Cave diving, exploration and science

 In Bohol, Cave diving, Exploration, Fieldwork

Exploring new frontiers has always been something humans have been attracted to. The excitement of encountering the unknown, learning more about the world we live in is what broadens our minds.

Ahead of our trip to the Hinagdanan cave of Bohol, we all hoped to find a new species, an adaptation or maybe just an endemic species. Along with the biological aspect of our trip, we also had the possibility of exploring another pool that was reported to be connected to the main pool of the cave through an underwater tunnel, by local free divers. The cave had not been explored by SCUBA before and so we decided to train as much as we could to the limits of non-technical divers.

We entered the cave with expectations and excitement, ready to implement the survey plans made by Annelise and Dolf, MCP’s resident Science officers. We did a quick initial survey of the pool just snorkelling to get a feel for the general layout of the pool and were excited to find possible tunnels that would first be explored by Soren, MCP’s diving safety officer and PADI instructor.

Soon, considering our findings, we started discussing how we could get as much data out of the few shorts days we had in the cave. Our aim in this multi-team endeavour was to survey all the living creatures in the aquatic part of the cave to provide comprehensive info to be added to the final report of SUAKREM (Silliman University Angelo King Research And Environment Center,) sponsored by JICA (Japan International Coorporation Agency.) The report will be used to ensure the utilisation of the cave is aligned with preservation goals, and that the cave is adequately protected.

The main method of sampling to survey smaller invertebrates and fish was to use home-made traps with bait that would be laid out on transects on the bottom of the floor of the pool. A two member team spent much of the morning laying out these transects carefully while the rest of the team checked and prepared traps. Simultaneously, Soren was exploring the cave which must have easily been the one activity everyone wished they could do.

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Deployed trap – thirty were deployed at intervals along the cave floor

The traps were baited and tagged and laid out at equal distances along the transect. Even as we were laying out the traps, we were amazed to see some crabs and fish that were quite large already in the first traps laid out. We then allowed these traps to lay overnight to get a good sample size for the survey. Meanwhile, Soren had been diving previously unexplored tunnels into new chambers that the main pool was connected to. Although we all understood the rationale, we were of course sorry to hear that because of many restrictions (preventing divers travelling side by side) and silty conditions, the rest of the volunteer team couldn’t safely explore these parts of the cave system. This meant that he would have to map and video these spaces alone.

The second method employed for sampling was to swim along the bottom with a scoop net to ensure samples of those animals that were too large for the traps. At the end of our first day, Dolf managed to get some of these samples as well.

Pictures from survey of HinagdananThe next two days were spent emptying all the traps and resetting them to ensure we had collected enough data about all the animals that lived in the cave.
Just the simple task of emptying the traps and documenting the animals was a very good reminder of how tedious research really can be. You need to be accurate but do so in a timely manner to not harm the animals and ensure the traps were then laid out around the same time as the day before. If PADI had a crab photography speciality, there’s no doubt our volunteers would be able to pass that!

Over the few days we managed to find 4 species of crabs that would need to be confirmed by careful analysis and referencing. We also found one species of fish. Although this doesn’t seem like a very diverse ecosystem, if you consider the physical parameters of the cave, we could at least observe that the animals seem to be specialised to the cave environment.

Spending a few days in a hot, damp, smelly cave can be tiring but it did manage to give the MCP volunteers a taste of how real field work can be and our findings will contribute to a better understanding of a rather specialised ecosystem. The real is actually going on at the time of writing this blog article – volunteers and staff are spending many hours analysing hundreds of photos and writing the final report.

Lastly a big thanks to Holger Horn of Philippine Fundivers for sponsoring tanks and weights for the duration of the expedition.

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