Jonathan and Sasha graduate

Graduation time is a celebration of years of hard work. Today, it was the turn of Sasha Dines PhD and Jonathan Bell MSc. 

Sasha did her PhD on the use of acoustics to monitor populations of the Indian Ocean humpback dolphin (Sousa plumbea) - allegedly South Africa's most endangered mammal (other mammals may also be threatened). Her PhD worked involved years of deploying microphones into the sea in areas where the dolphins occur, and then trawling through thousands of hours of recordings listening for the occassional whistle or moan. Sasha found that acoustic monitoring might be a superior way of assessing the populations of Indian Ocean humpback dolphin as each individual has it's own signature whistle that can be recognised. 

Jonathan (aka JJ) spent several years looking into the perceptions of members of the public into how they perceived the right for access onto their properties to remove invasive species. Jonathan also looked into the best times in which to remove invasive Guttural Toads from urban properties. It turns out that the toads are most easily captured at night when the lights are on (not as simplistic as you might think!). 

We are very proud of the achievements of both Sasha and Jonathan and congratulate them again on their graduation. It has been  a privalege to have them as members of the MeaseyLab at Stellenbosch University. We look forward to hearing more about their achievements in future.

Dines, S. (2025) Applied passive acoustic monitoring of South Africa's most threatened marine mammal, the Indian Ocean humpback dolphin (Sousa plumbea). Stellenbosch University, PhD thesis

Bell, J.J. (2025) Right time, right place: a mixed method approach for invasive species management. Stellenbosch University, MSc thesis

Adding an important data point on African frogs

Big data syntheses need data, and the majority of scientific data still comes from the nothern hemisphere power houses of USA and Europe with China fast catching up. However, there is still a lot of the rest of the world out there. It is important that studies are made, especially in the southern hemisphere in data poor areas. Today, a new paper on the "Vulnerability of amphibians to global warming" was published in Nature. The article used physiological data from all over the world, but one continent had hardly any data available to the authors.

The African continent is especially data poor:

 

With only 4 data points on it, Africa is a notably large continent with a hardly any data. It is satisfying then that the one data point (shown in Cape Town) comes from the study of Carla Wagener (see here). This study looked at the physiological performance of tadpoles from high and low altitude locations of the African clawed frog, Xenopus laevis.

Obviously, Africa needs more data points, but we are very pleased that we were able to contribute to such an important study.

Literature

Pottier, P., Kearney, M.R., Wu, N.C. et al. Vulnerability of amphibians to global warming. Nature (2025). https://doi.org/10.1038/s41586-025-08665-0 

Wagener, C., Kruger, N., Measey, J. (2021) Progeny of Xenopus laevis from altitudinal extremes display adaptive physiological performance. J Exp Biol 1 April 2021; 224 (7): jeb233031. doi: https://doi.org/10.1242/jeb.233031

Temperature profiles from the Tanabe Peninsula, Japan

Regular readers of this blog will know that in July 2024 I visited the Tanabe Peninsula in Japan with Kento Takata to see the amazing project by Hiroshi Doei to rid the peninsula of invading Xenopus laevis (see here). I just reveived an update from Kento and it seems that the population has been exterminated! This is an amazing feat for Hiroshi Doei (see picture below) who spent more than 16 years of daily visits to this site. 

Kento also sent data downloaded from two Hobo loggers that I left in Japan. You can see them here in his hands:

The temperature profiles show that the Tanabe Peninsula gets very hot in summer and gets to near freezing in winter. This is close to the extremes of temperatures that we saw near Bloefontein in South Africa (see here). 

These frogs lived in a relatively extreme habitat for Xenopus, which are used to mild winters in Jonkershoek where most of them were shipped from (see here). 

Right time, Right place - in defense of his MSc thesis

Jonathan Bell used to work at NCC with his principle project being co-ordination of the Guttural Toad removal plan. During that time we had a lot of interactions and it was clear that Jonathan had great ideas of how to improve the efficiency of the eradication campaign. However, there was not a lot of time in his life for doing an MSc. Some years later though, Jonathan re-located to working for the Invasive Species Unit at the City of Cape Town, and there was a positive encouragement for him to do an MSc.

The idea for the first chapter of his project was to find out exactly why some people allowed access to their properties, and others did not. Using Jonathan's long list of contacts in areas invaded by the Guttural Toad and Polyphagous Shot-Hole Borer, he interviewed a series of different key informants to find out why they had or had not allowed access to their properties. The reasons were varied, but were aspects of socio-political, economic and environmental variables. Armed with their responses, Jonathan designed a questionnaire that he rolled out to 400 respondents in the City of Cape Town area. He found out that the type of Agents, Appointment Scheduling and Societal Influence were the most important categories chosen by people influencing whether or not they would allow access to their properties. Not only this, but he also found that these responses varied across an urban density gradient.

For his second chapter, Jonathan used a time to detection model (with the help of Dom Henry) to determine under what variables it would be most efficient to manage invasive Guttural Toads. This chapter too was a great success with several significant variables increasing the efficacy of contractors who were out to collect toads. 

Jonathan received a great mark for his defense presentation, and together with his thesis marks will graduate in March!

Congratualtions Jonathan!

Temperature of the water in a Jonkershoek pond

Temperature is pivotal to the functioning physiology of ectotherms, and for the principally aquatic frog Xenopus laevis the water temperature dictates the temperature of the animals throughout the year. We know that most of the invasive populations of X. laevis were sourced from the South African Cape region in general, and the Jonkershoek hatcheries near Stellenbosch in particular (van Sittert & Measey 2016). 

For the past year, I have had a temperature logger recording the water temperature just above the bottom in a pond in Jonkershoek. 

The same pond has been the source of Xenopus laevis for numerous studies, and likely contains animals that are closely related to those shipped from South Africa all over the world. 

The temperatures between November 2023 and 2024 show that the water reaches maximum temperatures in early February (27.32 C), and a low 6 months later in early August (7.98 C). Despite these extremes, the water temperature varied only 15 C between 10 and 25 C. This is relatively little change compared to the same loggers deployed in Kwa-Zulu Natal (see here). 

Thanks to Martine Jordaan and Andrew Turner who helped with the deployment and collection of this logger.