Chinook salmon population dynamics and life history strategies in the Squamish River watershed, BC, Canada

In light of the worldwide decline in wild fish stocks, hatchery programs are increasingly seen as an important fishery management tool. However, there has been considerable debate about the efficacy of releasing cultured fish. In the Squamish River watershed in British Columbia, Canada, adult spawner chinook populations have been severely depressed for decades despite high levels of artificial enhancement since the 1980s. Studies have noted that hatcheries have failed to stem the decline of salmon stocks and, in some cases, have exacerbated their decline, perhaps due to alterations in life history traits and strategies. We assessed differences in chinook biological traits and life history strategies between wild and hatchery stocks from the Squamish River watershed captured in 2006 using otolith microstructure and microchemistry.;Percent hatchery contribution to the spawner population (48%) was similar to historical data collected in the early 1990s. Analysis of biological traits demonstrated significant differences between hatchery and wild populations in sex ratio and body length. Historical comparisons indicated significant changes in mean age-at-maturity and age composition (shift to younger ages). Analysis of migration patterns using laser ablation inductively coupled mass spectrometry of otoliths revealed significant differences in wild and hatchery strontium, barium and magnesium concentrations, reflecting different environmental exposures and/or physiology. Migration patterns inferred from otolith microchemistry strongly suggest that captured fish were ocean-type chinook in which migration to sea occurred in their first year and individuals remained in coastal areas in adulthood. These results confirmed a shift from the historical stream-type strategy.;Observed results in biological traits and life history strategies may be linked to the continued depression in overall population abundance due to hatchery practices. However, environmental stochasticity may also be influencing the population. Hatchery supplementation does not appear to be harmful in the short term and can minimize short-term extinction risks; however, long-term supplementation may have resulted in deleterious consequences in the Squamish River chinook population. A successful supplementation program will require integrating clear and measurable conservation goals and objectives, altering current hatchery mating and rearing practices, the promotion of a scientifically defensible approach, and the use of an adaptive management plan.