Changes across a Decade in Size, Growth, and Body Condition of Western Pond Turtle (<i>Actinemys marmorata</i>) Populations on Free-flowing and Regulated Forks of the Trinity River in Northwest California

Ashton, Donald T.; Bettaso, James B.; Welsh, Hartwell H.

doi:10.1643/cp-15-253

Cited by 22 publications

(25 citation statements)

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“…Western pond turtles inhabit the Trinity River system in Trinity County, California, U.S.A. (Fig. ; Reese & Welsh, ,b; Ashton et al ., ). The construction of two dams, an upper (Trinity) and a lower (Lewiston), on the Main Stem was completed in 1964.…”

Section: Methodsmentioning

confidence: 99%

“…In contrast, the South Fork maintains its natural flow and temperature characteristics with summer water temperatures reaching 24 °C. The two rivers are otherwise climatologically similar (Reese & Welsh, ,b; Ashton et al ., ).…”

Section: Methodsmentioning

confidence: 99%

“…We use the models to detect population differences in female growth trajectories and age at reproductive maturity between two populations of western pond turtles. One population occurs in the unregulated South Fork Trinity River (South Fork), while the other population occurs in the dammed main stem of the Trinity River (Main Stem; Reese & Welsh, ,b; Ashton, Bettaso & Welsh, ). The Main Stem experiences controlled hypolimnetic flows from the dam, maintaining a thermal regime that is colder than normal for the region.…”

Section: Introductionmentioning

confidence: 99%

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Evidence of counter‐gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

et al. 2015

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1. Counter-gradient growth, where growth per unit temperature increases as temperature decreases, can reduce the variation in ectothermic growth rates across environmental gradients. Understanding how ectothermic species respond to changing temperatures is essential to their conservation and management due to human-altered habitats and changing climates. 2. Here, we use two contrasting populations of western pond turtles (Actinemys marmorata) to model the effect of artificial and variable temperature regimes on growth and age at reproductive maturity. The two populations occur on forks of the Trinity River in northern California, U.S.A. The South Fork Trinity River (South Fork) is unregulated, while the main stem of the Trinity River (Main Stem) is dammed and has peak seasonal temperatures that are approximately 10°C colder than the South Fork. 3. Consistent with other studies, we found reduced annual growth rates for turtles in the colder Main Stem compared to the warmer South Fork. The South Fork population matured approximately 9 year earlier, on average, and at a larger body size than the Main Stem population. 4. When we normalised growth rates for the thermal opportunity for growth using water-growing degree-days (GDD), we found the reverse for growth rates and age at reproductive maturity. Main Stem turtles grew approximately twice as fast as South Fork turtles per GDD. Main Stem turtles also required approximately 50% fewer GDD to reach their smaller size at reproductive maturity compared to the larger South Fork turtles. 5. We found we could accurately hindcast growth rates based on water temperatures estimated from the total volume of discharge from the dam into the Main Stem, providing a management tool for predicting the impacts of the dam on turtle growth rates. 6. Given the importance of size and age at reproductive maturity to population dynamics, this information on counter-gradient growth will improve our ability to understand and predict the consequences of dam operations for downstream turtle populations.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evidence of counter‐gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

et al. 2015

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“…Populations inhabiting intermittent streams exhibit lower body conditions than those in perennial streams (Bondi and Marks, 2013). Ashton et al (2015) studied populations occupying two very different forks of the Trinity River in California providing vBCI values for comparison and contrast with our sample. The Main Fork of the Trinity River has a dam that results in altered flows and colder summer discharge temperatures than the unregulated and normothermic South Fork.…”

Section: Reduced Body Condition Of Turtles and Poor Water Qualitymentioning

confidence: 90%

“…The sex ratio of males and females was compared with a chi-squared (x 2 ) test. Following Ashton et al (2015), we calculated volumetric body condition indices (vBCI) of male and female turtles using the formula:…”

Section: Data Collection and Analysismentioning

confidence: 99%

The effects of drought and fire in the extirpation of an abundant semi-aquatic turtle from a lacustrine environment in the southwestern USA

Lovich

Quillman²,

Zitt³

et al. 2017

Knowl. Manag. Aquat. Ecosyst.

