Examining mortality of mature Atlantic salmon (Salmo salar) and its effects on iteroparity
LE3 .A278 2010
Master of Science
The abundance of wild Atlantic salmon ( Salmo salar) populations has continued to decline since the late 1980s as a result of mortality from sources other than fishing. In this thesis I describe two projects that were employed to investigate mortality of mature salmon in the LaHave River, Nova Scotia, Canada. In the first I developed a hierarchical Bayesian model based on the ratios of biological characteristics in adult count data collected from 1978 to 2008 to estimate mortality and life history parameters. The estimates from the model of mortality in the first year, which includes spawning, kelt migration and reconditioning period showed a steady increasing trend throughout the time series. Mortality estimates from the model for the second year following maturity, which is mainly during the marine phase, also showed an increasing trend but one that was more cyclical and coincided with the North Atlantic Oscillation Index. The probability of consecutive spawning is very low in the LaHave River but was somewhat greater for 1 sea winter ( 1SW) males and 2 sea winter ( 2SW) females. It is suggested that these differences may be due to differing life history strategies where females choose to achieve a greater body size either before or after maturity and males choose either to maximize their chance of survival or maximize their mating success by being as large as possible. Survival rates were also found to be greater in 2SW males than in 1SW males and this may be due to the advantage larger males have during mate competition. The second was a field study where the downstream migration of 30 kelts tagged with acoustic transmitters was monitored using 26 underwater receivers at 8 locations from April to October 2006. During the kelt migration, twenty seven of 30 tags were detected as they left the coastal environment five weeks after release, indicating a possible 90% kelt survival to coastal departure. Migration time from release to the outermost coastal receivers 24 km below the tide limit took an average of 14 days but varied from 3 to 32 days. About 40% of the kelts lingered and were active in the lower estuary. Five kelts monitored with depth transmitters migrated mostly at the surface in all habitats with occasional brief decent to the bottom.
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