Where are the turtles when they are not? Underwater refuges used by Hydromedusa tectifera COPE, 1869 in a suburban stream

Abstract

Habitat requirements of Hydromedusa tectifera from an urban impacted stream from the Buenos Aires province, the Rodriguez stream, are here studied. We describe the type of underwater refuges, how they are used in different stream sections, stream margins, year season, size class and sex of the individuals, and analyze patterns of recurrence and aggregative use of refuges. Fieldwork was carried out from March 2017 to January 2018. Turtles were caught manually recording the following variables: site, transect and margin, sex, straight carapace length, and weight. Substrate types are differently used according to stream section, stream margin, year season and size class of individuals, but no difference was found between sexes. In the whole stream, most used refuges were the hollows on the margins (55.05%), followed by marginal aquatic vegetation (19.27%). Turtles of all class sizes and both sexes refuge into hollows on the stream margins. Despite different microhabitats provide refuge to turtles during all year seasons, hollows are the most important refuge during extreme cold and extreme hot seasons. In addition, turtle recaptures evidence a recurrence and aggregative pattern in the use of refuges. This information provides insight into the key aspects of the microhabitat requirements of the species and will be certainly useful in mitigating and preventing negative effects of the current stream management policies. It is worth highlighting the need to keep the stream margins unaltered to favor the presence of turtles in urban environments.

Tortugas dulceacuícolas de la Reserva Ecológica Ciudad Universitaria-Costanera Norte, Buenos Aires, Argentina

“…Ecología Austral 34:203-212 fondo y raramente se la ha visto salir del agua (Cabrera 2017;Semeñiuk et al 2020;Alcalde 2021). Si bien Cabrera (2017) indica que tiene mayor actividad durante los períodos crepuscular y nocturno, Alcalde y Sánchez observaron que también se encuentra activa durante el día (Alcalde et al 2021).…”

Hydromedusa tectifera Cope 1870 – South American Snake-necked Turtle, Argentine Snake-necked Turtle, Tortuga Cuello de Vibora, Cágado Pescoço de Cobra

“…-Few data are available on the population status of H. tectifera. Two studies have described the abundance, density, activity pattern, and population structure for the species: in Toro Muerto mountain stream, Córdoba (Lescano et al 2008) and in Rodriguez lowland stream, Buenos Aires (Semeñiuk et al 2019). Both studies collected turtles all year but differed in identifying peak activity periods.…”

“…Both studies collected turtles all year but differed in identifying peak activity periods. Semeñiuk et al (2019) caught most turtles during temperate days in autumn and spring (March-April and September-November, respectively). In contrast, Lescano et al (2008) noted that turtle activity was concentrated in the warmer months (September-March).…”

“…In contrast, Lescano et al (2008) noted that turtle activity was concentrated in the warmer months (September-March). The differences between the studies are surely an artifact caused by the collection methodology: Lescano et al (2008) trapped at night and Semeñiuk et al (2019) collected during daylight hours. Both studies reported similar sex ratios and abundances; Semeñiuk and colleagues caught 109 turtles in three stream sections (1.8 km total) with a sex ratio slightly favoring males of 1.22:1, and Lescano et al caught 96 turtles in one stream section (2.0 km) with a sex ratio also slightly favoring males of 1.3:1.…”

“…Semeñiuk et al (2020) studied habitat use and preferences for a population of H. tectifera inhabiting a polluted urban stream in Buenos Aires. Turtles used four types of underwater refuges during the year: dams of garbage and floating vegetation, denuded bottom surfaces, burrows along the stream margins, and raised marginal aquatic vegetation, with the last two being the most used by turtles of both sexes and of all size classes.…”