Doctoral Theses

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Browsing Doctoral Theses by Subject "Abundance"

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    Reintroduction and management of at-risk freshwater turtles in an urban wetland complex in a protected area
    (2023-12-15) Wijewardena, Tharusha
    A headstarting program for the Blanding’s turtle (Emydoidea blandingii) was initiated by the Toronto Zoo in 2012 to supplement a functionally extinct population in the Rouge National Urban Park (RNUP) in Toronto, Ontario, Canada. Data collected from multiple years of radio- tracking (2014–2021) and mark-recapture (2018–2021) surveys were used to evaluate the success of the headstarting program. Based on demographic data, survival of headstarted turtles remained high, except during a mass-mortality event when a substantial decline in survival was observed. Male:female sex ratio measured using incubation temperatures shifted from 1:1.5 in captivity to 1:1 in the wild, and size-class distribution of the population remained juvenile- biased. Release methods did not improve post-release outcomes in terms of survival, somatic growth rate, body condition, or movement patterns, and headstarted turtles sustained similar health to wild juvenile conspecifics in other Ontario populations. Headstarted turtles selected hibernacula similar to wild adult conspecifics, and there was weak evidence towards sociality, specifically in terms of familiarity (i.e., individuals from the same release cohort) in overwintering site selection. Demographic data from other resident freshwater turtles indicated that multiple sources of ongoing threats and catastrophes can affect population stability. Headstarting also affected community diversity by shifting species richness and evenness. Overall, Blanding’s turtle headstarting program showed progress, but continued monitoring will be required to determine if headstarting will achieve its desired conservation goals. Conservation actions targeting multiple life-stages of the Blanding’s turtles will be necessary to address root causes of population decline and to ensure that the population will reach a self-sustaining level.