Ichthyological Adventures in the Boiling River of Peru

August 2018 was my tenth anniversary at LSU, and I spent it in Peru. The Museum of Natural Science, where I am Curator of Fishes, almost always has someone in Peru; it often seems that there are more folks from the Museum in Peru than in Baton Rouge. It was finally my time to see what the fuss was all about.

I was invited to go to Peru, and specifically to the Boiling River, by Andrés Ruzo a PhD Candidate at Southern Methodist University in Dallas, he is also a Peruvian and a National Geographic Explorer. Andrés has written a book and given a TED talk on his discoveries from this important and unique river: I highly recommend them both. Andrés has an infectious energy and that is a large part of why I wanted to go on this trip. He and I talked at the TED conference this last April and he showed me pictures of some fishes that he had photographed from the Boiling River. He showed me a picture of what he called a “suckerfish,” I told him that the spikey-faced catfish in his picture was from the genus Ancistrus. We realized then that that I might actually be helpful if I brought some biological expertise to his geological mystery.

The region Andrés was targeting had not been previously sampled by any ichthyologist, in fact, before Andrés recognized the scientific importance of this area a few years ago, no scientists had collected in this area - period. Given its unique ecology and geology I thought the Boiling River would be an excellent opportunity to discover new species; particularly as it is part of the super diverse Amazon basin (home to more than 3000 fish species).

The Boiling River runs through a small Peruvian shamanic village called Mayantuyacu and has the traditional name Shanay-Timpishka (or ‘Boiled by the heat of the Sun’ River). It took a plane ride from Lima to Pucallpa and then another few hours of off road driving in Toyota Hiluxes to get to the remote village. As we approached the village you started feeling a strange heat and could see steam rising above the tree tops well before you laid eyes on the river.

As you would guess this river gets very hot, so much so that there are no fishes in the areas that get the hottest. (Notably, Andrés has found some interesting non-vertebrate extremophiles living in the hottest sections.) So why would an ichthyologist go where there are no fishes? Well, the hottest sections are very hot, but it wasn’t continuously hot throughout the river; so, I was curious how fishes got into the areas that are cooler, between geothermal pockets. Also, I wondered if there were fishes trapped in cooler pools of water adjacent to the main river.

According to Andrés the Boiling River is the world´s largest known thermal river, flowing hot for 6.24 km (of the 9km system) and reaching max widths and depths of 25 meters and 4.5 meters. It is also uniquely the only thermal river that is non-volcanic (the nearest volcano is over 700 kilometers away). Besides the geological work Andrés was also there to raise awareness about the destruction happening to the surrounding region, which was losing rainforest at a rate of about half a soccer field a minute. Andrés’s field team included his father, other folks from National Geographic, schoolteachers, students, a social media guru and a chaperone. If you think that sounds like a pretty novice crew let me tell you they were not. The two high school students in particular, both 17 were absolutely brilliant – one was an excellent drone flyer, GIS guru and mapper (McClain Martensen) and the other (Kyle Smith) earned more than his keep with his card tricks and water quality testers (that he engineered himself - including the welding and programming). I was flabbergasted that Andrés’s team was able to 3D model the region based on the drone and water data, all while we were still in the field. I was also amazed at how everyone got along so easily. Even after long days of hiking and bruising climbs everyone stayed cheerful despite sometimes less than agreeable conditions (bugs, heat, lost drones, no electricity, etc.).

 Our accommodations were in a little village famous for its use of medicinal plants. We had no electricity most of the day and the food was purposefully bland as many people were avoiding salt, caffeine and other foods that might interfere with the medicines. The water we drank came straight from the river, and I would wake up each morning and bring a cup and tea bag straight to the river each morning. It was unbelievable how hot the water was – especially given how fast it flowed. The amount of energy needed to heat that much water that quickly must be absolutely massive. The steam coming off the river produced a lovely ghostly cover around us, at times it was indescribable dense, a thick warm fog that could obscure the fingers in front of your face. My first field site was a bit downstream from the hottest  part of the river itself – I knew there were no fish there, but recording the absence of fish in my fieldnotes could be a valuable data point in the future. Perhaps if the oil companies in the adjacent region, or even the Peruvian government have their way, this area may be flooded by damning or other anthropogenic influences. Perhaps then the Boiling River will have fish in it, and I wanted to be able to say I sampled it before any of that happened – hoping it never does. Throwing a castnet into the waters I had to be very careful not to have it snag; going into the water to untangle a net in near-boiling temperatures was not going to happen. As I pulled it back out of the water, predictably empty, some water splashed on my leg and it stung for the rest of the day. Walking along the river, sometimes over wet rocks at night, we had to be weary of the river’s power - falling in could mean severe burns, or worse.

