Using Otolith Microstructure to Determine Natal Origin of Lake Ontario Chinook Salmon

Abstract

Stocking of hatchery-reared Chinook salmon Oncorhynchus tshawytscha in Lake Ontario has led to the development of a sport fishery that provides high economic returns to local communities. However, increased natural or “wild” production resulting from the naturalization of hatchery Chinook salmon to the system could result in changing salmonine dynamics that would require alteration of management practices in Lake Ontario. Using young-of-the-year (age-0) Chinook salmon of known origin—from hatchery and wild sources—we established a baseline for separating these two groups using otolith microstructure. Hatchery-reared Chinook salmon hatch earlier than wild Chinook salmon, and back-calculated hatch dates from otoliths correctly classified 97% of fish of known origin. A second protocol developed for determining the origin of Chinook salmon used the daily growth characteristics in the vicinity of 300 μm from the center of the otolith. Measuring the width of 20-d growth from 300 μm inward toward the origin correctly classified 100% of known hatchery fish and 89% of known wild fish. These measurements were used to determine the origin of Chinook salmon smolts caught in the nearshore of Lake Ontario adjacent to the Salmon River, New York, in 2000 and 2001. In both years, the nearshore population was dominated by naturally produced fish (85% to 89%). These results indicate that natural reproduction of Chinook salmon may play a larger role in Lake Ontario than previously thought.