In April 2015, scientists aboard research vessel Soairse came across a sinister discovery; carcass after carcass of dead whales washed up on the shores of Patagonia’s south-western fjords. The team recorded 300 dead sei whales, confirmed as the largest mass mortality of the species in history. 

Further north, a year later, the Chilean salmon farming industry was in a state of panic as its stock plummeted by the ton. Over US$800 million worth of salmon suffocated and died within a fortnight. The third largest producer of salmon in the world lost 12% of its fish. 

It was a sobering time for Chile’s marine environment. Scientists blamed rising ocean temperatures and harmful algal blooms. A hot year with weak winds had reduced ocean circulation and led to increased volumes of nutrient-rich water reaching surface waters where the algae flourished. As the algae died, its decomposition consumed the oxygen, suffocating marine life. The algae was also blamed for poisoning the whales.

As a marine biologist, I wondered if there was any connection between these two events. I decided I should go to Patagonia to find out more. 

Punta Arenas sits on the Magellan Strait, a sea route which separates mainland South America and Tierra del Fuego (named after the bonfires of the native people, who had developed seal-like blubber to protect them from the harsh winters). The Strait is the most important natural passage between the Atlantic and Pacific Oceans and, as I looked through my binoculars, I was not surprised to see the “blows” of passing whales. Local cetacean expert, Benjamin “Benja” Caceras, confirmed that they were seis and that they had been particularly abundant this season. 

Benja sat on the huge spine of a sei whale in an old warehouse that smelled of lanolin. He told me that the Welsh colonisers had once processed their wool here and he now hoped to turn the warehouse into a museum. He was surrounded by a macabre collection of skins, skeletons and skulls: sei whales, beaked whales, sperm whales, dolphins, sealions, penguins, pumas, armadillos, beavers, otters, flamingos, turtles, eagles, lizards insects and owls. Every taxon was represented in various states of taxidermy. 

I asked Benja about the dead sei whales. Had they really been poisoned by toxic algae, working its way up the food chain? He was not convinced. Necropsy samples had been taken at the time and results showed presence of the algae, but they were inconclusive. He said that underwater methane vents in the area had been especially active in 2016, the gas bubbling to the surface where sei whales skim-feed for plankton. Could the gas have displaced oxygen in their lungs? It seemed unlikely but an interesting hypothesis. There were also stories of orcas chasing sick whales and stranding them on the shore and, to my despair, ten more dead whales had been spotted by a passing plane earlier that week.

I went back to the hotel to meet Will Darwin, an English videographer who had recently returned to Punta Arenas from an expedition aboard Saoirse. Perhaps he had some answers. Will and I sat huddled by the open fire in the lounge of the Hotel Cabo de Hornos in Patagonia. Outside, winter was approaching and a cold wind from the South whipped down the streets as brave locals edged past our window, hanging onto ropes laid along the pavements to stop them getting blown away on their way to the shops. Will showed me images and videos taken from drones of orcas playing with entrails, but we decided they were more likely to have come from a sealion than a whale and he had not seen any of the recent mortalities. However, more encouragingly, he had recorded the first ever sighting of a young blue whale in the Gulf of Peñas. (He knew it was young because it was ‘only’ 20m long, as opposed to the 36m that an adult blue whale measures.)