL-1) for channel catfish (8.9 ±2.2, n=6), yellow perch (8.1 ±3.9, n=6) and chinook salmon (17.3 ±2.7, n=6) increased significantly compared to controls (5.0 ±1.1, 0.3 ±0.19, and 10.2 ±3.5, respectively) following 1 hour of exposure to strobe lights. After 7 h, plasma cortisol levels were similar to controls for all fish taxa. Fathead minnows showed no detectable response to strobe lights at either 1 or 7 h of exposure. Behavior experiments showed that the mean distance moved from the strobe light varied significantly between test and control fish and was highest for largemouth bass (mean distance after 1 h = 8.3 m) followed by chinook salmon (7.3) and yellow perch (7.3), then channel catfish (5.1). In comparison, avoidance behavior by fathead minnows did not differ between fish exposed to strobe lights and those used in controls. Although a significant increase in cortisol level was useful for predicting an avoidance response, stress response alone was a poor indicator of relative sensitivity of individual fish taxa to strobe lights. Direct observations of avoidance behavior revealed that largemouth bass, chinook salmon, and yellow perch were more sensitive to strobe lights than channel catfish and fathead minnows. Lack of both a stress response and avoidance behavior by fathead minnows indicates low sensitivity of this species to strobe lights and warrants further investigation into the effectiveness of strobe lights on cyprinid species. I evaluated the influence of strobe lights on distribution and abundance of pelagic zooplankton sampled from Lake Oahe from August 17 to September 15, 2004. On August 17 and August 19, 2004, zooplankton were collected at night during two time periods (0 and 5 h) in the absence of any strobe lights. Data from these samples were used as controls to account for time variation in zooplankton densities. On August 23, August 31, and September 15, 2004, zooplankton collections were made with the strobe lights turned off (time= 0 h, control) and again after 5 h of strobe light illumination (time 5 h, treatment) to quantify the influence of strobe lights on zooplankton distribution in the water column. Depth-specific densities of Daphnia spp. and calanoid and cyclopoid copepods were similar at both time periods (0 and 5 h) on August 17 and 19 in the absence of strobe light illumination. In comparison, samples from August 23-September 15 revealed that strobe lights significantly (P<0.016) reduced densities of Daphnia spp. and calanoid and cyclopoid copepods after 5 h of exposure. The most pronounced reduction in Daphnia spp. densities occurred in the upper (0-10 m) water column. Calanoid and cyclopoid copepod densities were significantly reduced at all three sampling depths, implying that these taxa were retreating to deeper and darker waters. Hence, avoidance of illuminated areas by zooplankton, combined with the phototactic avoidance of lights by rainbow smelt, may help reduce fish attraction to strobe lights. To my knowledge, this was the first study to show that strobe lights influence pelagic zooplankton distribution.

Library of Congress Subject Headings

Fishes -- Effect of light on -- Oahe, Lake (S.D. and N.D.)
Zooplankton -- Effect of light on -- Oahe, lake (S.D. and N.D.)
Stress (Physiology)
Dams -- Environmental aspects -- Oahe, Lake (S.D. and N.D.)



Number of Pages



South Dakota State University


Copyright © 2006 Nathan S. Richards. All rights reserved.