Fishing guppies
Our guppy experiment is set up to study life-history changes caused by harvesting. This involves monitoring of the populations, and harvesting at regular intervals. Now it is the time for the third harvest.
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In practice, harvesting guppies means lots of work: handling and marking the fish, meticulous measurements, and photographing.
We are harvesting one population each day. First all guppies in a tank are caught. Using a mesh, the fish are pre-sorted into 'small' and 'big' ones, and ones that are near the threshold size are control-measured. One fourth of either small or big ones, depending on the treatment (or of all, in case of size-independent harvest), are then destined to be today's catch. Harvested fish are measured and photographed, and preserved for later genetic analyses. A sub-sample of the remaining fish are also measured and photographed. Furthermore, the smallest guppies are also marked, such that we have some idea about the age structure of the population.
