Gastric Evacuation and Daily Ration of Naturally Produced Age‐0 Chinook Salmon in Lake Ontario

Almost 30 years after natural reproduction of Chinook salmon Oncorhynchus tshawytscha was discovered in Lake Ontario tributaries, little is known about the feeding dynamics of these fish after they enter the lake. This study assesses consumption by naturally produced age‐0 Chinook salmon as they enter the nearshore region of Lake Ontario after emigrating from the Salmon River, New York, a major U.S. tributary of Lake Ontario. Evacuation rate, estimated as a function of temperature in controlled laboratory experiments, ranged from 0.214/h at 10°C to 0.352/h at 19°C. Diel field sampling for daily ration estimates occurred on three dates in late spring (June 6, 12, and 18, 2001). Although no consistent diel feeding pattern was observed, Chinook salmon maintained an elevated gut fullness value throughout the day and did not feed after dark. Moreover, daily rations (grams [dry weight] of ration per 100 g of dry fish weight), which ranged from 27.54 (SE = 3.07) on June 12 to 33.27 (3.7) on June 6, were high compared with the values obtained in similar studies. Comparisons of daily ration estimates with bioenergetics model estimates showed that juvenile Chinook salmon were consuming prey at or above their maximum estimated daily ration. Daily ring counts of sagittal otoliths confirmed that the Chinook salmon in this investigation were naturally produced. Our results indicate that current food conditions in the nearshore waters of Lake Ontario are suitable for sustaining maximum consumption rates by naturally produced juvenile Chinook salmon that have recently migrated into the lake from spawning tributaries.