This is one of those really sharp charts with all of the pertinent details showing a congruent sequence of events and descriptors.
Scientists working in the Chilean Patagonia came to a nasty surprise one day when they found several whales stranded on a beach. In the course of their investigation they ended up finding about 360 dead whales on the region’s coast (which, according to previous studies was a small fraction of the likely total number of dead whales).
The scientists suspected that what killed the whales was a toxin released by an overgrown microscopic algae population that lives in the sea in that region, which is known to cause harm to marine fauna when ingested. The locals refer to the phenomenon as the “red tide” because the sea water becomes red when that happens.
The querent heard about whale “group suicides” in the past and wondered if this was a case of such an event. So asked to know what could have been the cause.
The whales are signified by Mercury, L12, large animals.
Let’s get “suicide” out of the way first. There is no testimony for turned L12 (the Sun) harming Mercury; which is the main testimony for suicide. Notice that the Moon is separating from a trine with the Sun. Here the trine shows the querent was emotionally stimulated by the idea of whales committing suicide, nothing more. No suicide in this chart.
To see the whales’ past let’s rewind the chart back to see Mercury’s previous aspects in Cancer.
Mercury opposed Saturn, turned L6. That is, the whales became ill. Saturn can signify many things. However, it is indeed the natural ruler of toxin. Mercury was conjunct Venus’ antiscion while conjoining Saturn. That is, the whales got ill because of the food they ate (turned L2) was poisoned. The antiscion aptly hints at eating something without seeing or noticing it. In summary: the whales were unaware they were eating poisoned food.
After becoming ill the whales die; shown by Mercury conjoining Mars (turned L8).
Where is L8?
In a water sign.
If death had a color here what color would it be? Red — Mars.
We could not have a better description of the Red Tide being linked to the cause of their death.