Abstract

Harmful algal blooms (HABs) have affected salmon farms in Chile since the early 1970’s, causing massive losses of fish. The two largest HABs registered in the last decade occurred in 2002 and 2009, during which Alexandrium catenella blooms killed tons of salmon over an extended geographical area in southern Chile. At the beginning of 2016, high and persistent densities of harmful algae were detected in the estuarine and marine ecosystems of southern Chile. Mortality for this latter event reached 27 million salmon and trout (i.e. 39,000 tons). Unfortunately, a quantification of threshold concentrations of harmful algae that could affect the health of farmed salmon in southern Chile is still lacking. Here we quantified critical concentration levels, i.e. thresholds over which the behavior of farmed salmon is affected, using generalized linear (GLM) and mixed models (GLMM). An extensive database from southern Chile covering from 1989 to 2016 was analyzed. The database included salmon behavior, cell densities of microalgae and oceanographic factors. For all microalga species analyzed, the higher the cell density the greater the probability of detecting anomalous behavior. For Gymnodinium sp., a threshold density of 9200 cells/ml was calculated. For Alexandrium catenella, 150 cells/ml was estimated as a threshold value although it varies according to the tidal phase. A low threshold value equal to 1 cell/ml for Chatonella sp. was found to be associated with anomalous salmon behavior. Preliminary analyses were conducted to quantify the relationship between cell densities surpassing threshold values and salmon mortality. Funded by: INCAR 15110027, INTESAL.