Results
Water tests
The water tests were carried out by several teams so that mean values could be determined and the error rate could thus be minimised. JBL PROAQUATEST water tests for pH, GH, KH, O2, Fe, K and Mg freshwater were used. The Greisinger electronic device GLF 100 was used for conductivity and water temperature. The GPS data were determined either by mobile phone or with a reTrace Lite from Celestron. The lux values above water were determined with a PealTech 5086 meter.
Air temperature and relative humidity
The waterproof data logger was hung outside in the courtyard of Hotel Toninas. Unfortunately, the sensor also received direct sunlight, which led to the high maximum temperatures. It logged the data from Nov 17-24, 2022. The maximum values were 41.18 °C at 3:15 pm and 93.68 % relative humidity. The minimum values were: 23.4 °C at 5:36 am and 38.49 % relative humidity at 3:15 pm.
Air temperatures and relative humidity at the different locations were measured with the JBL TerraControl Solar.
PAR measurements
Our expedition member Kai carried out the PAR measurements: The PAR value indicates the amount of photosynthetically active radiation in the total radiation of sunlight. In other words, the amount of radiation that plants can use for their energy production (photosynthesis). The measuring device was held with its sensor uncovered in the direction of the sun, moved slightly and the highest value noted. Then it was put into a waterproof cover and the process repeated. In this way, it was possible to determine how much the cover reduced the value (875-790 = 85). The value displayed under water thus corresponded to about 90 % of the real value. At a depth of 30 cm the value dropped to 455 and at a depth of 100 cm to 400. As with lux measurements under water, submerging the measuring device below the surface leads to the greatest reduction due to the reflection of the water surface (42 %). Further lowering to twice the depth (100 cm) then reduces the PAR value by only 12 %! (PAR measuring device: Spectrum Technologies, unit µmol m2 s-1).
Water temperatures
We measured the water surface temperature at each site. At some sites, water samples were also collected from greater depths using a fish transport bag filled underwater and then measured.
Water temperatures comparison dry/rainy season
Only very rarely do we get information about the water temperatures during the different seasons. However, since water temperatures are often the deciding factor for fish spawning, it’s a very relevant issue. The first JBL expedition visited the areas around Puerto Inirida in February 2022, the second JBL expedition in November 2022.
The Rio Atabapo showed a surface temperature of 30.4 °C during the dry season in February (February 2020: 32.5 °C). In November, at the end of the rainy season, the temperature dropped to around 28-29 °C. In smaller rivers, the differences were also 2-4 °C.
Water temperatures day/night comparison
With the help of a waterproof data logger (ELV WTDL1-2, we were able to record the water temperature every 3 seconds. Because we only stayed in each place for a short time, the data logger could only be attached from Nov. 23, 2022 at 12:48 lunchtime until the next afternoon, Nov. 24, 2022 at 3:21pm. It was placed in a river, within a small lagoon with low flow velocity and shade. It was attached to a branch with a snap hook in a river, but within a small lagoon with little flow velocity and in the shade at a water depth of about 40 cm. The drop during the night was 1.5 °C, but only in the lagoon. In the main rivers, no lower water temperature was measurable at night.
Feeding trials under water
It is of course a unique opportunity feeding aquarium food to wild fish, which have never experienced it before. Each participant therefore had a few tins of JBL PRONOVO food in their luggage and were able to test for themselves how the fish reacted to the JBL food in their habitats at any time, if visibility under water permitted.
