Author: Benjamin Martin

Publisher:

Published: 2010

Total Pages:

ISBN-13:

The growth and survival of larval fish are influenced by a suite of biotic and abiotic factors. Because aquatic systems are characterized by strong heterogeneity in biotic and abiotic conditions along a vertical gradient, the vertical distribution of larval fish can profoundly affect their growth and survival. In large systems such as the Great Lakes, vertical distribution patterns can also influence dispersal and ultimately settlement events. Despite its importance during early life stages, little is known about vertical distribution patterns of larval fish in Lake Michigan. My objective was to describe the vertical distribution of the larval fish community in pelagic waters of Lake Michigan and determine which biotic and abiotic factors most strongly influence their vertical distribution. Additionally with controlled laboratory experiments I sought to determine how two of these factors (light intensity and prey density) influence the foraging success of a fish species with a pelagic larval stage, yellow perch (Perca flavescens). To determine vertical distribution, the upper 27 meters of the water column was divided into six discrete depth bins where larval fish and zooplankton were collected, in addition to recording light intensity, and temperature. Larval fish from 5 species were collected during the study: alewife (Alosa pseudoharengus), bloater (Coregonus hoyi), burbot (Lota lota), deepwater sculpin (Myoxocephalus thompsonii), and yellow perch (Perca flavecens). Among the five species, I observed three general patterns of larval distribution. Alewife and yellow perch larvae were restricted to the epilimnion, deepwater sculpin were restricted to the hypolimnion, and bloater and burbot were collected throughout the upper 27 m of the water column, and exhibited diel differences in distribution patterns. My analysis elucidates the importance of abiotic over biotic factors in the structuring of larval fish vertical distribution in Lake Michigan, as temperature was shown to influence the distribution of most species, while density of crustacean zooplankton did not. The inter-specific differences of vertical distribution observed among the 5 species collected have important consequences for dispersal, settlement, and recruitment variability. In the laboratory I examined the influence of light intensity on foraging success and prey selection of larval yellow perch at both high (150 zooplankton/L) and low (25 zooplankton/L) prey densities, with a mixture of zooplankton taxa common to lakes containing yellow perch. In addition to light intensity and prey density, the effect of ontogeny of yellow perch larvae was examined by using fish ranging from 9 to 15 mm. The results of my study indicated that larval yellow perch are well adapted to feed at a wide range of light intensities, as there was no difference in foraging success between light intensities ranging from 0.1 to 60 ℗æmol s-1 m-2 PAR. Increasing prey density from 25 to 150 (zooplankton/L) significantly improved the foraging success of larval yellow perch. However, the influence of prey density on foraging success of larval yellow perch was dependent on fish length, with improved foraging success with increased prey density occurring only for larger larvae. Overall, prey selection by larval fish was influenced by light intensity, prey density, and fish length, but the set factors which influenced selection for specific prey types differed. The results of this study combined with evidence from other field and laboratory work, highlight the need for a better understanding of the influence of prey density on foraging success throughout ontogeny.