Chilean research published in the journal Scientific Reports, analyzed the mass mortality of 2016.

Pamela Silva, La Tercera. In summer 2016, the Chilean fishing industry experienced one of its most tragic episodes. In just two weeks’ time, more than 40,000 tons of salmon -the equivalent of two years of fishing production- were found dead. This generated more than 80 million dollars in losses.

An anomalous increase in “red tide” or “harmful algal blooms” (HABs) in northern Patagonia created an excessive proliferation of phytoplankton species. In large quantities, these microalgae emit a toxin that affects fish gills, obstructing water exchanges and suffocating the fish.

An interdisciplinary study conducted by four Chilean researchers and published in the journal, Scientific Reports, reported the reasons behind the growth of this phytoplankton species.

The study concluded that, in the summer of 2016, a series of climatological, hydrological, ecological, and oceanographic anomalies occurred. Had they not all happened simultaneously, the phytoplankton would not have grown explosively as they did, and the salmon would not have died. These coincidences began with the El Niño phenomenon.

“This is the first work to offer a scientific explanation for these phenomena,” says José Luis Iriarte, from the Research Center Dynamics of High Latitude Marine Ecosystems (IDEAL), who worked with Jorge León-Muñoz, of the Interdisciplinary Center for Aquaculture Research (INCAR), Mauricio Urbina, from the Faculty of Natural and Oceanographic Sciences of the Universidad de Concepción, and René Garreaud, from the Center for Climate and Resilience Research (CR)2.

León-Muñoz explains that when the El Niño phenomenon occurs, it means less rain for people living in the south. “And every year, less rain falls in the south, but that year [2016] was coupled with another variable that weakened the winds that bring rain to the continent, which caused the south to get very little rain in 2015,” explains the researcher.

During a normal year, 1.800 millimeters of rain falls in Puerto Montt, but in 2016 only 900 millimeters fell. This, in addition to low levels of snowmelt, caused river flows in the area to be the lowest recorded in 500 years. This resulted in the region’s driest summer in 60 years.

To compound the situation, the second semester of 2015 saw an abundance of clear days in southern Chile. This increased the area’s normal radiation and elevated, to an anomalous degree, the warming of the water.

Thus, the southern coastal system ceased being a fjord. Such a state is produced when salinity is low at the surface and much higher at depth.

“What we propose is that seawater was dominant, bringing many nutrients from the bottom; [that plus] radiation and the water column generated all the conditions for this great bloom to occur, which under normal conditions would not happen,” says León-Muñoz.

Climate change

Although Iriarte notes that “All these processes are unpredictable, they are a coincidence,” part of the study explains that the exacerbation of climate change could cause this coincidence to occur more often in the future.

Though the El Niño phenomenon is a completely natural event -neither controlled nor influenced by humans- the weakening of the winds that bring rain to the continent is, in fact, due to human action through the emission of polluting gases.

Researchers agree that a main conclusion of the study is that this is not a one-time phenomenon but that it is very likely to happen again. Although there is not much one can do to prevent it – Chile alone can’t stop climate change – “What can be done is to become aware that it can happen again and take some mitigation measures in this regard. What happened on a large scale can happen again,” reflects Muñoz-León.

The expert clarifies that the study addresses what happened prior to the dumping of salmon off Chiloé.

“The bloom of Pseudochattonella cf. verruculosa started towards the end of February 2016, and peaked in the first days of March, causing great mortality in farmed salmon that were dumped during the last two weeks of March 2016. This article did not investigate the causes of blooms occurring after the second week of March, which were comprised of different species and had a distinct impact on salmon farming,” he explained.