Great Lakes Biological Diversity

FINAL REPORT
Contributing Factors in Habitat Selection by Lake Sturgeon (Acipenser fulvescens)

EXECUTIVE SUMMARY 

Lake sturgeon diets were examined over three different size classes obtained from the mainstem St. Lawrence River below the St. Lawrence – FDR Power Project during the early summer and late fall / winter seasons. The benthic evaluations to determine prey densities and substrate types were conducted within juvenile and adult habitats. Total fish captures ranged in size from 341 mm to 1498 mm total length. Stomach contents were removed for examination using a gastric lavage method. The dominant prey type for the 300-650 mm size class was determined to be Dipteran larvae (chironomidae) in the summer and Malacostraca (gammaridae) in the fall.  Molluscs (Dreissenidae) and gastropods first appeared in the 651–1001 mm size class and were the dominant prey type identified within the 1002 -1352 mm size class during the summer and fall sampling events.  Chironomidae and brachycentridae were the two most abundant prey types found in samples of macrobenthos samples collected from areas identified as juvenile habitat.

ACKNOWLEDGEMENTS 

This project was made possible through funding from the United States Environmental Protection Agency Great Lakes National Program Office grant number GL97517201. The data presented, and the conclusions and opinions expressed in this report are those of the author. Immeasurable patience and technical guidance was readily available from USEPA technical project managers Robert Beltran and Sandra Hellman and quality assurance manager Louis Blume.  The field component of this study was completed with the tireless assistance from field technicians Robert Colombo and Jessica Howard.

INTRODUCTION 

The lake sturgeon (Acipenser fulvescens), once widely distributed among the Great Lakes, Hudson Bay and Mississippi drainages maintains only a fraction of its former range and abundance due to habitat loss and over-exploitation. The New York State Department of Environmental Conservation (NYSDEC) closed the sturgeon fishery in 1976 (Carlson 1995) and listed the species as “Threatened” in 1983.   The single largest stock of lake sturgeon remaining in New York State waters is located in the St. Lawrence River below the FDR St. Lawrence Power Project (power project) located at Massena, New York.  This remnant stock has been the focus of ongoing research efforts conducted by scientists at the State University of New York, College of Environmental Science and Forestry (SUNY CESF) to determine the population dynamics, movement and habitat requirements of this threatened species in a large riverine system modified by the development of the St. Lawrence Seaway and large hydropower projects.  

The life history requirements of lake sturgeon are associated with the use of a broad range of habitat types for spawning, nursery, juvenile and adult forage areas and their respective migration corridors (Threader 1998).  Identification of the habitats utilized throughout a species life history is key to the successful restoration and recovery efforts which may involve habitat enhancements, reintroduction or protection of the existing stock and the remaining viable habitat. Telemetry results and catch per unit effort data indicate that juvenile lake sturgeon below the St. Lawrence-FDR Power project demonstrate high levels of site fidelity to patches of substrate dominated by silt (Hayes and Werner 2002). During the same study, chironomidae and brachycentridae were the two most abundant prey types identified in macrobenthos samples collected from areas considered juvenile habitat.  Correspondingly, preliminary diet samples collected from juvenile sturgeon indicated that soft bodied invertebrates were the dominant prey type represented within that size group. Adult sturgeon within the same study area were found over a larger range of heterogeneous habitat type. Evidence of large scale bivalve mussel predation in adult areas along with preliminary diet evaluations and direct observation of adults feeding on the bivalves suggested that the invasive Dreissenid bivalves may comprise a significant component of the sturgeon diet.

Differences in preferred prey densities could account for the apparent habitat partitioning observed between juvenile and adult lake sturgeon and the patchy distribution of the smallest of sturgeon size classes. This study examines the diet of different size classes of lake sturgeon to investigate shifts in prey preference related to body size and to determine if exotic Dreissenid mussels comprise a significant component of the sturgeon diet. This study also examines the apparent differences in juveniles and adult habitat relative to preferred prey items.

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