Michael J. Connerton

Majority of age-3 Chinook salmon (Oncorhynchus tshawytscha) in Lake Ontario were wild from 1992 to 2005, based on scale pattern analysis

ABSTRACT Stocking of hatchery-raised Chinook salmon has been the principal tool utilized by fishery managers for controlling alewives in Lake Ontario and elsewhere in the Great Lakes. Stocked Chinook salmon are also often viewed by anglers as the principal source of maintaining catch rates. Stocking levels are often controversial and set with limited information about the relative contribution of wild fish to lake-wide populations. Recent research documenting large numbers of age-0 fish in tributaries suggested that wild reproduction was increasing and greater than previously thought. Estimating the contribution of wild Chinook salmon is imperative for successful management of this economically important recreational fishery. To differentiate wild from hatchery-derived Chinook salmon, we developed and validated a classification rule from scale pattern analysis of known-origin fish that was based on the area of the scale focus and the distance between the scale focus and the first circulus. We used this technique to determine the annual proportion of anglercaught, age-3 wild Chinook salmon in Lake Ontario from 1992 to 2005. On average over 14 years, the annual proportion of wild age-3 Chinook salmon was 62% (±13.6%, 95% CI), but has varied between 24% (±9.4%) and 82% (±11.2%). Wild fish have been a high proportion of the Chinook salmon population in Lake Ontario since the late 1980s throughout a period when the lake underwent considerable changes, suggesting that wild and hatchery-origin Chinook salmon are both important components for managing the predator-prey dynamics in Lake Ontario and maintaining angler catch rates.

Evaluation of Offshore Stocking of Lake Trout in Lake Ontario

Abstract Restoration stocking of hatchery-reared lake trout Salvelinus namaycush has occurred in Lake Ontario since 1973. In U.S. waters, fish stocked through 1990 survived well and built a large adult population. Survival of yearlings stocked from shore declined during 1990–1995, and adult numbers fell during 1998–2005. Offshore stocking of lake trout was initiated in the late 1990s in response to its successful mitigation of predation losses to double-crested cormorants Phalacrocorax auritus and the results of earlier studies that suggested it would enhance survival in some cases. The current study was designed to test the relative effectiveness of three stocking methods at a time when poststocking survival for lake trout was quite low and losses due to fish predators was a suspected factor. The stocking methods tested during 2000–2002 included May offshore, May onshore, and June onshore. Visual observations during nearshore stockings and hydroacoustic observations of offshore stockings indicated that r...

Contribution of wild-origin chinook salmon (Oncorhynchus tshawytcha) to the spawning run in the Salmon River, New York

We examined the contribution and distribution of wild-origin chinook salmon (Oncorhynchus tshawytcha) in the Salmon River, New York, during the 2005 spawning run. To determine the origin of each fish, we used scale metrics and a recently developed discriminant function model. We estimated that approximately 32% (∼20,000 individuals) of chinook salmon were of wild-origin and that there was a greater proportion of wild fish in younger age groups than in older groups (age-1 = 48.6%, age-2 = 47.2%, and age-3 = 21.1%). We also observed spatial differences in the distribution of wild- and hatchery-derived fish, with a higher proportion of wild-origin chinook salmon in the lower section of the river (47.5%) than in the upper sections (28.2%). The lowest proportion of wild fish was found in the Salmon River hatchery (12.4%), located in the upper section of the river. These findings suggest that wild-origin fish were more evenly distributed along the river, whereas hatchery fish were more likely to reach the upper parts of the river or enter the hatchery.