Demographics and morphometrics of marsh terrapins (Pelomedusa galeata) and serrated hinged terrapins (Pelusios sinuatus) populations in KwaZulu-Natal, South Africa: skewed size-class bias concerns

Abstract

Little is documented on the population demographics and morphometrics of wild freshwater turtles (hereafter terrapins) in South Africa. From February 2016 to October 2019, we trapped and recorded morphometric and biological data for serrated hinged terrapins Pelusios sinuatus (n\u2009=\u200997) and marsh terrapins Pelomedusa galeata (n\u2009=\u200951) in KwaZulu-Natal Province, South Africa. We visited two areas (Ndumo Game Reserve and Tala Private Reserve) regularly during the study period. Data were also intermittently obtained from eight other study areas across the province. We recorded age class, and morphometrics (including carapace length, carapace width, body mass and sex) for each terrapin caught, and also noted injuries. We uniquely marked all captured terrapins on the peripheral scutes around the hindleg region of the carapace, so to record any recaptures. A size-class bias was observed, with most individuals being large mature adults. Juveniles for P. sinuatus only accounted for 11 of the total 97 individuals (11.3%). Juveniles for P. galeata only accounted for 4 of the total 51 individuals (7.8%). There were significant differences in the three main morphometric variables between the adult male and female P. sinuatus, whereas there were no morphological differences between the adult male and female P. galeata. We recaptured only one P. sinuatus and two P. galeata. There is a concern that continued anthropogenic pressures, changing land use, and increased droughts are resulting in a skewed size-class bias towards older, larger, more resilient adult individuals.