Historical mass strandings of jumbo squid (Dosidicus gigas) in the Eastern Pacific Ocean: patterns and possible causes

Mass stranding events of different taxonomic groups are periodic in certain coastal regions worldwide, but the underlying causes for these occurrences are not yet fully understood. In the Eastern Pacific Ocean (EPO), the most frequent and documented mass strandings correspond to the jumbo squid Dosidicus gigas, but the different hypotheses proposed to explain this phenomenon fail to predict it. Here, we assembled a database with historical stranding occurrences from the nineteenth century to 2022, highlighting the dramatic increase in strandings since the year 2000 along the EPO. The most common regions for jumbo squid strandings in the northern hemisphere are USA and Mexico, whereas in the southern hemisphere these events have mostly occurred in Chile. In both hemispheres the strandings are frequent in summer months. Although we assessed different hypothetical causes (e.g., post-spawning mortality, high temperatures, toxins from harmful algal blooms, human disturbance), we did not find enough evidence to support any of them. Besides, the need to experimentally test the plausible cause(s), we also discuss an alternative ecophysiological hypothesis associated with upwelling shadows and the species' diel migratory behavior, highlighting the importance of stranding events as key components of global nutrient cycles.

Automated summary

Mass stranding events of jumbo squid have dramatically increased in the Eastern Pacific Ocean since 2000, with the most common occurrences observed in the USA, Mexico, and Chile. Despite evaluating various hypothetical causes, no conclusive evidence was found to support any of them. In addition to the need for experimental testing of plausible causes, an alternative ecophysiological hypothesis related to upwelling shadows and the species' diel migratory behavior is discussed, emphasizing the importance of stranding events in global nutrient cycles.