Dan van Blerk's study on Ghost Frog tadpoles is published

Readers of this blog will know that Dan van Blerk spent an entire summer season out in the streams of the Western Cape catching alien fish and Ghost frog tadpoles. If you've already forgotten see here and here.

Now Dan's first chapter of his MSc is published

This study shows unequivocally that invasive fishes have a negative impact on Ghost Frog tadpole abundance, something that we only knew before from anecdotal studies. Dan went to 111 sites across 26 streams finding that tadpole abundance decreases by around 18 times in the presence of invasive fish species.

The other thing that Dan uncovered is the real lack of data on the distribution of invasive fish in streams of the fynbos. This meant that they were absent from places where he thought they would be present and present in places where he thought they would be absent. 

This publication will be important in adding evidence for conservation decisions on the removal of invasive fishes from streams in the fynbos.

Van Blerk, D., Melotto, A., Pegg, J., Measey, J. (2023) Invasive fishes negatively impact ghost frog tadpole abundance. BioInvasions Records 12(4): 1121-1138. https://doi.org/10.3391/bir.2023.12.4.24 pdf

There's a frog in my tadpole

Sometimes a photograph can instantly give you a whole lot more information on a topic than you ever knew. 

This is a cropped close-up of a picture that I showed on the blog a few weeks back (see here). At the time that I took the picture, and later when I selected it for the blog post, I had completely failed to spot this metamorphosing frog in the image. I had never fully appreciated how the new frog in a metamorphosing tadpole was formed. Perhaps because of the colour of this Xenopus laevis frog from an invasive population in Tucson, Arizona, is so stark, you can clearly see through the transparent tadpole flesh the form of the frog coming through.

Note how the head of the tadpole and head of the frog appear to be completely different, yet the sensory organs (eyes, nares, etc.) are functioning on the tadpole and joined by nerves to those same sites on the frog head. Note also the way in which the fore-limbs (that always appeared to come at an odd place on the tadpole) are perfectly situated in relation to the frog head. 

Over the next week or so, the tadpole head will regress in size and the tail will start to shrink as the final stages of metamorphosis take place. Sensory organs will relocate into the frog head. 

A demanding way to spend your weekend

While at the Amphibian Foundation at the end of my trip to the USA, I took advantage of an offer to conduct a snake handling course (level 1) that they offer (see here). I've been in situations that have called for venomous snake handling in the past, and have always felt a little under prepared. Now with the course completed I know how to be safer when faced with a venomous snake on the ground, and a group of people that want it moved away.

Looking a little overgrown (after 2 months in the field without a haircut), I was outfitted with gaiters to prevent fangs going through my trousers. Guided by a set of expert instructors I learned how to handle heavy snakes on hooks (notice the braced position of the hooks under the forearms), and importantly how to safely get the snake into a tied bag and sealed bucket keeping it more than arms length at all times. 

Being in Atlanta, we became familiar with several of the regions most venomous snakes including the Eastern Timber Rattlesnake (Crotalus horridus - above), the Eastern Copperhead (Agkistrodon contortrix), Cottonmouth (Agkistrodon piscivorus), and Eastern Diamondback Rattlesnake (Crotalus adamanteus  - below). 

As you can see, the snakes were all very beautiful and it was a great pleasure working with them. Carefully following each of the steps according to instructions allowed us to bag up the snakes in a very safe manor. Run by the Rattlesnake Conservancy, these courses offer experienced and professional tuition in a relaxed and friendly environment.

As you can see, I gained my certificate of competence and feel a lot more confident about how to tackle venomous snakes in future.