Fox, M.G. Environ Biol Fish (1993) 38: 379. doi:10.1007/BF00007532
Poor natural recruitment of a Georgian Bay walleye stock that spawns in the Shawanaga River has been attributed to poor survivorship of early life stages. I investigated whether low zygote survival was part of the problem by conducting an in-situ incubation experiment with artificially fertilized eggs from the Shawanaga and the nearby Magnetawan River stocks. Both rivers have low buffering capacity (5–6.5 mg·l−1 alkalinity), but moderately low pH (5.5) had only been recorded in the Shawanaga. Zygotes were reared in both rivers. Minimum pH during incubation was 6.2 in the Shawanaga and 6.8 in the Magnetawan River. Mean survival rate to hatching strongly favoured the native stock in both rivers (86 vs. 25 % in the Shawanaga River and 80 vs. 40% in the Magnetawan River), and these differences were statistically significant. The results suggest that viability of Shawanaga zygotes is not a problem, but a low pH effect on zygote survival could not be inferred from the relatively high pH of Shawanaga water in the spring of 1990. The large difference in hatching success between native and non-native stocks was unexpected, and may have been the result of stock-specific adaptation to differing cation: anion and/or metal concentrations in the two rivers, or to some other factor.
Early life history Egg Incubation pH Rehabilitation Stizostedion