           

We sampled each day in different parts of the river, moving upstream as far as we could go, which also meant a great deal of hiking. Much of my catch was in dipnets (small handheld nets) and castnets, as much of the collecting had to be done adjacent to the river in little pools of water, rather than the Boiling River itself. I also collected along the Pachitea, the major drainage near by. Which besides the Boiling River also led to the mouth of the ‘Salt River’ (which had high salt content despite being far from the ocean) and the ‘Hot River’ (which was warm, but far cooler than the Boiling River).

            I was upset when I woke up early one morning to hear rain - a tremendous amount of rain. I had hoped to have had a full day of collecting, but I knew the four inches of rain we would ultimately get that day would prevent that from happening. One notable thing I discovered was that the rain had made the Boiling River much more hospitable – so much so that you could swim in it, and we did. The river, instead of being the clear steamy steady stream it usually was had become a Willy Wonka-esque muddy hot chocolate stream with an incredibly fast flow; far too fast to throw a net into. On that rainy morning I felt like we were given a one-day pass to experience the river without its power – I also feared that this chocolate version of the river might be the future if damming and river diversions upstream every happened. I also thought: ‘so this was obviously how fishes and other animals could get upstream to cooler areas of the river.’ Mystery solved – sort of. Despite the fast flow, the fishes I saw in the previous days could likely move upstream in those conditions. What remains unclear is how they would get above some of the more physically complex areas that are only accessible by going up waterfalls and up vertical cliffs.

Bujurquina

            One notable catch was a small fish in the genus Rivulus that I caught serendipitously. I found it only after one of the members of the team slipped and fell into a little puddle of water between some rocks high above the river. I stuck my dipnet in the puddle and found this little fish. I was unable to ID it to species, so it may represent something new. After the rains, I went back to the same locality and found that the water trickled down from rocks above which I climbed. There was a steady flow of water from an area that seemed independent of the Boiling River (now named the Sheripiari´s – N – Creek by Andrés), and because of the additional rain the pools up the rocks were now connected by a small cascade of water. I collected two more specimens of the Rivulus. Even further upstream as far as we could go is a large pool of water where we collected more catfishes but also beautiful cichlids in the genus Bujurquina – I was very surprised to see these cichlids so high up the path. These cichlids attach their eggs to loose leaves that are then guarded by both parents; once the eggs develop a bit more they are taken into the parents’ mouths for further development. These fish most likely got here during the rainy season, when more of this area is flooded, and the water cooler.

I left the Boiling River with more questions than answers. We also left on foot, because even the mighty Hiluxes could not go up the now muddied post-rain paths. The path back to the main Pachitea River was one that I dreaded as we had walked it several times. In full sunlight with all your field gear (including a bucket of dead fish in formalin) it was not the easiest exit, in fact it had been one of the hardest walks I’ve ever done (particularly the time when returning from a full day of collecting we had all run out of water and were utterly dehydrated). Never-the-less I knew if the village wasn’t so remote the fishes probably wouldn’t be that interesting. Being remote protected this land, but it grows less and less remote each day. From when Andrés first started coming here to today the surrounding forests are being decimated for logging and for other commercial interests. We saw and heard illegal logging, and with ‘economic progress’ the river will become less and less protected. I know that unlike our team, who had asked the Shaman permission to collect and study the river, others might not be so willing to seek approval from the local indigenous people. I hope to see the Boiling River again one day, to feel its strange heat, and to study its mysterious fishes once more. I hope on my return others will have learned from Andrés and others just how special this area is, and how worthy it is of preservation and protection.