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-We documented a significant mortality event affecting a southwestern pond turtle (Actinemys pallida) population living in a lake in southern California, USA. The area around the lake was impacted by a large wildland fire in 2013 that occurred during a protracted drought. As the mortality event was still unfolding, we collected data in 2014 on water quality, demographic structure, and short-term survivorship of the population. Water quality was poor with low levels of dissolved oxygen and high salinity of up to 45.90 ppt. Many turtles were severely emaciated and coated with a pale mineralized layer on their shells and skin. Estimated survival rate was low leading to a projected 90% decline in 134 days and a high probability of extirpation within a year. The lake was dry in September 2015 with no evidence of live turtles. Necropsies and low volumetric body condition indices suggested death by starvation. Although this semi-aquatic species has the ability to aestivate in upland habitats during periods of low water or move to other nearby water bodies, it is unlikely that many were able to do so because of their extremely poor condition and the severity of the drought conditions throughout the area.Keywords: climate / evaporite / starvation / survivorship / water quality Résumé -Les effets de la sécheresse et du feu dans l'anéantissement d'un abondant vertébré semiaquatique dans un milieu lacustre du sud-ouest des États-Unis. Nous avons relevé un événement de forte mortalité affectant une population de tortues du sud-ouest (Actinemys pallida) vivant dans un lac au sud de la Californie, États-Unis. Les environs du lac ont été touchés par un grand incendie forestier en 2013 qui s'était produit au cours d'une sécheresse prolongée. Comme l'événement de mortalité continuait à se dérouler, nous avions recueilli des données en 2014 sur la qualité de l'eau et sur la structure démographique et la survie à court terme de la population. La qualité de l'eau était faible avec de bas niveaux d'oxygène dissous et une salinité élevée allant jusqu'à 45,90 ppm. De nombreuses tortues étaient gravement émaciées et revêtues d'une couche minéralisée pâle sur leurs carapaces et leurs peaux. Le taux de survie estimé était faible, ce qui a entraîné un déclin attendu de 90 % en 134 jours et une probabilité de disparition élevée dans un délai d'un an. Le lac était à sec en septembre 2015 sans aucune preuve de tortues vivantes. Des nécropsies et de faibles indices de condition corporelle volumétrique suggéraient la mort par inanition. Bien que cette espèce semi-aquatique ait la capacité d'estiver dans les habitats des hautes-terres pendant les périodes de basses eaux ou de se déplacer vers d'autres plans d'eau avoisinants, il est peu probable que beaucoup de tortues aient pu le faire en raison de leur très mauvais état et de la sévérité des conditions de sécheresse dans toute la région.

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On a razor's edge: Status and prospects of the critically endangered Bellinger River snapping turtle, Myuchelys georgesi

Chessman

Ruming

Jones

et al. 2020

Aquatic Conservation

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In the summer and autumn of 2015, the Bellinger River snapping turtle (Myuchelys georgesi), a narrow‐range endemic of eastern New South Wales, Australia, suffered mass mortality from epidemic disease, apparently caused by a previously unknown virus. Information on the current population size and structure of M. georgesi, and the body condition and growth of the surviving individuals, is needed to support planning of conservation actions. Population estimates are also needed for a sympatric population of the widely distributed Macquarie turtle (Emydura macquarii), which has probably been introduced to the Bellinger River and may threaten the persistence of M. georgesi through hybridization, competition, and disease transmission. Data from five turtle surveys between November 2015 and November 2018 were used to estimate populations of the two species in the Bellinger River by an analysis based on habitat extent and turtle detectability. Changes in the body condition of M. georgesi and the body growth of both species were also assessed. Current populations of ~150 M. georgesi and ~500 E. macquarii are indicated, although the uncertainty of these estimates is high. The estimate for M. georgesi represents a decline of >90% from the historical population. Moreover, about 88% of the surviving M. georgesi are immature, and only about 5% are mature females. However, the body condition of the survivors has improved recently. Growth models suggest that M. georgesi matures later than E. macquarii, which may provide the latter with a competitive advantage. Evidence presented here does not support a previous hypothesis that M. georgesi were predisposed to disease through malnutrition and consequently reduced immune competence caused by high water temperatures and low river flows. Continuing disease, hybridization, and interspecific competition are probably the greatest threats to the persistence of the species.

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Changes across a Decade in Size, Growth, and Body Condition of Western Pond Turtle (Actinemys marmorata) Populations on Free-flowing and Regulated Forks of the Trinity River in Northwest California

Cited by 22 publications

References 68 publications

Evidence of counter‐gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

Evidence of counter‐gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

The effects of drought and fire in the extirpation of an abundant semi-aquatic turtle from a lacustrine environment in the southwestern USA

On a razor's edge: Status and prospects of the critically endangered Bellinger River snapping turtle, Myuchelys georgesi

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